This blog post is provided by Michel Laforge and tells the #StoryBehindthePaper for the paper “Plasticity and repeatability in spring migration and parturition dates with implications for annual reproductive success”, which was recently published in Journal of Animal Ecology. In their paper they find that caribou acclimate the timing of their migration and when they give birth to the timing of spring snow melt and plant green-up.

Animals evolve to time important life history events to when environmental conditions are optimal. For example, many species reproduce when food resources are most abundant to facilitate feeding offspring, to give young the greatest chance of survival. For herbivores, the highest abundance of resources occurs in spring with the flush of new, highly digestible spring vegetation (green-up), which maximizes fat gain and results in higher survival of young. Timing the reproductive period to when resources are most abundant is, however, not always straightforward, since the timing of the peak in resource abundance such as green-up, along with cues that may signal resource abundance, vary from year-to-year, often considerably. A useful strategy for animals in this case is to respond to changes in the environment by altering the timing of important events such as reproduction to properly match the abundance of resources via behavioural plasticity.

As long-term averages change, however, plasticity may be insufficient. Natural selection favours individuals that are best adapted to current environmental conditions. As those conditions change, variation in the population must exist upon which natural selection can act. That is, the trait in question must vary consistently among individuals and must be transmissible across generations. Calculating differences among individuals can therefore provide a vital first step towards determining whether a trait or behaviour could change in response to changing selective pressures. This is especially important in light of climate change which is resulting in unprecedented environmental change to which populations must either acclimate or adapt to.

In a recent paper in The Journal of Animal Ecology, we investigated plasticity of caribou (Rangifer tarandus) migration timing to changes in the timing of spring snowmelt, and plasticity in timing of parturition (giving birth) to both timing of snowmelt and spring green-up in Newfoundland. We also quantified differences among individuals in timing of migration and timing of parturition that could have important implications in a changing climate as spring events such as snowmelt and green-up occur earlier in the year.

We found that timing of migration in caribou was plastic to the timing of snowmelt in spring, as caribou migrated later when snowmelt occurred later. Caribou also gave birth to calves earlier in spring when snowmelt occurred earlier and when green-up occurred earlier. Plasticity in parturition suggests a direct link between the environment caribou experience and their behaviour and reproductive ecology. Observed plasticity will hopefully confer some resilience for caribou in the face of climate change.

We also found some evidence that timing of migration was a trait that varies among individuals, suggesting that timing of migration could be transmissible across generations — which may be important to allow migration behaviour to adapt to changing conditions, especially if they continue to change beyond the range to which individuals can acclimate. Conversely, we found no evidence of timing of birth being consistent among individuals, which suggests little possibility of an adaptive response in the timing of birth.

Caribou are a species of concern throughout their circumpolar distribution, and climate change represents a potential challenge to their persistence. Our study provides cautious optimism for caribou by showing the potential of plasticity to mitigate some of the effect of changing environmental conditions on their movement and reproductive ecology. Despite observed plasticity, a lack of repeatability in timing of parturition suggests a limited potential for an evolutionary response to change.

Author bio

Michel P. Laforge – Mike (@MamlSpatialEcol) studies movement, migration, and habitat selection behaviour of ungulates and how inter- and intra-seasonal change in resource quality and abundance affects these behaviours at the individual-level. He is currently a post-doc at the University of Wyoming.

Read the paper

Read the full paper here: Laforge, M. P., Webber, Q. M. R., & Vander Wal, E. (2023). Plasticity and repeatability in spring migration and parturition dates with implications for annual reproductive success. Journal of Animal Ecology, 92, 1042– 1054. https://doi.org/10.1111/1365-2656.13911