Author: Beth Preston

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Cold winters drive 8-year population cycles for a beetle pest in agriculture

/ Beth Preston / 1 Comment
This blog post is provided by Sara Emery and tells the #StoryBehindthePaper for the paper “Cold winters drive consistent and spatially synchronous 8-year population cycles of cabbage stem flea beetle”, which was recently published in Journal of Animal Ecology. In their paper they explore regular cycles of the cabbage stem flea beetle in Sweden, investigating what impacts these cycles including climatic conditions in the winter.

For centuries, natural historians and scientists have observed that some species cycle very consistently between years in which the population is small and years in which it is large. The classic example many of us are taught when we learn about ecology is the 10-year boom and bust population cycles of snowshoe hares monitored from fur trapping records over the past 300 years in Canada and the Northern United States. Indeed, when the boom-and-bust cycles of snowshoe hares are plotted with lynx populations, a specialist predator of snowshoe hares, we see a remarkably consistent real-life example of the Lotka-Volterra predator-prey equation. Peaks and valleys in lynx populations follow shortly behind and are offset from those of the hare population. But ecological processes are hardly ever so consistent, and in other species for which population cycles are observed (lemmings/voles, moths in forests) scientists have argued about what causes cyclic population patterns, from climate oscillations, latitude, plant quality or specialist predator populations to self-regulation, in which a species reduces its reproductive output. The drivers of cyclicity have been hotly debated over the past 50 years, but research has been constrained by a lack of long-term data.

Data from insects monitored in agricultural fields over decades by government extension agencies and pest control advisers have been used, historically, to inform within-year management recommendations. These data also offer an expansion to the foundation of species being evaluated to assess the drivers of population cycles and may discount some hypotheses. If species have population cycles in annual agriculture crops planted every year, for example, it discounts the long-held hypothesis that changes in perennial plant quality drive population cycles of herbivores.

Fig 1. The mean annual cabbage stem flea beetle larval density across 3,045 winter oilseed rape fields over 50 years in Southern Sweden. The population peaks approximately every eighth year.

For decades crop advisors and farmers in southern Sweden had observed that an agricultural pest in their winter oilseed rape (canola) fields, the cabbage stem flea beetle (Psylliodes chrysocephala) had consistent boom-and-bust cycles, just like the snowshoe hare (Fig 1). This was surprising, ecologically, for two reasons: 1) winter oilseed rape (or canola) is an annual crop planted and harvested in different fields each year, meaning plant quality is an unlikely driver of the cycles, and 2) annual cropping systems are exposed to high levels of disturbance, making a tightly coupled predator-prey system (e.g. lynx/hare) harder to imagine. Cabbage stem flea beetle adults feed and oviposit at the base of newly emerged winter oilseed rape plants from September through October (Fig 2). The damage of greater concern, however, is caused by stem and leaf mining from overwintering larvae (Fig 3).

Fig 2. Adult cabbage stem flea beetle (L), photo credit: Dimitri Geystor. Winter oilseed rape seedling with characteristic stippling damage from adult cabbage stem flea beetle feeding (R), photo credit: Sara Emery.

We leveraged 50 years of data from over 3,000 winter oilseed rape fields in southern Sweden, where cabbage stem flea beetle larvae were monitored (Fig 4), to quantify synchrony and cyclicity. We find that when the population of cabbage stem flea beetle in one subregion is booming the others are too across all five subregions (high spatial synchrony). We verified farmer observations that there are 8-year population cycles of cabbage stem flea beetle (Fig 5).

Fig 3. Larva of cabbage stem flea beetle emerging from a winter oilseed rape stem, photo credit: Gille San Martin.

In addition to quantifying both the cyclicity and synchrony of cabbage stem flea beetle populations across Southern Sweden, our results show that cold winters drive these cycles. Cold winters, in turn, are affected by The North Atlantic Oscillation weather system. This represents a significant step forward in recognizing that population cycles persist, even in highly disturbed landscapes, despite resource variability in location and area planted and pesticide use. It also highlights that climatic oscillations are an important driver of population cycles.

Fig 4. Map of Sweden, highlighted in grey, and the southern Scania region of cabbage stem flea beetle larvae data collection, in red.

Knowledge of the regional cyclicity can be used to predict larval abundance in an individual year, which is important for predicting future boom and bust years, but not for understanding between-field variability. By including field-specific variables known to affect larval survival, we improved our predictions of the larval density on the field scale.  We show that warmer autumns increase larval densities, while later planting date of the crop and cold winters decrease larval densities.  

Fig 5. This analysis shows strong correlations of cabbage stem flea beetle larval population sizes on the 8-year timescale.  Warmer colors show stronger autocorrelation and black lines indicate significance. We can see that population sizes 8 years apart are strongly correlated with each other (timescale) across the entire sampling period (year). For more information on how to interpret this figure see the associated paper!

Cold weather synchronizes populations, drives cyclicity and explains subregional deviations from cycles in cabbage stem flea beetle larval densities in southern Sweden. It is difficult to predict how climate change, which is expected to result in warmer, wetter winters in Sweden, may alter these historically consistent population patterns.

Author bio: Sara Emery

I am an applied ecologist currently working as a postdoctoral researcher at UC Davis. In my research I seek to understand the influence of global climate change on insect phenology using long-term historic data sets.

Twitter: @saraeemery

Website: https://karp.ucdavis.edu/people/sara-emery/

Read the paper

Read the full paper here: Emery, S.E., Klapwijk, M., Sigvald, R., Bommarco, R. and Lundin, O. (2022), Cold winters drive consistent and spatially synchronous 8-year population cycles of cabbage stem flea beetle. J Anim Ecol. Accepted Author Manuscript. https://doi.org/10.1111/1365-2656.13866

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מעבר להתרגלות: סביבה אנושית משפיעה על התנהגות הבריחה של סיקסקים בתגובה לאדם ולתן

/ Beth Preston / Leave a comment
בלוג זה מסופק על ידי בר-זיו מיכאל, סופר ארן, גורובוי אדל ושפיגל אור ומספר את #הסיפורשמאחוריהמאמר למאמר “מעבר להתרגלות פשוטה: בתי גידול עירוניים משפיעים על תגובת הבריחה של סיקסקים מאיום אנושי ולא אנושי“, שפורסם לאחרונה בעיתון של Journal of Animal Ecology. במאמר שלהם הם השתמשו בשיטה יחודית עם “ג’יפ-תן” כדי לחכות טורף מסוג תן, וחקרו איך סיקסקים מגיבים לאיום מסוג חדש וכך גם לאדם.

Click here for the English version of this blog post.

הסיקסק (Vanellus spinosus) היא ציפור מונוגמית שנשארת עם בן זוגה כל השנה. בזמן עונת הרבייה, רואים כיצד הסיקסקים שומרים על הקן ועל האפרוחים בצורה אגרסיבית עם קריאות רמות ותוקפים את מי שמתקרב בעזרת דורבן נסתר הנמצא בקצה הכנף. מין זה נחשב לאחד ממיני החופמאים הנפוצים ביותר בישראל, וניתן למצוא אותו במגוון גדול של בתי גידול הכולל סביבות טבעיות וכן ערים צפופות. דבר זה הינו די מפתיע, בהתחשב בכך שאוכלוסיות רבות של חופמאים הולכות ומתמעטות ברחבי העולם כיוון שהם דוגרי קרקע. בתי גידול טבעיים ברחבי העולם נהרסים בשביל צרכי האדם, דבר שמשפיע לרעה על מינים רבים שלא יכולים להתמודד עם השינויים המהירים הללו. סיקסקים לעומת זאת, לא רק מראים צמיחה בכמות שלהם, הם גם מצליחים לגדל צאצאים עד לגיל בגרות בתוך פארקים ואפילו ליד כבישים מהירים.

זוג סיקסקים (Vanellus spinosus) באזור בנוי. ניתן לראות סיקסקים רבים בישובים בעמק חרוד (צפון מזרח לישראל), אנו בדקנו כיצד החיים בבתי הגידול האלה משפיעים על התנהגות הבריחה שלהם (תמונה: אביחי רן).

בעוד חלק מהסיקסקים מעדיפים לחיות בקרבת אדם, זה לא תקף כלפי כולם. רוב הסיקסקים נמצאים באזורים טבעיים עם מפגשים מועטים עם אנשים. חיות בר שנמצאות בסביבות אדם בדרך כלל מראות מגוון התנהגויות אותן ניתן לסווג כהתנהגויות אמיצות, שלא מופגנות בבעלי-חיים מאותו המין מסביבות טבעיות. התגובות האמיצות הללו יכולות להיווצר בגלל הפחתה בפחד מאדם (או במילים אחרות התרגלות לאנשים ולבתי גידול עירוניים). לחילופין, יכולות תגובות אלו להצביע על מצב עמוק יותר אותו יוצר בית הגידול העירוני (למשל שפרטים בעלי תכונות אופי אמיצות יותר ימשכו לסביבות עירוניות).

סיקסק בודד בעיר בית-שאן, נשאר רגוע למרות שאנשים עוברים לידו. התרגלות לבני אדם יכולה להשפיע על התנהגות הבריחה שלהם ועל מרחק הבריחה ההתחלתי (FID). (תמונה: אביחי רן).

דרך פשוטה ומוכרת לבדוק אומץ במבחני שדה הוא לבדוק את מרחק הבריחה האופטימלי של החיה. בכלליות, בעלי חיים שבורחים מהר מדי מאיום שמתקרב לא יצליחו לנצל בצורה מלאה את סביבתם, בעוד שפרטים שנוטים לברוח מאוחר מדי עלולים להסתכן בטריפה. ההתנהגויות שבעלי חיים מציגים לאחר הבריחה חשובות גם כן, מכיוון שטורפים מסוכנים יותר דורשים תגובה מהירה יותר, וכך גם לברוח רחוק יותר ולמצוא מקום להתחבא. טורפים שונים גם דורשים אסטרטגיות שונות, לדוגמא כאשר מאיום מסוים כדאי לברוח מהר ורחוק, בריחה מאיום אחר יכולה להוות נטל. האסטרטגיות הללו יכולות גם להשתנות בין סוגים שונים של בתי גידול, ולדוגמא בסביבה עירונית פרטים שפוחדים בקלות ויברחו מכל אדם שעובר לא יהיו מסוגלים לנצל את הבית גידול באופן יעיל, ויעדיפו לחפש מזון במקום אחר.

תן זהוב (Canis aureus), אחד הטורפים המרכזיים של הסיקסקים והקינים שלהם בשדות חקלאיים. דימינו התקרבות של תן לסיקסקים כדי לבדוק האם התנהגות הבריחה שלהם נובעת מהתרגלות לבני אדם. (תמונה: מיכאל בר-זיו)

במאמר חדש שהתפרסם בעיתון Journal of Animal Ecology, בדקנו את התנהגויות הבריחה של סיקסקים. בדקנו קודם את מרחק הבריחה ההתחלתי שלהם, לאחר מכן את צורת הבריחה (ברגל או בתעופה), ולבסוף בחנו את המרחק אליו הם ברחו. בדקנו את ההתנהגויות הללו בין שלושת בתי גידול מרכזיים (סביבת אדם, בריכות דגים ושדות), וביצענו השוואה בין שני סוגי איום שמתקרבים (אדם או תן). בעוד בני אדם נפוצים בקיבוצים וישובים, תנים יותר נצפים באזורים טבעיים. תנים גם ידועים בכך שהם טורפים קינים של סיקסקים, אפרוחים ולפעמים גם בוגרים. כדי לדמות התקרבות של תן, השתמשנו בפוחלץ של תן צעיר רכוב על מכונית מסוות הנשלטת באמצעות שלט רחוק (בשם “ג’יפ-תן”). כדי למצוא סיקסקים בבתי גידול שונים, חיפשנו אותם בזמן נסיעה ברכב. בחרנו באסטרטגיה זו כי סיקסקים נוטים להתייחס פחות לרכבים, דבר שאפשר לנו לזהות אותם בקלות מבלי להפריע להם. ברגע שזיהינו סיקסק, התחלנו לבחון את התנהגויות הבריחה שלו באמצעות אדם או תן.

הרכבת ה”ג’יפ-תן” מודל של תן שנועד לדמות התקרבות של טורף. השתמשנו במודל זה כדי להסיק האם סיקסקים מסביבה אנושית התרגלו לבני אדם, או שהם אמיצים באופן כללי בפני טורפים שמתקרבים אליהם.

מטרת מחקר זה הייתה להבין: 1) האם פרטים שנמצאים בסביבה אנושית מראים התנהגויות אמיצות יותר באופן כללי משאר בתי הגידול? 2) אם כן, האם ההתנהגות האמיצה הזאת נובעת מהתרגלות לבני אדם, או שהיא מצביעה על תופעה נרחבת יותר (כמו למשל שסביבת אדם מושכת פרטים בעלי אופי אמיץ יותר)? אם סיקסקים מראים תגובה חזקה יותר לתן מאשר לאדם, זה אומר שככל הנראה סיקסקים התרגלו לאנשים בבתי הגידול הללו. לעומת זאת, אם אנחנו רואים שסיקסקים מגיבים בצורה זהה לשתי האיומים שמתקרבים יתכן וזה מצביע על אפקט עמוק יותר שסביבה אנושית יוצרת כלפי בעלי חיים.

מבחינת השאלה הראשונה, מצאנו שאכן סיקסקים שנבדקו בסביבות אדם היו אמיצים יותר בכל התנהגויות הבריחה שלהם. ראשית, הם הראו שהם נותנים לאיום להתקרב יותר לפני שבורחים, דבר שני, גם לאחר הבריחה הם עדיין הציגו התנהגויות אמיצות שכללו בריחה ברגל ובריחה לטווח קצר. תופעה מעניינת שעלתה כשבדקנו את השאלה השנייה היא שסיקסקים מסביבות אדם מגיבים באומץ גם לתן שמתקרב. תוצאות אלה מראות לא רק שסיקסקים אמיצים באופן כללי לבני אדם בבתי גידול אלו, אלה יותר חשוב, הן מראות שהאומץ שהסיקסקים מפגינים לא מגיע מהתרגלות לבני אדם אלה מסיבה אחרת.

קבוצה של סיקסקים מתקבצים באזור תעשייה ליד בית שאן (תמונה: מיכאל בר-זיו)

תוצאות אלו יכולות לתת לנו רמז לאפקט שהפרעות אנושיות יכולות לגרום בבעלי-חיים. המאמר שלנו מראה שיש פרטים שיכולים להתאים את עצמם לסביבת אדם, אך במחיר מסוים. בשביל לעשות זאת, הם צריכים לדכא את תגובת הפחד שלהם. אסטרטגיה זו עלולה להיות מסוכנת, שכן למרות שרוב האנשים לא ינסו לפגוע בהם, ברגע שיתקרב אליהם גורם מסוכן שכן יבקש לפגוע יהיה להם קשה יותר להימנע מסיטואציה זו. בעולם שמשתנה במהירות והופך ליותר עירוני, ממצאים כאלה הם הכרחיים על מנת שנוכל להבין את השפעת הפיתוח והבנייה על אוכלוסיות של חיות בר, ואפילו במינים שבמבט ראשון נראה שהם יותר עמידים להפרעות אלו.

קראו את המאמר כאן:

Bar-Ziv, M., Sofer, A., Gorovoy, A., & Spiegel, O. (2022). Beyond simple habituation: Anthropogenic habitats influence the escape behaviour of spur-winged lapwings in response to both human and non-human threats. Journal of Animal Ecology, 00, 1– 13. https://doi.org/10.1111/1365-2656.13858

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Beyond simple habituation: Anthropogenic habitats influence the escape behavior of spur-winged lapwings in response to both human and non-human threats

/ Beth Preston / Leave a comment
This blog post is provided by Bar-Ziv Michael, Sofer Aran, Gorovoy Adel and Spiegel Orr and tells the #StoryBehindthePaper for the paper “Beyond simple habituation: Anthropogenic habitats influence the escape behavior of spur-winged lapwings in response to both human and non-human threats“, which was recently published in Journal of Animal Ecology. In their paper they use a unique “Jack-Truck” to simulate a jackal predator, and explore how lapwings respond to novel predators and humans.

לחצו כאן בשביל הבלוג בשפה העברית

Spur-winged lapwings (Vanellus spinosus) are monogamous birds that tend to stay with their partner all year round. During the breeding season they guard their nest and chicks with intimidating calls, attacking everything that get close with sharp spurs located on their wings. This species is considered to be one of the most common waders in Israel, and can be found in a variety of habitats, including natural habitats, as well as dense cities. This fact is quite surprising, considering that wader populations are declining worldwide due to the fact that they nest on the ground. Natural habitats across the world are being destroyed to make way for human needs, which in turn negatively affect a large number of species that cannot cope with the changes. Lapwings, on the other hand, not only represent a growing population, but they are also found to be able to nest and raise their chicks into adulthood in parks and even next to highways.

A couple of Spur-winged lapwings (Vanellus spinosus) in a built-up area. Lapwings occupy various settlements in the Harod Valley (north-east of Israel), and we explored how living in these habitats affects their escape behavior (Photo: Avichai Ran)

While some lapwings prefer to live next to human settlements, not all of them do. Most of the lapwings stay in more natural areas with fewer encounters with humans. Wild animals that live in proximity to humans usually present a bolder set of behaviors, which differ from populations of the same species that live in a more natural habitat. Those bolder responses can be a result of fear reduction toward humans (in other words, habituation to an urban environments), or alternatively present a larger effect that the urban environment creates (for example individuals with bolder personality reside in more urban settings).

A spur-winged lapwing in the town of Beit-She’an, keeping calm in face of passing pedestrians. Habituation to humans may affect their escape behavior and flight initiation distance (FID). (Photo: Avichai Ran)

A simple and well-known method to test boldness in field conditions is testing the animal’s flight initiation distance behaviour (or FID). Generally, animals that escape too early from an approaching threat will not be able to fully exploit their environment, while on the other hand those that are escaping too late might be at risk of getting caught by a predator. The behaviours animals present after their initial escapes are important as well, because more lethal predators may require a faster reaction, fleeing further away and finding a place to hide. Different predators also require different escape strategies, and while with one type of threat it is worthwhile escaping fast and far, in others it can be a burden. Those strategies can also differ between habitat types, for example, in urban settings individuals that are too scared and will flee from every person passing by, won’t be able to exploit this habitat properly and might prefer to forage in other areas.

A golden jackal (Canis aureus), one of the main predators for lapwings and their nests in the natural and agricultural habitats. We simulated an approaching jackal to generalize lapwings’ response beyond habituation to humans. (Photo: Michael Bar-Ziv)

In a recent paper in the Journal of Animal Ecology, we tested the escape behaviour of spur-winged lapwings. More specifically, we first looked at their flight initiation distance, their mode of escaping (by foot or flight), and finally what distance they fled. We tested those behaviors between three habitat types (human-dominated, water ponds, and fields), and compared them to two kinds of approaching predators (a human and a jackal). While humans are abundant in urban settings, jackals tend to be found in natural environments. Jackals also prey on lapwing nests, chicks, and potentially also on the adults. To mimic an approaching jackal, we used a taxidermy of a young jackal mounted on top of a camouflaged, off-road remotely controlled vehicle (named “Jack-Truck”). To find lapwings in the different environments, we searched for them while driving. We choose this strategy because lapwings tend to be less alert to driving vehicles, which made it easy to notice them without disturbing them. Once a lapwing was spotted, they were approached by a human, or a jackal and the escape sequences mentioned above were recorded.

Assembling the “Jack-Truck”, a jackal model used to simulate an approaching jackal. We used this Jack-Truck to determine if lapwings within settlements are merely more habituated to humans, or whether they are generally bolder in face of an approaching predator (Photo: Assaf Uzan).

The purpose of this experiment was to understand 1) if individuals found in urban setting show a general bolder response to approaching threats when compared to other habitats? And 2) if so, does this bolder response derive from simple habituation to humans, or does it represent a larger phenomenon (such as human settlements attracting generally bolder individuals)? If lapwings showed a stronger reaction to the jackal compared to a human in human-dominated environments it might hint towards habituation, because they were more afraid of a novel predator. On the other hand, having the same reaction to both predator types might suggest a deeper effect those habitats have over these animals.

Examining our first question, we found that lapwings from human-dominated habitats were bolder in most of the sequences of the escaping behavior. First, as expected, they presented a shorter FID when approached. Secondly, even after escaping they still presented bolder behaviors by fleeing to a shorter distance and more likely to escape by running (rather than flying). Interestingly, when considering our second question, we found that lapwings tested in human-dominant habitats presented a bolder respond to both a human as well as a jackal approaching. Those results show that lapwings not only present a bolder behavior in human settlements, but more importantly, it shows that habituation to humans cannot be the only explanation for the bolder response.

A group of spur-winged lapwings gathering near a construction site next to the town of Beit-She’an (Photo: Michael Bar-Ziv)

Those results can give us a hint of the effects human disturbance have on animals. Our paper shows that some individuals can become accustomed to human settlements, but it has a cost. To do so, they will need to reduce their fear response. This can be a dangerous strategy, because while most people will not try to harm them, once a more lethal predator approaches them, it could be more difficult for them to avoid this situation. In a fast-changing world that is becoming more urbanized, findings like these are essential for understanding the impact human-development has on wildlife populations and communities, even in species that at a first glance appear more resilient to those changes.

Read the paper

Read the full paper here: Bar-Ziv, M., Sofer, A., Gorovoy, A., & Spiegel, O. (2022). Beyond simple habituation: Anthropogenic habitats influence the escape behaviour of spur-winged lapwings in response to both human and non-human threats. Journal of Animal Ecology, 00, 1– 13. https://doi.org/10.1111/1365-2656.13858

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Dispersal mode and competition type matter for outcomes of the competition-colonization trade-off

/ Beth Preston / 1 Comment
This blog post is provided by Ilia Maria Ferzoco and Shannon McCauley and tells the #StoryBehindthePaper for the paper “Breaking down the components of the competition-colonization trade-off: New insights into its role in diverse systems“, which was recently published in Journal of Animal Ecology. In their concept paper they explore how dispersal and competition might impact how species compete and coexist, depending on how they can compete and colonise new areas.

If you go out to a pond, or go out for a hike in the forest, even though many of us are great naturalists, we often encounter organisms that seem nearly indistinguishable. These species may live in the same places, behave in similar ways, and even look so similar that we need experts to tell them apart. But, these are different species, seemingly occupying similar niches and yet they are able to live together. The question of how similar species coexist has been a huge puzzle in ecology – what allows similar species to coexist?

Coexistence of similar species may depend on niche partitioning in aspects of space and/or time that are not immediately observable. One way they can do this is through the competition-colonization (CC) trade-off. This is the idea that the ability to be a good disperser (or successfully move and establish at a new habitat patch) trades-off with the ability to be a good competitor locally. By separating in these two life history strategies, the two species can coexist regionally in the landscape, as the more effective disperser will move onto habitat patches in which the dominant competitor has not yet arrived.

However, there is active debate in the literature about the importance of this competition-colonization trade-off for species coexistence. This trade-off has been well documented in passive dispersers such as plants and passively dispersing microorganisms, and the CC trade-off literature really took root (pardon the pun) from these passive disperser systems. However, our understanding in actively dispersing organisms like many animal systems which are characterized by making their own dispersal decisions and powering their own movement, remains relatively limited. We believe the debate in the literature stems largely from not explicitly considering the role of dispersal mode and competition type on this trade-off.  Therefore, progress in reconciling this debate will come from thinking explicitly about dispersal mode and competition type.

This adult dragonfly is an active disperser, making decisions about movements and powering its own flight (Photo credit: Shannon McCauley)

In this Concept paper we recently published, we wanted to understand how dispersal mode comes into play with the competition-colonization trade-off, and how the type of competitive dominance could impact the presence of the trade-off in a range of systems. With dispersal mode, we considered distinctions of passive and active dispersal. For type of competitive dominance, we distinguish differences between competitive response vs competitive effect. Namely, competitive response is the ability to withstand resource depletion, and competitive effect is the ability to pre-empt resources. We combined an outline of this framework for integrating dispersal mode and competitive type with a review of the existing literature in which we categorize systems based on these dimensions.

Here we developed a conceptual trait-based framework that outlines how dispersal mode and type of competitor may interact to shape this trade-off at the stage of dispersal and establishment in a variety of systems, in order to orient effective empirical tests of the CC trade-off and encourage researchers to fill in gaps in our understanding of this trade-off empirically. This framework links traits underlying competitive dominance and dispersal ability in systems that range from passive to active dispersal and measuring competitive response vs competitive effect. For example, propagule or body size tends to be negatively correlated with dispersal ability in passive dispersers (but positively related to competitive ability), whereas, in active dispersers like many animals, large body size can confer both a dispersal and competitive advantage depending on the ecological context. Thus, these relationships between species traits and competitive or dispersal abilities should depend on the competitive contexts and dispersal scenarios, and that recognition of these specific contexts will aid in guiding empirical investigations of the CC trade-off. Overall, we show that trade-offs between dispersal and competition may be very multifaceted in real systems especially when considering the differences that may come about depending on traits underlying performance in passive or active dispersal and in the ecological contexts experienced by the organisms. Our review found mixed support for competition-colonization trade-offs but also critically we found that some systems are so understudied that it’s not possible to reach general conclusions about how common this trade-off is for many groups of organisms, particularly those that disperse actively.

Diagram of distinctions for passive and active dispersal systems across response and effect competition contexts for the competition-colonization trade-off.

Ultimately, ecological communities are shaped by a number of processes occurring locally and/or regionally. In order to understand patterns of biodiversity, integrating our understanding of how processes at various scales interact in a variety of systems is essential. Although dispersal mode and type of competition is just one set of ecological contexts investigated in this paper, more research into the various contexts impacting interactions between competitive rank and dispersal ability in real world systems is needed to understand whether the CC trade-off operates in a range of systems. Our hope with this Concept paper is that we are moving one step closer to understanding how trade-offs in competition and dispersal impact community assembly in a range of diverse systems, and we hope that the framework outlined will help to prompt effective assessment of this performance trade-off and its role in shaping community structure.

About the authors

Ilia Maria Ferzoco is a PhD candidate at the University of Toronto, in the Department of Ecology and Evolutionary Biology, based at Department of Biology, University of Toronto Mississauga. Her studies focus on the mechanisms structuring freshwater pond insect communities. Her MSc, from which this papers’ ideas developed, examined coexistence in semi-aquatic insects via the competition-colonization trade-off. In her PhD, she investigates the processes structuring the ecological diversity and functional composition of urban stormwater pond insect communities.

Shannon McCauley is an Associate Professor at the University of Toronto Mississauga, graduate department of Ecology and Evolutionary Biology. Her research deals with the community ecology of freshwater insects. She uses dragonflies and other aquatic insects to investigate freshwater community structure involving dispersal, connectivity, biotic interactions, and the effects of climate change and urbanization, while integrating processes at local and regional levels.

Read the full paper here:

Ferzoco, I. M. C., & McCauley, S. J. (2022). Breaking down the components of the competition-off: New insights into its role in diverse systems. Journal of Animal Ecology. 1–15. https://doi.org/10.1111/1365-2656.13845

Why do birds of a feather flock together?

/ Beth Preston / Leave a comment
This blog post is provided by Shannon Buckley Luepold and tells the #StoryBehindthePaper for the paper “Habitat detection, habitat choice copying, or mating benefits: what drives conspecific attraction in a nomadic songbird?“, which was recently published in Journal of Animal Ecology. The authors explored why wood warblers settle near each other, comparing hypotheses about other birds acting as a signal of good habitat, simply copying other birds, or gaining mating benefits from settling near others.
Conspecific attraction and why it matters:

The tendency for animals to settle in locations where other members of their species are already present (“conspecific attraction”) has long intrigued behavioural ecologists. This behaviour has also drawn the attention of conservation biologists, who have explored how conspecific attraction might facilitate settlement in desired locations. Despite longstanding interest in this topic, however, there is still much uncertainty about why attraction occurs. Importantly, the more we can learn about why animals choose to settle near other individuals, the better equipped we are to understand why they might not make this choice when we desire or expect them to.

Study species:

In our study, we investigated conspecific attraction during breeding habitat selection in the wood warbler Phylloscopus sibilatrix. Wood warblers are migratory songbirds that breed in the temperate forests of Europe and spend much of the non-breeding season in sub-Saharan Africa. Weighing in at only 10 grams, these lemon-colored birds sing a silvery trill song that has been likened to the sound of a spinning coin on a marble slab. Natural history accounts often describe wood warblers forming “territory clusters” during the breeding season, and birds have been attracted to settle near speakers broadcasting conspecific song in both Switzerland and Poland. We studied a population of wood warblers breeding in the Swiss Jura Mountains.

Singing male wood warbler (Photo credit: Sandro Carlotti).
Our hypotheses:

We tested three hypotheses for why conspecific attraction occurs in male wood warblers. Two of these were based on social information (i.e. information that is gained from observing or interacting with other individuals). According to the habitat detection hypothesis, the presence of others at location X informs individuals looking for somewhere to settle that the habitat at location X might be good, and is certainly worth checking out. Whether attracted individuals choose to remain at this exact location or not, however, depends on their own assessment of the habitat. Thus, this hypothesis predicts that within a forest, spatial variation in habitat will be more important than conspecific locations as a predictor of male settlement patterns. Alternatively, the habitat choice copying hypothesis suggests that settling individuals are simply copying (i.e., imitating) the choices of others, which, by definition, means they do not make (or heed) their own assessment of the habitat. Thus, this hypothesis predicts that conspecific locations will be more important than spatial variation in habitat as a predictor of male settlement patterns.

The third hypothesis that we tested was the female preference hypothesis, which suggests that males derive mating benefits from being in a group. According to the female preference hypothesis, females prefer males that are aggregated because this facilitates comparison of potential mates. Thus, this hypothesis predicts a positive relationship between male pairing success and male aggregation.

Reduced nest predation is another common hypothesis for territory aggregation that is based on group benefits, but we considered it less relevant for wood warblers because predation often happens in contexts when group defense behaviours do not typically occur (e.g., at night, by relatively large mammals).

Wood warbler nest being predated by a marten (Photo credit: Shannon Luepold)
Wood warbler nest being predated by a fox (Photo credit: Shannon Luepold)

Our methods:

To determine the relative importance of spatial variation in conspecific presence and habitat features, we first manipulated the locations where social information was available by broadcasting wood warbler songs from an array of speakers in several forests. We did this for two breeding seasons (unluckily for our field team carrying car batteries for the playback stations, wood warblers have a habit of choosing the steepest hills for breeding sites…).

Intrepid field assistants carrying song playback sets on a snowy April day (Photo credit: Florian Moser).

We then used point pattern analyses to assess whether speaker locations or spatial variation in habitat features was the stronger predictor of male settlement patterns.

We used an unconventional approach to represent spatial variation in habitat features. Given that female wood warblers prospect for nest sites and choose them with little regard for male territory boundaries, we assume their choices reflect the presence of habitat features they find attractive. Therefore, we used kernel density estimation to create maps of spatial variation in “habitat attractiveness,” which were based on all known wood warbler nest locations within a forest (including up to 10 years of data). Of course, when making the habitat attractiveness maps for predicting male settlement in year t, we did not include nests from year t because male and female locations within the same year are not independent. With this approach we avoided making assumptions about which specific habitat features birds were cueing in on, and instead based our definition of attractive habitat on patterns in the choices of the birds themselves.

To address the female preference hypothesis, we determined the spatial arrangement of males that were available to each settling female. Then we determined the “connectivity” of each male in a female’s set, a metric from metapopulation theory which we used to represent the number and proximity of neighboring males. With this information, we could model whether males that were more aggregated (i.e., with higher connectivity) were more successful in gaining a mate.

Female wood warbler in nest (Photo credit: Michael Gerber).
What we found:

We found that spatial variation in habitat was more important than conspecific (speaker) locations as a predictor of male settlement patterns, and we found that being aggregated did not increase a male’s success in attracting a mate. Thus, our data were most consistent with the habitat detection hypothesis, suggesting that singing conspecifics simply alert other individuals to the presence of potential habitat. The ultimate benefit of using social information in this way could be reduced search time, which may be especially relevant for species like the wood warbler that move breeding sites both within and between years.

Wood warbler habitat in the Swiss Jura Mountains (Photo credit: Lukas Linder).
Going forward:

The results of our study highlight the hierarchical process behind settlement decisions and underscore the contingent nature of conspecific attraction. We encourage future research on these topics to carefully distinguish making the same choice as others from copying the choice of others. When studying clustered distributions, it may be useful to consider the processes by which animals detect and assess habitat in addition to explanations based on benefits that accrue from aggregation per se.

Author bio

Shannon Luepold recently received her PhD from the University of Zürich and is currently a postdoctoral researcher at the Swiss Ornithological Institute. She is broadly interested in the behavioural ecology and natural history of birds, but is particularly fascinated by social interactions and vocal behaviour.

Read the paper

Read the full paper here: Luepold, S. B., Kokko, H., Grendelmeier, A., & Pasinelli, G. (2022). Habitat detection, habitat choice copying or mating benefits: What drives conspecific attraction in a nomadic songbird? Journal of Animal Ecology, 00, 1– 12. https://doi.org/10.1111/1365-2656.13844

Climate Change Genomics workshop: Vulnerability, adaptations & applications

/ Beth Preston / Leave a comment
How can genetic and genomic tools improve our capacity to assess species vulnerability and study adaptations to climate change? Orly Razgour, Tin Hang (Henry) Hung, Regina Kolzenburg, and Brenna Forester report on their international online 3-day workshop held in September 2022.

Climate change is producing a range of new selection pressures, forcing species to shift their ranges to track suitable climates or adapt to changing conditions in order to survive. Despite the importance of genetic diversity for species ability to respond to environmental change, it has been largely overlooked in conservation policy, and genetic/genomic tools remain under-utilized in conservation management. Recent reviews, collaborative networks and initiatives have highlighted the importance of considering genetic diversity and the community of researchers using genetic/genomic tools to study impacts of climate change has been growing, with several new approaches and frameworks developed over the past few years.

The Climate Change Genomics workshop, organised jointly by the British Ecological Society Climate Change Ecology and Ecological Genetics Special Interest Groups, was convened with the goals of discussing methodological developments, evidence, and applications as a research community to foster the development of best practices for applying genetic and genomic tools to climate change research. The workshop brought together international experts, early career researchers, and everyone in between, working across a variety of ecological systems to promote better integration of genomic approaches in both climate change research and biodiversity conservation. Each day of the workshop contained two sessions featuring invited and contributed talks followed by a breakout discussion relevant to the state of the field. The workshop included presentations from 19 invited speakers and 27 submitted presentations, as well as group and panel discussions, and was attended by more than 150 participants from around the world covering research across all continents.

Day 1 of the workshop focused on methods to assess vulnerability to climate change using genomic tools. The workshop opened with an invited talk by Dr Ary Hoffmann, who provided a synthesis of climate change adaptation research in Drosophila, emphasizing the importance and limitations of adaptive potential in response to changing climate, variation in responses across species, and challenges associated with interpreting -omics data. Following on from this, Dr Line Bay presented work on the enhancement of coral reef heat and bleaching tolerance and its application to conventional and active coral reef management. Dr Chris Barratt then discussed the assessment of intraspecific climate change vulnerability through the integration of environmental, ecological and molecular data. In the second session of Day 1, Dr Kristen Ruegg presented on the use of citizen science data, measures of fitness, hindcasting, and analysis of historical genetic samples to validate estimates of genomic offset to improve climate change predictions. Dr Thibaut Capblancq built on this topic with his presentation on modelling the genotype-environment relationship in a climate change context and its value for informing conservation planning. The final invited talk of the day was from Dr Steven Franks who explored genomic responses to drought in the annual plant Brassica rapa and how these responses were revealed by evolve-and-resequence studies in natural and experimental populations.

Participants and attendees joined breakout sessions to discuss frontiers in methods development for assessing climate change vulnerability, as well as best practices for applying these methods. Key discussion points included the importance of developing criteria for validation of climate change projections, accounting for novel environments and uncertainty, and the need for simulation studies and open data sharing.

Day 2 of the workshop focused on evidence of genetic adaptation and responses to climate and climate change. Dr Lesley Lancaster started off the invited talks with a presentation on genetic signatures of rapid range expansion in a model damselfly species. Dr Carla Sgro followed up with a discussion of the complexities of recent genomic and phenotypic evidence for range shifts and climatic adaptation in Drosophila. Next, Dr Jon Bridle presented research on the narrowing of future ecological resilience in a European butterfly due to evolutionary adaptation in response to climate change. Dr Ann-Marie Waldvogel finished out the first session with her talk on the importance of temperature when studying climate adaptation, both in terms of its direct effects on organismal physiology as well as at the level of biochemical processes. The second session began with a talk from Dr Sally Aitken on the genomics of climate adaptation in long-lived conifers, including the importance of assessing the impact of geographic scale on genomic offset predictions of maladaptation. Next, Dr Jorge Ramos presented on population genetic signatures of a recent marine range expansion in Australia. Dr Chris Funk ended the day of invited talks with a presentation on predicting vulnerability to climate change by linking environmental heterogeneity to genetic and phenotypic variation in cold-adapted mountain stream frogs.

Breakout sessions discussed how to move beyond identifying genetic adaptations to climate and toward identifying adaptive responses to climate change in long-lived organisms. The challenges and value of working with historical datasets were noted, along with the critical value of long-term studies. Participants also discussed best practices for evaluating evidence for adaptive responses to climate change through integrating multiple lines of evidence, disentangling plasticity from genetic change, and using high quality, annotated, chromosome-level genomes.

Day 3 wrapped up the workshop with applications of genetic/genomic tools in policy, conservation management and monitoring. Dr Chris Brauer started the day off with a talk on a decade of conservation genomics applications in the recovery of two species of threatened pygmy perches in southeastern Australia. Dr Olivier Broennimann then presented work on prioritizing genomic sampling based on environmental marginality to maximize the detection of locally adapted populations and potential adaptational lag under climate change. Next, Dr Rajeev K. Varshney discussed genomics-assisted breeding for the development of climate change ready and nutrition-dense crops to promote food security in developing countries. In the second session, Dr Sean Hoban talked about the use of genetic indicators and ecogeographic summaries to promote the conservation of genetic diversity and climate change resilience, even in the absence of genetic data. Dr Shawna Zimmerman then presented research on the conservation implications of adaptive divergence in two North American habitat specialists, the greater sage-grouse and white-tailed ptarmigan. Finally, Dr Jessica Wright discussed the use of genomics-informed seed transfer in post-fire reforestation of climate-change impacted landscapes in California.

Each session ended with panel discussions including all of the day’s speakers addressing how to move the field forward to ensure better integration of genomic approaches in climate change research, management and policy. Speakers, participants and attendees also discussed overall best practices for applying climate change genomics. Discussions focused on the importance of long-term adaptive monitoring in applied climate change research, considering societal involvement, including community science, building research jointly with stakeholders, as well as expanding collaboration across disciplines.

The broad engagement with the workshop highlights the growing interest in the emerging field of climate change genomics and the need to develop best practices and to promote translation of research into climate change policy and adaptive conservation management.

For more on Understanding climate change response in the age of genomics, take a look at our Special Feature.

Kuishi pamoja kunawezekana: fisi madoa wanaongiliana na mifugo nyakati za mchana hufanya vizuri

/ Beth Preston / 1 Comment
Chapisho hili la blogu limetolewa na Arjun Dheer na Philemon Naman na linaambia #StoryBehindthePaper kwa jarida la ‘Ufugaji wa kila siku haupunguzi uajiri wa vijana wala kuinua mzigo wa fisi wenye madoadoa’, ambayo ilichapishwa hivi majuzi katika Journal of Animal Ecology. Katika utafiti wake, anachunguza athari za ufugaji kwa idadi ya fisi walio na madoadoa katika Ngorongoro, na kugundua kuwa hawaonekani kuwa na mkazo na idadi ya watoto walioajiriwa haikutofautiana kati ya maeneo yenye ushawishi wa kibinadamu na maeneo yasiyo na.

Blogu inaweza kupatikana kwa Kiingereza hapa.

Binadamu huweza kuathiri wanyamapori, lakini si rahisi mara zote kutathmini athari zinazohusiana na uhifadhi. Kwa hakika, shughuli za kibinadamu huweza kuathiri wanyama katika njia nyingi- wanaweza kulazimika kutuepuka na kuwa makini zaidi usiku, kubadilisha maeneo ya malisho na hata kubadili mlo. Mara nyingi imekuwa ikidhaniwa kuwa athari hizi ni mbaya kwa wanyama na kwamba wanyamapori hupata tabu kukabiliana na mabadiliko hayo ya kitabia.  Hakika, hili ni suala la kiuhifadhi linaloleta sintofahamu. Je, ni kweli?

Si lazima. Wanyama wengi huweza kubadili tabia zao kuendana na mabadiliko hayo katika mazingira yao bila kuathiri uwezo wao wa kuishi na kuzaliana. Mabadiliko ya kitabia, kwa hivyo haimaanishi kuwa kuendelea kwa idadi ya wanyamapori kunatishiwa. Kujua kuwa idadi ya wanyama iko kwenye tishio la kutoweka ni ngumu. Na ni vigumu hasa kufanyia tafiti spishi kubwa, zinazoishi muda mrefu – kama vile fisi madoadoa (Crocuta crocuta) – ambao mara nyingi huingia kwenye migogoro na wanadamu na hivyo kuhitaji kupewa kipaumbele ili kukuza kuishi pamoja na binadamu. Kufanya utafiti wa hivi kunahitaji data za muda mrefu, unaojikita hasa katika vipengele viwili vikuu: usawa wa kibiolojia na fiziolojia.

Usawa wa kibiolojia unarejelea uwezo wa kiumbe kuishi, kuzaliana, na kuchangia uzao kwa kizazi kijacho. Fiziolojia ni dhana pana inayorejelea jinsi mwili wa kiumbe unavofanya kazi kunakoruhusu kuishi na kuzaliana. Kupima mabadiliko katika vigezo hivi ni muhimu sana kwa uhifadhi kwa sababu ya namna yanavyoathiri moja kwa moja kuendelea kuwepo kwa wanyamapori. Na ndivyo hasa tulivyochunguza.

Fisi mwenye madoadoa akiwa karibu na wafugaji wa Kimasai na ng’ombe wao wakichunga katika Kreta la Ngorongoro. Picha: Oliver Höner

Tulitumia jaribio la asili kuchunguza koo za fisi zilizofikiwa na ambazo hazikufikiwa na shughuli za binadamu. Kwa utafiti wetu, tulikusanya data kwa miaka 24 (1996-2019) kutoka kwa vikundi nane vya kijamii vya fisi (“koo”) wanaoishi katika eneo la Kreta ya Ngorongoro, Tanzania. Koo mbili za Kreta – ambazo tunaziita Airstrip na Forest – zilikabiliwa na ufugaji unaofanywa na jamii ya Wamasai kutoka 1996-2016. Ufugaji ni shughuli na mtindo wa maisha ulioenea duniani kote ambapo watu hufuatana na mifugo yao kwenye malisho ya malisho, vyanzo vya maji, na kulamba madini. Koo zingine sita hazikuathiriwa na ufugaji. Hili lilitupatia jaribio la asili: tuliweza kulinganisha jinsi koo zilizofikiwa/athiriwa na ufugaji zilivyo ikilinganishwa na zile ambazo hazikufikiwa/athiriwa na ufugaji.

Kupima uzalianaji na ukuaji wa watoto hutoa taarifa muhimu juu ya “afya” ya koo za fisi. Ili kupima athari za usawa wa kibiolojia, tulilinganisha uzalianajia na ukuaji wa watoto – yaani, idadi ya watoto waliosalia na kukua – katika koo zilizofichuliwa na ambazo hazijafichuliwa. Kuhusu fiziolojia, tulilinganisha mkusanyiko wa glukokotikoidi kwenye kinyesi chao, au ‘mkazo’. Kiwango cha “mfadhaiko au mkazo” huonyesha mzigo unaoongezeka ambao kiumbe hupitia kutokana na matukio ya maisha, iwe ni mwingiliano wa kijamii na wenza katika kikundi au usumbufu unaosababishwa na binadamu. Ili kufanya hivyo, tulikusanya sampuli za kinyesi 975 kutoka kwa fisi 475 tofauti katika kipindi chetu cha utafiti na kupima ‘mfadhaiko au mkazo’ katika kila mmoja.

Mwisho kabisa, ili kutenganisha athari za ufugaji na hali nyingine za mazingira, tulikusanya pia data kuhusu mambo mengine katika kipindi cha utafiti wetu – matukio ya milipuko ya magonjwa, hatari ya kukutana na simba, na upatikanaji wa mawindo.

Kinyume na matarajio yetu, uzalianaji na ukuaji wa watoto katika koo zilizofikiwa na ufugaji ulikuwa juu kidogo kuliko katika koo ambazo hazikufikiwa. Vile vile, “athari za mkazo” ilifanana sana kati ya fisi kutoka makundi yaliyoathiriwa na yale ambayo hayakuathiriwa. Kwa ujumla, inaonekana kwamba ufugaji haukuwa tishio hata kidogo kwa koo zilizofikiwa na ufugaji katika Kreta ya Ngorongoro. Koo zilizofikiwa na ufugaji zilifanya sawasawa na koo ambazo hazikufikiwa, na pengine zilifanya vyema kidogo zaidi!

Sababu mbili kubwa zinazoweza za kwa nini hakukuwa na athari hasi kwa koo zilizoathiriwa ni kwamba ufugaji (i) ulikuwa wa kutabirika, kwani ulitokea kwa njia mahususi za kuingia na kutoka nje ya Kreta na (ii) ulifanyika wakati wa mchana tu. Kwa sababu ulikuwa unatabirika, huenda fisi waliweza kuzoea mwenendo wa kila siku wa ufugaji bila masuala mengi. Na kwa sababu ilitokea wakati wa mchana, ilimaanisha ufugaji haukuleta usumbufu sana kwa tabia kuu za fisi – yaani kuwinda na kunyonya. Kunyonya kwa watoto wachanga mara nyingi hutokea wakati wa mchana, lakini mama wanaweza kuwa na uwezo wa kurekebisha nyakati za kunyonya usiku ili kuepuka ufugaji.

Mtoto wa fisi mwenye madoadoa hupumzika kunyonya wakati wa mchana. Picha: Arjun Dheer

Juu ya hayo yote, mfumo wa kijamii wa fisi unaweza kuwa na umesaidia. Koo za fisi zina mfumo madhubuti wa uongozi au mfumo wa cheo. Fisi wa vyeo vya juu huwa wanachangia watoto wengi zaidi kwa idadi, na kutokana na sababu kadhaa, wana uwezekano mdogo wa kukabiliwa na changamoto kama vile ufugaji. Inawezekana kwamba fisi wa ngazi za chini wanaweza kuwa wamefyonza athari zozote za ufugaji; watoto wao wengi hufa hata katika nyakati nzuri zaidi. Wanapokabiliwa na ufugaji, watoto wao wanaweza kufa mapema tu, na kuacha utendaji wa jumla wa ukoo bila kuathiriwa.

Hatimaye, wingi wa mawindo ya Kreta la Ngorongoro ikilinganishwa na ukubwa wa idadi ya fisi (yaani, “mawindo mengi kwa kila mmoja”) yanaweza kuwa yamelinda koo zilizofikiwa kutokana na athari mbaya za ufugaji. Bonde la kreta ina msongamano mkubwa zaidi wa mamalia wakubwa Duniani, na hiyo inamaanisha kuwa fisi hufurahia mawindo mwaka mzima, angalau wakati mwingi wa kipindi chetu cha utafiti. Hii inaweza kuwa iliruhusu fisi mama kutoa maziwa mengi ili kulea watoto wenye afya nzuri, na hatimaye kuzifanya koo hizo ziendelee kuzaa.

Matokeo yetu yana maana kubwa… lakini yanapaswa kutafsiriwa kwa tahadhari. Matokeo yetu yanapendekeza kwamba shughuli za binadamu zinaweza kuwa endelevu na salama kuishi pamoja na wanyamapori mradi tu hazisumbui sana tabia kuu. Pili, tumeangazia umuhimu wa kuzingatia athari za shughuli za binadamu kwa kuzingatia mifumo ya kitabia ya mnyama na mfumo wa kijamii. Na tatu, kwa kupima uzaaji na ukuaji wa watoto katika ngazi ya koo, tumetoa mbinu mpya ya utafiti wa mwingiliano wa binadamu na wanyamapori unaolenga spishi zinazoishi katika vikundi.

Kwa yote yaliyosemwa, matokeo yetu yanahusu hali maalum sana. Katika maeneo ambayo shughuli za binadamu ni kali zaidi na hali ya kimazingira sio bora kuliko katika Kreta, ufugaji unaweza kuwa na athari kubwa hata kwa viumbe vinavyobadilika kitabia kama vile fisi madoadoa. Tunawahimiza wanasayansi wengine kufanya tafiti zinazozingatia aina mbalimbali za shughuli za binadamu na wanyama walio na mifumo mbalimbali ya kijamii na mifumo ya kitabia ili tuweze kuendelea kutengeneza mikakati inayotegemea ushahidi ya kuishi pamoja.

Wasifu wa mwandishi

Arjun Dheer ni mwanafunzi wa shahada ya uzamivu anayefanya kazi na Utafiti wa Fisi wa Ngorongoro, mradi unaosimamiwa na Leibniz Institute for Zoo and Wildlife Research ya nchini Ujerumani. Anafanya utafiti kuhusu mwingiliano kati ya maisha ya binadamu-wanyama katika eneo la Hifadhi ya Ngorongoro, Tanzania. Philemon Naman ni mtafiti msaidizi wa Utafiti wa Fisi wa Ngorongoro.

Soma karatasi

Soma karatasi: Dheer, A., Davidian, E., Courtiol, A., Bailey, L. D., Wauters, J., Naman, P., Shayo, V., & Höner, O. P. (2022). Diurnal pastoralism does not reduce juvenile recruitment nor elevate allostatic load in spotted hyenas. Journal of Animal Ecology, 00, 1– 12. https://doi.org/10.1111/1365-2656.13812

Coexistence is possible: spotted hyenas exposed to daytime pastoralism do just fine

/ Beth Preston / 3 Comments
This blog post is provided by Arjun Dheer and tells the #StoryBehindthePaper for the paper ‘Diurnal pastoralism does not reduce juvenile recruitment nor elevate allostatic load in spotted hyenas‘, which was recently published in Journal of Animal Ecology. In his study, he explores the impact of pastoralism on spotted hyena populations in Ngorongoro, discovering that they don’t seem stressed and numbers of recruited cubs didn’t differ between areas with human influence and areas without.

The blog can be found in Swahili here.

Humans affect wildlife, but it’s not always easy to assess the conservation-relevant impacts. In fact, we affect them in so many ways – they might be forced to avoid us and become more active at night, alter where they look for food, or even change their diet. It is often assumed that these effects are bad for the animals, and that wildlife struggles to cope with those behavioral changes. Surely, this is an issue of serious conservation concern. But is it really?

Not necessarily. Many animals can adjust their behavior to changes in their environment without this affecting their ability to survive or reproduce. Changes in behavior thus do not always mean that the persistence of a wildlife population is actually threatened. To figure out whether a population’s persistence is threatened is difficult. And it is especially difficult when studying larger, longer-lived species – such as spotted hyenas (Crocuta crocuta) – which often come into conflict with humans and thus need to be prioritized to promote coexistence. Doing such an investigation requires long-term data, focused particularly on two main elements: fitness and physiology.

Fitness refers to the ability of an organism to survive, reproduce, and contribute offspring to the next generation. Physiology is a broad concept referring to the functions in an organism’s body that allow it to survive and reproduce. Measuring changes in these variables is very conservation-relevant because of how directly they impact a wildlife population’s continued presence. And that is exactly what we investigated.

A spotted hyena in proximity to Maasai pastoralists and their cattle grazing in the Ngorongoro Crater. (Photo: Oliver Höner)

We used a natural experiment to study hyena clans exposed and unexposed to human activity. For our study, we collected 24 years of data (1996-2019) from the eight spotted hyena social groups (“clans”) resident on the floor of the Ngorongoro Crater, Tanzania. Two of the Crater clans – which we call the Airstrip and Forest clans – were exposed to pastoralism conducted by the local Maasai community from 1996-2016. Pastoralism is a globally widespread human activity and lifestyle whereby people accompany their livestock to grazing pastures, water bodies, and mineral licks. The other six clans were not exposed to pastoralism. This provided us with a natural experiment: we could compare how the exposed clans performed compared to the unexposed ones.

Measuring juvenile recruitment provides key information on the “health” of hyena clans. To measure fitness effects, we compared juvenile recruitment – that is, the number of surviving offspring – in exposed and unexposed clans. As for physiology, we compared the concentration of glucocorticoids in their poop, or “stress”. The level of “stress” indicates the cumulative burden an organism experiences due to life events, be it social interactions with groupmates or repeated human disturbance. To do so, we collected 975 poop samples from 475 different hyenas across our study period and measured the “stress” in each and every one.

Last but not least, in order to disentangle the effect of pastoralism from other environmental conditions, we also collected data on other factors during the course of our study period – the occurrence of disease outbreaks, the risk of encountering lions, and prey availability.

Contrary to what we expected, juvenile recruitment in the exposed clans was slightly higher than in the unexposed clans. Similarly, “stress” was very similar between hyenas from the exposed and unexposed categories. Altogether, it seems that pastoralism did not pose a threat to exposed clans in the Ngorongoro Crater spotted hyena population at all. The exposed clans did just as well as the unexposed clans, if not slightly better!

Two potentially big reasons why there was no negative effect on the exposed clans are that the pastoralism (i) was predictable, as it occurred strictly on dedicated paths into and out of the Crater and (ii) happened only during the day. Because it was predictable, the hyenas may have been able to adjust to the daily rhythm of the pastoralism without much issue. And because it occurred during the day, it meant the pastoralism was not very disruptive to key behaviors in the hyenas – namely hunting and suckling. Suckling of very young cubs does often occur during the daytime, but the mothers may have been able to adjust the suckling times to the night in order to avoid the pastoralism.

A spotted hyena cub takes a break from suckling during the daytime. Photo: Arjun Dheer

On top of all that, the hyena social system might have played a role. Hyena clans have a strict hierarchy or ranking system. Top-ranked hyenas tend to contribute more cubs to the population, and due to several factors, are less likely to be directly exposed to challenges such as pastoralism. It is possible that the lower-ranking hyenas might have absorbed any effects of the pastoralism; most of their cubs die even in the best of times. When exposed to pastoralism, their cubs may just die earlier, leaving the clan’s overall performance unaffected.

Finally, the Ngorongoro Crater’s rich prey abundance relative to the size of the hyena population (i.e., very high “prey per capita”) might have protected the exposed clans from experiencing serious effects of pastoralism. The Crater has one of the highest densities of large mammals on Earth, and that means the hyenas enjoy a banquet of delicious food year-round, at least during most of our study period. This may have allowed mother hyenas to produce plenty of milk to raise healthy cubs, and ultimately may have kept the clans productive.

Our results have strong implications… but should be interpreted with caution. Our findings suggest that human activity may be sustainable and conducive to coexistence with wildlife provided they are not too disruptive to key behaviors. Second, we have highlighted the importance of considering the effects of human activity in light of an animal’s behavioral patterns and social system. And third, by measuring juvenile recruitment at the level of clans, we have offered a new approach to the study of human-wildlife interactions focused on group-living species.

All that being said, our findings apply to a very specific situation. In areas where human activities are more intense and environmental conditions less ideal than in the Crater, pastoralism may have a stronger effect even on behaviourally flexible species such as the spotted hyena. We encourage other scientists to conduct studies that focus on a variety of human activities and animal species with various social systems and behavioral patterns so we can continue developing evidence-based strategies for coexistence.

Author bio

Arjun Dheer is a doctoral student working with the Ngorongoro Hyena Project, based at the Leibniz Institute for Zoo and Wildlife Research. He studies human-carnivore coexistence in Ngorongoro Conservation Area, Tanzania. Follow him on Twitter @ArjDheer and the Hyena Project at @HyenaProject and on YouTube at www.youtube.com/c/hyenaproject!

Read the paper

Read the full paper here: Dheer, A., Davidian, E., Courtiol, A., Bailey, L. D., Wauters, J., Naman, P., Shayo, V., & Höner, O. P. (2022). Diurnal pastoralism does not reduce juvenile recruitment nor elevate allostatic load in spotted hyenas. Journal of Animal Ecology, 00, 1– 12. https://doi.org/10.1111/1365-2656.13812

Predicting What Extinctions Could Mean for Lemurs and the Forests They Call Home

/ Beth Preston / Leave a comment
This blog post is provided by James Herrera and tells the #StoryBehindthePaper for the paper “Drivers and Consequences of Structure in Plant–Lemur Ecological Networks“, which was recently published in Journal of Animal Ecology. In their study the authors explore how lemurs and plants are interconnected in ecological networks, and the impacts of plant or lemur extinctions on these networks. This post was originally posted on the Duke research blog here.

New research shows that lemurs and their food trees are tightly linked in ecological networks, and that the extinction of lemurs will have cascading effects on ecosystem functions.

The Critically Endangered black-and-white ruffed lemur, Varecia variegata, is one of the lemurs that eats the most fruit. When they consume the fruit, they pass the whole far from the mother tree, effectively aiding in seed dispersal. (Photo credit: Laura De Ara)

Lemurs are the primates found only on Madagascar. They are unique in many ways, and like many organisms, they fit in complex ecological networks. These networks include interactions between lemurs and their food trees. Many interactions are beneficial, or mutualistic; for example, lemurs eat the fruits of trees and disperse their seeds, providing a critical service to the trees. If lemurs go extinct — 98% of species are threatened with extinction due to human activities — the links in the ecological network will be severed, with potentially negative impacts on the trees.

Research published in the Journal of Animal Ecology by Ph.D. student Camille DeSisto, of the Duke University Nicholas School of the Environment, and James Herrera, from the Duke Lemur Center, shows how tightly linked lemurs and trees are in their interaction networks, and the negative impacts of extinction on network resilience. If lemurs do in fact disappear, many trees will be left without a way to disperse their seeds, and may not be able to reproduce effectively.

DeSisto and Herrera used advanced techniques in social network analysis, including exponential random graph models, to test which traits of lemurs and trees predict their probability of interaction. The lemurs with the highest probability of interactions with trees were large, fruit-eating species with a short gestation length, occurring in arid habitats, and with a threat status of Least Concern. Closely related plants were more likely to interact with the same lemur species than distantly related plants, but closely related lemurs were not more likely to interact with the same plant genus.

Simulated lemur extinction tended to increase network structure in some properties, including connectance (% of realized interactions out of all possible interactions) and modularity (how many unique cliques or subcommunities form in the network), but decrease nestedness (the tendency for specialists which feed on only a few trees to be a subset of generalists which feed on many trees) and robustness (tolerance to future extinctions), compared to pre‐extinction networks. Networks were more tolerant to plant than lemur extinctions.

The silky sifaka, Propithecus candidus, is one of the most endangered primates in the world. Unlike some lemurs, the sifaka have antagonistic relationships with trees, eating leaves and prey on seeds, rather than pass them intact. (Photo credit: Laura De Ara)

By simulating the loss of lemur and plant species, the authors could predict how network structure will erode over time if threatened lemurs and trees go extinct. The results showed that if the most well-connected lemurs in the network were to disappear, the percentage of trees with interactions would quickly decline, compared to scenarios in which lemurs were removed randomly or if the least-well connected lemurs went extinct. Given the threat status and geographic range size of lemurs, the percentage of trees that would lose their interacting lemurs would be greater than that expected if lemur extinctions were random.

The bamboo lemur, Hapalemur occidentalis, is a highly specialized species, eating mostly bamboo leaves. They do, however, occasionally eat fruits, and often spread the seeds effectively. (Photo credit: Laura De Ara)

Results also showed that if lemurs go extinct, the resilience of the networks to further disturbance would decrease. This indicates that the current links between lemurs and trees are critical to the stability of these complex ecological networks.

To prevent the loss of key ecosystem functions like seed dispersal, it is critically important to protect lemurs and trees, which depend so crucially on one another for survival. DeSisto is currently conducting field research in Madagascar, studying how well seeds germinate when eaten by lemurs. She created a tree nursery in the forest to grow the seeds obtained from lemur faeces, and already has several species germinating. Interestingly, she is also showing how lemurs disperse the seeds of vines, which are an important yet understudied food source when tree fruits are not available. She will continue her research across multiple seasons, to determine how changes in plant phenology affect seed dispersal patterns.

Author Camille DeSisto and assistant Feno Telessy examine the seeds germinating from lemur faeces.
Amazingly, seeds from lemur faeces are already germinating after only one month. Some tree seeds take months or even a year before germinating.

Many conservation programs are currently striving to safeguard Madagascar forests and the diverse species found only in these natural habitats. The Duke Lemur Center has an active conservation program in the northeast, called the DLC-SAVA Conservation Initiative. This program takes a community-based approach to conservation, partnering closely with local stakeholders and actors to develop projects that address the needs of both lemurs and people. By co-creating projects that include alternative and sustainable livelihood strategies, both nature and people benefit from conservation. Natural ecosystems provide important services for people, including locally, such as protecting watersheds and pollinators, as well as globally, such as carbon sequestration. Without the native forests, and the lemurs that call those forests home, people would lose the valuable and irreplaceable services forests provide.

Read the paper

Read the full paper here: DeSisto, C., & Herrera, J. P. (2022). Drivers and consequences of structure in plant–lemur ecological networks. Journal of Animal Ecology, 00, 1– 13. https://doi.org/10.1111/1365-2656.13776

Male rock hyraxes that maintain an isochronous song rhythm achieve higher reproductive success

/ Beth Preston / Leave a comment
This blog post is provided by Vlad Demartsev, Michal Haddas-Sasson, Amiyaal Ilany, Lee Koren and Eli Geffen and tells the #StoryBehindthePaper for the paper ‘Male rock hyraxes that maintain an isochronous song rhythm achieve higher reproductive success‘, which was recently published in Journal of Animal Ecology. In their study, they explore whether singing ability in male hyraxes is linked to the number of offspring that they produce.

Rhythm is found in many biological processes including some of the basic physiological functions of living organisms. Firing of neurons, breathing, heartbeat, pace of movement; those are just few examples for processes in which rhythm stability is important and can indicate health and stamina of the organisms. On the other hand, irregularities in those rhythms could be a sign of illness or poor condition. When choosing mates, animals often identify cues indicating health and quality of the potential partner and various courtship displays advertising individual fitness have evolved. Some of those displays are broadcasted in the form of acoustic signals and bird songs are probably the best known example of this. Rhythmic performance can be related to underlying physiological processes like muscle control and breathing rate. As both humans and animals are quite good at spotting errors in rhythmic sequences, rhythm stability can be used for evaluating performers’ quality. Additionally, stable and predictable rhythm can help to synchronize performance of multiple individuals like musicians in a band or birds singing in a chorus.  

Charles Darwin, and several other scholars since him, have suggested that human music might have evolved with a similar function of courtship. Rhythmic structure is a fundamental feature of many musical styles and keeping the “right” rhythm is vital for a good musical performance. The rhythmic signatures existing in musical styles can also be found in animal songs supporting the idea of common functionality or at least common preconditioning for rhythm sensitivity in animals and humans.  Especially interesting are the relatively rare cases of singing mammals. Only a few mammalian taxonomic branches have been shown to perform songs – long and complex sequences of calls with clearly identifiable syntactic and also rhythmic structure. Whales are widely known for their songs, as well as gibbons for their long and elaborate great calls. A slightly less familiar singing mammal is the rock hyrax – a medium sized herbivore from sub-Saharan Africa, the Middle East and the Arabian Peninsula.

Male rock hyrax singing (Photo credit: Eran Gissis)

Rock hyraxes live in groups of up to 30 individuals. In a group there is usually one adult resident male, adult females, juveniles and pups of both sexes.  Hyraxes communicate mainly vocally and about 10 different call types have been identified in their repertoire. Males of this species emit long and complex songs that function as advertisement in courtship and competition with other males. These songs are individually unique and it is likely that hyraxes in the area can identify males by their singing. Mostly, male hyraxes sing by themselves, but in some cases two or three males sing in response to each other but they do not form choruses or sing in unison.  Rock hyraxes breed seasonally, with the mating season lasting two weeks in mid-summer. Both males and females can mate with multiple partners so it is not always clear who is the father of the pups. Females are pregnant for ~ 8 months and give birth to 1-5 pups. The pups are being taken care of by the whole group. Adult and juvenile hyraxes are seen babysitting mixed litters (pups from multiple mothers) and all the group takes part in predator defense.

In the past 25 years we have been studying the rock hyrax population at the Ein Gedi Natural Reserve, located on the coast of the Dead sea in Israel.  Over the course of this long term study we have collected DNA samples of hundreds of animals and reconstructed the family tree of our study population.  By performing genetic analysis, we identified who were the parents of each individual hyrax and calculated the number of surviving pups each male had in each year of its life. We also recorded hundreds of songs from identified males and linked the songs a male performed to the count of surviving sons and daughters that it fathered in the same year. We were interested in figuring out if the rhythmic structure of the songs was related to the male hyrax’s reproductive success and if males singing at a stable and consistent rhythm had more surviving offspring.

Song of a male rock hyrax (Amiyaal Ilany)

We found that male hyraxes who sang more frequently in a given year also fathered slightly more pups. We also found that males who managed to keep precise song rhythm, produce sequential song elements (calls) at nearly identical intervals, had more surviving offspring in comparison to males that made more “errors” or in general did not emit calls with equal intervals.  Interestingly the absolute tempo of the songs (fast or slow) was not important, only the ability to sing isochronally – with equal spacing between notes. We don’t yet know if the isochronous singing of hyrax males is attractive to females as an independent trait or if it makes the whole song more predictable and easier to follow and allows for a better or quicker evaluation of the singing male as a potential mate.

We only found one main rhythmic category (isochrony) in the songs of hyraxes while in other animal systems multiple rhythmic patterns can be present in a signal. Mixed rhythmic patterns could be a result of collective signalling. With multiple callers, while it is often important to stay generally in synch with the group, having some level of rhythmic flexibility could be useful for highlighting individual performance. So, unlike hyraxes that sing mostly solos, individuals in chorus singing species might strategically deviate from isochronous stability to stand out from the unison crowd.   But this is already a question for the next study.

Male rock hyrax
Read the paper

Read the full paper here: https://doi.org/10.1111/1365-2656.13801