When species can decide whether to disperse or not

This blog post is provided by Xiaozhou Ye and tells the #StoryBehindthePaper for the paper “Maintenance of biodiversity in multitrophic metacommunities: dispersal mode matters”, which was recently published in Journal of Animal Ecology. In their paper they investigate whether distinct dispersal modes (such as random or fitness-dependent dispersal) impact residing metacommunity biodiversity. The answer is yes. Read on to find out more.
Does species-level dispersal mode matter for community-level biodiversity?

Different species adopt various dispersal modes: some rarely move, some disperse randomly with water or wind, while many others disperse actively to evade predators and avoid food scarcity – a process known as fitness-dependent dispersal. These distinct dispersal modes are generally considered asadaptations at the species level, but do they also have far-reaching impacts on the biodiversity of their residing metacommunities – a collection of communities linked by dispersal?

Our recent theoretical paper in the Journal of Animal Ecology found the answer to be YES. Adopting fitness-dependent dispersal strategy helps maintaining metacommunity diversity: species-level adaptation in this instance happens to also benefit the community as a whole. But not only this. Our study provides a dispersal mode-dependent understanding of dispersal’s effect on metacommunities extending the conclusions of previous studies focused on random dispersal. Here’s what we’ve learned.

Figure 1: White-throated redstart can disperse actively to seek food. Photo: Maoqin He
Dispersal “translates” habitat heterogeneity and connectivity to diversity

The dispersal process acts as a vital connection between landscape features – such as habitat heterogeneity and connectivity – and biodiversity. We can think of the landscape as a blueprint for metacommunities. Habitat heterogeneity gives rise to diverse habitat patches, which support various local communities, allowing dispersal to potentially influence community compositions. Habitat connectivity, another crucial component of the blueprint, makes dispersal a possibility. However, it is ultimately up to the species to “interpret” this blueprint, as they could choose to disperse or not according to their own dispersal mode and strategy, even if dispersal is possible and can make a difference. In other words, the dispersal choice of the species “translates” the landscape blueprint to species distribution and biodiversity across scales.

Figure 2: The landscape provides a blueprint for biodiversity. Photo: Xiaozhou Ye
Different dispersal modes lead to different “translations”

This “translation” process dictates why dispersal mode matters for biodiversity. For instance, habitat connectivity directly leads to increased dispersal rates in randomly dispersing species, but not necessarily in species with fitness-dependent dispersal. For the latter, when the current patch is good enough they may simply decide to stay, so the real dispersal rate does not increase with increasing habitat connectivity. As a result, habitat connectivity has a weaker impact on metacommunities composed of such species, as our results demonstrate.

Similarly, habitat heterogeneity also impacts randomly dispersing and fitness-dependent dispersing species differently. Heterogeneous landscapes contain diverse habitats thus the potential to host diverse species. However, from a single species’ viewpoint, they simultaneously give rise to suitable (“good”) and unsuitable (“bad”) habitat patches. Random dispersing species are more vulnerable to “bad” patches in the landscape, because they would eventually linger in “bad” patches by chance. On the other hand, fitness-dependent dispersing species can actively escape from “bad” habitat patches, thus remain unharmed. Our results found metacommunity diversity to reflect this distinction. While habitat heterogeneity nurtures biodiversity when species dispersal is fitness-dependent, it is not beneficial and can even be harmful to metacommunity diversity in metacommunities dominated by randomly dispersing species.

Figure 3: Scenedesmaceae mostly disperse randomly with water flow. Photo: Pubin Hong
The limiting scenario: extremely strong fitness-dependent dispersal approaches isolated systems

We can get a deeper understanding of how fitness-dependent dispersal maintains metacommunity diversity by examining the extreme scenario, although it may not occur in nature. With extremely strong fitness-dependent dispersal, the species distribution and biodiversity of metacommunities are strikingly similar to that of isolated communities – except that dispersal sustains some small populations that would otherwise go extinct.

This similarity is not a coincidence: indeed, similar species distribution emerges from two distinct mechanisms. In isolated communities, community composition arises from the species sorting process: survival of the suitable. While with extreme fitness-dependent dispersing species, active habitat selection of the species effectively avoids unsuitable patches, achieving the same species distribution as that in isolated system (assuming the metacommunity doesn’t have another alternative stable state with reasonably large attraction basin, to be precise). This “suitable” species distribution would be disturbed if dispersal were random, reducing diversity at the metacommunity level (β and γ diversity), although increasing local (α) diversity.

Taxa-specific management strategies for conservation

Species have their own ways. We need to learn how the species interpret and respond to the landscape. By applying this knowledge, we can design landscape management strategies in a taxa and context-dependent manner. While habitat heterogeneity and connectivity are great for metacommunities dominated by fitness-dependent species, they can be detrimental for metacommunities with randomly dispersing species and should be treated with caution.

Figure 4: Conservation of birds and planktons may require different strategies. Photo: Lisen Ye
Read the paper

Read the full paper here: Ye, X., & Wang, S. (2023). Maintenance of biodiversity in multitrophic metacommunities: Dispersal mode matters. Journal of Animal Ecology, 00, 1–13. https://doi.org/10.1111/1365-2656.13933

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