Ecology for Backyards

One goal of our study is to understand how these plants are interacting with the insects and birds in the urban ecosystem. We refer to these interactions as the urban food-web. Almost every species of insect herbivore can successfully reproduce only on the native plant lineages with which they have shared an evolutionary history. Insects cannot adapt rapidly to evolutionarily novel plants because they may have specialized adaptations to detoxify, sequester, and excrete the noxious phytochemical defenses of one host plant, but typically cannot breaking down the defenses of other plants. Thus, landscapes dominated by non-native plants, whether unwanted invasives or desirable ornamentals, are unlikely to support the same diversity and biomass of insect herbivores as landscapes dominated by native host plants. Moreover, if the presence of non-native plants compromises insect biomass, it follows that populations of insectivores such as birds will also be compromised. 

Plants have a wide array of chemical and physical defences against being eaten by herbivores. Defensive chamicals may ossur throughout the plant or may occur in specialized tissue. These chemicals may make the plant  toxic, or indigestible for herbivores to eat it.  For example, white clover can produce cyanide, which is deadly. Some chemicals are made by the plant in response to being grazed by an herbivore. By producing chemicals only when needed, the plant can conserve its' resources for its own growth and reproduction. This is an adaptive, evolutionary process in which plants gained the chemical defense mechanisms to avoid over predation.

To understand Community Ecology, we will look at how species interact with one another within an area.  The interactions that species have in ecosystems are: Competition, Predation, Herbivory, Mutualism, and Parasitism.  The overall idea is that “communities are bound together by a shared environment, and a network of influence each species has on the other” (2013, Nielson).

Competition occurs when one species out-competes another for resources.  Invasive species have been known to outcompete many native species. (2013, Nielson). 

Predation occurs when one species benefits from the loss of another species, usually one is eaten or consumed, such as when a bird captures and consumes a caterpillar (2013, Nielson). 

Herbivory occurs when an animal consumes part of a plant, such as when a caterpillar consumes a leaf.

Mutualism occurs when both organisms receive beneficial resources from each other.  The relationship between bees and flowering plants is mutualism; bees pollinate many plants, allowing the plants to produce seeds. (2013, Nielson). 

Parasitism occurs when one organism, such as a parasitoid wasp, benefits at the expense of another, in this case a caterpillar. Parasitoid wasps lay their eggs on insect larvae. The wasp larvae burrow into the body of the host, eventually killing them. It can  be considred a slow motion form of predation (Carroll and Salt, 2004).

 Herbivores: Although plants defend themselves against being eaten, herbivores have strategies to help them overcome these defenses. Caterpillars, the larval stage of moths and butterflies, probably consume the most plant material of all insects. A caterpillar may sever the canal on a plant that would deliver toxins and then feed on the tissue. An herbivore may feed at a time early in spring when the plant is less well protected; winter moths that feed on early spring oak leaves can gain considerable weight. Some caterpillars might incorporate the plant chemical defenses to protect itself. Herbivores may avoid being eaten by burrowing inside the plant or trimming a leaf so as to conceal it had been eaten. Some insectivores actively look for signs of leaf damage to find their prey.

Predators: Predation occurs when one organism consumes another. In the garden, it typically means one animal capturing and eating insects. In spring, when birds are nesting, 96% of all terrestrial birds in North America rear their young in part or entirely on insects (Dickinson 1999). A study of eastern bluebird nestlings in northwest Tennessee by Dr. David Pitts determined the foods fed to baby bluebirds by parents consisted of 22.4% grasshoppers, 14.7% crickets, 16.3% spiders, 25% caterpillars, 2.4% moths, and 19.2% less frequently fed or unidentified items. Bluebird parents feed babies for about three weeks after they leave the nest.Rose-breasted Grosbeaks, Scarlet Tanagers, many kinds of warblers, and other "canopy" birds feed on caterpillars that eat the leaves of trees. As soon as the tiny insects hatch, they begin feeding on the tiny soft leaves first opening up. Swallows, swifts, nighthawks, flycatchers, some warblers, and Cedar Waxwings snap up insects flying in the air. Flycatchers, warblers, and waxwings flutter out from a branch when they spot a succulent insect. Blackbirds, bluebirds, sparrows, crows, wrens, and other birds feed on big caterpillars, beetles, grubs, and other medium and large insects and spiders they find near the ground. Chickadees, nuthatches, creepers, woodpeckers, and the Black-and-white Warbler find insect eggs, larvae, or pupae in the crevices of tree bark. Woodpeckers can hear bugs chewing within the wood, and dig them out! Some birds are generalist predators, such as Yellow-rumped warblers, and can eat a wide variety of insects.



Butterfly and Caterpillar plants.doc400.5 KB