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

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

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