Linking edge effects and patch size effects: Importance of matrix nest predators

Abstract

a b s t r a c tThe edge effect is usually considered to be the proximate cause of area sensitivity in forest birds. We tested if birds nesting in large patches are less vulnerable to the edge effect using a simple model that assumes an increase in patch size reduces the probability of a matrix predator moving to the core areas of forest and that larger perimeter/area ratios result in a higher number of matrix predators per unit of area. The probability of a nest being successful decreased asymptotically with an increase in either the patch penetration distance of predators or predator density, but those effects were reduced when patch size was increased. Large patches have a lower probability of being affected by an Allee effect and they can function as sink habitats only if penetration distance and predator density are largely increased. However, the transition from an Allee effect to a sink condition occurs with a small increase in penetration distance and predator density. Since birds nesting in large patches are less vulnerable to an increase in matrix predator populations, persistence of bird populations may be possible by increasing the size of habitat patches that can act as source populations.

The fine-scale utilization of forest edges by mammalian mesopredators related to patch size and conservation issues in Central European farmland

“…In addition we analyzed the effect of habitat variables that characterize the degree of habitat fragmentation and loss at landscape scale and that may affect the distribution and landscape use of carnivores (Virgós et al 2002;Gehring and Swihart 2003;Pita et al 2009). In particular, we calculated proportion of forest cover and proportion of edges which was defined as the length of edges per unit of forest cover (e.g., Vergara and Hahn 2009). These characteristics were calculated within a 1-km radius area centered at each edge scent station (Gehring and Swihart 2003).…”

“…Effective conservation steps should concentrate on landscape structure and configuration-such as the spatial relationship between individual landscape elements-because landscape structures can have major impact on predator-prey interactions (Donovan et al 1997;Chalfoun et al 2002;Virgós et al 2002;Gehring and Swihart 2003;Pita et al 2009). Larger forest patches should have an adequate proportion of core area to increase nest success, because mammalian predators move deep into forest interiors less frequently (Vergara and Hahn 2009).…”

“…The edge effect (i.e., higher predation pressure in habitat edges) is one of the causes of above mentioned population sinks of many species (Andrén 1994;Oehler and Litvaitis 1996;Crooks 2002;Larivière 2003;Ewers and Didham 2007;Vergara and Hahn 2009). First, predators usually exhibit enhanced activity along habitat edges compared to core habitats (Andrén and Angelstam 1988;Paton 1994;Söderström et al 1998;Batáry and Báldi 2004;Š álek et al 2010), resulting in an adverse effect on the viability of populations due to general increase of habitat edges in fragmented landscapes (Saunders et al 1991;Murcia 1995;Vergara and Hahn 2009). Second, fragmented landscapes often maintain higher densities of generalist predators, including corvids and/or mammalian mesopredators (Andrén 1992(Andrén , 1995Crooks and Soulé 1999;Crooks 2002), suggesting that predation risk might be affected by the size of habitat patches and/or the overall degree of habitat fragmentation.…”

The Interplay Between Landscape Structure and Biotic Interactions

“…On the other hand, pollination rates on understory plants did not differ by patch and matrix arrangement [64]. Simulation models showed that proximity to the matrix edge can influence Allee effects and rates of predation by matrix-sourced nest predators, but if bird nest habitat patches are large enough, these effects can be ameliorated [146]. Field experiments show that visitation by pollinators is significantly higher in clover patches surrounded by bare ground than in those surrounded by grass [93].…”

Experimental food supplementation increases reproductive effort in an antbird in subtropical Brazilian Atlantic Forest fragments

“…The decreased nest predation rate in the largest fragment may be the result of several interactions (Sinclair et al 2005, Cain et al 2006, Vergara and Hahn 2009. Greater food abundance may have allowed less activity at nests (Skutch 1949(Skutch , 1985 and greater nest attentiveness (Chalfoun and Martin 2007).…”