▪ Abstract In large-herbivore populations, environmental variation and density dependence co-occur and have similar effects on various fitness components. Our review aims to quantify the temporal variability of fitness components and examine how that variability affects changes in population growth rates. Regardless of the source of variation, adult female survival shows little year-to-year variation [coefficient of variation (CV 30%). Old females show senescence in both survival and reproduction. These patterns of variation are independent of differences in body mass, taxonomic group, and ecological conditions. Differences in levels of maternal care may fine-tune the temporal variation of early survival. The immature stage, despite a low relative impact on population growth rate compared with the adult stage, ma...

https://www.jstor.org/stable/pdfplus/221737.pdf

Temporal Variation in Fitness Components and Population Dynamics of Large Herbivores

Recent long-term studies of population ecology of large herbivorous mammals suggest that survival of prime-aged females varies little from year to year and across populations. Juvenile survival, on the other hand, varies considerably from year to year. The pattern of high and stable adult survival and variable juvenile survival is observed in contrasting environments, independently of the main proximal sources of mortality and regardless of whether mortality is stochastic or density-dependent. High yearly variability in juvenile survival may play a predominant role in population dynamics.

/pdf/population-dynamics-of-large-herbivores-variable-recruitment-2q069u3srv.pdf

Population dynamics of large herbivores: variable recruitment with constant adult survival.

Recently, the results from several long-term individual-based population studies of ungulates have been published. One major conclusion is that the population dynamics of ungulates in predator-free environments is strongly influenced by a combination of stochastic variation in the environment, and population density. Both density dependence and environmental stochasticity operate through changes in life history traits, correlated with variation in body weight. This generates delays in the response of the population to changes in environment. In the absence of predation, a stable equilibrium is therefore unlikely to exist between an ungulate population and its food resources. This thorough understanding of the mechanisms generating population fluctuations suggests that studies of ungulates will provide an important source for examining effects of long-term changes in the environment, for instance, resulting from a climatic change.

Environmental stochasticity and population dynamics of large herbivores: a search for mechanisms

Despite decades of research, the roles of climate and humans in driving the dramatic extinctions of large-bodied mammals during the Late Quaternary period remain contentious. Here we use ancient DNA, species distribution models and the human fossil record to elucidate how climate and humans shaped the demographic history of woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox. We show that climate has been a major driver of population change over the past 50,000 years. However, each species responds differently to the effects of climatic shifts, habitat redistribution and human encroachment. Although climate change alone can explain the extinction of some species, such as Eurasian musk ox and woolly rhinoceros, a combination of climatic and anthropogenic effects appears to be responsible for the extinction of others, including Eurasian steppe bison and wild horse. We find no genetic signature or any distinctive range dynamics distinguishing extinct from surviving species, emphasizing the challenges associated with predicting future responses of extant mammals to climate and human-mediated habitat change.

https://www.sjsu.edu/anthropology/docs/coursematerials/Bellifemine/naturemegafauna.pdf

Species-specific responses of Late Quaternary megafauna to climate and humans

In an age- or stage-structured population, a given change on a proportional scale of different fitness components has different effects on the population growth rate. Because earlier studies have shown that variability is selectively disadvantageous for long-lived iteroparous species, fitness components whose variation has greatest impact on the population growth rate are expected to be canalized against temporal variability. We present here a test for such a canalization of fitness components most influential for population growth. If canalization occurs, (1) within a given population the variance of canalized fitness components should be less than that of noncanalized components, and (2) among populations an inverse relationship should occur between the potential demographic impact of fitness components and their temporal variability. We tested these hypotheses using data on age-dependent survival of ungulates. As expected for long-lived vertebrates, elasticities and sensitivities of adult survival were...

https://www.jstor.org/stable/pdfplus/3450073.pdf

Temporal variation in survival of mammals: a case of environmental canalization?

Pour une forte densite la survie des jeunes diminue mais non celle des adultes se trouvant dans la classe d'âge reproductrice et la plus abondante, la fecondite des subadultes, descend au-dessous du seuil de taille corporelle pour la maturite, la fecondite des adultes n'est pas affectee. La limitation des ressources dependant de la densite est plus apparente pour les fortes densites de population

T. Skogland

Papers

The effects of density-dependent resource limitations on the demography of wild reindeer