Stochastic seasonality and nonlinear density-dependent factors regulate population size in an African rodent

Abstract

Ecology has long been troubled by the controversy over how populations are regulated. Some ecologists focus on the role of environmental effects, whereas others argue that density-dependent feedback mechanisms are central. The relative importance of both processes is still hotly debated, but clear examples of both processes acting in the same population are rare. Key-factor analysis (regression of population changes on possible causal factors) and time-series analysis are often used to investigate the presence of density dependence, but such approaches may be biased and provide no information on actual demographic rates. Here we report on both density-dependent and density-independent effects in a murid rodent pest species, the multimammate rat Mastomys natalensis (Smith, 1834), using statistical capture-recapture models. Both effects occur simultaneously, but we also demonstrate that they do not affect all demographic rates in the same way. We have incorporated the obtained estimates of demographic rates in a population dynamics model and show that the observed dynamics are affected by stabilizing nonlinear density-dependent components coupled with strong deterministic and stochastic seasonal components.

Protected areas as biodiversity benchmarks for human impact: agriculture and the Serengeti avifauna

“…Furthermore, the lack of raptors in agriculture, particularly the rodent specialists (e.g. black-shouldered kite (Elanus caeruleus), long-crested hawk eagle (Spizaetus ayresii )) that are abundant in savannah, may be the cause of frequent outbreaks of rodents such as Mastomys natalensis reported for agriculture (Leirs et al 1997). These ecosystem functions are now the focus of future work.…”

Declines in large wildlife increase landscape-level prevalence of rodent-borne disease in Africa

“…By contrast to larger-bodied mammals, rodents, particularly smallsized species (i.e., <500 g), are often relatively robust to human disturbance and many species live commensally with humans (33,34). Due to their generally rapid reproductive rates and small home range sizes, populations can fluctuate dramatically over both small spatial and temporal scales, and in response to declines or removals of either rodent predators or rodent competitors, including large herbivores (35)(36)(37). Because both large predators and herbivores face a high risk of decline from human disturbances (6,10), susceptible host regulation may be a strong potential pathway by which wildlife loss can affect human disease risk.…”

Population dynamics of small mammals in semi-arid regions: a comparative study of demographic variability in two rodent species

“…The seasonal reproductive rate per adult female (R a ) of leaf-eared mice was calculated from unpublished data), pregnancy rates were determined from 853 adult females, and litter size was estimated to be approximately three (Meserve & Le Boulengé 1987). The monthly reproductive rate per adult female (R a ) of multimammate mice was calculated from Leirs et al (1993Leirs et al ( , 1997, pregnancy rates and litter size were determined from 5196 females captured in snap trapping studies.…”

“…Monthly demographic rates used to parameterize the periodic matrix models. (R a = [(per cent of reproductive females)´(0.5´litter size)´1.33´1.50] (according to Leirs et al 1997) represents the monthly reproductive rate per adult female (sex ratio at birth being assumed to be 0.5) and S a represents the monthly adult survival rate. Survival from newly born to sub-adult, S a , is assumed to be fully dependent on the mother's survival.…”