Two‐species occupancy models: a new parameterization applied to co‐occurrence of secretive rails

Abstract

Two-species occupancy models that account for false absences provide a robust method for testing for evidence of competitive exclusion, but previous model parameterizations were inadequate for incorporating covariates. We present a new parameterization that is stable when covariates are included: the conditional two-species occupancy model, which can be used to examine alternative hypotheses for species' distribution patterns. This new model estimates the probability of occupancy for a subordinate species conditional upon the presence of a dominant species. It can also be used to test if the detection of either species differs when one or both species are present, and if detection of the subordinate species depends on the detection of the dominant species when both are present. We apply the model to test if the presence of the larger Virginia Rail (Rallus limicola) affects probabilities of detection or occupancy of the smaller California Black Rail (Laterallus jamaicensis coturniculus) in small freshwater marshes that range in size from 0.013 to 13.99 ha. We hypothesized that Black Rail occupancy should be lower in small marshes when Virginia Rails are present than when they are absent, because resources are presumably more limited and interference competition should increase. We found that Black Rail detection probability was unaffected by the detection of Virginia Rails, while, surprisingly, Black and Virginia Rail occupancy were positively associated even in small marshes. The average probability of Black Rail occupancy was higher when Virginia Rails were present (0.74 +/- 0.053, mean +/- SE) than when they were absent (0.36 +/- 0.069), and for both species occupancy increased with marsh size. Our results contrast with recent findings from patchy forest systems, where small birds were presumed to be excluded from small habitat patches by larger competitors.

Evidence that climate sets the lower elevation range limit in a high‐elevation endemic salamander

“…We fit conditional two‐species occupancy models (Richmond et al., 2010), which estimates the probability of occupancy for a subordinate species conditional upon the presence of a dominant species, which allow for differences in occupancy and detection probabilities of P. shenandoah conditional on the presence and/or detection of P. cinereus . We tested models which represented whether the occupancy of P. shenandoah was conditional [ψ SC different than ψ Sc ] or unconditional [ψ S ; i.e., setting ψ SC  = ψ Sc ] on the presence of P. cinereus [ψ C ] and whether occupancy of either species was influenced by site covariates.…”

“…There are two related processes that influence the observation of a range edge: an ecological process where a population responds to a biotic or abiotic gradient, and a statistical process where variation in abundance of individuals across space is only partially observed (e.g., Grant, 2014). Ignoring the issue of partial observability may induce bias in the detection of range limits and species interactions, as the presence of one species may influence both the detection and the occurrence of another (Richmond, Hines, & Beissinger, 2010). …”

How does climate change cause extinction?

“…prey, hosts). Twospecies occupancy models [99] could be applied to test for the impacts of these and other types of interspecific interactions. Identifying the particular interactions that are responsible for climate-related extinctions may be challenging, given the diversity of interactions and species that may be involved.…”

Detecting diversity: emerging methods to estimate species diversity

“…The rarity of a species also influences detectability and the probability of detecting a species is positively related to its abundance [15][16][17]. Less appreciated is that the local abundance of another species (e.g., a competitor or predator) can influence the behavior of the focal species, resulting in either positive or negative changes in detectability [18][19][20]. Substantial heterogeneity in detection among individuals can also occur within species.…”