Climate warming is associated with smaller body size and shorter lifespans in moose near their southern range limit
©2017 John Wiley & Sons Ltd. Publisher’s version of record: https://doi.org/10.1111/gcb.14015
Despite the importance of body size for individual fitness, population dynamics andcommunity dynamics, the influence of climate change on growth and body size isinadequately understood, particularly for long-lived vertebrates. Although temporaltrends in body size have been documented, it remains unclear whether thesechanges represent the adverse impact of climate change (environmental stress con-straining phenotypes) or its mitigation (via phenotypic plasticity or evolution). Con-cerns have also been raised about whether climate change is indeed the causalagent of these phenotypic shifts, given the length of time-series analysed and thatstudies often do not evaluate–and thereby sufficiently rule out–other potentialcauses. Here, we evaluate evidence for climate-related changes in adult body size(indexed by skull size) over a 4–decade period for a population of moose (Alcesalces) near the southern limit of their range whilst also considering changes in den-sity, predation, and human activities. In particular, we document: (i) a trend ofincreasing winter temperatures and concurrent decline in skull size (decline of 19%for males and 13% for females) and (ii) evidence of a negative relationship betweenskull size and winter temperatures during the first year of life. These patterns couldbe plausibly interpreted as an adaptive phenotypic response to climate warminggiven that latitudinal/temperature clines are often accepted as evidence of adapta-tion to local climate. However, we also observed: (iii) that moose with smaller skullshad shorter lifespans, (iv) a reduction in lifespan over the 4-decade study period,and (v) a negative relationship between lifespan and winter temperatures during thefirst year of life. Those observations indicate that this phenotypic change is not anadaptive response to climate change. However, this decline in lifespan was notaccompanied by an obvious change in population dynamics, suggesting that climatechange may affect population dynamics and life-histories differently.