Abstract
Population extinction is a fundamental ecological process which may be aggravated by the exchange of organisms between productive (source) and unproductive (sink) habitat patches. The extent to which such source-sink exchange affects extinction rates is unknown. We conducted an experiment in which metapopulation effects could be distinguished from source-sink effects in laboratory populations of Daphnia magna. Time-to-extinction in this experiment was maximized at intermediate levels of habitat fragmentation, which is consistent with a minority of theoretical models. These results provided a baseline for comparison with experimental treatments designed to detect effects of concentrating resources in source patches. These treatments showed that source-sink configurations increased population variability (the coefficient of variation in abundance) and extinction hazard compared with homogeneous environments. These results suggest that where environments are spatially heterogeneous, accurate assessments of extinction risk will require understanding the exchange of organisms among population sources and sinks. Such heterogeneity may be the norm rather than the exception because of both the intrinsic heterogeneity naturally exhibited by ecosystems and increasing habitat fragmentation by human activity.
Highlights
Population extinction structures biological communities (Chave 2004; Chase 2007), landscapes (Condit et al 2002), and the worldwide distribution of biodiversity (Brooks et al 2006; Davies et al 2006)
Fundamental to progress in community ecology (Holyoak et al 2005) and biogeography (Hubbell 2001; Volkov et al 2003), and critical for informing conservation actions in increasingly fragmented landscapes (Fahrig 2003; International Union for the Conservation of Nature (IUCN) 2006), the theory of population extinction has rarely been tested with controlled experiments (Belovsky et al 1999; Drake 2005; Griffen and Drake 2008a; Drake and Griffen 2010)
Ecology and Evolution published by John Wiley & Sons Ltd
Summary
Population extinction structures biological communities (Chave 2004; Chase 2007), landscapes (Condit et al 2002), and the worldwide distribution of biodiversity (Brooks et al 2006; Davies et al 2006). Fundamental to progress in community ecology (Holyoak et al 2005) and biogeography (Hubbell 2001; Volkov et al 2003), and critical for informing conservation actions in increasingly fragmented landscapes (Fahrig 2003; International Union for the Conservation of Nature (IUCN) 2006), the theory of population extinction has rarely been tested with controlled experiments (Belovsky et al 1999; Drake 2005; Griffen and Drake 2008a; Drake and Griffen 2010). We follow Fahrig (2003) in using “fragmentation” to refer to the subdivision of a population, separate from effects of habitat a 2013 The Authors.
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