November 23, 2010
Koalas As Picky Leaf-Eaters, Ancient Insects In Warm Climates And California’s Forest Fires
Ask the Eucalyptus connoisseurs
Koalas may be the pickiest marsupials around: They evolved to feed almost exclusively on the leaves of Eucalyptus trees, and they are highly selective when it comes to which species and even which individual trees they visit. When the furry leaf-eater settles on a particular tree, it relies on a number of factors, including taste, to make its selection. In a study published in the November issue of Ecology, a journal of the Ecological Society of America (ESA), researchers used koala feeding preferences to design a new method that could help ecologists and conservationists map habitats.Ben Moore and colleagues from the Australian National University and the Macaulay Land Use Research Institute in Scotland collected and analyzed leaves from all the trees available to koalas in a Eucalyptus woodland using a near-infrared spectroscopic model. To define "palatability" in koala terms, the researchers tested leaves on captive koalas and recorded how much they ate: They found that the koalas ate less foliage when it contained lots of lipid-soluble phenolic chemicals known as formylated phloroglucinol compounds (FPCs). The researchers then tracked koala tree visits in a Eucalyptus woodland to show that tree preferences of wild koalas could be predicted using the taste preferences of the captive koalas. The researchers also determined the chemical composition of the trees' leaves and other factors such as tree size and neighborhood quality, or how attractive each tree's neighbors were to koalas.
Specifically, koalas spend more time in large trees; however, the individual trees they prefer depend on the taste of the leaves and the "neighborhood" in which the tree is growing. Although tree size and taste are most important to the koalas, the researchers found that trees were visited more often if they were surrounded by smaller, less palatable trees or by larger, more palatable trees. Moore and colleagues explained that trees surrounded by smaller, unpalatable trees were probably more attractive by comparison. At the other extreme, trees surrounded by other large, palatable trees were visited more frequently because koalas were attracted to these high-quality areas.
"This method uses a new technique to combine our understanding of animal behavior with the chemical, spatial and physical aspects of the environment to make a map of koala habitat, as koalas see it," said Moore. "Our approach can aid ecologists in tracking and examining the presence or absence of animal populations in different areas"”and it can measure plants' susceptibility to herbivory"”by determining the quality and value of a habitat from the herbivore's point of view."
"Palatability mapping: a koala's eye view of spatial variation in habitat quality" from ESA's journal Ecology is open-access and available at http://www.esajournals.org/doi/pdf/10.1890/09-1714.1.
Author Contact: Ben Moore, [email protected]
Ancient insects preferred warmer climates
For millions of years, insects and plants have coevolved"”leaf-eaters adapting to the modifications of their hosts and plants changing to protect themselves from herbivory. The abundance and diversity of both insects and plants have varied depending on changes in climate. However, according to a study published in the November issue of Ecological Monographs, a journal of the Ecological Society of America, abnormally high global temperatures have historically lead to a greater diversity and abundance of insects, separate from plant diversity and adaptations.
Ellen Currano formerly from Pennsylvania State University and colleagues examined a total of 9071 fossilized leaves at nine sites of the Bighorn Basin in Wyoming that had fossils dating back 52.7 to 59 million years ago. This particular location contains fossils created during a period when global temperatures gradually warmed to the greatest sustained highs of the last 65 million years. In addition to this gradual rise, there was also a temporary spike in temperature and partial pressure, similar to the weight, of carbon dioxide in the atmosphere and a subsequent cooling period.
From the fossils during this six million year span, the researchers identified 107 plant species and recorded multiple types of insect feeding damage. They paid special attention to variations of insect feeding on one leaf, indicating the presence of multiple species of insects. By comparing these findings with the established temperature records, Currano and colleagues found that a rise in global temperature"”both gradual and abrupt"”led to an increase in insect populations. Surprisingly, the increase in insect diversity and abundance was not necessarily correlated with changes in plant diversity or abundance, suggesting that warmer temperatures directly affected insect numbers.
This relationship, said the authors, can be attributed to insect migration: As temperatures rose, insects could move northward and to previously uninhabitable altitudes. These climate shifts, then, may have also caused insect migration over higher latitude land bridges connecting North America, Europe and Asia.
"Our findings indicate possible changes to come as a result of anthropogenic climate change," said Currano. "As temperatures rose some 60 million years ago, tropical and subtropical insects were able to migrate northward to Wyoming. It is likely that present-day anthropogenic warming will lead to similar distributions of insect populations and cause an increase in herbivore damage."
"Fossil insect folivory tracks paleotemperature for six million years" from ESA's journal Ecological Monographs is available open-access at http://www.esajournals.org/doi/pdf/10.1890/09-2138.1.
Author Contact: Ellen Currano, [email protected]
California's controlled fires boost biodiversity
In certain ecosystems, such as the mixed-conifer forests of the Sierra Nevada region of the western United States, fires are a natural and essential occurrence for maintaining forest health. However, for many decades, resource managers in California and other western states prevented or suppressed natural fires to limit the potential for catastrophic spread.
Suppressing fire in this region for long periods has led to an unusually large increase in the number of small trees and excess accumulations of logs, branches and needles on the forest floor. Currently, forest managers are using prescribed--also called controlled--fires, thinning and other methods to reduce tree densities and ground debris that could serve as fuel. However, as explained in Ecosphere, an open-access journal of the Ecological Society of America, the ways in which these fuel-management practices affect the biodiversity of these forests is not well understood.
To answer this question, Karen Webster formerly from Sequoia and Kings Canyon National Parks in California, and Charles Halpern from the University of Washington, Seattle, used more than two decades of data on changes in the abundance and diversity of plants following prescribed burning in these mixed-conifer forests. They analyzed data collected periodically from 51 forest plots that were burned once, twice or not at all during the 20-year study period.
The researchers found that after ten years, burned plots supported more than twice as many native plant species as nonburned plots, and the once-burned plots showed a nearly threefold increase by year twenty. In addition, species diversity increased with severity of burning and nonnative species did not benefit from fire. In general, plots that were burned twice showed patterns similar to those burned only once, suggesting that the use of repeated burning to reduce fuel accumulations does not have a damaging effect on the native vegetation.
"Information on the ecological consequences of reintroducing fire to these forests is critical for park managers," said Webster, "especially with current operational constraints. For example, air quality regulations and budget limitations require managers to be as effective as possible with controlled burns. Our findings offer important insights that can aid park managers in developing approaches to reduce risk of fire, and at the same time, enhance biological diversity. Long-term studies of the effects of reintroducing fire to these forests are extremely valuable, both for current management and for the future, given threats such as climate change and the spread of nonnative species."
"Long-term vegetation responses to reintroduction and repeated use of fire in mixed-conifer forests of the Sierra Nevada" appears in ESA's newest journal Ecosphere"”an online-only and open-access publication"”at http://www.esajournals.org/doi/full/10.1890/ES10-00018.1.
Author contact: Charles Halpern, [email protected]
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