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5.2.2: Community Interactions

  • Page ID
    37239
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    Learning Objectives
    • Define herbivory
    • Give examples of defenses against predation and herbivory

    Herbivory

    Herbivory describes the consumption of plants by animals, and it is another interspecific relationship that affects populations. Unlike animals, plants cannot outrun predators or use mimicry to hide from hungry animals (with a few exceptions). Some plants have developed mechanisms to defend against herbivory. Other species have developed strategies that rely on hungry animals; for example, herbivory provides a mechanism of seed distribution that aids in plant reproduction.

    Defense Mechanisms against Predation and Herbivory

    The study of communities must consider evolutionary forces that act on the members of the various populations contained within it. Species are not static, but slowly changing and adapting to their environment by natural selection and other evolutionary forces. Species have evolved numerous mechanisms to escape predation and herbivory. These defenses may be mechanical, chemical, physical, or behavioral.

    Galapagos Iguana eating cactus leaf
    Monarch caterpillar on a Milkweed
    Figure \(\PageIndex{1}\): (top) Galapagos Land Iguana eating cactus pad with spines from a prickly pear cactus. (bottom) a monarch caterpillar feeds on a milkweed plant. Images by Kammy Algiers (CC-BY).

    Mechanical defenses, such as the presence of thorns on plants, may discourage herbivory by causing physical pain to the predator (Figure \(\PageIndex{1}\), top). Chemical defenses are also produced by many plants to discourage herbivory. Milkweed plants (Asclepias spp.) produce chemical defenses that protect them against most herbivores. However, as shown in Figure \(\PageIndex{1}\) (bottom), monarch caterpillars (Danaus plexippus) have evolved a way around these defenses. Monarch butterflies lay their eggs on milkweed plants, the preferred source of food for their developing larvae. If the caterpillars can survive the initial flood of sticky latex when they first bite into the leaf (a front line defense for the milkweed), they can continue to consume the tissues. These tissues contain toxins, but the caterpillar is able to store, rather than metabolize, these toxins and make its own body toxic to predators. 

    Plants can also be good sources of camouflage for animals. Often times, animals will blend in with the plants they sit on to avoid being detected by predators. The tropical walking stick is an insect with the coloration and body shape of a twig which makes it very hard to see when stationary against a background of real twigs (Figure \(\PageIndex{2}\)). In another example, the chameleon can change its color to match its plant surroundings (Figure \(\PageIndex{2}\)). Both of these are examples of camouflage, or avoiding detection by blending in with the background.

    Green walking stick insect that resembles the stem on which it sits.
    Green chameleon that resembles a leaf.
    Figure \(\PageIndex{2}\): (top) The tropical walking stick and (bottom) the chameleon use body shape and/or coloration to prevent detection by predators. Credit top: modification of work by Linda Tanner; credit bottom: modification of work by Frank Vassen.

    Contributors and Attributions

    Modified by Kammy Algiers from the following sources:


    This page titled 5.2.2: Community Interactions is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Melissa Ha, Maria Morrow, & Kammy Algiers (ASCCC Open Educational Resources Initiative) .

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