Historical records reveal the distinctive associations of human disturbance and extreme climate change with local extinction of mammals

Abstract

Accelerated anthropogenic impacts and climatic changes are widely considered to be responsible for unprecedented species extinction. However, determining their effects on extinction is challenging owing to the lack of long-term data with high spatial and temporal resolution. In this study, using historical occurrence records of 11 medium- to large-sized mammal species or groups of species in China from 905 BC to AD 2006, we quantified the distinctive associations of anthropogenic stressors (represented by cropland coverage and human population density) and climatic stressors (represented by air temperature) with the local extinction of these mammals. We found that both intensified human disturbances and extreme climate change were associated with the increased local extinction of the study mammals. In the cold phase (the premodern period of China), climate cooling was positively associated with increased local extinction, while in the warm phase (the modern period) global warming was associated with increased local extinction. Interactive effects between human disturbance and temperature change with the local extinction of elephants, rhinos, pandas, and water deer were found. Large-sized mammals, such as elephants, rhinos, and pandas, showed earlier and larger population declines than small-sized ones. The local extinction sensitivities of these mammals to the human population density and standardized temperature were estimated during 1700 to 2000. The quantitative evidence for anthropogenic and climatic associations with mammalian extinction provided insights into the driving processes of species extinction, which has important implications for biodiversity conservation under accelerating global changes.

Keywords: climate change; conservation; human disturbance; local extinction; mammals.

Fig. 1.

Temporal variation of the survival rates, cropland coverage, human population density, and temperature for the 11 mammal species or groups of species at the county or prefecture level. (A) Survival rates (percent, i.e., the proportion of survived grids compared to all distributed grids in history) of 11 large mammal species or groups of species caused by local extinctions in China (the same below). (B) Average cropland coverage (percent, from AD 900 to 2000). (C) Average human population density (HPD, persons per km², from AD 900 to 2000). (D) Average summer air temperature (degrees Celsius, from AD 900 to 1999). Time resolution was 10 y after 1700 and 100 y before 1700. Different colored lines represent the survival rates (A), or average cropland coverage (B), average human population density (C), and average summer air temperature (D) of the 11 mammal species or groups of species in their distributed grids.

Fig. 2.

Relationship between body mass (kilograms) and the average proportion of survived grids of the 11 mammal species or groups of species during 4 study periods from 905 BC to AD 2000 (A), from AD 1000 to 2000 (B), from AD 1500 to 2000 (C), and from AD 1911 to 2000. (D) Body mass was log-transformed. Blue shadows are the confidence intervals of the fitted linear regression models (indicated by the blue lines).

Fig. 3.

Relationship of the local extinction probability with the average human population density (A, premodern period; B, modern period) and the average standardized summer air temperature (C, premodern period; D, modern period). The analysis was conducted using stGAM methods. The average local extinction probability for human population density (or standardized temperature) was estimated using the standardized temperature (or human population density) and coordinates of each grid in Eq. 1. Different colored lines represent the responses of local extinction probability of the 11 mammal species or groups of species to different stressors.

Fig. 4.

Diagram of the stGAM method to estimate the associations of anthropogenic stressors (human population density) and climatic stressor (temperature) with the local extinction probability (presence or absence) of mammals. For each grid of each species’ distributional range, only data of 2 sampling years were used (i.e., the sampling year of presence and absence). The absence year (i.e., extinction year) was 1 y after the last observation. The presence year was the year 50 y before the absence year. The average value of stressors of the last 50 y before the sampling years of presence or absence was used to examine their associations with the local extinction probability (presence or absence) of mammal species of this grid.