herbivory


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Herbivory

The consumption of living plant tissue by animals. Herbivorous species occur in most of the major taxonomic groups of animals. Herbivorous insects alone may account for one-quarter of all species. The fraction of all plant biomass that is eaten by herbivores varies widely among plants and ecosystems, ranging from less than 1% to nearly 90%. In terms of both the number of species involved and the role that herbivory plays in the flow of energy and nutrients in ecosystems, herbivory is a key ecological interaction between species.

Herbivory usually does not kill the plant outright, although there are striking exceptions (such as bark beetle outbreaks that decimate conifer trees over thousands of square kilometers). Nevertheless, chronic attack by herbivores can have dramatic cumulative effects on the size, longevity, or reproductive output of individual plants. As a consequence, plants have evolved several means to reduce the level of damage from herbivores and to amellorate the impact of damage.

Many plants possess physical defenses that interfere mechanically with herbivore feeding on or attachment to the plant. In addition, plant tissues may contain chemical compounds that render them less digestible or even toxic to herbivores. Many plant compounds even can cause death if consumed by unadapted herbivores. While natural selection imposed by herbivores was the likely force driving the elaboration of these plant chemicals, humans have subsequently found many uses for the chemicals as active components of spices, stimulants, relaxants, hallucinogens, poisons, and drugs. An exciting recent finding is that some plants possess induced resistance, elevated levels of physical or chemical defenses that are brought on by herbivore damage and confer enhanced resistance to further damage.

Herbivores can either avoid or counteract plant defenses. Many herbivores avoid consuming the plant tissues that contain the highest concentrations of toxic or antinutritive chemicals. Herbivores have also evolved an elaborate array of enzymes to detoxify otherwise lethal plant chemicals. Because few herbivores have the ability to detoxify the chemical compounds produced by all the plant species they encounter, many herbivores have restricted diets; the larvae of more than half of all species of butterflies and moths include only a single genus of plants in their diets. Some insect species that have evolved the means to tolerate toxic plant chemicals have also evolved ways to use them in their own defense. Larvae of willow beetles store plant compounds in glands along their back. When the larvae are disturbed, the glands exude droplets of the foul-smelling compounds, which deter many potential predators.

If a plant evolved the ability to produce a novel chemical compound that its herbivores could not detoxify, the plant and its descendants would be freed for a time from the negative effects of herbivory. A herbivore that then evolved the means to detoxify the new compound would enjoy an abundance of food and would increase until the level of herbivory on the plant was once again high, favoring plants that acquire yet another novel antiherbivore compound. These repeated rounds of evolution of plant defenses and herbivore countermeasures (coevolution) over long periods of time help to explain similar patterns of evolutionary relatedness between groups of plant species and the herbivorous insect species that feed on them.

Plants and their herbivores seldom occur in isolation, and other species can influence the interaction between plants and herbivores. For example, mammalian herbivores often rely on gut microorganisms to digest cellulose in the plant material they consume. Thus, herbivory occurs against a backdrop of multiple interactions involving the plants, the herbivores, and other species in the ecological community.

herbivory

[hər′biv·ə·rē]
(ecology)
The consumption of plants without killing them.
References in periodicals archive ?
Herbivory effects on wetland vegetation types, however, is poorly documented.
We documented the appearance and elevated abundance of the uncommon dingy purplewing butterfly, Eunica monima (Stoll) (Lepidoptera: Nymphalidae), and pronounced herbivory on its host plant Bursera simaruba (L.
Although we tried to collect leaves without herbivory or pathogen damages this was not possible for some seedlings growing in pastures.
The ramifications of white-tailed deer herbivory have not necessarily been limited to forests.
In order to quantify leaf area lost by herbivory, we randomly collect 25 leaves of each plant.
Due to high rates of herbivory, we placed rodent-screens over all surviving plants at site A12 in June 2011 and site A3 in October 2011.
Based on observations of damage, our aim was to evaluate whether insect herbivory or fungal pathogens negatively influenced blowout penstemon seed production or viability, reducing seed available for seed banks and seedling recruitment.
Plants are not passive victims in this relationship; they have evolved defensive adaptations to herbivory that include both physical barriers and chemical defenses.
The results match the findings of Branson (2010) who found high reductions in grass biomass from temporally separated early season herbivory is required to reduce nymphal survival in A.
Exclosures are broadly described as fenced areas and are often used in white-tailed deer herbivory studies (Englund and Meyer 1986; Anderson 1994; Augustine et al.