Species Range Expansions: Remaining Resilient Against the Effects of Climate Change

The way in which climate change affects organisms is an ongoing and highly researched area. One key aspect of this research is an understanding of how species react to new climatic conditions and the implications it may pose to their overall success. The alteration of species phenologies – the developmental and seasonal life history events of organisms – can be a result of climate change (1). Examples include insect emergence events – meaning when species of insects hatch or enter their adult stage (i.e. aquatic mosquito larvae becoming terrestrial in the early spring) – or bird migrations, both of which occur at a specific time each year. It has been seen that climate change can advance, delay, or cause no change to these events (2). Moreover, it is understood that altered phenologies can cause several problems for species and their interactions.

Climate-induced species range shifts build on research on altered phenologies. Species ranges are a way of describing the area in which a particular species inhabits throughout their life. Climate change can cause new conditions resulting in species either thriving, becoming extinct, or having to migrate to a new area to survive. These reactions are dependent on the species’ physiological responses to the new local environmental and climatic conditions (2); furthermore, the way in which these conditions may affect these organisms’ bodily processes and life-histories can determine persistence or extinction (2).

A recent study conducted by C.S. Rushing et al. examined how migratory behaviour and winter geography can impact asymmetrical range shifts of eastern birds in response to recent climate change (3). This study used 43 years of monitoring data (a scientists dream worth of data) to examine the extent of latitudinal range shifts of 32 species of birds native to eastern North America. These species were split up into resident species and neotropical migratory species, meaning species that remain here for the winter and species that migrate south for the winter. It was found that there was an asymmetric impact on these two groups of birds. Resident species that remained in North America throughout the year were seen to respond to earlier, warmer temperatures posed by climate change through a colonization and expansion of the northern margins of their range – meaning they moved further north as a reaction to the change in climatic conditions of their typical range. These resident species were able to successfully respond to these novel conditions by relocating to the northern limit of their range boundary. As mentioned earlier, one of the three ways species can respond to climate change is to migrate to a new area to survive.

The birds who migrate south for the winter, on the other hand, were seen to display an opposite pattern. These species experienced a decrease in the southern margin of their range as well as no observed increase in the northern limits of their range. So, the latitudinal distributions of species which remain for winter increased, while the opposite occurred for species that migrate south for the winter. As a result, populations of neotropical birds in North America continue to have severe population decreases, while resident species populations have remained relatively stable.

The biggest take home from the Rushing et al. piece is that the ability of a species to colonize newly suitable areas is one of the biggest ways to remain resilient to the effects of climate change. However, species that are unable to colonize new areas will be at risk of population decreases and extinction due to climate-induced range contractions. More specifically, Rushing et al. raise several concerns on the susceptibility of neotropical migratory birds due to climate change. This long-term research study has raised implications over the mechanisms driving range boundaries of neotropical migrants and how climate change may be affecting the interactions of the breeding and non-breeding seasons of these particular species.