Migrating Robins and Hibernating Marmots

In this post I will explore the problem of phenological (seasonal) changes affecting altitudinal migrants and hibernating species. A paper by Inouye et al. (2000) studied the effects of climate change on american robins (Turdus migratorius) and yellow-bellied marmots (Marmota flaviventris) in the Colarado Rocky Mountains. 

The site was the Rocky Mountain Biological Laboratory in Gothic, Colarado at an elevation of 2,945 m. Temperatures can reach -40 celsius and the area experiences over 7 months of snow cover a year. Annual observations showed that the beginning of the growing season at the site had not significantly changed over the past 25 years (P = 0.9) although air temperatures have slightly increased. This may be due to the slight increased volume of snowfall occurring each year.

Robins are an example of altitudinal migrants, who migrate to lower altitudes during the winter months when food is unavailable. The date that robins have been sighted has been proven not be be statistically significant (P = 0.110) but Inouye et al. (2000) believe it to be biologically significant. First sightings of robins moved on average 8.4 days earlier over the 26 years from 1974-2000. This difference has been attributed to the changing phenology of low altitude areas, initiating an earlier spring migration. High altitudes are not shifting phenologically at the same rate as the lower altitudes, causing potential problems to altitudinal migrants over food availability. Robins arriving in the Colarado Rockies will have to wait longer for the snow to melt for food to become available. While robins are able to make the 10-20 km journey back to the low altitudes, if the resources are only available for a certain period of time the robins could find themselves running out of food.

Another way species adapt to extremely low temperatures is hibernation. Marmots in the area typically begin hibernation in August/September after a period of fat accumulation  and body mass gain. The video below shows how Vancouver Island marmots hibernate and how important the period after emergence is.

Marmots are beginning to emerge significantly earlier (P = 0.029), on average 23 days over the past 23 years. This change is believed to be attributed to local air temperature which has been seen to have increased, approximately 1.4 degrees, which is also believe to be the cause of marmot emergence. As they are emerging earlier when there is still significant snow cover, food is scarce and additional stress may be put onto the marmot’s bodies to maintain a high body temperature while their fat reserves run low. While they are not able to eat immediately after emergence, after they reactivate their digestive system feeding is crucial. Prolonged snow cover may also caused decreasing litter size and frequency of reproduction.

Climate models predict increased winter precipitation in the Rockies of the magnitude of 20-70% and problems with altitudinal migrants and hibernating species will persist and most likely worsen. This is just one example of differing local and global changes in climate that can cause problem to migrating species. Spatial variability of changing temperatures may yet become a bigger problem than global mean temperature rise when studying highly mobile species.

Clement Reid - a Victorian Botanist ahead of his time

Diving straight into a a study on species migration, Pearson’s (2006) paper focuses on the uncertainty with which we can model species migration. I believe this will be a recurring theme when exploring the debate on climate change and species migration.

From examining fossil pollen data of postglacial migration of tree populations in North America, he concluded that migration rates were of the order of 100 m - 1000 m per year. These rates seem phenomenally fast and are often described as “Reid’s paradox” in recognition of Clement Reid, a Victorian botanist, who could not understand how such species could migrate so fast. A theory has been put forward where by this staggering rate of migration is explained by local dispersal from isolated populations that have managed to persist in microclimates where the regional climate has been ill-suited. The low density populations would not show up on the pollen record and hence might explain the massive rate of migration beyond the reconstructed climate ranges. This phenomenon is known as glacial refugia*.

This theory may pose problems looking towards the future. It is estimated that plant species will have to migrate at rates of over 1000 m per year in order to keep up with the current warming. Encouragement initially came from examining the historical records that hinted that such rates were possible, however McLachlan et al. (2005) believe that the migration rates were an order of magnitude slower (100 m per year) and the cause for optimism is unfounded.

Thomas et al. (2004) estimated species extinction from climate change for 1103 endemic species that cover approximately 20% of the earth. When using the maximum warming scenarios he estimated that the species, as he put it, “committed to extinction” were 21% - 23% if migration rates keep up with climate change and 38 - 52% if they do not. This is quite a frightening prospect.

New research is constantly adding to our knowledge and improving our understanding of the responses to climate change. It just goes to show that our predictions are filled with uncertainties and, frankly, guesswork. Future modeling needs to focus on local scale climates and possible refugia in areas that would be regionally unsuitable. This however is complex due to the difficulty in predicting local space climate change. Future dispersal models should not rely on unrealistic migration rates and instead should incorporate localized populations and genetic traits. Pearson’s (2006) findings gives us no cause for optimism when contemplating species response to climate change while arguing we need more research and information to reduce model uncertainty.

* There will be more detail of glacial refugia in subsequent posts.

Introduction

Global Climate Change has become the main issue of the 21st Century. Over the past 100 years the earth’s climate has warmed approximately 0.6 degrees celsius, with this figure set to rise to between 2% and 6% over the next 100 years. For a recap of global warming and a possible solution, see the video below:

Joking aside, this warming will alter habitats across the globe. In the northern hemisphere, where most  research takes place, species tend to migrate northwards or to higher altitudes.  However the landscape of today is much different compared to the post glacial period, as the presence of humans often provides barriers to migration. Species, however, do not react to average temperature rises, rather to regional changes which are highly specially heterogeneous (Figure 1).

Figure 1. Spatial variability in annual temperature since 1976 relative to 1961 and 1990 baselines (% degree per decade) (Walther et al. 2002)

Themes such as study of phenology, range and community shifts and ecosystem dynamics will be used to explore the consequences of the warming. Also considered will be possible genetic adaptations to global climate change such as changes in body size and natural events such as flowering and egg laying. This blog will explore how species will react to the changing climate and discover whether the earth will become Too Hot To Handle.

My interest in the area of biogeography, specifically species migration, stems from an enjoyment of studying a large range of species as well as how they behave. It is how species are located spatially and temporally as well as how they distribute that fascinates me. I also believe it is important for species conservation, as an understanding of species resiliency and adaptation techniques will help us protect future global biodiversity.

The main papers that I will be studying will focus on different species and their adaptation to changing climates including historical, modern-day and future struggles. I will also be examining the key themes of species migration modeling such as the bioclimate envelope as well as theories such as isolated refugia. The blog will follow a range of bird, animal and plant species.