Author: Julie

To understand how mule deer use fire-impacted areas, consider the season and account for their predators

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This blog post is provided by Taylor Ganz and tells the #StoryBehindthePaper for the paper ‘Interactive effects of wildfires, season, and predator activity shape mule deer movements‘, which was recently published in Journal of Animal Ecology. In their study, they investigate how changes in food availability and predator vulnerability, due to wildfires, impact mule deer.

Across the American West, wildfires are becoming more frequent, larger, and more intense. In the Methow Valley and Okanogan region of north-central Washington, nearly 40% of the area has burned since 1985. Mule deer, white-tailed deer, moose, black bears, bobcats, cougars, coyotes, and recently returned wolves live across this area. While wildfires can shape wildlife habitat, the impacts of the recent fires on these species – and the interactions between them – is unclear. Given the decline of mule deer across the American West, primarily attributed to changes in habitat, we were especially interested in understanding how mule deer navigated burns while managing predation risk from cougars and wolves.

To examine how wildfire impacted mule deer, we captured and GPS collared 150 adult female deer along the Methow Valley and considered their movement as they encountered a range of fire impacts over the year. We also caught cougars and wolves to fit them with GPS collars. Using these predator locations, we mapped which areas they used most heavily, allowing us to consider how mule deer managed predation risk in fire-affected areas.

Wildfires tend to increase shrubby and herbaceous vegetation on which mule deer feed. Here, a camera trap image shows a mule-deer doe in a burned forest where fireweed, grasses and shrubs have re-grown. Copyright: Sarah Bassing

Wildfires can have a wide range of effects depending on the characteristics of the burn. We considered low, moderate, and high severity fires over time spans from 0 to 35 years post-fire. Fires impact forests by initiating nutrient cycling, triggering the growth of fire-adapted plants, burning understory vegetation, and in more severe fires, even removing the forest canopy. Generally, burns increase the shrubby and herbaceous vegetation deer favor for food in the summer. As expected, we found deer tended to select for burns in the summer to access this improved forage.

Mule deer (GPS locations of collared deer in 2019 shown in blue) encounter a variety of wildfire impacts through the course of the year. Fires are shown with yellow (older burns) to orange (more recent fires) shading. Copyright: Taylor Ganz

But the growth of this vegetation and increase in deadfall post-fire can also impact the hunting efficacy of predators. Cougars hunt by stalking and ambushing prey, and understory re-growth and accumulation of deadfall provide the hiding cover for cougars to approach deer undetected. Where cougar activity was higher, deer were generally more likely to reduce their selection of burned areas with better forage to avoid an increased risk of cougar predation. Mule deer’s response to cougars in burns also depended on the severity and time since the fire, suggesting that response to cougars reflected the ways that fire restructured the habitat. Deer balanced this food-safety tradeoff, and we found that they were no more likely to die from cougars or other predators in burned areas than in unburned areas.

Unlike cougars, wolves hunt by chasing down prey over long distances in open landscapes. Where wolf activity was higher, wildfire created a win-win situation for deer, improving summer forage quality and providing hiding cover from wolves. Because of this, deer were even more likely to use burns where wolf activity was high. Wolves have been naturally recolonizing the area over the last couple of decades. They occur at lower densities in the region compared to cougars, so effects on deer could increase if the local wolf population grows.

In the winter, snow can accumulate to deeper levels in burned versus unburned forests because snow accumulates in the understory rather than being intercepted by the canopy-cover. In this camera-trap photo, a mule deer buck moves through a burned forest in an early autumn snowfall. Copyright: Sarah Bassing

In the winter, we found that deer avoided burned areas. When fire removes the canopy cover that would otherwise catch falling snow, deeper snow accumulates in burned forests than in unburned forests. Deeper snow in burns had two effects: First, deeper snow cover would inhibit deer access to the forage buried beneath it. Second, deer struggle to escape from predators in areas of deep fluffy snow where their hooves sink deeply, while predators’ paws act as snowshoes. Still, we found that deer avoided burns more strongly with increased cougar activity and less strongly with increased wolf activity, reflecting the hunting styles of these predators.

Our study showed that wildfires impact ungulate species such as mule deer through multiple pathways, shaping food availability and vulnerability to predators with seasonally dependent effects. In snowy areas where burns occur on winter range, these impacts could be concerning if wildfires functionally reduce available habitat for deer when they avoid burned areas.

Read the full paper here: Ganz, T. R., DeVivo, M. T., Kertson, B. N., Roussin, T., Satterfield, L., Wirsing, A. J., & Prugh, L. R. (2022). Interactive effects of wildfires, season and predator activity shape mule deer movements. Journal of Animal Ecology, 00, 1–16. https://doi.org/10.1111/1365-2656.13810

About the Author

This blog post was written by Taylor Ganz. Taylor Ganz is a Ph.D. candidate in the Prugh Lab at the University of Washington, where she studies carnivore-ungulate interactions as part of the Washington Predator-Prey Project.

El tamaño si importa: ¿Como afectan los rasgos el rol de los peces depredadores en las tramas tróficas y redes espaciales en el Río Paraná Medio?

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Este posteo fue proporcionado por Dalmiro Borzone Mas y Pablo Scarabotti y nos cuenta #StoryBehindthePaper para el trabajo “Simetrías y asimetrías en los roles topológicos de los peces depredadores entre las redes de ocurrencia y las tramas tróficas” el cual fue recientemente publicado en el Journal of Animal Ecology. En este estudio ellos exploran como las redes de ocurrencia y las tramas tróficas tienen una estructura modular y como los rasgos se relacionan con la capacidad de conexión de las especies en cada tipo de red. Ellos encontraron que las redes de ocurrencia y las tramas tróficas de la llanura aluvial del Río Paraná medio son modulares y que los grandes depredadores son conectores en las tramas tróficas, mientras que las especies pequeñas tiene un rol importante como conectores en las redes de ocurrencia.

Los ecosistemas son entidades complejas donde las especies interactúan entre ellas y con su ambiente formando redes ecológicas. La representación de un sistema como una red es una herramienta útil para entender cómo se relacionan los componentes y que importancia tienen estas relaciones en su funcionamiento. En función de la red ecológica que estudiemos, los componentes, denominados nodos e interacciones pueden ser entidades diferentes. En una red trófica, los nodos representan a los depredadores y sus presas, y las interacciones muestran quién se come a quién. También es posible construir redes para ver qué relaciones hay entre las especies y los hábitats que utilizan. En estas redes, denominadas redes de ocurrencia, las especies y los sitios son los nodos de la red mientras que las interacciones muestran qué hábitats utiliza cada especie. En las redes ecológicas, las especies se conectan formando “bloques” que interactúan más frecuentemente entre sí que con el resto de las especies. Estos bloques, son denominados módulos, y su presencia es muy común en redes de plantas-polinizadores, tramas tróficas y espaciales. Sin embargo, los módulos no se encuentran completamente aislados, existiendo especies que tienen muchas conexiones con módulos vecinos, permitiendo la cohesión de la red. Estas especies son denominadas conectoras modulares, y tienen un rol central en la unión, dinámica y estabilidad de las redes.

Figure 1: Example of modular spatial network. The circles are sites, where the names represent the type of environment (MR = Major rivers, SC = secondary channels, CL = connected lake and IL = isolated lake). The color of each circle shows which space module it belongs to. The diamonds are predators, where the size represents the body size of species and the importance in the connection between modules (from white with low connection role to red with high connection role). Figure credit: Dalmiro Borzone Mas 

En un estudio recientemente publicado en el Journal of Animal Ecology, nos propusimos analizar la forma en la cual los peces depredadores del río Paraná y su llanura de inundación actúan como conectores en las redes de ocurrencia y en las tramas tróficas. Nuestras principales hipótesis fueron (a) los peces depredadores son importantes conectores en las tramas tróficas y las redes espaciales y (b) el tamaño corporal es un rasgo clave que determina el rol de conexión. Analizamos cuáles son los rasgos corporales que se relacionan con la capacidad de conexión de cada especie y cuando estos rasgos tienen el mismo efecto en las redes de ocurrencia y en las tramas tróficas.  Nuestras preguntas de investigación fueron: ¿Las redes de ocurrencia y las redes tróficas del río Paraná tienen una estructura modular? y ¿Qué rasgos se relacionan con la capacidad de conexión modular de las especies en cada tipo de red?

Figure 2: Images of different types of environments (A-D) and some predators species analyzed in the study (e: R.microlepis, f = A.pantaneiro, g = S.maculatus, h = P.corruscans y i = P.nattereri). Image credit: Patricio Alvarenga

El tamaño corporal es un rasgo clave en ecología; este rasgo funcional determina la tasa metabólica, diversidad de presas, tolerancia a las condiciones ambientales adversas, entre otras propiedades. A su vez, la ecomorfología de cada especie (por ejemplo, la forma del cuerpo y el tipo de dientes) puede brindar información sobre la relación entre el organismo y el ambiente como la capacidad de natación y forma de captura de presas. En este sentido, tanto el tamaño corporal como la ecomorfología pueden determinar las interacciones que tiene cada especie, y su rol como conector en la red. Sin embargo, el efecto de cada rasgo en el rol de conector puede no ser el mismo en las tramas tróficas y las redes de ocurrencia. Por ejemplo, mientras más grandes son los depredadores, presentan una mayor diversidad de presas, pero también aumentan los requerimientos ambientales óptimos para poder permanecer en un hábitat particular. En este sentido, el tamaño corporal puede tener un efecto positivo en la conexión modular en las redes tróficas (permitiendo capturar un espectro más amplio de presas) pero negativo en las redes de ocurrencia (prohíbe la permanencia en sitios con condiciones ambientales severas).

Figure 3: Top: Distribution of sample sites, environment types and study area. Bottom: Predator fishes analyzed in the study. Image credit: Patricio Alvarenga

Para responder nuestras preguntas realizamos muestreos en el campo, donde registramos qué tipo de depredadores había en cada hábitat y que presas consumían mediante el análisis de contenidos estomacales. La llanura aluvial del Río Paraná es un área con una gran diversidad de hábitats, con cauces de más de un kilómetro de ancho y 20 metros de profundidad, arroyos que serpentean entre las islas de la llanura de inundación, y lagunas que se encuentran dentro de las islas que pueden estar conectadas o aisladas dependiendo de la altura del río. Además de esta enorme diversidad de hábitats, el río también presenta variaciones estacionales importantes en cuanto a la temperatura y el caudal. La altura del río puede variar entre de 3 a 4 metros en un mismo año, produciendo un cambio profundo en la estructura del hábitat y el aislamiento de las comunidades. En nuestro estudio incluimos 16 especies de peces como los depredadores más importantes del sistema, incluyendo especies de importancia comercial como el surubí pintado (P. corruscans), el dorado (S. brasiliensis), la raya de río gigante (P. brachyura) y tres especies de pirañas (dos especies de Serrasalmus y P. nattereri).  En el diseño del muestreo consideramos la variación estacional en la temperatura y el nivel del río, y definimos cuatro situaciones ambientales: Temporada cálida con el río bajo o alto y temporada fría con el río bajo o alto. Se muestrearon 152 comunidades donde capturamos 3048 individuos y se registraron 1277 interacciones tróficas. A su vez, medimos el peso promedio y 30 rasgos relacionados con la ecomorfología de las especies. Posteriormente, calculamos la modularidad de las redes en cada situación ambiental, el valor de conexión intermodular de cada depredador (valor-c) y la relación entre el valor-c y los rasgos (tamaño corporal y ecomorfología).

Figura 4: Muestreo realizado en una laguna conectada de la llanura aluvial del Río Paraná medio.

Nuestros resultados establecieron que las redes espaciales y las tramas tróficas de la llanura aluvial del Río Paraná son sistemáticamente modulares. A su vez, observamos que las especies de gran tamaño tienen una alta capacidad de conexión en las tramas tróficas, mientras que las especies de pequeño tamaño tienen una buena capacidad de conexión en las redes de ocurrencia. Este efecto asimétrico del tamaño corporal se relaciona con los mecanismos que denominan las interacciones en cada red; donde el mayor tamaño ofrece la posibilidad de capturar mayor variedad de presas, pero dificulta la supervivencia en sitios con condiciones ambientales rigurosas. Además, observamos que los rasgos ecomorfológicos relacionados con la conexión de los módulos cambian en las distintas situaciones ambientales. Este trabajo permitió comprobar que las redes de la llanura aluvial del río Paraná son modulares y que ciertas especies tienen roles claves conectando los módulos de las redes. A su vez, el efecto asimétrico del tamaño corporal nos indica que debemos ser cautos para inferir los roles en una red ecológica basándonos en redes de otro tipo. Finalmente, esta estructura modular es sostenida en el tiempo por especies con roles dinámicos, reflejando cambios en la relación entre sus rasgos y su capacidad de conexión en cada situación hidro-climática.

Leer el artículo

Borzone Mas, D., Scarabotti, P., Alvarenga, P., & Arim, M. (2022). Symmetries and asymmetries in the topological roles of piscivorous fishes between occurrence networks and food webs. Journal of Animal Ecology, 00, 1–13. https://doi.org/10.1111/1365-2656.13784

Sobre los autores

Dalmiro Borzone Mas es estudiante de doctorado en el Instituto Nacional de Limnología (INALI) y el Centro Universitario Regional Este (CURE). Sus estudios se centran en comprender los mecanismos que dan forma a las redes ecológicas y el rol de los depredadores como conectores del sistema.

Pablo Scarabotti es investigador en el Instituto Nacional de Limnología (INALI) y profesor de ecología en la Universidad Nacional del Litoral (UNL) en Santa Fe Argentina. Sus investigaciones tratan sobre ecología comunitaria y poblacional de los peces neotropicales de agua dulce.

Size does matter: how do traits affect the role of predatory fish on food webs and spatial networks in the middle Paraná River?

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This blog post is provided by Dalmiro Borzone Mas and Pablo Scarabotti and tells the #StoryBehindthePaper for the paper “Symmetries and asymmetries in the topological roles of piscivorous fishes between occurrence networks and food webs“, which was recently published in the Journal of Animal Ecology. In their study, they explore whether occurrence networks and food webs of the Paraná River have a modular structure and which traits are related to the modular connection capacity of the species in each type of network. They find that occurrence networks and food webs of the Paraná River floodplain are indeed modular and that large predatory species have a role as food web connectors, whereas small species have a role as connectors in occurrence networks.

This post is also available in Spanish.

Ecosystems are complex entities where species interact with each other and with their environment, creating ecological networks. The representation of a system as a network can be useful to understand how the components are related to each other, and the ways in which they interact. Depending on the ecological network we are studying, the components (called nodes and links) can be different entities. In a food web, nodes represent preys and predators, and links indicate trophic interactions (who eats whom). It is also possible to build networks to analyze the relationships between species and the habitats they use. In these networks, called occurrence networks, species and sites are the nodes while the links indicate the habitats used by each species. In ecological networks, species can aggregate in blocks that interact more frequently with each other than with the remaining species. These blocks are called modules, and their presence is a prominent feature in many kinds of networks such as spatial networks, plant-pollinator interactions and food webs. However, network modules are not completely isolated, since there are species that have many interactions with other modules. These species are called modular connectors, and they play a central role in the cohesion, dynamics, and stability of networks.

Figure 1: Example of modular spatial network. The circles are sites, where the names represent the type of environment (MR = Major rivers, SC = secondary channels, CL = connected lake and IL = isolated lake). The color of each circle shows which space module it belongs to. The diamonds are predators, where the size represents the body size of species and the importance in the connection between modules (from white with low connection role to red with high connection role). Figure credit: Dalmiro Borzone Mas 

In a study recently published in the Journal of Animal Ecology, we analyzed the way in which piscivorous fish in the Paraná River and its floodplain act as connectors in occurrence networks and food webs. Our main hypotheses were that (a) predatory fish are important connectors of the compartments of food webs and occurrence networks and (b) that body size is a key trait driving this function. We analyzed which body traits were related to the connection capacity of each species and whether these traits have the same effect on occurrence networks and food webs. Our research questions were: Do the occurrence networks and food webs of the Paraná River have a modular structure? And, which traits are related to the modular connection capacity of the species in each type of network?

Figure 2: Images of different types of environments (A-D) and some predators species analyzed in the study (e: R.microlepis, f = A.pantaneiro, g = S.maculatus, h = P.corruscans y i = P.nattereri). Image credit: Patricio Alvarenga

Body size is a key trait in ecology; it determines the metabolic rate, the diversity of prey ingested, and the tolerance to adverse environmental conditions, among other properties. In turn, the ecomorphology of each species (for example, the shape of the body and the type of teeth) can provide information on swimming ability and prey capture strategy. In this sense, both body size and ecomorphology can determine the interactions that each species has and its role as a connector in the network. However, the effect of each trait on a species’ role as modular connectors may not be the same in occurrence networks and food webs. For example, larger predators have greater diversity of prey, but this is offset by having greater environmental requirements to remain in a particular habitat. In this sense, body size can have a positive effect on the ability of the species to connect the food web compartments (allowing the capture of a broader spectrum of prey) and a negative effect on the ability to connect occurrence networks (prohibiting permanence in sites with harsh environmental conditions).

Figure 3: Top: Distribution of sample sites, environment types and study area. Bottom: Predator fishes analyzed in the study. Image credit: Patricio Alvarenga

To answer our questions, we performed field surveys, where we recorded the types of habitats and the prey consumed by each of sixteen predatory fish species. The Paraná River and its floodplain conform a complex ecosystem with a great diversity of habitats. These habitats range from channels of more than a kilometer wide and 20 meters deep, small streams meandering between the islands of the floodplain, to lakes located within the islands that can be connected or isolated depending on the river level. In addition, the river exhibits significant seasonal variations in temperature and flow. The height of the river can vary between 3 to 4 meters in the same year, producing a deep change in the structure of the habitat and the isolation of the communities. In our study, we included 16 of the most important predatory fishes, including commercially important species such as the spotted surubí (P. corruscans), the dorado (S. brasiliensis), the giant river stingray (P. brachyura) and three species of piranhas (two species of Serrasalmus and Pygocentrus nattereri). In the sampling design, we considered the seasonal variation in temperature and river level, defining four environmental situations: Warm season with low or high river level and cold season with low or high river level. One hundred and fifty two communities were surveyed with 3048 individuals and 1277 trophic interactions recorded. For each species, we recorded the mean weight and 30 ecomorphological traits describing the body shape and coloration. Subsequently, we calculated the modularity of the networks in each environmental situation, the intermodular connection value of each predator (c-value) and the relationship between the c-value and the traits (body size and ecomorphology).

Figure 4: Sampling in a connected lake on the floodplain of the middle Paraná River. Image credit: Francisco Alonso

Our results showed that the occurrence networks and food webs of the Paraná River floodplain are systematically modular. In turn, we observed that the large predatory species have a role as food web connectors, whereas small species have a role as connectors in occurrence networks. These different effects of body size reflect the underlying mechanisms that drive the interactions in each network; where a large body size offers the possibility of capturing a greater variety of prey, but makes survival difficult in sites with harsh environmental conditions. In addition, we observed that the ecomorphological traits related to the connection of the modules change in different environmental situations. This work demonstrated that the networks of the Paraná River are modular and that certain species have key roles connecting the network modules. In turn, the asymmetric effect of body size tells us that we should be cautious about inferring roles in an ecological network based on other types of networks. Finally, this modular structure is sustained through time by species with dynamic roles, reflecting changes in the relationship between their traits and their ability to connect in each situation.

Read the paper

Borzone Mas, D., Scarabotti, P., Alvarenga, P., & Arim, M. (2022). Symmetries and asymmetries in the topological roles of piscivorous fishes between occurrence networks and food webs. Journal of Animal Ecology, 00, 1–13. https://doi.org/10.1111/1365-2656.13784

About the authors

Dalmiro Borzone Mas is a PhD student at the National Institute of Limnology (INALI) and at the Eastern Regional University Center (CURE). His studies focus on understanding the mechanisms that shape ecological networks and the roles of predators as system connectors.

Pablo Scarabotti is a researcher at the National Institute of Limnology (INALI) and professor of ecology at the National University of the Litoral in Santa Fe, Argentina. His research deals with the population and community ecology of neotropical freshwater fishes.

Bee declines: what’s the stress all about?

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This blog post is provided by Aoife Cantwell-Jones and tells the #StoryBehindThePaper for the paper “Signatures of increasing environmental stress in bumblebee wings over the past century: Insights from museum specimens”, which was recently published in the Journal of Animal Ecology. The authors looked at how bumblebee wing asymmetry has changed over the 20th century. They found that wing asymmetry started increasing around 1925 and that warmer and wetter years coincided with higher wing asymmetry.

Museums are special places. As a child I loved peering through display cases at rows of carefully preserved animals showcasing the diversity of life. These curated displays are windows into the past, providing a sneak-peek into Earth’s history. My favourites though were always the pinned insects – their intricate wings glinting with reflected light and little labels next to them describing where and when that insect had been found. I never imagined however how much went on behind the scenes at museums or how much biological data these specimens could contain.

I got my first glimpse of this during my master’s degree at Imperial College London, where I had an amazing opportunity to join a collaboration between my supervisors Drs Richard Gill and Andres Arce and a network of UK museums. This network included some of the UK “museum greats” – the Natural History Museum (London), National Museums Scotland (Edinburgh), Oxford University Museum of Natural History, Tullie House Museum and Art Gallery Trust (Carlisle), and World Museum (Liverpool). This collaboration focused on bumblebees – important insect pollinators – to better understand how human activities are driving their long-term trends.

Figure 1: Pinned bumblebee (Bombus muscorum) specimens from National Museums Scotland (photo: Andres Arce).

Bumblebees are facing a number of threats, and some species are showing evidence of declines. While a number of factors are prime suspects of driving declines, including land-use change, pesticide use, spread of invasive species and bee diseases, and climate change, how populations are responding is less well known. One challenge we face in disentangling and quantifying the cause(s) of declines is that a bee can be experiencing many of these potential stressors at the same time. Another problem is that the impact of these stressors on bee populations may not be immediately visible. For example, the effect of climate one year might not show until many years later.

One solution is to use some measure of stress that causes an immediate and permanent change to the individual experiencing it. Just like humans accumulate scars through hard times, bumblebee wings are thought to become asymmetrical if they experienced stressful conditions during development (also known as fluctuating asymmetry). We therefore speculated that we should see changes in bumblebee wing asymmetry over the 20th century, as humans have had an increasingly wide impact on the natural environment.

We therefore painstakingly photographed and measured the wings of bumblebee museum specimens from around the UK over the 20th century. This involved many hours of staring at computer screens trying to delimit bumblebee wing shapes or type up the information in the specimen labels. We chose to focus on four species, representing both relative “winner” and “loser” species, and we looked at how wing asymmetry changed between 1900 and 2000. Additionally, to start to investigate possible causes, we also looked at which climate conditions correlated with higher wing asymmetry.

Figure 2: Pinned bumblebee specimen (Bombus lapidarius) (photo: Andres Arce).

Whilst we found a lot of variation in the degree of symmetry across specimens, an overall pattern emerged. On average, bumblebees at the end of the 20th century had less symmetrical wings. Intriguingly, wing asymmetry did not seem to just increase linearly between 1900 and 2000, but rather the increase seemed to start around 1925. We also found that warmer and wetter years coincided with higher wing asymmetry.

While we could only look for correlations with our data, the trend of higher asymmetry under warmer years is disquieting, given these years should increase in frequency with climate change. These insights into past stress are however just the beginning for this project. Wing asymmetry is a potential proxy of stress, and more work is currently being done to look at morphological and genomic changes. Progress is also being made to associate other drivers with such responses. This should give a more mechanistic insight into why some bumblebee species have been more vulnerable to change over the past century.

Museums will always have a special place in my heart, not only for their role in inspiring young scientists through their beautiful collections, but also for the research they enable, including revealing the past century of stress for bumblebees.

Read the paper

Arce, A. N., Cantwell-Jones, A., Tansley, M., Barnes, I., Brace, S., Mullin, V. E., Notton, D., Ollerton, J., Eatough, E., Rhodes, M. W., Bian, X., Hogan, J., Hunter, T., Jackson, S., Whiffin, A., Blagoderov, V., Broad, G., Judd, S., Kokkini, P. … Gill, R. J. (2022). Signatures of increasing environmental stress in bumblebee wings over the past century: Insights from museum specimens. Journal of Animal Ecology, 00, 1–13. https://doi.org/10.1111/1365-2656.13788

Artificial selection in human-wildlife feeding interactions.

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This blog post is provided by Laura L. Griffin and tells the #StoryBehindthePaper for the paper “Artificial selection in human-wildlife feeding interactions“, which was recently published in the Journal of Animal Ecology. In their study, they link human-wildlife feeding interactions with the production of heavier offspring, identifying these interactions as a driver for artificial selection. Here, author Laura L. Griffin tells us more.
Fallow deer herd resting in Phoenix Park, Dublin, Ireland. (Photo: Laura L. Griffin)

Humans are constantly encountering wild animals – whether intentionally or unintentionally, and whether we realise it or not. Typically, these encounters occur through activities such as hunting, fishing, hiking, or tourism, amongst many others, and unravelling how these activities impact the wildlife around us has become one of the most interesting challenges for modern ecologists. We now know that, in general, our activities have a number of previously unrealised effects on wild populations, spurring the need to identify and explore these impacts further.

One human activity that has become increasingly popular in recent times is hand-feeding wild animals. People often say that it allows them to feel a connection with these animals, that they believe that they’re helping them in some way, and that it makes for good content on their social media accounts. In fact, videos and pictures of people feeding wildlife quite often go viral across different social media platforms. Nevertheless, it is of fundamental importance that we pause to explore how these interactions are affecting the wildlife involved – especially as these interactions are typically self-motivated, meaning that the offered foods are usually not part of these animals’ natural diet.

A visitor tempts deer over for a selfie using a granola bar in Phoenix Park, Dublin. (Photo: Srivats Chari)

Our study was based in Phoenix Park, Dublin, Ireland; the largest, walled park in any European capital and host to roughly 10 million visitors per year. The resident fallow deer population, present in the Park since the mid-1600s, is now commonly fed by well-meaning visitors, prompting concerns for deer welfare. In particular, there is concern about whether this feeding is occurring randomly, so all deer receive some food, or whether it only involves a few individuals.

We have now revealed that the likelihood for a deer to interact with people for food (a behaviour that we refer to as ‘begging’) falls on a repeatable spectrum, with only about 24% of the population actually consistently begging for food. In fact, we could broadly categorise the entire population into three categories: consistent beggars, occasional beggars, and rare beggars.

Consistent beggar approaches visitors to get a carrot. (Photo: Laura L. Griffin)

As expected, we were able to show that those deer that beg more also receive a larger amount of human foods – including bread, crisps, carrots, apples, and biscuits. This means that the deer at this site have drastically different diets from one another, i.e. those on a more natural diet made up primarily of grass (rare and occasional beggars) and those that are on a human-supplemented diet (consistent beggars). Immediately we began to wonder whether this intake of human foods could be benefiting or negatively affecting these consistent beggars in terms of reproduction. For example, if human food allows them to invest more heavily in in-utero fawn development, similarly to them receiving a high-concentrate feed, then you would anticipate that the offspring of consistent beggars would be considerably heavier than the offspring of other mothers in the Park. Other research at this site has shown that heavier offspring have a distinct survival advantage during early life (Amin et al. 2022) which would mean that, if the ingestion of human food results in heavier offspring, artificial selection of these mothers’ genetics could be at work.

Two female fallow deer try to swallow apples fed to them by visitors. (Photo: Srivats Chari)

We measured the birthweights of 134 fawns over 3 years, and found that the fawns of mothers that were classified as consistent beggars were significantly heavier than fawns of mothers classified as occasional or rare beggars. Notably, these mothers occurred in the same herds, across the same grazing areas, and all had equal opportunity to interact with people – leaving this difference in begging behaviour as the defining difference that could be causing this disparity in birthweight. It also stands to reason that if this is occurring in this population, then it is very likely also the case across other populations and species as well. This marks these human-wildlife feeding interactions, for the first time, as a driver for artificial selection of this begging behavioural trait, which is likely associated with bolder personality types. Now that this has been identified at our site, we can work to test methods aiming to reduce these impacts through public education, which can also be applied to other sites experiencing similar interactions (Griffin et al. 2022b).

Further reading

GRIFFIN, L. L., HAIGH, A., AMIN, B., FAULL, J., NORMAN, A. & CIUTI, S. 2022a. Artificial selection in human-wildlife feeding interactions. Journal of Animal Ecology.
GRIFFIN, L.L., HAIGH, A., CONTEDDU, K., ANDALOC, M., MCDONNELL, P. and CIUTI, S., 2022b. Reducing risky interactions: Identifying barriers to the successful management of human–wildlife conflict in an urban parkland. People and Nature.
AMIN, B., VERBEEK, L., HAIGH, A., GRIFFIN, L.L. and CIUTI, S., 2022. Risk-taking neonates do not pay a survival cost in a free-ranging large mammal 2.

Newborn fawns hiding in the grass shortly after birth. (Photo left: Laura L. Griffin, Photo right: Clíódhna Hynes)

Mountain lion predation on wild donkeys rewires an ancient food web

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This blog post is provided by Erick Lundgren and tells the #StoryBehindThePaper for the paper “A novel trophic cascade between cougars and feral donkeys shapes desert wetlands“, which was recently published in the Journal of Animal Ecology. Contrary to popular belief, they find that mountain lions are capable of hunting wild donkeys, positively affecting wetlands due to changes in donkey activity levels.

Around 12,000 years ago, several species of equid roamed North and South America. These animals were ubiquitous over the last 35 million years but went extinct during the late Pleistocene, most likely due to hunting by recently arrived humans. More recently, wild horses and donkeys, relatives of these extinct animals, have established thriving wild populations on these same continents. As introduced organisms, these animals are considered ‘‘invasive’ by many conservationists. In part, this is due to long standing claims that these animals have no natural predators, leading to high population growth rates and strong ecological effects relative to native herbivores. As such, government agencies in the USA and elsewhere commit significant resources to eradicating or regulating introduced wild equid populations.

Wild donkeys in Death Valley National Park. © Michael Alfuso

We too, despite our interest in whether introduced equids restore lost ecological functions, had accepted this claim. We took for granted that mountain lions, the only extant predator to substantially overlap with wild equids, were too small to effectively hunt wild donkeys and horses. We were wrong. Quite by chance, we captured two predation events of wild donkeys by mountain lions using camera traps. It quickly became obvious that predation of wild donkeys by mountain lions was not only possible but was extremely common. Many wetlands we visited while studying the effects of donkeys on wetland vegetation and water availability had several fresh donkey kills every month, suggesting that lions were killing a donkey a week. Indeed, other researchers recently found that mountain lions in the deserts of Nevada have become specialized in hunting wild horses.

Predation of wild donkeys by mountain lions, captured in the Sonoran Desert of Arizona (a-b) and Death Valley National Park (c-d). ©The Authors

While predation can influence population size, it also changes prey behavior. Prey tend to be more cautious in areas of high predation risk, creating a “landscape of fear”. These behavioral changes can modify how prey populations affect their environment: areas of high predation risk tend to be used more sparingly, leading to reduced impacts on vegetation, soil, and so on. 

To find out if this was happening with wild donkeys we installed camera traps at desert wetlands in Death Valley National Park, comparing sites with mountain lion predation of donkeys to sites without predation. At sites that lacked predation, donkeys were active an average of ~5.5 hours a day on hot days and were active day and night. However, at nearby sites with predation, donkeys were only active ~40 minutes a day and avoided visiting at night, which is when mountain lions are most active and most effective at ambush predation. 

We then conducted vegetation surveys to understand if these behavioral changes corresponded with altered donkey effects on these ecologically important wetlands. We found that sites with predation had significantly less trampled ground, fewer trails, and more vegetation cover. 

Sites without mountain lion predation (left) have significantly reduced canopy cover, more trampled bare ground, and higher trail density than sites with mountain lion predation (right) ©Authors

Mountain lions and several equid species cooccurred for several million years. However, mountain lions are largely considered to have been too small to hunt equids, which were instead preyed upon by larger now-extinct predators, like sabertooth cats and dire wolves. Our results suggest that mountain lions are filling in these lost roles and rewiring an ancient food web. Similar results have been found in many novel ecosystems where extant predators rapidly adjust to consume novel prey. As such, our study adds to evidence that ecosystems are more dynamic and resilient than typically considered.

Detail from “Trapped in Time”, ©Mark Hallett, courtesy La Brea Tar Pits

Many conservationists have long sought the removal of wild equids in order to return ecosystems to a semblance of how they were when first described. This aim has converged with that of the meat industry, who also wish to remove feral equids in order to increase livestock stocking rates. Meanwhile, other state and federal agencies kill mountain lions to protect livestock or to boost populations of popular game species, like bighorn sheep. Instead of chasing ideals of ecological purity, our results suggest that increasing protections for predators offers a new, and pragmatic, vision of flourishing and dynamic wild landscapes in North America and beyond.

Read the full paper here: Lundgren, E. J., Ramp, D., Middleton, O. S., Wooster, E. I. F., Kusch, E., Balisi, M., Ripple, W. J., Hasselerharm, C. D., Sanchez, J. N., Mills, M., & Wallach, A. D. (2022). A novel trophic cascade between cougars and feral donkeys shapes desert wetlands. Journal of Animal Ecology, 00, 1–10. https://doi.org/10.1111/1365-2656.13766

Which genes and functions respond to environmental change?

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This blog post is provided by Katharina Wollenberg Valero and tells the #StoryBehindThePaper for the paper “Functional genomics of abiotic environmental adaptation in lacertid lizards and other vertebrates“, which was recently published in the Journal of Animal Ecology. This paper is part of the Journal of Animal Ecology Special Feature: “Understanding climate change response in the age of genomics”. In their study, they investigate which genes and functions determine adaptation to the abiotic environment and whether distinct species use similar or different genes for this

Our rapidly changing climate, both in terms of slowly increasing global temperature and in terms of weather extremes, requires us to better understand the genetic mechanisms by which animals respond to changes in their abiotic environment. Comparing the genomes of different species which have adapted to very diverse environmental conditions in the past with each other, could enable us to distinguish which of the approximately ~20,000 genes in a genome are used to adapt to environmental changes, and which functions these genes have. In our study, we compared the widespread group of lacertid lizards with other vertebrates (Wollenberg Valero et al., 2021).

Podarcis muralis, a lacertid lizard. Photo credit: Miguel Vences.

Lacertid lizards occur in a wide variety of climates from the African Namib to the Arctic Circle, and from lowlands to mountainous regions. In a previous study (Garcia-Porta et al., 2019), we found that these lizards prefer temperatures that are closely aligned to the climate of the environment they inhabit, hinting at preferred temperatures being the result of genetic adaptation. In this present study, we used the same data set to identify these genes in lacertids and determine which of them align with changes in climate. We then compared these genes to those identified in other studies of vertebrates to gain a more comprehensive picture of which genes and functions determine adaptation to the abiotic environment, and whether distinct species use similar or different genes for this.

We first identified 200 genes under positive diversifying selection from our lacertid dataset (the true number may be higher as we only analyzed adult transcriptomes), with species living in hot areas having more genes under intensified selection than species living in cold areas. Several of these genes had experienced accelerated evolutionary rates in response to hot, warm, or cold climates (measured as average annual hours above 30℃ in each species’ habitat). There was also a (non-significant) trend for association of evolutionary rates of these genes between warm habitats and high preferred temperatures. In contrast, there was strong association of evolutionary rates of genes under selection of higher evaporative water loss (Figure 1) and general skeletal morphology with cooler habitats. This matches recent observations that water balance is an important physiological property determining resilience to climate change in squamate reptiles (Le Gaillard et al., 2021).

Figure 1. Negative correlation of evolutionary rate parameters between evaporative water loss (iwl) and hours above ℃ in 200 genes under positive diversifying selection in lacertid lizards.

We then compiled these genes into a dataset containing 902 genes under selection to different abiotic environments in other vertebrate species, from fish to humans. Functions of these genes matched up well (23%) with functions we previously predicted would be important for climate adaptation, based on a set of physiological responses commonly observed in response to changes in temperature (Wollenberg Valero et al., 2014; Rodriguez et al., 2017). However, “localization and transport” was also a new, unpredicted cellular function of many of these genes (Figure 2). Interestingly, these genes were strongly connected to each other functionally and were to 18% involved in the organismal stress response. It makes sense that adaptation to different environments involves alterations to stress response pathways.

Figure 2. Pie chart showing functions of 902 genes with signatures of selection to abiotic environmental changes. Cf denotes previously predicted candidate functions.

Another exciting discovery was that 43% of these genes responded to environment-related selection in more than one species. We tested whether this pattern was uncovered by chance, (just by means of accumulating genes from different studies), by running 100,000 simulations of the number of draws that need to be performed to find the same number of genes at least twice (from a reduced set of genes that have the same functions). This revealed that this number was unlikely to have happened by chance, and consequently our findings indicate that even in a pool of tens of thousands of genes, the fact that these genes are organized into functional modules may narrow down the evolutionary search space for beneficial variants in response to changing environments (see also Wollenberg Valero, 2020). Studies are already underway to identify or manipulate heat-resistant variants (e.g., in corals, Cleves et al., 2020). The identification of genes and functions causally involved with climate adaptation will further enable such work in the future.

Read the paper

Read the full paper here: Wollenberg Valero, K. C., Garcia-Porta, J., Irisarri, I., Feugere, L., Bates, A., Kirchhof, S., Jovanović Glavaš, O., Pafilis, P., Samuel, S. F., Müller, J., Vences, M., Turner, A. P., Beltran-Alvarez, P., & Storey, K. B. (2022). Functional genomics of abiotic environmental adaptation in lacertid lizards and other vertebrates. Journal of Animal Ecology, 91, 1163– 1179. https://doi.org/10.1111/1365-2656.13617

References
  • Cleves, P.A., Tinoco, A.I., Bradford, J., Perrin, D., Bay, L.K. and Pringle, J.R., 2020. Reduced thermal tolerance in a coral carrying CRISPR-induced mutations in the gene for a heat-shock transcription factor. Proceedings of the National Academy of Sciences, 117(46), pp.28899-28905
  • Garcia-Porta et al. Environmental temperatures shape thermal physiology as well as diversification and genome-wide substitution rates in lizards. Nature Communications 10:4077 (2019). Read online at: https://rdcu.be/bQE2n
  • Wollenberg Valero, K.C., Pathak, R., Prajapati, I., Bankston, S., Thompson, A., Usher, J. and Isokpehi, R.D., 2014. A candidate multimodal functional genetic network for thermal adaptation. PeerJ, 2, p.e578.
  • Rodríguez, A., Rusciano, T., Hamilton, R., Holmes, L., Jordan, D. and Wollenberg Valero, K.C., 2017. Genomic and phenotypic signatures of climate adaptation in an Anolis lizard. Ecology and evolution, 7(16), pp.6390-6403.
  • Wollenberg Valero, K.C., Garcia‐Porta, J., Irisarri, I., Feugere, L., Bates, A., Kirchhof, S., Jovanović Glavaš, O., Pafilis, P., Samuel, S.F., Müller, J. and Vences, M., 2021. Functional genomics of abiotic environmental adaptation in lacertid lizards and other vertebrates. Journal of Animal Ecology. https://doi.org/10.1111/1365-2656.13617
  • Wollenberg Valero, K.C., 2020. Aligning functional network constraint to evolutionary outcomes. BMC Evolutionary Biology, 20(1), pp.1-14.
  • Le Galliard, J.F., Chabaud, C., de Andrade, D.O.V., Brischoux, F., Carretero, M.A., Dupoué, A., Gavira, R.S., Lourdais, O., Sannolo, M. and Van Dooren, T.J., 2021. A worldwide and annotated database of evaporative water loss rates in squamate reptiles. Global Ecology and Biogeography, 30(10), pp.1938-1950.

SPECIAL FEATURE: Understanding climate change response in the age of genomics

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The June issue of Journal of Animal Ecology is out now and includes a Special feature, Understanding climate change response in the age of genomics.

As global temperatures continue to rise, there is a major threat to species and ecosystems worldwide. In order to develop conservation and mitigation strategies, an understanding of how animal populations respond to changing environments is crucial. This Special Feature highlights emerging genomics approaches and how they can help us develop this understanding of how species respond to climate change. Blog Associate Editor, Julie Koch Sheard had a chat with Guest Editors for the feature, Maren Wellenreuther and Zachary Fuller about the motivation behind it and some of the papers included.

The Editorial for Understanding climate change response in the age of genomics is free to read here. All papers in the feature are also free to read for a limited time in issue 91:06.

Read the #StoryBehindthePaper for some of the featured articles here:

White seabream (Diplodus sargus). Credit: Robert A Patzner.
Striped red mullet (Mullus surmuletus). Credit: A. Dalongeville.
The characteristic love heart shaped ‘mating wheel’ formation of Ischnura elegans. Credit: Rachael Dudaniec
Some of the study species included in the special feature, which you can read about in the above-mentioned stories behind the papers.

Songbird parents coordinate in space and time

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This blog post is provided by Davide Baldan and tells the #StoryBehindThePaper for the paper “Songbird parents coordinate offspring provisioning at fine spatio-temporal scales“, which was recently published in the Journal of Animal Ecology.

Being a parent is certainly not an easy job. It takes a considerable amount of time and energy to successfully raise offspring. That is why each parent would like, if possible, to slack off and make its partner work harder. This desire generates a conflict of interest between the parents, commonly known as sexual conflict. Decades of research have suggested that parents do not work at their maximum capacity, and because of that, offspring and parents could suffer reduced fitness. To reduce the cost of parental conflict, researchers also point out that parents should constantly monitor each other and coordinate their activity, but we lack a clear understanding of the mechanisms by which parental coordination can occur.

In a recent paper in the Journal of Animal Ecology, we explored offspring provisioning behaviour of great tit (Parus major) pairs and investigated how parents coordinate their foraging movements. The great tit is a small passerine bird commonly breeding in European forests. Its breeding ecology has been studied for more than 50 years and it has become a model species to study parental care in the wild. Passerine birds, such as great tits, are hard working parents. Once chicks hatch, parents feed them with caterpillars and insects found in the territory near the nest. Great tit parents can visit the nest to feed the chicks once every 2 minutes and keep up with this rhythm for about 15-20 days until chicks fledge.

Great tits (Parus major). Photo credit: NIOO-KNAW

In this study, we monitored great tit reproduction in a woodland forest in the Netherlands during their breeding season. When chicks have hatched and are being fed, we captured parents at the nest and tagged them with a small-radio receiver. These tags are worn like a small backpack and transmit a radio pulse every 5 seconds, which is logged by small portable receivers. We placed receivers in a grid in the territory around the nest to triangulate the location of both parents during their provisioning activity. This allowed us to remotely monitor and collect undisturbed data of great tit foraging movements in their natural settings. We found that the foraging behaviour of great tit parents is highly coordinated in space and time, with parents changing their foraging locations in conjunction with their partners’ movements. This study represents the first detailed spatial and temporal description of foraging coordination in songbird parents in a natural context and opens a new avenue of research on breeding ecology of small birds.

Great tits (Parus major). Photo credit: NIOO-KNAW

These findings are also important for our understanding of how potential conflict between parents may be resolved. New evidence indicates that parental cooperation is more prevalent than we previously thought in animal families, and the more we investigate, the more we learn about the mechanisms that parents use to work together.

Read the paper

Read the full paper here: Baldan, D. & van Loon, E. E. (Early view). Songbird parents coordinate offspring provisioning at fine spatio-temporal scales. Journal of Animal Ecology. https://doi.org/10.1111/1365-2656.13702

Could apex predators limit the seed dispersal of fleshy-fruit plants? A rewilding scenario involving mammal carnivores.

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This blog post is provided by Tamara Burgos and tells the #StoryBehindThePaper for the paper “Predation risk can modify the foraging behaviour of frugivorous carnivores: implications of rewilding apex predators in plant-animal mutualisms”, which was recently published in the Journal of Animal Ecology.

Tamara Burgos is carrying out her PhD in Ecology at the University Rey Juan Carlos, Madrid, Spain. Her research interests focus on trophic cascades and the ecological effects of apex predator reintroductions on key ecosystem functions which carnivores are involved in, such as seed dispersal. Her fascination by the world of mammal carnivores have led Tamara Burgos to be involved in several conservation projects where the main goal was the study of Iberian lynx (Lynx pardinus) populations in Spain. This feline is one of the most endangered in the world and it was near extinction at the end of the 20th century. Nowadays, lynx populations are recovering largely thanks to conservation and reintroduction programs where several stakeholders are involved, from private landowners to governments.

The Iberian lynx, like other apex predators such as bears and wolves, is known for controlling the abundances of smaller mesopredators, such as foxes or Egyptian mongooses and altering their behaviour and activity patterns. For this reason, cascading effects triggered by the rewilding process of apex predators worldwide became the main focus of Tamara’s research.

Iberian lynx (Lynx pardinus) just released into the wild in Central Spain with a monitoring collar via GPS. Credit: Tamara Burgos.

William J. Ripple and Robert L. Beschta planted the seed, studying these cascade effects from wolves to primary producers in Yellowstone National Park, after the reintroduction of the grey wolf in the 90’s. New research studies were appearing progressively involving different trophic levels in the study of trophic cascades, however nobody thought of mesocarnivores as potential direct controllers of plant populations and vegetation structure.

During her Master thesis on the effects of releasing apex predators on mesopredator and prey abundances, Tamara and her supervisor, Emilio Virgós realised that reintroductions of large predators could affect plants, not only via control of large herbivore populations but also via mesopredator suppression. Many medium-sized carnivores play a key role in ecosystem functioning as agents of seed dispersal, by consuming a great quantity and variety of fleshy-fruits. Foxes, badgers or martens have a generalist and opportunistic diet and they often feed on fruit, especially in ecosystems where this is an abundant resource. Therefore, if apex predators can control mesopredator abundances, this top-down effect could have indirect consequences for many fleshy-fruit plants whose seed dispersal depends mostly of mesocarnivores.

Red fox (Vulpes vulpes) feeding on Iberian pear fruits. Foxes are effective seed dispersers because they spread the seeds across large distances and bring them to vacant habitats, thus playing an important role in the recolonization of old or abandoned labour fields. Video recorded by camera-trapping. Credit: Tamara Burgos.

Meanwhile, Jose M. Fedriani studied the seed dispersal patterns of the Iberian pear (Pyrus bourgaeana) in Southern Spain and discovered that carnivore mammals were the main seed dispersers for this tree in Mediterranean ecosystems. Tamara and Emilio saw a perfect opportunity for collaboration and together they designed Tamara’s thesis project on trophic cascades and plant-disperser mutualisms, which she is currently working on.

The research team found the perfect place to develop this study: Sierra de Andújar Natural Park. After a long process of social dinners and bar meetings with hunters and landowners, Tamara and colleagues were allowed to carry out their research study on their lands. However, there were still some obstacles to overcome. Working with mutualist interactions where carnivores are involved can be challenging because these animals are elusive and difficult to observe when they are mainly interacting with plants. The best solution that the authors found was to design a natural experiment by using technology. Camera-traps are useful devices to study carnivores in many aspects of their biology such as behaviour or demography. Thus, the authors offered pear fruits beneath fruiting Iberian pear trees and analysed the foraging behaviour by the frugivorous carnivores recorded by camera-traps. They compared the number of visits, fruits consumed and feeding behaviour of individuals which coexisted with the Iberian lynx, and individuals which inhabited outside the lynx distribution range by selecting sites with lynx and sites where the lynx was extinct inside the Natural Park.

Small Iberian pear tree (Pyrus bourgaeana) probably dispersed by a badger (you can see the badger latrine beneath the tree). Credit: Tamara Burgos.

The study reveals a potential trophic cascade from an apex predator to a fleshy-fruit plant mostly dispersed by carnivores. They found that 70% and 100% of fox and stone marten visits, respectively, occurred at pear trees located outside Iberian lynx territories. Moreover, the study showed that foxes co-existing with lynx consumed 38% less fruit and were therefore less efficient frugivores. They consumed less fruit per unit of time and made shorter visits to pear trees, both behavioural features typically linked to an anti-predatory response. A larger competitor can easily predate foxes and martens and the predation risk perceived inside lynx ranges could lead them to use surrounding areas more intensively to avoid conflictive encounters with lynx.

Therefore, understanding the ecological interactions among the different levels of food webs is essential to design suitable conservation strategies and predict potential cascading effects in altered ecosystems. Rewilding programs should consider trophic cascades as a powerful mechanism, which can alter key ecosystem functions in contrasting ways. However, this is only the starting point and future research is necessary to shed more light on this issue, for what they hope will be more papers and research projects approaching cascading effects from reintroductions on mutualist interactions where carnivores are involved.