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| The researchers measured the length, width and height of moose skulls to study the impact of climate change on the iconic Northwoods species. The team measured 662 moose skulls and observed a 16 percent decrease in size over 40 years. Credit: Sarah Bird/Michigan Tech |
Moose on Isle Royale, Michigan, USA are evolving rapidly in response to environmental change, especially climate change.
Unlike nearby populations of moose which have halved in the past 12 years, the Isle Royale moose population has increased by more than twenty percent per year for the last six years - but they are getting smaller. Measurements of skulls collected over a forty year period show they have shrunk by about sixteen percent. Life-span is also reducing.
Researchers from Michigan Technological University led by Sarah Hoy, a research fellow in the School of Forest Resources and Environmental Science (SFRES) set out to understand this difference in population dynamics in populations that were geographically close and subject to very similar climate change and yet were moving in opposite directions. The other population was the Minnesota and Lake Superior moose.
The team identified two other major factors in the ecology of the two different populations, in addition to rising temperatures:
- The presence of a fatal brain worm parasite in the northern Minnesota population which has become infected from white-tailed deer which are moving north due to climate change. There are no white-tailed deer on Isle Royale which is free of the parasitic worm.
- Change in predator population as wolf numbers have been severely reduced to just two on Isle Royale last year. This is probably the main factor in the near tripling of the island moose population, but it does not account for the smaller size or the shorter lifespan.
By examining and skulls collected over forty years then team believe they have identified a trend in moose born in warm years being smaller and less healthy in general, leading to an overall shrinkage in size and lifespan. A species adapted for cold appears to be suffering heat stress at temperatures rise. They suggest the way to restore a healthy population would be to restore the wolf population to its former numbers.
Here we have a very clear example of ecological and environmental change leading to a measurable phenotypic change in an isolated population.
The peer-reviewed results of the research are published in Global Change Biology which regrettably is behind a paywall. Publication is prior to the copyediting, typesetting, pagination and proofreading process,
Reference:
Sarah R. Hoy, Rolf O. Peterson and John A. Vucetich
Climate warming is associated with smaller body size and shorter lifespans in moose near their southern range limit
Global Change Biology, 2017 DOI: 10.1111/gcb.14015
'via Blog this'
This is Bergmann's Rule in action, an article about which the authors cite in their references. From the figure in its Wikipedia entry: "Bergmann’s rule is an ecologic principle stating that body mass increases with colder climate. Data demonstrating such a relationship in Swedish moose are shown... In addition to being a general pattern across space, Bergmann's rule has been reported in populations over historical and evolutionary time when exposed to varying thermal regimes." In other words, this is a completely expected result; moose are known to become smaller as the climate becomes warmer. The only surprise may be that it's happening more quickly than one might predict, as it's happening faster than mere genetic change over generations might explain. Instead, it seems to be a developmental response; moose grow to smaller sizes as an interaction with their environments over their lifetimes. Given the choice in the abstract between phenotypic plasticity or evolution, I choose phenotypic plasticity.
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