Spatial heterogeneity in habitat quality and dispersal - individual decisions and their population dynamic consequences

Lead Research Organisation: University of Reading
Department Name: Sch of Agriculture Policy and Dev


As a population gets larger breeding success and survival generally declines due to increased competition for resources such as food or breeding sites. This process is called density-dependence, and it has been a core theme in population ecology for decades, not least because it is pivotal to understanding how populations might respond to environmental change, such as habitat loss or changes in climate. We know that density-dependence occurs in populations across a wide range of species, but we have a rather limited idea of the processes involved. This lack of understanding is particularly acute for species of conservation concern. As a result, models of population dynamics used to aid decisions about their conservation often lack density-dependence, or make strong assumptions about the mechanisms involved. Our lack of knowledge is particularly pronounced when considering the dispersal decisions of individuals in spatially variable environments, even though theory predicts that these will play a key role in density-dependence. Also, it is increasingly recognized that behaviours that are sensible for individuals to adopt because they leave more offspring do not necessarily lead to best possible population-level performance. For improved ecological understanding of population processes, it is therefore essential to form a link between individual dispersal decisions and their population-level consequences. One way such links may operate is through the so-called 'buffer effect' in which an increasing proportion of individuals are forced to occupy poor quality habitat as a population grows, thereby driving down the breeding success and survival of individuals within the population. Spatial distribution patterns consistent with this idea are widespread in vertebrates. However, we have a limited idea about the individual dispersal decisions that underlie these patterns, or the wider implications for population growth or persistence. In this project, we propose to address these issues using a mix of theoretical and empirical approaches, the latter being based on one of the most complete long-term datasets available on a vertebrate population (the Mauritius kestrel). Our approach is novel in that we are attempting to develop a framework that allows us to (1) explain how individual dispersal decisions in space generate patterns of spatial occupancy and density-dependence, and (2) explore the consequences of dispersal decisions for population growth and persistence in the face of environmental change. As a result, our research will provide general insights into the ecology of dispersal, an understanding of how dispersal generates spatial distribution patterns and density-dependence, and a theoretical framework for linking dispersal to population dynamics.


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Description Our project looked at the role dispersal plays in population regulation. In particular, we were interested in understanding how wild animals use space as they disperse from the area in which they are born, and what effect this has on the population of which they are part. This has important implications for how individuals and populations respond to environmental change. We explored these ideas in a tropical wild bird population.

We found that females dispersed further from home when breeding opportunities were limited. Females experienced a cost in terms of reduced reproductive success when they dispersed long distances. Interestingly, these costs can last a lifetime, which is the first time anyone has shown significant long-term costs.

We also found that dispersal can have strong effects on the population. After leaving home, individuals disperse into high quality habitat before settling to breed. Competition in these high quality habitats strongly regulates the population because it reduces the survival of young birds.
Exploitation Route Further details are given in the Narrative Impact section
Sectors Environment,Leisure Activities, including Sports, Recreation and Tourism,Government, Democracy and Justice

Description Our project was based on long-term data from an endangered bird species in Mauritius, and conducted in partnership with several conservation organisations. This partnership has been in place since about 2000. Our findings are fed directly into a long-term species conservation programme, and help design conservation actions on the ground. Recent work has shown that this programme, together with a number of others in Mauritius, have had a major, positive conservation impact on threatened species (Young, R.P. et al. 2014 Biological Conservation 180, 84-96). As a result, Mauritius is one of only a few countries in the World that has achieved net improvements in their biodiversity (Rodrigues A.S.L. et al. 2014. PLoS One 9, e113934). Our research has contributed directly to these impacts.
First Year Of Impact 2000
Sector Environment
Impact Types Societal

Description Fellowship to Deborah Arlt
Amount £100,000 (GBP)
Organisation Swedish Research Council 
Sector Public
Country Sweden
Start 01/2010 
End 12/2012
Description Durrell Wildlife Conservation Trust (DWCT) 
Organisation Durrell Wildlife Conservation Trust
Country Jersey 
Sector Charity/Non Profit 
PI Contribution We design and run the science that feeds into DWCT's conservation programmes in Mauritius; we manage long-term datasets; and we help design conservation actions on the gorund
Collaborator Contribution DWCT has worked for over 30 years on threatened species and ecosystem restoration programmes in Mauritius. We use long-term datasets collected by DWCT and other partners (MWF and NPCS) in our research, which includes NERC grants and studentships
Impact Regular reports and co-authored papers
Description Partnership with Mauritius Wildlife Foundation (MWF) 
Organisation Mauritius Wildlife Foundation
Country Mauritius 
Sector Charity/Non Profit 
PI Contribution The work funded by our NERC grant fed into conservation programmes being run by MWF on endangered species management and ecosystem restoration. This is part of a long-term partnership between MWF and University of Reading.
Collaborator Contribution MWF organise long-term data collection on various conservation programmes with our help (i.e. we manage databases on their behalf). These data have formed the basis for various NERC grants. MWF then uses science outputs in their threatened species and ecosystem restoration programmes.
Impact Regular reports on science. Co-authored publications.
Description Partnership with the National Parks and Conservation Services (NPCS), Government of Mauritius 
Organisation Government of Mauritius
Department National Parks and Conservation Service
Country Mauritius 
Sector Public 
PI Contribution The science generated by our NERC grants has fed directly into threatened species and ecosystem restoration work in Mauritius
Collaborator Contribution NPCS are the Government Department responsible for conservation action in Mauritius
Impact Regular update reports on various conservation projects
Start Year 2006