Isolating the role of the matrix at patch and landscape scales

Global increases in habitat loss and fragmentation have resulted in non-habitat landcover, or the matrix, becoming an increasingly prominent feature of landscapes. The matrix can influence the population dynamics of species in fragments by modifying processes operating locally on individual patches (e.g. edge effects on survival) or at landscape scales (e.g. inter-patch dispersal). However, the relative magnitude of patch- vs. landscape-scale matrix effects on the populations found in patches remains unclear. We established 12 experimental landscapes in which we controlled for habitat amount and fragmentation while manipulating the quality of the matrix around (i) individual habitat patches and (ii) across the entire landscape in a factorial design. We then compared the magnitude of local- and landscape-scale matrix effects on a specialist herbivore, Chelinidea vittiger (Hemiptera: Coreidae). Population size in fragments was influenced by both patch- and landscape-scale treatments: Population size increased in patches surrounded by high-quality matrix, but only in landscapes dominated by low-quality matrix, due in part to decreased inter-patch movements in these landscapes. In contrast, the effects on both survival and reproductive output were solely at the patch-scale, with both lower in patches surrounded by low-quality matrix. Our results underscore the outsized importance of matrix habitat immediately adjacent to fragment edges-despite the fact that patch-scale manipulations affected only a fraction (3%) of the area that landscape-scale manipulations did, patch-scale effects were more common. The relationship between dispersal, population size and scale-dependent effects of matrix quality emphasizes the need to explicitly consider the spatial scale at which different processes operate when predicting responses to habitat fragmentation. Our results also suggest the matrix immediately adjacent to habitat remnants is of particular importance when considering alternative strategies for landscape conservation or restoration.