# Demography and Population Dynamics of a Small Mammal Assemblage in Chilean Semiarid Thorn‐Scrub Habitat: A 30‐Year Study

## TL;DR

A 30-year study in Chile's semiarid region reveals how rainfall affects the survival and population growth of small mammals.

## Contribution

The study provides the first comprehensive demographic analysis of a small mammal community in semiarid Chile using a 30-year dataset.

## Key findings

- Population sizes and survival rates of small mammals strongly correlate with seasonal and annual rainfall patterns.
- Core species show similar responses to environmental changes, while opportunistic species respond differently.
- Recruitment has a stronger influence on population dynamics than survival rates across all species.

## Abstract

Characterizing population dynamics in heterogeneous environments requires comprehensive long‐term data. We monitored seven small mammals in replicated sites in a semiarid Chilean thorn‐scrub habitat over 30 years using monthly capture–mark–recapture (CMR) sampling. We applied a superpopulation CMR modeling framework to examine the following: (i) How do population sizes and demographic parameters vary seasonally and over time? and (ii) Are there commonalities in the variation of those parameters either seasonally or annually? Capture probabilities among four “core” species (
Octodon degus
,
Phyllotis darwini
, Abrothrix olivacea, and
Thylamys elegans
) varied strongly over time, as did apparent survival among years and rainfall seasons, with individuals generally experiencing higher survival during the wet season. Recruitment measures also showed strong annual and seasonal variation, with higher numbers in wet seasons and years. Capture probability in three “opportunistic” species (
Abrocoma bennettii
,
Abrothrix longipilis
, and
Oligoryzomys longicaudatus
) varied over time, as did survival and recruitment across rainfall or reproductive seasons. As predicted, annual and seasonal variation in rainfall strongly influenced the survival and recruitment of most species, and their populations increased rapidly following rainfall events. Unsurprisingly, core species shared similar overall responses to environmental drivers; opportunistic species responded differently to seasonal or annual variation in rainfall, perhaps reflecting their origins in non‐thorn‐scrub habitat. Finally, for all species, population size correlated more strongly with the number of recruits than with survival, suggesting that the former has a greater influence on the dynamics of our study populations. This study provides the first insight into the demography of the entire small mammal community at our study site, and in particular, the demography of
A. bennettii
,
A. longipilis
, and
O. longicaudatus
from semiarid habitat. Our results, based on the longest time series in South America, provide comprehensive demographic information on a diverse small mammal community, and offer novel insight into community‐level response to changing climate.

Using the longest and most comprehensive demographic database available in temperate South America, we characterize the population dynamics of an entire community of small mammals in a semiarid environment in north‐central Chile using a superpopulation CMR modeling framework. Abiotic drivers—annual and seasonal rainfall—are the strongest influences on survival and recruitment, and core species (those present in effectively all monthly surveys over 30 years) share similar responses to environmental drivers. In contrast, opportunistic species, which appear to favor more mesic habitats that occur near our core study area and therefore disappear for months to years during dry periods, responded individualistically to seasonal or annual variation in rainfall. For all species, population size correlated more strongly with the number of recruits than with survival, suggesting that the former has a greater influence on the dynamics of our study populations.