Emigration is costly, but immigration has benefits in human-altered landscapes

Fragmented habitats are a signature of anthropogenically disturbed landscapes. When human activities act to disaggregate once-contiguous forest or other terrestrial ecosystems, and convert intervening spaces into a ‘matrix’ of agriculture, roads and urban areas, it can be difficult for resident species to sustain connected populations (Saunders, Hobbs & Margules 1991). Dispersal ability and inter-patch migration rates are therefore important determinants of a species’ ability to persist and navigate throughout these human-altered environments. But mobility can also be a double-edged sword (Fahrig 2007). Movement involves certain risk to individuals, resulting in costs to energy expenditure that amplifies with time spent moving, and increased mortality risk that has the potential to deplete source populations of potential future breeders. The trade-off between the benefits and costs of mobility in fragmented landscapes and its implications for extinction risk have consequently been a central problem for conservation.