Movement and selection by migratory ungulates in dynamic landscapes: plasticity and individual difference in a changing world

Laforge, Michel P. (2021) Movement and selection by migratory ungulates in dynamic landscapes: plasticity and individual difference in a changing world. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

A fundamental aspect of many ecological systems is that they fluctuate in habitat quality through time. A common strategy among species is therefore to time reproduction, which is energetically expensive, to when resources are most abundant. A challenge for animals in adopting such a strategy is dealing with environmental change at intra- and inter-annual scales. Within years, migrating individuals can track areas of resource abundance throughout the season to increase energy intake. Alternatively, individuals may time reproduction to coincide with when resources are most abundant, at the cost of being able to track those resources spatially due to young that reduce movement capacity. For either strategy to be successful, individuals must deal with interannual changes in the timing of resource abundance, which threatens to decouple resources and consumers via trophic asynchrony. This is especially important in light of climate change which continues to advance the timing of spring events. Animals or populations can cope with this change in the timing of spring in two ways: individuals can be plastic to change and acclimate their behaviour to annual conditions, and/or populations can adapt if there are consistent differences among individuals in the timing of life-history behaviours that are transmissible across generations, resulting in selective pressures that result in an adaptive response. I tested these ideas in caribou (Rangifer tarandus) in Newfoundland and in migratory herbivores in Wyoming, USA. I demonstrate that caribou follow a gradient of melting snow to time their migrations, and as such give birth during the peak of resource availability (green-up). I then demonstrate that timing of migration and timing of parturition are plastic to timing of melting snow and are correlated. I tested for an effect of forage, conspecific density, and predation risk on calf mortality in two populations of caribou and found that avoidance of predators predicted calf survival in one of the two populations. Finally, I found that migratory ungulates in Wyoming had high repeatability in migration timing and were plastic to the timing of annual green-up. The results of my thesis are overall positive news for the conservation of migratory herbivores faced with changing environmental conditions in the Anthropocene.

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