An Empirical and Mechanistic Explanation of Abundance-Occupancy Relationships for a Critically Endangered Nomadic Migrant

Interspecific abundance-occupancy relations along estuarine gradients

Do interspecific abundance-occupancy (A-O) relationships vary systematically along environmental gradients? A-O relationships of macrobenthic assemblages of seagrass and adjacent bare-sediment were compared at series of sites along two types of estuarine gradient; the longitudinal one of the main axial channel, and a transverse one from that channel into progressively smaller channels and creeks enclosed within fringing saltmarsh. Three general features emerged: A-O regression slopes were remarkably uniform across all the disparate assemblages and sites (1.04 ± 0.08); values of R2 were very high (≈0.96); and where small but significant differences between sites occurred, they were associated with the stronger gradients (i.e. those with the larger differentials in abundance and smaller compositional similarities). In two such cases, slope values were correlated with position along the gradient (although only at the margin of statistical significance). Variation in A-O relationships along estuarine gradients does clearly occur, but their constancy leaves the stronger impression.

Effects of occupancy estimation on abundance-occupancy relationships

Abundance-occupancy relationships predict that species that occupy more sites are also more locally abundant, where occupancy is usually estimated following the assumption that species can occupy all sampled sites. Here we use the National Ecological Observatory Network small-mammal data to assess whether this assumption affects abundance-occupancy relationships. We estimated occupancy considering all sampled sites (traditional occupancy) and only the sites found within the species geographic range (spatial occupancy) and realized environmental niche (environmental occupancy). We found that when occupancy was estimated considering only sites possible for the species to colonize (spatial and environmental occupancy) weaker abundance-occupancy relationships were observed. This shows that the assumption that the species can occupy all sampled sites directly affects the assessment of abundance-occupancy relationships. Estimating occupancy considering only sites that are possible for the species to colonize will consequently lead to a more robust assessment of abundance-occupancy relationships.

Contributions of Distribution Modelling to the Ecological Study of Psittaciformes

We provide an overview of the use of species distribution modeling to address research questions related to parrot ecology and conservation at a global scale. We conducted a literature search and applied filters to select the 82 most relevant studies to discuss. The study of parrot species distribution has increased steadily in the past 30 years, with methods and computing development maturing and facilitating their application for a wide range of research and applied questions. Conservation topics was the most popular topic (37%), followed by ecology (34%) and invasion ecology (20%). The role of abiotic factors explaining parrot distribution is the most frequent ecological application. The high prevalence of studies supporting on-ground conservation problems is a remarkable example of reduction in the research–action gap. Prediction of invasion risk and assessment of invasion effect were more prevalent than examples evaluating the environmental or economic impact of these invasions. The integration of species distribution models with other tools in the decision-making process and other data (e.g., landscape metrics, genetic, behavior) could even further expand the range of applications and provide a more nuanced understanding of how parrot species are responding to their even more changing landscape and threats.