Spatial scale matters when modeling avian co‐occurrence

Abstract

The spatial scale at which competition alters the spatial distribution of a species is important to consider when evaluating competitive interactions between species. The two‐species occupancy model was developed to evaluate competitive interactions between two species while accounting for imperfect detection. However, no studies have incorporated spatial scale into such models. We developed an approach to incorporate spatial scale when evaluating species co‐occurrence using the two‐species occupancy model and tested our approach on two wetland passerines: the Yellow‐headed Blackbird (Xanthocephalus xanthocephalus) and the Marsh Wren (Cistothorus palustris). We surveyed for Yellow‐headed Blackbirds and Marsh Wrens using point counts at wetlands throughout Iowa in 2009 and 2010. We assigned observations to one of three distance bins: ≤20, ≤60, and ≤100 m and then created encounter histories for each distance bin for the two‐species occupancy model and modeled co‐occurrence as a function of habitat covariates for each distance bin. We also modeled co‐occurrence using all observations regardless of distance. We found that Yellow‐headed Blackbirds were less likely to co‐occur with Marsh Wrens at both the ≤60 and ≤100 m scales. However, using all observations, we found that Yellow‐headed Blackbirds and Marsh Wrens co‐occurred independent of one another. This result illustrated that failure to incorporate spatial scale in evaluations of species co‐occurrence could lead to incorrect inferences on co‐occurrence of different species. The two‐species co‐occurrence occupancy model is a valuable tool that allows researchers to evaluate the presence of competitive interactions between species, and incorporating spatial scale into these models provides information on how species partition resources at different spatial scales within a patch. Understanding species co‐occurrence patterns across multiple spatial scales provides valuable information that is useful for a better understanding of the mechanisms of competitive interactions between two species and aiding the restoration and management of habitat for multiple species.

Predator density influences nest attendance of Yellow‐headed BlackbirdsXanthocephalus xanthocephalus

“…Our study is the first, however, to document changes in nest attendance behaviour in a species targeted by this aggressive nest predator. This finding, coupled with the already existing knowledge that these two species segregate breeding territories in co‐occupied marshes (Leonard & Picman , Harms & Dinsmore ), demonstrates behavioural plasticity of blackbirds as a function of the potential threat of Marsh Wrens to their nests. Behavioural plasticity in response to the threat of nest predation has been demonstrated by other species of songbirds with different types of predators (e.g.…”

Tree species co‐occurrence patterns change across grains: insights from a subtropical forest

“…, Reitalu et al. , Laporta and Sallum , Harms and Dinsmore ). Both outcomes are equally insightful and may increase our understanding of spatial relationships among species.…”

“…Therefore, the grain size of sampling and analysis becomes crucial to the ecological interpretation of co-occurrence patterns. Ideally, studies of species co-occurrence should be based on sampling grains that capture the outcome of ecological processes on site occupancy (Harms and Dinsmore 2016). While this might sound straightforward, determining the right grain size is likely to be extremely difficult, especially because many ecological processes happen across multiple scales (Belmaker et al 2015).…”

Impacts of Shallow Lake Restoration on Vegetation and Breeding Birds in Iowa

“…However, unlike these studies, Yellow-headed Blackbirds were common breeders and tended to occur in the same sites as Marsh Wrens in our study area. Both species are aggressive territory defenders and Yellow-headed Blackbirds are known to exclude Marsh Wrens from their territories (Bump 1986, Harms andDinsmore 2015). In this case, it could be that Yellow-headed Blackbirds exclude Marsh Wrens from areas with deeper water.…”