Why we should care about movements: Using spatially explicit integrated population models to assess habitat source-sink dynamics.

Matthieu Paquet,Pär Forslund,Jonas Knape,Debora Arlt,Matthew Low,Tomas Pärt,Elise Zipkin

doi:10.1111/1365-2656.13357

Matthieu Paquet, Pär Forslund + Show 5 more

Open Access

https://doi.org/10.1111/1365-2656.13357

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Abstract

Assessing the source–sink status of populations and habitats is of major importance for understanding population dynamics and for the management of natural populations. Sources produce a net surplus of individuals (per capita contribution to the metapopulation > 1) and will be the main contributors for self‐sustaining populations, whereas sinks produce a deficit (contribution < 1). However, making these types of assessments is generally hindered by the problem of separating mortality from permanent emigration, especially when survival probabilities as well as moved distances are habitat‐specific.To address this long‐standing issue, we propose a spatial multi‐event integrated population model (IPM) that incorporates habitat‐specific dispersal distances of individuals. Using information about local movements, this IPM adjusts survival estimates for emigration outside the study area.Analysing 24 years of data on a farmland passerine (the northern wheatear Oenanthe oenanthe), we assessed habitat‐specific contributions, and hence the source–sink status and temporal variation of two key breeding habitats, while accounting for habitat‐ and sex‐specific local dispersal distances of juveniles and adults. We then examined the sensitivity of the source–sink analysis by comparing results with and without accounting for these local movements.Estimates of first‐year survival, and consequently habitat‐specific contributions, were higher when local movement data were included. The consequences from including movement data were sex specific, with contribution shifting from sink to likely source in one habitat for males, and previously noted habitat differences for females disappearing.Assessing the source–sink status of habitats is extremely challenging. We show that our spatial IPM accounting for local movements can reduce biases in estimates of the contribution by different habitats, and thus reduce the overestimation of the occurrence of sink habitats. This approach allows combining all available data on demographic rates and movements, which will allow better assessment of source–sink dynamics and better informed conservation interventions.

Highlights

Habitat quality typically varies both in space and time, and such habitat heterogeneity is expected to have profound impacts on populations' dynamics, persistence and evolution (Liu et al, 2011; Pulliam & Danielson, 1991; Ronce & Kirkpatrick, 2001)
Habitat quality likely varies in time (Johnson, 2004; Loreau et al, 2013), resulting in temporal variation of source–sink dynamics (Furrer & Pasinelli, 2016; Loreau et al, 2013) and difficulties in assessing the net contribution of different habitats and the conditions under which they may shift from source to sink
We found that including natal, in comparison to breeding, local movements were mostly responsible for the increase in estimated per capita contributions, which is not surprising given that natal dispersal is on average more extensive than breeding dispersal (Greenwood & Harvey, 1982, see Appendix 3 Figure A3 2)

Summary

Introduction

Habitat quality typically varies both in space and time, and such habitat heterogeneity is expected to have profound impacts on populations' dynamics, persistence and evolution (Liu et al, 2011; Pulliam & Danielson, 1991; Ronce & Kirkpatrick, 2001). Habitat quality likely varies in time (Johnson, 2004; Loreau et al, 2013), resulting in temporal variation of source–sink dynamics (Furrer & Pasinelli, 2016; Loreau et al, 2013) and difficulties in assessing the net contribution of different habitats and the conditions under which they may shift from source to sink. In most cases, it is highly challenging to distinguish mortality from permanent emigration and obtain accurate estimates of surpluses or deficits of individuals produced per habitat or population (Runge et al, 2006) This is true at the scale of the habitat-specific subpopulations (exchanges between sources and sinks within the population) and at larger spatial scales (movements between populations). A failure to do so will produce biased estimates of habitat differences in per capita contribution to the population, and incorrect assessments of habitat-specific source–sink dynamics

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