Caribou and the Climate: the Impact of Global Warming on A Migratory Herbivore

The conversation surrounding global warming tends to be rather anthropocentric. When we speak about global warming and its consequences, we focus on ways in which changes in climate will impact human systems. This is understandable, seeing as these are the changes that will affect our lives the most. It is important to realise however, that we are not alone in our dependence on a stable climate. All life-forms, micro- or macroscopic, have been shaped to fit their circumstances through evolution. Over the course of countless generations, descent with modification has continually moulded us to fit the selective pressures of our environment. Climate is no exception in this, with many life-forms being directly connected and adapted to the Earth’s climate in some way, shape, or form. Moreover, throughout evolutionary history, species have adapted to one-another resulting in intricately balanced and interconnected biological systems. Relationships in biological systems are in turn also influenced by their abiotic surroundings, including the local climate. The summation of biotic and abiotic connections in a given area can be described with the oh-so-popular term “ecosystem”. When we consider all the parts that constitute these ecosystems and how they are directly or indirectly connected to the planet’s climate, it becomes apparent that global warming can have far-reaching consequences for them and the species that they encapsulate. In this piece, I will describe an example of how these consequences may manifest themselves.

Phenology denotes the study of plant and animal life cycles, and how they interact with climate. The degree to which species are capable of adapting their life-cycles to climate change varies depending on the relationship between the two. This variance in adaptability can cause relationships between species to break down, with potentially dire consequences for the organisms that depend on- or are controlled by the species involved. In a 2007 study, Post and Forchhammer provide a compelling example of this phenomenon by examining the effects of climate change on the reproductive success on Barren-Ground Caribou (Rangifer tarandus groenlandicus) in West Greenland.

Image 1: Grazing Barren-Ground Caribou

Barren-Ground Caribou are migratory animals that time their migration in accordance with the length of day and night cycles, an adaptation known as photoperiodism. The specific area in their migratory path that coincides with the production of young is known as their calving range. As is the case with other migratory herbivores, Barren-Ground Caribou have evolved such that the time of year in which they migrate to their calving range coincides with the time of year in which resources are the most readily available. For Barren-Ground Caribou, this peak occurs at the start of the plant growth season due to emergent plant tissue offering them the highest nutritional value. By synchronising the production of young with the green-up of species on which they feed, the Caribou maximize their reproductive output as well as the likelihood of survival for their offspring. Over recent years however, climate change has disturbed this relationship.

Contrary to the photoperiodism displayed by the Caribou, the plants on which they rely for nutrition have generally adapted their life-cycle to seasonal temperature variation. Several studies have already documented a shift of plant life-cycles at high latitudes in response to rising global temperatures, with growth season now occurring earlier in the year. The earlier occurrence of plant-growth season, and by extension peak resource availability for Barren-Ground Caribou, poses a problem due to the fact that the Caribou do not base their migratory life-cycles on temperature averages, and have consequently not adapted the timing of their offspring production to the recent climate shift. This phenomenon is known as a trophic mismatch and can have devastating consequences for affected populations. Post and Forchhammer observed a 300% drop in offspring production for Barren-Ground Caribou in Greenland since 1993, accompanied by a marked increase in mortality rates for the remaining offspring. The interconnected nature of species within an ecosystem means that rapid decline in one species can have sweeping effects across biological systems. Predators that prey on the Caribou may be impacted by a sudden drop in food supply, while plants that are usually controlled by them may experience explosive growth, thereby outcompeting other plants. These are just a few examples of how de-synchronization of various species’ life cycles as a consequence of climate change can cause extensive damage to ecosystems.

I’ll be the first to say it: climate change is nothing new. Life on Earth has existed for billions of years and has adapted to changes more drastic than those we are seeing the Anthropocene. With this in mind, there are still two things worth noting:

  1. While natural systems are capable of adapting to climate change, this adaptation takes time. The speed at which climatic change takes place (which is currently very high) is therefore an important factor in the damage that it can cause to natural systems.
  2. While natural systems may, given enough time, recover from rapid climatic change, the widespread disappearance of species and subsequent system-collapse could have far-reaching implications for humans around the world. Life will ultimately be fine. For us humans, this is uncertain.

Ecosystems’ immense complexity and unique nature make them unpredictable as far as responses to climate change go. Systems and species will undoubtedly be differentially affected by global warming, and it is important that we are cautious when making grand, sweeping statements about the effects of climate change on ecosystems. Still, it is important to consider how intimately ecosystems and climate are connected. It is important that we are aware of the influence that we can have on the natural world, and thereby, potentially our own.

Post, E., & Forchhammer, M. C. (2007). Climate change reduces reproductive success of an Arctic herbivore through trophic mismatch. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 363(1501), 2369–2375. doi:10.1098/rstb.2007.2207

3 thoughts on “Caribou and the Climate: the Impact of Global Warming on A Migratory Herbivore

  1. I found your blogpost really interesting and I agree that it is important to not always look at climate change with an anthropocentric view. I think that protecting species and biodiversity is really important because it will also in the end protect us and our food sources.

    Regarding your first point about climate change happening on a really short timescale making it difficult for species to adapt, I was wondering if you know if evolution occurs on like a ‘fixed’ timescale that is dependent on a species’ reproduction rate or if it is also dependent on the speed and strength of environmental pressures such as climate change? Ultimately, my question would be if you know what influences the speed at which evolution occurs?

    For your second point, I was wondering if the future of humans is really so uncertain? I thought humans especially will ultimately be fine but that many people won’t be fine depending on where they live and how much money they have, which is linked to issues surrounding climate refugees etc. Could you elaborate on that? I’d be interested in hearing your opinion!


  2. Nice blogpost! I am very interested in ecology so am intrigued with the impact of climate change on ecological processes, and as a result on human livelihood as well.
    However, there are people out there – such as climate change denialists – who may wonder why we should care about species vulnerability and species going extinct. I’m curious as to what you would tell someone who may respond to this post with comments such as: “well why should I care if animals like the caribou are affected by climate change?” or “who cares if changes in caribou migratory behavior potentially impacts an ecosystem?”

    One possible response that you slightly touched upon could be that “the widespread disappearance of species and subsequent system-collapse could have far-reaching implications for humans”. But, how so? How could you convince or argue with someone who is either a climate change denialist or doesn’t necessarily care for nature and biodiversity that we should care about it?

    Personally, I would argue that not only does ecology have a variety of cultural (i.e. medicinal), health, and economic (i.e. food supply, recreation, tourism) values, but it can also have aesthetic value for our future generations. I would like to know that our future children can experience the same ‘abundance’ of nature as we can. Or, maybe, another response to such a comment could be to simply say that it is a matter of the feeling guilty.

    I’m curious and think it’d be valuable to hear how you (or someone else) would respond to this!


  3. Hey Jonah, really cool and interesting blogpost. I think the example of the Caribou as showing the devastating changes caused by climate change on biodiversity and then the trophic consequences of such changes is really valuable. However, for some species, conservation projects can maybe assist in keeping the species and their larger ecosystems well and living. I know for example that in Joshua Tree national park they are trying to help (the extremely slow moving) Joshua tree upwards to prevent its extinction under increasing drought in the Southwest of the US. They are doing this partly based on the paleo-ecological history of the species, potentially helping it colonize an area that is within its former range ( While the Joshua Tree is a species that is virtually unable to migrate on its own, such ‘assisted migration’ maybe easier for species that are highly mobile like the Caribou? Do you have any idea on whether the biological habits of such animals could be altered to help them survive? Conversely, I would imagine such interventions would be especially complicated for migratory animals that are used to historic seasonal patterns of vegetation growth. I was wondering if you are aware of any ‘assisted migration’ conservation projects of migratory animals that have worked in the past. As you probably know a lot more about ecology than I do, I was also wondering whether you have an opinion on whether such assisted migration projects deserve resources? This is along the lines of the question ninahees also asks. For the Joshua Tree National Park, there is a clear economic incentive, namely to keep tourists coming. Such interventions may help humans, like in the case of the Caribou, maybe less directly valuable to us. As you describe that ‘nature’ in the end will be fine, what makes such interventions worthwhile? Should conservation interventions depend on whether it aids the thrive of humans?


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