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Mammals influence nearly all aspects of energy flow and habitat structure in modern terrestrial ecosystems. However, anthropogenic effects have probably altered mammalian community structure, raising the question of how past perturbations have done so. We used functional diversity (FD) to describe how the structure of North American mammal palaeocommunities changed over the past 66 Ma, an interval spanning the radiation following the K/Pg and several subsequent environmental disruptions including the Palaeocene–Eocene Thermal Maximum (PETM), the expansion of grassland, and the onset of Pleistocene glaciation. For 264 fossil communities, we examined three aspects of ecological function: functional evenness, functional richness and functional divergence. We found that shifts in FD were associated with major ecological and environmental transitions. All three measures of FD increased immediately following the extinction of the non-avian dinosaurs, suggesting that high degrees of ecological disturbance can lead to synchronous responses both locally and continentally. Otherwise, the components of FD were decoupled and responded differently to environmental changes over the last ~56 Myr.

 

The significant extinctions in Earth history have largely been unpredictable in terms of what species perish and what traits make species susceptible. The extinctions occurring during the late Pleistocene are unusual in this regard, because they were strongly size-selective and targeted exclusively large-bodied animals (i.e., megafauna, >1 ton) and disproportionately, large-bodied herbivores. Because these animals are also at particular risk today, the aftermath of the late Pleistocene extinctions can provide insights into how the loss or decline of contemporary large-bodied animals may influence ecosystems. Here, we review the ecological consequences of the late Pleistocene extinctions on major aspects of the environment, on communities and ecosystems, as well as on the diet, distribution and behavior of surviving mammals. We find the consequences of the loss of megafauna were pervasive and left legacies detectable in all parts of the Earth system. Furthermore, we find that the ecological roles that extinct and modern megafauna play in the Earth system are not replicated by smaller-bodied animals. Our review highlights the important perspectives that paleoecology can provide for modern conservation efforts. 

Cities and agricultural fields encroach on the most fertile, habitable terrestrial landscapes, fundamentally altering global ecosystems. Today, 75% of terrestrial ecosystems are considerably altered by human activities, and landscape transformation continues to accelerate. Human impacts are one of the major drivers of the current biodiversity crisis, and they have had unprecedented consequences on ecosystem function and rates of species extinctions for thousands of years. Here we use the fossil record to investigate whether changes in geographic range that could result from human impacts have altered the climatic niches of 46 species covering six mammal orders within the contiguous United States. Sixty-seven percent of the studied mammals have significantly different climatic niches today than they did before the onset of the Industrial Revolution. Niches changed the most in the portions of the range that overlap with human-impacted landscapes. Whether by forcible elimination/introduction or more indirect means, large-bodied dietary specialists have been extirpated from climatic envelopes that characterize human-impacted areas, whereas smaller, generalist mammals have been facilitated, colonizing these same areas of the climatic space. Importantly, the climates where we find mammals today do not necessarily represent their past habitats. Without mitigation, as we move further into the Anthropocene, we can anticipate a low standing biodiversity dominated by small, generalist mammals.

 

Functional traits mediate the interactions of species among themselves and with their environment, providing a link between diversity and ecosystem function. Crucially, the loss of biodiversity can jeopardize the functionality of ecosystems. Much focus is on predicting the impacts of current and future species loss; however, modern ecosystems have undergone biodiversity decline throughout the Late Quaternary, starting with the Pleistocene megafaunal extinctions. Thus, the fossil record offers the opportunity to investigate the long‐term legacy of biodiversity erosion and how this is affecting modern ecosystems in a cumulative manner. We aimed to investigate changes in functional diversity and redundancy of a local mammal community at Hall’s Cave, a site with a continuous record from 21,000 years ago to the present. Additionally, we included several common introduced species in the modern community to test whether they restore some lost ecological function.

Central Texas.

Late Pleistocene to Present.

Mammals.

We used eight functional traits (mass, diet, arboreality, cursoriality, soil disturbance, group size, activity period and migration habit), which, collectively, describe the ecological role of a species and its influence on ecosystem processes, to construct a multidimensional functional space. The functional richness, range and distribution of the Hall’s Cave community and the degree of functional redundancy were characterized statistically over time.

We found that declines in functional diversity were greater than expected given the decrease in species richness, implying that lost taxa contributed higher than average distinct ecological function. Functional distances between the remaining species increased through time, leading to reduced functional redundancy in younger communities. However, recently introduced taxa increased functional diversity to levels similar to those in the Holocene and partly restored the functional space occupied by Late Pleistocene fauna.

Our local‐scale analysis demonstrates how prolonged biodiversity erosion not only leads to functionally depauperate communities, but, crucially, lowers ecological resilience to future disturbance.