On the relative importance of space and environment in farmland bird community assembly

Abstract

The relative contribution of ecological processes in shaping metacommunity dynamics in heavily managed landscapes is still unclear. Here we used two complementary approaches to disentangle the role of environment and spatial effect in farmland bird community assembly in an intensive agro-ecosystem. We hypothesized that the interaction between habitat patches and dispersal should play a major role in such unstable and unpredictable environments. First, we used a metacommunity patterns analysis to characterize species co-occurrences and identify the main drivers of community assembly; secondly, variation partitioning was used to disentangle environmental and geographical factors (such as dispersal limitation) on community structure and composition. We used high spatial resolution data on bird community structure and composition distributed among 260 plots in an agricultural landscape. Species were partitioned into functional classes, and point count stations were classified according to landscape characteristics before applying metacommunity and partitioning analyses within each. Overall we could explain around 20% of the variance in species composition in our system, revealing that stochasticity remains very important at this scale. However, this proportion varies depending on the scale of analysis, and reveals potentially important contributions of environmental filtering and dispersal. These conclusions are further reinforced when the analysis was deconstructed by bird functional classes or by landscape habitat classes, underlining trait-related filters, thus reinforcing the idea that wooded areas in these agroecosystems may represent important sources for a specific group of bird species. Our analysis shows that deconstructing the species assemblages into separate functional groups and types of landscapes, along with a combination of analysis strategies, can help in understanding the mechanisms driving community assembly.

Taxonomic and functional components of avian metacommunity structure along an urban gradient

“…Other avian metacommunity studies have also detailed the importance of environmental variables (species-sorting framework) on community structure [65][66][67][68]. As with other studies, unexplained variation was a major characteristic of metacommunity structure in human-modified landscapes, but environmental filtering and dispersal are often significant contributors [69].…”

Phylogenetic diversity and community assembly in a naturally fragmented system

“…This may be the case for the kipukas, given their very young age (~15 kya) and the harsh habitat that mimics true island dynamics. Support for neutral processes of community assembly have been found in a variety of isolated and/or fragmented organismal systems including aquatic bacteria communities in tree holes in the same area (Woodcock et al, 2007 ), farmland birds that exist in a fragmented agricultural landscape (Henckel et al, 2019 ), and cichlids in Lake Tanganyika (Janzen et al, 2017 ).…”

“…Under a neutral model of assembly, all species present in a regional community pool have an equal probability of colonizing and persisting in that local community (Hubbell, 2001;Rosindell et al, 2012). This neutrality implies that species differences (e.g., in traits) do not impact their presence or absence in the local com- (Woodcock et al, 2007), farmland birds that exist in a fragmented agricultural landscape (Henckel et al, 2019), and cichlids in Lake Tanganyika (Janzen et al, 2017).…”

Matrix quality determines the strength of habitat loss filtering on bird communities at the landscape scale

“…The division of habitats into smaller and more isolated fragments, separated by a nonhabitat matrix of human‐transformed land cover, alters not only the quantity but also the quality of the habitats in the landscape (Fischer & Lindenmayer, 2007; Haddad et al, 2015). Much has been studied on how habitat loss and fragmentation impact biodiversity in terms of the community and species deterministic responses (environmental filtering) and random demographic events leading to stochastic changes in community composition (ecological drift) (Baselga et al, 2015; Henckel et al, 2019). Nevertheless, the role of the landscape matrix in altering these deterministic and random assembly processes and thus the outcome of habitat loss on community composition is still unclear (Kupfer et al, 2006; Pardini et al, 2017).…”