# The influence of geographic ranges, climatic niches and temperature fluctuations on population variability

## TL;DR

This study finds that population variability in North American birds increases near their climatic niche limits and in areas with more temperature fluctuations, but not at the edges of their geographic ranges.

## Contribution

The study reveals that climatic niche limits and temperature variability, rather than geographic range edges, are linked to increased bird population variability.

## Key findings

- Population variability increases near niche limits and in areas with more variable temperatures.
- Population variability does not increase at geographic range edges.
- Phylogenetic history and species traits could not explain the observed patterns.

## Abstract

The existence of patterns in population dynamics across species geographic ranges and climatic niches is a pervasive idea in ecology. Population variability (i.e. temporal variability in population density) should hypothetically increase near range edges or niche limits because of less suitable environments in these areas, but the occurrence of such patterns remains largely unexplored. Further, fluctuations in temperature could pose demographic constraints on populations and also influence their variability. We used Breeding Bird Survey data to show that the population variability of 97 resident North American birds consistently increases towards their niche limits and in areas with more variable temperatures, but not towards their geographic range edges. However, our model has limited explanatory power, and phylogenetic history and species traits could not explain these results. These findings suggest that other factors, such as biotic interactions and resource availability, might be more important drivers of population variability in resident North American birds.