Ecology and evolution unfold in spatially structured communities, where dispersal links dynamics across scales. Because dispersal is multicausal, identifying general drivers remains challenging. In a coordinated distributed experiment spanning organisms from protozoa to vertebrates, we tested whether two fundamental determinants of local dynamics, top-down and bottom-up control, generally explain active dispersal. We show that both factors consistently increased emigration rates and use metacommunity modelling to highlight consequences on local and regional dynamics.

1. Contemporary climate change affects population dynamics, but its influence varies with landscape structure. It is still unclear whether landscape fragmentation buffers or amplifies the effects of climate on population size and the age and body size of individuals composing these populations.2. This study aims to investigate the impacts of warm climates on lizard life-history traits and population dynamics in habitats that vary in their connectivity. We monitored common lizardZootoca vivipara populations for 3 years in an experimental system in which both climatic conditions and connectivity among habitats were simultaneously manipulated. We considered two climatic treatments (i.e. present-day climate and warm climate [+1.4°C than present-day climate]) and two connectivity treatments (i.e. a connected treatment in which individuals could move from one climate to the other and an isolated treatment in which movement between climates was not possible). We monitored survival, reproduction, growth, dispersal, age and body size of each individual in the system as well as population density through time. 4. We found that the influence of warm climates on life-history traits and population dynamics depended on connectivity among thermal habitats. Populations in warm climates were (i) composed of younger individuals only when isolated; (ii) larger in population size only in connected habitats and (iii) composed of larger age-specific individuals independently of the landscape configuration. The connectivity among habitats altered population responses to climate warming likely through asymmetries in the flow and phenotype of dispersers between thermal habitats. 5. Our results demonstrate that landscape fragmentation can drastically change the dynamics and persistence of populations facing climate change.

Organisms rarely experience a homogeneous environment. Rather, ecological and evolutionary dynamics unfold in spatially structured and fragmented landscapes, with dispersal as the central process linking these dynamics across spatial scales. Because dispersal is a multi-causal and highly plastic life-history trait, finding general drivers that are of importance across species is challenging but highly relevant for ecological forecasting.We here tested whether two fundamental ecological forces and main determinants of local population dynamics, top-down and bottom-up control, generally explain dispersal in spatially structured communities. In a coordinated distributed experiment spanning a wide range of actively dispersing organisms, from protozoa to vertebrates, we show that bottom-up control, that is resource limitation, consistently increased dispersal. While top-down control, that is predation risk, was an equally important dispersal driver as bottom-up control, its effect depended on prey and predator space use and whether dispersal occurred on land, in water or in the air: species that routinely use more space than their predators showed increased dispersal in response to predation, specifically in aquatic environments. After establishing these general causes of dispersal, we used a metacommunity model to show that bottom-up and top-down control of dispersal has important consequences for local population fluctuations as well as cascading effects on regional metacommunity dynamics. Context-dependent dispersal reduced local population fluctuations and desynchronized dynamics between communities, two effects that increase population and community stability.Our study provides unprecedented insights into the generality of the positive resource dependency of dispersal as well as a robust experimental test of current theory predicting that predator-induced dispersal is modulated by prey and predator space use. Our experimental and theoretical work highlights the critical importance of the multi-causal nature of dispersal as well as its cascading effects on regional community dynamics, which are specifically relevant to ecological forecasting.