Tag Archives: range limits

A role for biotic interactions in limiting species’ range limits

Biotic interactions are more often important at species’ warm versus cool range edges (2021) Paquette & Hargreaves, Ecology Letters, https://doi.org/10.1111/ele.13864

Image credit: Malonecr7, CC BY-SA 3.0, via Wikimedia Commons, image cropped

The Crux

In the natural world, most organisms are limited by the environment as to where they can live. While this can be as drastic as a whale being limited to the ocean and humans being limited to the land, there are also more subtle limitations. That is, black and grizzly bears live in temperate environments, but polar bears are inhabit the arctic where it is MUCH colder. Due to the limitations imposed by the environment, black and grizzly bears cannot live further north.

Historically, most studies have focused on abiotic variables (i.e., non-living), like temperature and precipitation, as there is a clear role for the climate in determining where and when a species can live. However, biotic variables (i.e., living) like predation or competition can also play a role in defining the limits of a species range, though this has proven more difficult to test than abiotic factors, as many tests of biotic variables produce species-specific results. Charles Darwin proposed a framework in 1859 that the importance of biotic interactions would vary predictably with latitude and elevation. That is, at cooler, high-altitude locations abiotic interactions would be more important, while biotic interactions would be more important at warmer, low-altitude locations. Although a number of studies have attempted to test the three predictions (see Did You Know? ) derived from this framework, the results are contradictory and come from data testing different predictions using different data. Today’s authors sought to test all three predictions at once in order to resolve these contradictory results.

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Location Location Location

Biotic interactions are more often important at species’ warm versus cool range edges, Paquette & Hargreaves, 2021 Ecology. https://doi.org/10.1111/ele.13864

Image credit: Trey Ratcliff, CC BY-NC-SA 2.0

The Crux

In nature, we usually refer to the given area in which a species is found as a species range. The size of these vary, even between species that are very similar in appearance. For example, many of the dragonflies and damselflies I worked with during my PhD research could be found all over the state of Arkansas, but others had more limited ranges, and could only be found in the more southern lakes that I visited. Often, species are limited to these areas because the environmental conditions, such as temperature, are favorable to them, and the change in those conditions beyond the boundaries of their range will lead to them suffering. Knowing which factors limit the range of a given species is important for management policies, as knowing the temperature limits can inform predictions about the effects of climate change, while knowledge of natural enemies (like predators) can help with the containment of invasive species.

Previous work on the constraints experienced by species at their range limits tend to focus on abiotic factors (temperature, precipitation, etc.), as these data are easily quantified and there are very extensive records available. However, biotic factors (interactions with predators/competitors, the availability of prey) can also limit the range of a species. Though biotic factors are important, they are more difficult to quantify than abiotic factors, and are often species-specific. That is, the effect of a competitor on limiting the range of one species won’t be the same on another species. Interestingly, biotic interactions may be more important in warmer range limits, while the abiotic may be more important in the cooler range limits. Today’s authors used data from a number of studies to test just that idea.

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