Friday, January 30, 2015

Insects are picky eaters

...uncertainty persists regarding fundamental features of herbivore diet breadth, including its relationship to latitude and plant species richness. Here, we use a global dataset to investigate host range for over 7,500 insect herbivore species covering a wide taxonomic breadth and interacting with more than 2,000 species of plants in 165 families. We ask whether relatively specialized and generalized herbivores represent a dichotomy rather than a continuum from few to many host families and species attacked and whether diet breadth changes with increasing plant species richness toward the tropics.

After decades of field work from dozens of sites around the world, and after two years of combing through and analyzing data, researchers have reported on global patterns in the diets of insect herbivores. They report that most insect herbivores, such as caterpillars, find and feast on just one kind of plant in any one location, rather than eating everything in sight.

This result is something that many scientists have known intuitively for a long time, but it has not before been quantified on such a large scale. Actually a lot of prior studies had disagreed on whether or not insect herbivores in the tropics have more narrow diets than their temperate relatives. The study shows that insects in  the tropics are indeed more specialized, and this was evident across hemispheres and across unrelated taxonomic groups.

No doubt this study is important for ecosystem management. Variation in insect diet has implications for numerous ecological and evolutionary processes, including effects of environmental disturbance, the stability of networks of interacting species and the top-down effects of predators being controlled by the level of herbivore diet specialization. 

We need to know what insects eat when doing ecosystem restoration, and we shouldn't assume that species with generalist feeding habits will necessarily fill the same ecological roles as more specialized species.

While I was reading this new publication I was reminded of another one, today almost 11 years old and one of the most frequently cited DNA Barcoding paper:

A. fulgerator is a complex of at least 10 species in this region. Largely sympatric, these taxa have mostly different caterpillar food plants, mostly distinctive caterpillars, and somewhat different ecosystem preferences but only subtly differing adults with no genitalic divergence. Our results add to the evidence that cryptic species are prevalent in tropical regions, a critical issue in efforts to document global species richness.

Maybe it is time to revisit our species number estimates once again. Not only did we learn that in the tropics herbivore insect species are largely specialists but also we've come to accept that they are hard to find due to a lack of morphological variation between species. 

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