Data from: Empirical tests of harvest-induced body-size evolution along a geographic gradient in Australian macropods

1. Life-history theory predicts the progressive dwarfing of animal
populations that are subjected to chronic mortality stress but the
evolutionary impact of harvesting terrestrial herbivores has seldom been
tested. In Australia, marsupials of the genus Macropus (kangaroos and
wallabies) are subjected to size-selective commercial harvesting.
Mathematical modelling suggests that harvest quotas (ca. 10–20 % of
population estimates annually) could be driving body-size evolution in
these species. 2. We tested this hypothesis for three harvested macropod
species with continental-scale distributions. To do so, we measured more
than 2 000 macropod skulls sourced from wildlife collections spanning the
last 130 years. We analysed these data using spatial Bayesian models that
controlled for the age and sex of specimens as well as environmental
drivers and island effects. 3. We found no evidence for the hypothesized
decline in body size for any species; rather, models that fit trend terms
supported minor body size increases over time. This apparently
counterintuitive result is consistent with reduced mortality due to a
depauperate predator guild and increased primary productivity of grassland
vegetation following European settlement in Australia. 4. Spatial patterns
in macropod body size supported the heat dissipation limit and
productivity hypotheses proposed to explain geographic body-size variation
(i.e., skull size increased with decreasing summer maximum temperature and
increasing rainfall, respectively). 5. There is no empirical evidence that
size-selective harvesting has driven the evolution of smaller body size in
Australian macropods. Bayesian models are appropriate for investigating
the long-term impact of human harvesting because they can impute missing
data, fit non-linear growth models and account for non-random spatial
sampling inherent in wildlife collections.