Differential response of Sichuan snub-nosed monkeys to climate change and human activities

Aim: Determining the mechanisms by which climate change and human
activities affect patterns of ecological specialization in different
genetic units of the same species is crucial for developing local or
regionally-based conservation solutions. This study uses species
distribution models and genetic analysis to 1) identify evidence of
intraspecific differences in the population size and distribution of the
three extant lineages (Sichuan/Gansu (SG), Qinling (QL), and Shennongjia
(SNJ)) of Sichuan snub-nosed monkeys; and 2) determine why some lineages
have lower population numbers, a smaller geographical distribution, and
are more threatened with extinction. Location: China Methods: We used
n-dimensional hypervolume modeling and Genotype–Environment Association
(GEA) models to compare the climatic niches of three snub-nosed monkey
lineages, SDMs to reconstruct the historical, current, and future
distributions of each lineage, and SMC++ to calculate their effective
population sizes. Results: We found evidence of: 1) climatic niche
differentiation among the SG, QL, and SNJ lineages of Sichuan snub-nosed
monkeys; 2) geographical isolation combined with a decrease in population
size during the LGM resulted in ecological specialization among these
three lineages; and 3) a decline in climatic suitability and
anthropogenically-driven land conversion, combined with small population
size and a narrow distributional range, indicate that the SNJ lineage is
at a greater risk of extinction than the SG and QL lineages. Main
conclusions: We demonstrate that during the LGM a reduction in habitat
suitability driven by climate change, in concert with decreasing
population size resulted in the geographical isolation of the three
Sichuan snub-nosed monkey subpopulations, leading to lineage differences
in ecological specialization. GEA models and hypervolume models
demonstrated that the three lineages occupy different ecological niches.
Based on lineage-level models, the SNJ and QL lineages should be the
immediate focus of conservation efforts due to their small effective
population size and expected future reductions in available suitable
habitat. The modeling approach used here is robust and can be applied
effectively to examine the biogeography, recent evolutionary history, and
effective population size of other endangered animal taxa.