How does forest species specialization affect the application of the island biogeography theory in fragmented landscapes?

Abstract

Aim Overall species richness in habitat remnants is seldom explained by the island biogeography theory (IBT). In this study, we tested the effectiveness of the IBT in explaining species richness of forest birds with or without considering the effect of the different forest specialization of species (generalist, edge and interior; community analysis). We also identified single species and groups of species that could serve as indicators of different fragmentation degrees (indicator species analysis). Location Broadleaved forests in western Lombardy (northern Italy). Methods We evaluated bird species richness in 344 forest fragments. Fragment area (FA), distance from the nearest source area (> 1000 ha) (DSA) and number of neighbouring fragments (NF) were calculated for each fragment. Using Poisson generalized linear models, we compared a model that evaluated the relationships between fragment covariates and species richness to a model that also considered the effect of forest species specialization on each relationship. Moreover, we investigated the association between each species and particular fragmentation conditions by calculating the IndVal index. Results The application of the IBT to species richness performed significantly better if we took into account forest species specialization when evaluating the effect of fragment covariates. In particular, the positive effects of FA and NF and the negative effect of DSA were significantly stronger on interior species rather than on generalist and edge species. Using the IndVal index we identified six species in three groups strongly associated with specific fragmentation degrees. Main conclusions The results showed the strong influence of the specialization of species on their distribution in fragmented landscapes. Interior species were the best candidates as a proxy of fragmentation effects. However, the indicator species analyses revealed that not all interior species showed the same sensitivity to fragment covariates.

Winners and losers: How the elevational range of breeding birds on Alps has varied over the past four decades due to climate and habitat changes

“…The two projects provided a large amount of data collected over wide areas, but since they did not rely on multiple surveys in the same season, it was impossible to account for species detection probability. However, the large dataset used for this research should overcome the potential limit of imperfect detection, reducing the noise produced by stochasticity in species discovery (Dondina et al, ). In addition, Fuller and Langslow () highlight that 10‐min point counts are satisfactory in detecting more than 70% of birds present at the census site and recommend how “counts exceeding 10 min are wasteful of field effort which could be used to improve other aspects of sampling”, such as the number of sampling units (see also Matsuoka et al, ).…”

“…Finally, since species‐specific ecological traits are known to affect species responses to environmental changes (Copeland, Bradford, Duniway, & Butterfield, ; Dondina, Orioli, D'Occhio, Luppi, & Bani, ; Dondina, Orioli, Massimino, Pinoli, & Bani, ; Luppi, Dondina, Orioli, & Bani, ; Williams et al, ), we considered the species’ breeding habitat and migration habit as ecological traits potentially affecting the elevational responses of birds.…”

Temporal Variation of Ecological Factors Affecting Bird Species Richness in Urban and Peri-Urban Forests in a Changing Environment: A Case Study from Milan (Northern Italy)

“…Indeed, source areas usually produce a surplus of individuals that can disperse to less favourable areas. As demonstrated by island biogeography theory [47], if there is no immigration of individuals from source areas, animal populations that occupy isolated habitat patches may be subject to extinction [28]. Similarly, populations of forest birds within UPUFs may be negatively affected by the absence of source areas that provide new sources of genetic variation.…”

“…In the case of the urban region of Milan, they appear to be a valuable element to support adjacent forest patches colonization. In this context, spatially aggregated UPUFs may work synergistically, generating the so-called "archipelago effect", to host richer bird assemblages compared to more isolated patches [28]. However, given the complexity of the urban environment in terms of heterogeneity of the land-cover mosaic and disturbance pressures [54], further studies testing the actual capacity of specific forest patches to act as functional corridors (i.e., with data on bird movements) are needed.…”

“…From the original sets of urban and peri-urban forest patches, for each period we select only the patches where point counts were performed. Moreover, we exclude all patches larger than 1000 ha and all those composed of broadleaved or mixed forests, because they could be considered as source areas for the target forest-dependent bird species in our study area [28]. In those large patches, the percentage of observed forest-dependent species ranged from 71% to 97% of the whole pool of forest-dependent species in the time- [29], and starting from the 2000 and 2012 cartographies, we calculated the following landscape variables for each patch: patch area (PA), minimum distance from the nearest source area (DSA; i.e., a forest patch larger than 1000 ha), surface occupied by forests (SF) in a buffer of 1000 m (see [19,28] for studies which adopted a similar buffer size), number of neighboring forest (NF) patches in a buffer of 1000 m, surface occupied by urban areas (excluding urban green areas) in a buffer of 1000 m (SU) and number of neighboring urban (NU) patches in a buffer of 1000 m. For each UPUF, we also consider the type of urban or peri-urban forest (TYPE; e.g., green urban area, broadleaved forest, tree plantation), if it was included in a protected area or not (PrA/notPrA) and if it was classified as an urban or as a peri-urban forest (URB/PERI-URB).…”