Abstract
Understanding the spatial and temporal dynamics of species assemblages is a main challenge in ecology. The mechanisms that shape species assemblages and their temporal fluctuations along tropical elevational gradients are particularly poorly understood. Here, we examined the spatio-temporal dynamics of bird assemblages along an elevational gradient in Ecuador. We conducted bird point counts at three elevations (1000, 2000 and 3000 m) on 18 1-ha plots and repeated the sampling eight times over two years (216 hours in total). For each plot, we obtained data of monthly temperatures and precipitation and recorded the overall resource availability (i.e., the sum of flower, fruit, and invertebrate resources). As expected, bird richness decreased from low to high elevations. Moreover, we found a significant decrease in bird abundance and richness and an increase in evenness between the most and least humid season at each of the three elevations. Climatic factors were more closely related to these temporal fluctuations than local resource availability. While temperature had significant positive effects on the abundance of birds at mid and high elevations, precipitation negatively affected bird abundance at low and mid elevations. Our study highlights that bird assemblages along tropical elevational gradients can show pronounced seasonal fluctuations. In particular, low temperatures and high precipitation seem to impose important constraints on birds. We conclude that potential changes in climate, due to global warming, are likely to affect the spatio-temporal dynamics of bird assemblages along tropical elevational gradients.
Highlights
Understanding the spatial and temporal patterns in species’ abundance and richness along environmental gradients is a fundamental challenge in ecology [1]
We found that the median distance of birds to the observer did not differ significantly among elevations (Generalized linear mixed effects model, low elevation compared to mid elevation: β = -0.18, z = -1.45, p = 0.15; low elevation compared to high elevation: β = -0.15, z = -1.25, p = 0.21) and between season (β = -0.16, z = -1.56, p = 0.12), indicating that the detectability of birds was similar across elevations and seasons
Our findings suggest that the temporal fluctuations in tropical bird assemblages in our study region likely occur due to temporary constraints related to climatic conditions rather than due to resource limitations
Summary
Understanding the spatial and temporal patterns in species’ abundance and richness along environmental gradients is a fundamental challenge in ecology [1]. Many studies have shown that climate [2,3] and productivity [4,5] determine the structure of species assemblages across. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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