Predator avoidance and foraging for food shape synchrony and response to perturbations in trophic metacommunities

The response of species to perturbations strongly depends on spatial aspects in populations connected by dispersal. Asynchronous fluctuations in biomass among populations lower the risk of simultaneous local extinctions and thus reduce the regional extinction risk. However, dispersal is often seen as passive diffusion that balances species abundance between distant patches, whereas ecological constraints, such as predator avoidance or foraging for food, trigger the movement of individuals. Here, we propose a model in which dispersal rates depend on the abundance of the species interacting with the dispersing species (e.g., prey or predators) to determine how density-dependent dispersal shapes spatial synchrony in trophic metacommunities in response to stochastic perturbations. Thus, unlike those with passive dispersal, this model with density-dependent dispersal bypasses the classic vertical transmission of perturbations due to trophic interactions and deeply alters synchrony patterns. We show that the species with the highest coefficient of variation of biomass governs the dispersal rate of the dispersing species and determines the synchrony of its populations. In addition, we show that this mechanism can be modulated by the relative impact of each species on the growth rate of the dispersing species. Species affected by several constraints disperse to mitigate the strongest constraints (e.g., predation), which does not necessarily experience the highest variations due to perturbations. Our approach can disentangle the joint effects of several factors implied in dispersal and provides a more accurate description of dispersal and its consequences on metacommunity dynamics.

Metacommunity dynamics and the spurious detection of species associations in co-occurrence analyses: patch disturbance matters

Many methods attempt to detect species associations from co-occurrence patterns. Such associations are then typically used to infer inter-specific interactions. However, correlation is not equivalent to interaction. Habitat heterogeneity and out-of-equilibrium colonization histories are acknowledged to cause species associations even when inter-specific interactions are absent. Here we show how classical metacommunity dynamics, within a homogeneous habitat at equilibrium, can also lead to statistical associations. This occurs even when species do not interact. All that is required is patch disturbance (i.e. simultaneous extinction of several species in a patch) a common phenomenon in a wide range of real systems. We compare direct tests of pairwise independence, matrix permutation approaches and joint species distribution modelling. We use mathematical analysis and example simulations to show that patch disturbance leads all these methods to produce characteristic signatures of spurious association from "null" co-occurrence matrices. Including patch age (i.e. the time since the last patch disturbance event) as a covariate is necessary to resolve this artefact. However, this would require data that very often are not available in practice for these types of analyses. We contend that patch disturbance is a key (but hitherto overlooked) factor which must be accounted for when analysing species co-occurrence.

The effect of colonization dynamics in competition for space in metacommunities

One of the main factors that determines habitat suitability for sessile and territorial organisms is the presence or absence of another competing individual in that habitat. This type of competition arises in populations occupying patches in a metacommunity. Previous studies have looked at this process using a continuous-time modeling framework, where colonizations and extinctions occur simultaneously. However, different colonization processes may be performed by different species, which may affect the metacommunity dynamics. We address this issue by developing a discrete-time framework that describes these kinds of metacommunity interactions, and we consider different colonization dynamics. To understand potential dynamics, we consider specific functional forms that characterize the colonization and extinction processes of metapopulations competing for space as their limiting factor. We then provide a mathematical analysis of the models generated by this framework, and we compare these results to what is seen in nature and in previous models.

Letters: Complex response of beta diversity to dispersal in meta-community models

Dispersal is one of the most important drivers of community assembly. The conventional belief that dispersal leads to biotic homogenization (lower beta diversity) has been recently challenged by an experiment conducted in nectar microbes (Vannette & Fukami, 2017), showing that dispersal could lead to community divergence. In this paper, I re-examined the relationship between beta diversity and local dispersal in a range of theoretical models: from the classic island biogeography model and meta-population model to a meta-community model that incorporates biotic interactions. I find that the emergence of hump-shaped beta diversity-dispersal relationship is closely related to local dispersal (rather than global dispersal), non-neutrality and biotic interactions. The results reveal rich metacommunity dynamics in relation to dispersal types and biotic interactions which might be overlooked in previous theoretical and empirical studies. The findings call for more realistic experimental manipulations on dispersals in future community assembly studies.

Disturbance, patches and mosaics

This chapter introduces the range of biological and physical processes that disturb soft sediment. It introduces the concept of disturbance regimes that connect the extent, frequency and magnitude of disturbance. Post-disturbance recovery processes are described in terms of processes that occur within the disturbed patch and processes that influence recovery from outside the patch. Moving on from the patch scale, the chapter introduces the concept of patch dynamics and the concept of the seafloor as a mosaic of patches at different stages of recovery from disturbance. Connectivity between patches is a critical factor linking local recovery processes to landscape-scale processes. This mosaic perspective leads to the introduction of metacommunity dynamics and the potential for heterogeneous landscapes to fragment and eventually homogenise seafloor communities as a consequence of the loss of large habitat-defining species.