Patch occupancy and abundance of local populations in landscapes differing in degree of habitat fragmentation: a case study of the colonial black‐headed gull, Chroicocephalus ridibundus

Abstract

Aim This study investigated whether habitat fragmentation at the landscape level influences patch occupancy and abundance of the black-headed gull, Chroicocephalus ridibundus, and whether the response of the species to environmental factors is consistent across replicated landscape plots.Location Water bodies (habitat patches) in southern Poland.Methods Surveys were conducted in two landscape types (four plots in each):(1) more-fragmented landscape, in which habitat patches were small (mean size 2.2-6.2 ha) and far apart (mean distance 2.5-3.1 km); and (2) less-fragmented landscape, in which habitat patches were large (mean size 9.2-16.5 ha) and separated by short distances (mean 0.9-1.4 km). Observations were performed twice in 284 potential habitat patches during the 2007 breeding season.Results Colonies were significantly more frequent and larger in the lessfragmented landscapes than in the more-fragmented ones. Probability of patch occupancy and number of breeding birds were positively related with patch size and these relationships were especially strong in the more-fragmented landscapes. In the less-fragmented landscapes, the occurrence of black-headed gulls was negatively related to the distance to the nearest local population, but in the morefragmented landscapes such a relationship was not detected. As distance to the nearest habitat patch increased, the probability of the patch occupancy decreased in the more-fragmented landscapes. Moreover, abundance was negatively influenced by distance to the nearest habitat patch, especially strongly in morefragmented landscapes. Proximity of corridors (rivers) positively influenced the occupation of patches regardless of landscape type. The number of islets positively influenced occupancy and abundance of local populations, and this relationship was stronger in the more-fragmented landscapes.Main conclusions Our results are in agreement with predictions from metapopulation theory and are the first evidence that populations of blackheaded gulls may have a metapopulation structure. However, patch occupancy and abundance were differentially affected by explanatory variables in the morefragmented landscapes than in the less-fragmented ones. This implies that it is impossible to derive, a priori, predictions about presence/abundance patterns based on only a single landscape.

Are invasive species drivers of native species decline or passengers of habitat modification? A case study of the impact of the common myna (Acridotheres tristis) on Australian bird species

“…The results of our study suggest that the effects of habitat modification and invasive species 344 are interrelated. Many species are strongly influenced by habitat, with greater abundance in high 345 quality habitat than in low quality habitat (Kajzer et al 2011). However, high quality habitat for one 346 species may not constitute high quality habitat for another species (Didham et al 2005b;347 Farnsworth 2004;MacDougall and Turkington 2005).…”

An invasive gull displaces native waterbirds to breeding habitats more exposed to native predators

“…During the breeding season, which lasts from the end of March to the beginning of June at inland reservoirs, the colonies are located predominantly on either islets or shores (Skórka et al 2005;Lenda et al 2010). The availability of islets is a factor that limits the local population sizes of many waterbirds (Amat 1985;Skórka et al 2006;Kajzer et al 2012). When the islets are overtaken by invasive species, this may lead to population declines in the native species.…”

Habitat Quality and Geometry Affect Patch Occupancy of Two Orthopteran Species

“…mammals: [30], insects: [45], spiders: [46], birds: [47]), even though the relationship between species occurrence and patch size may not always be strong [8]. In our study, the occurrence of the field cricket was positively related to patch size.…”