Impacts of global change on dispersal costs – DISPCOST

DISPCOST combines two approaches: the analysis of empirical data from two long-term monitoring programs of roe deer populations; and spatially explicit individual-based modelling.
The empirical part consists in collecting and analysing GPS and capture-mark-recapture data allowing to characterize individual dispersal, as well as the different estimators of dispersal costs: mortality rate, attrition rate (body growth, parasitism rate, stress level, …), energetic costs (through the use of accelerometers), time costs, delays in reproduction or increased senescence. The analysis of these data allows testing whether climate change and/or human-triggered landscape modifications affect the different types of dispersal costs (risk costs, energetic costs, time costs, deferred costs). During the first period, we worked in the field (captures to fit GPS collars or color bands, reproduction monitoring, density estimates, …) to pursue the collect of these data. Regarding the analyses, we first investigated risk costs and energetic costs: (i) we compared mortality risks between disperser and philopatric individuals in Aurignac; (ii) we performed calibration tests of the accelerometers.
The modelling part consists in the use of RangeShifter, a spatially explicit individual-based modelling platform. We will incorporate the results of the empirical analyses in this platform to infer how dispersal might evolve under different scenarios of global change, and how this could affect population dynamics. This modelling work will start in summer 2017.

During the first period of DISPCOST, we performed two annual sessions of captures, both in Aurignac and Chizé. They allowed fitting GPS collars (some of them combined with accelerometers) or color bands that will allow characterizing dispersal in marked individuals. The other types of demographic monitoring (reproduction, density, …) were also performed.
The preliminary analysis of risk costs in Aurignac suggests there are no mortality costs. This could be due to the fact that dispersers decrease the risks taken during the transfer step by moving mostly during at dawn, dusk and night. Those preliminary results will be backed up soon by new, more precise, analyses.
The analysis of the calibration tests of the accelerometers is still in progress. The first results show that this type of data can be quite complex, and highlight the importance of this calibration work. But they also show the strong potential of this approach for estimating the energetic costs of dispersal.

The largest part of the analyses and of the modeling is in progress or will start in the coming months, and will give results in the second phase of the project. Besides the usual field work (captures, demographic monitoring, …), the next steps will be the finalization of the analysis of demographic costs in Chizé and of risk costs in Aurignac; the start of the modeling work; and the analysis of the energetic costs of dispersal.

Léa Sueur’s master report: Estimation des coûts de risques liés à la dispersion chez le Chevreuil (Capreolus capreolus) en lien avec les changements anthropiques du paysage. 2016. Université de Lille 1.

Ongoing global change has made it crucial to understand the eco-evolutionary dynamics of dispersal. Indeed, human activities trigger direct or indirect (through climate change or habitat fragmentation) alteration of environmental conditions. Climate change also triggers a latitudinal and altitudinal shift in the location of suitable habitats. Demographic and genetic fluxes among populations in fragmented landscapes and the ability of species to track the shift of their climatic envelope are both contingent on the dispersal abilities of individuals. Moreover, as dispersal is the process that drives the spatial distribution of genotypes, it is key for adaptation to new environmental conditions. In the current context of rapid global change, a key question concerns how environmental modification will impact an individual’s dispersal decisions by altering the cost-benefit landscape of dispersing. The modifications of local conditions triggered by global change are predicted to affect dispersal in two ways. First, when confronted by these modifications, individuals may adjust locally to their novel conditions through phenotypic plasticity or rapid evolution. In this case, the costs associated with dispersal are likely to be affected by local changes in habitat quality and landscape characteristics, with consequences for dispersal rates and distances at the population level. Second, individuals may respond to global change by moving to areas where conditions are more favourable (e.g. latitudinal/altitudinal shift of species ranges in the case of global warming). This process of colonisation of novel suitable ranges will be mediated through dispersal movements of individuals. The rate at which this colonisation process will occur will largely depend on the dispersal cost-benefit landscape, and particularly the costs associated with long-distance dispersal events.
The current empirical and theoretical knowledge on the effects of global change on the costs of dispersal is still very limited. DISPCOST hence aims to fill this gap by evaluating how environmental drivers affect the costs of dispersal, and determining the consequences for population dynamics and the evolution of dispersal. DISPCOST will specifically address the following questions (the first two empirically, the last one theoretically, with spatially explicit individual-based models): 1) How do human-driven landscape modifications affect dispersal costs? 2) How does climate change affect dispersal costs? 3) What are the consequences of 1) and 2) on dispersal evolution and population functioning? Those questions will be addressed using the European roe deer (Capreolus capreolus) as a model species, in two study areas with contrasted environments. The reasons for the choice of this model species are first the existence of long-term monitoring programs that have generated data of exceptional quality on dispersal. These data will allow us to assess the whole range of dispersal costs. Second, this species has huge socio-economic impacts through forest/agricultural damage and vehicle collisions, as a disease vector, and as a source of revenue for rural communities through hunting. Hence, the expected repercussions for society are considerable.
Understanding how global change modifies the cost-benefit landscape of dispersal is essential to be able to predict the evolution of this life-history trait and, more generally, the impacts of global change on species spatial dynamics. DISPCOST will provide crucial knowledge to fill the current existing gap in this area. Moreover, the outcomes that DISPCOST will generate about the link between individual dispersal decisions, spatial population dynamics and species’ geographic range will have considerable importance for the management of this large herbivore and its impacts.