Seasonal dynamics with compensatory effects regulate populations of tropical forest marsupials: a 16-year study

Abstract

The conditions that a population experiences during one season can affect the strength of density dependence in the following season. In the tropics, many populations face their biggest challenges in the dry season due to limited food and cold-dry conditions. Seasonal environmental changes can be especially problematic for small, short-lived, seasonally breeding endotherms. To investigate the effects of seasonality on population dynamics, we studied five marsupial species in the Brazilian Atlantic Forest, using a 16-year dataset. We tested if (1) compensatory density feedback is stronger in the dry season, due to the high population sizes and limited food; (2) lower temperatures and the overall abundance of small mammals negatively affect dry season population growth rates; and (3) rainfall, a proxy for food availability, is positively related to wet season population growth rates. Population growth rates were regressed against seasonal population sizes and exogenous variables, and analyzed with linear autoregressive models. Seasonal compensatory density feedback occurred in both seasons, with compensation processes in just one season being sufficient to allow population persistence. Rainfall and the overall abundance of small mammals had little influence on populations, while colder temperatures decreased population growth rate of smaller species in both seasons. Although the study marsupials share similar life histories and phylogeny, they varied with respect to the season when compensatory density feedback was strongest. Our results demonstrate that seasonality plays a key role in driving marsupial population dynamics, and highlight the need to account for seasonality in demographic studies even in tropical environments.

Impact of climate on the population dynamics of an alpine ungulate: a long-term study of the Tatra chamois Rupicapra rupicapra tatrica

“…Following Ferreira et al (2016), we modeled population growth rate in a given year ( λ t ) as a function of past population sizes in current ( t ) and previous ( t -1 … t - i ) years. The linear autoregressive model was:where α t … α t - i are the slopes of the relationship between λ t and population size in a given year ( t … t - i ) and represent the strength of density dependence, and ε t represents the process noise.…”

Simple signals indicate which period of the annual cycle drives declines in seasonal populations

“…The need to identify the period of the annual cycle that is driving population declines is particularly pertinent to migratory species whose seasonal habitats are often separated by vast geographic distances and whose populations have experienced ongoing global declines (Wilcove & Wikelski 2008;Young et al 2016;Ceballos et al 2017). Several recent examples have demonstrated the insights gained from integrating information across the annual cycle to understand how changes in the environment drive population dynamics, both in the wild (Norris & Marra 2006;Luis et al 2010;Ferreira et al 2016;Woodworth et al 2017;Sutton et al 2019) and in experimental populations (Betini et al 2013a(Betini et al , 2014(Betini et al , 2017. Knowledge of when and where populations are limited has important implications for the targeting of conservation efforts and funding (Sheehy et al 2011).…”

CLIMATE-DRIVEN VARIATION IN SPACE USE BY THE NEOTROPICAL MARSUPIAL Metachirus nudicaudatus

“…The lack of density dependence on M. nudicaudatus movements enlightens the mechanism of population regulation. Previous studies in the study area have shown that M. nudicaudatus is regulated by a direct negative feedback (Ferreira et al 2016a), especially in the dry season (Ferreira et al 2016b), and suggested intraspecific competition for food resources and/or space as the main regulatory mechanisms. Space is not a limiting factor for this population, reinforcing that most of the intraspecific competition takes place during the dry season.…”