Abundance of Anolis bicaorum, and niche measurements of plots on the island Utila, Honduras

The question of what controls animal abundance has always been fundamental
to ecology, but given rapid environmental change, understanding the
drivers and mechanisms governing abundance is more important than ever.
Here, we determine how multidimensional environments and niches interact
to determine population abundance along a tropical habitat gradient.
Focusing on the endemic lizard Anolis bicaorum on the island of Utila
(Honduras), we evaluate direct and indirect effects of three interacting
niche axes on abundance: thermal habitat quality, structural habitat
quality, and prey availability. We measured A. bicaorum abundance across a
series of thirteen plots and used N-mixture models and path analysis to
disentangle direct and indirect effects of these factors. Results showed
that thermal habitat quality and prey biomass both had positive direct
effects on anole abundance. However, thermal habitat quality also
influenced prey biomass, leading to a strong indirect effect on abundance.
Thermal habitat quality was primarily a function of canopy density,
measured as leaf area index (LAI). Despite having little direct effect on
abundance, LAI  had a strong overall effect mediated by thermal
quality and prey biomass. Our results demonstrate the role of
multidimensional environments and niche interactions in determining animal
abundance and highlight the need to consider interactions between thermal
niches and trophic interactions to understand variation in abundance,
rather than focusing solely on changes in the physical environment.