Climate change affects species at the smallest scale, such as an individual’s biological rates, and at the global scale, such as range shifts and extinctions. Less known is how rising temperatures may affect species at the intermediate scale, particularly for the large amount of species that exist as metacommunities in a patchy habitat. Diversity in these types of communities is a product of both local species interactions and regional movement between patches, which are both likely to be affected by warming. But how?
Recent research takes a look at the effect of warming on insect diversity in a metacommunity of specialist herbivores that feed on milkweed plants. Five species – monarch butterflies, long-horned milkweed beetles, small milkweed bugs, and two species of aphids – were housed within pairs of enclosed milkweed cages built in southern Ontario that had either no connectivity, low connectivity, or high connectivity. These cages were then either warmed or left unwarmed, and insect and plant surveys were conducted for six weeks.
Two broad results emerged from the experiment. First, there was no uniform response to warming for all five species in terms of local interactions or regional dispersal. For example, warming increased monarch survival and population sizes of both aphid species, but decreased the longevity of milkweed bugs. The interaction between warming and connectivity led to a more rapid decline in diversity in unwarmed, low connectivity metacommunities, but overall responses were very species-specific. The variation in results provides one more example of how the effects of temperature changes can be complex and context-dependent.
Second, although connectivity between patches is generally beneficial, the risk of dispersing can outweigh the benefits if there are plenty of local resources. In this case, both monarch caterpillars and milkweed bugs had lower survival in connected metacommunities. However, for this experiment local conditions within patches turned out to be favorable, dampening the need for additional resources from other patches. The experiment highlights how dispersal risk can be incorporated into metacommunity responses.
The main message is that metacommunity diversity is shaped by both species’ response to warming and inter-patch connectivity, often in complex ways. The interaction between the two forces creates species-specific responses that may not be predictable when looking at temperature changes or connectivity alone. Incorporating spatial structure into measures of climate change response leads to a more accurate picture of diversity at the intermediate scale.
Grainger T. N. and B. Gilbert. 2017. Multi-scale responses to warming in an experimental insect community. Global Change Biology 23(12): 5151-5163.