Estimating Abundances of Interacting Species Using Morphological Traits, Foraging Guilds, and Habitat

We developed a statistical model to estimate the abundances of potentially interacting species encountered while conducting point-count surveys at a set of ecologically relevant locations – as in a metacommunity of species. In the model we assume that abundances of species with similar traits (e.g., body size) are potentially correlated and that these correlations, when present, may exist among all species or only among functionally related species (such as members of the same foraging guild). We also assume that species-specific abundances vary among locations owing to systematic and stochastic sources of heterogeneity. For example, if abundances differ among locations due to differences in habitat, then measures of habitat may be included in the model as covariates. Naturally, the quantitative effects of these covariates are assumed to differ among species. Our model also accounts for the effects of detectability on the observed counts of each species. This aspect of the model is especially important for rare or uncommon species that may be difficult to detect in community-level surveys. Estimating the detectability of each species requires sampling locations to be surveyed repeatedly using different observers or different visits of a single observer. As an illustration, we fitted models to species-specific counts of birds obtained while sampling an avian community during the breeding season. In the analysis we examined whether species abundances appeared to be correlated due to similarities in morphological measures (body mass, beak length, tarsus length, wing length, tail length) and whether these correlations existed among all species or only among species of the same foraging guild. We also used the model to estimate the effects of forested area on species abundances and the effects of sound power output (as measured by body size) on species detection probabilities.本研究构建了一款统计模型，用于估算在一系列生态相关点位开展点计数调查（point-count surveys）时所遇到的潜在互作物种的丰度——正如物种集合群落（metacommunity）场景中所呈现的那样。模型假设，具有相似功能性状（如体型）的物种的丰度间存在潜在相关性；此类相关性若存在，既可能存在于所有物种之间，也可能仅存在于功能相关的类群之间（比如同一觅食功能群（foraging guild）的物种）。同时，模型假设物种特异性丰度会因系统性与随机性异质性来源，在不同点位间存在差异。例如，若不同点位的丰度差异源于生境差异，则可将生境量化指标作为协变量纳入模型。自然地，这些协变量的量化效应被假设为因物种而异。本模型同时考虑了可检测性（detectability）对各物种观测计数的影响，该模块针对群落水平调查中难以被观测到的稀有或少见物种尤为关键。估算各物种的可检测性，需要通过不同观测者开展重复采样，或是由同一观测者开展多次点位回访。作为示例，我们将模型拟合至繁殖季鸟类群落采样所得的物种特异性鸟类计数数据。分析环节中，我们检验了物种丰度是否因形态性状（体重、喙长、跗跖长、翼长、尾长）的相似性而呈现相关性，并进一步验证此类相关性是存在于所有物种之间，还是仅局限于同一觅食功能群的物种。此外，我们还利用该模型估算了森林面积对物种丰度的影响，以及以体型为衡量指标的鸣声功率输出对物种可检测概率的影响。