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How can a plant
defend itself given it can not escape by movement? : Evidence that herbivory defenses are critical for plant survival can be found in the following article.... |
How can a plant defend itself given it can not escape by movement? :
Evidence that herbivory defenses are critical for plant survival can be found in the following article....
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Island plants wimps compared to mainland cousins [ from ENN] Put a non-native animal on an island and you can expect the native plants to pay a big price, according to a study published this month. Plants unique to Santa Cruz Island, for instance, don't stand a chance against introduced sheep, in part because they have smaller spines and contain fewer noxious compounds than their mainland cousins, say Lizabeth Bowen and Dirk Van Vuren of the University of California at Davis in the October issue of Conservation Biology. It has long been suspected that island species are more vulnerable to extinction because they lack defenses against introduced predators and herbivores, but the Bowen-Van Vuren study provides the first proof of why. Learning why island species are vulnerable to extinction is critical for two reasons. First, islands are home to much of the world's biodiversity -- for example, although they account for only 1.4 percent of the land surface, islands support 10 percent of all mammal species. Second, island species die out at a greater rate than mainland species: about three times as many island species have gone extinct since 1600. "We have provided the first evidence for a major cause -- if not the major cause -- of extinctions worldwide over the past 400 years," says Van Vuren. To test the theory that island species lack defenses against introduced predators, Bowen and Van Vuren compared six plants that live on Santa Cruz Island (which lies about 20 miles off the coast of southern California) with closely related mainland species. These plants include, Big-pod ceanothus (Ceanothus megacarpus), Island cherry (Prunus ilicifolia), Bush poppy (Dendromecon rigida), Mountain mahogany (Cercocarpus betuloides), Christmas berry (Heteromeles arbutifolia), and Scrub oak (Quercus dumosa). The researchers found that in general the island plants had fewer morphological defenses (spines were as much as 80 percent shorter and leaves were up to four times larger) as well as fewer chemical defenses (tannin levels were as much as 57 percent lower and phenol levels were as much as 73 percent lower). The researchers also showed that these under-defended island plants were far more palatable to non-native herbivores: when offered both mainland and island plants of the same species, hungry sheep ate as much as 2.5 times more of the latter. By wiping out island plants, introduced herbivores can also threaten the island animals that depend on them. For example, the palila, a bird unique to the Big Island of Hawaii, is endangered because sheep destroyed its forest habitat. Similarly, a snake unique to Round Island, which is in the Indian Ocean, has apparently gone extinct because populations of the lizards it ate plummeted after introduced rabbits and goats destroyed their palm savanna habitat. For more information, contact Dirk Van Vuren, UC Davis, (916)752-4181,.....email: dhvanvuren@ucdavis.edu. |
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Evolution of these molecules has occurred over a long period
of time....Over 30,000+ compounds are known to be produced by plants;
actual # unknown
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But
exactly how can a plant defend itself against both small and large herbivores.
At the most basic level we can start with external features that help
repel these eaters.... 1.
Morphological adaptations:
