One goal of our study is to understand how plants are interacting with the insects and birds in the urban ecosystem.
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 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.
Herbivory occurs when an animal consumes part of a plant, such as when a caterpillar consumes a leaf. 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.
Mutualism occurs when both organisms receive beneficial resources from each other. Pollination of flowers by bees is a good example of mutualism, bees take pollen and nectar, and the pollen transferred allows the plants to produce seeds. Pollinators and flowering plants have co-evolved over time, so that today many flowers have characteristics that certain pollinators prefer. From a flower’s perspective, a pollinator that is effective at transferring pollen is better. A bee, on the other hand, seems adept at perceiving the color yellow, and a flower having bilateral symmetry.
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 considered a slow-motion form of predation (Carroll and Salt, 2004). Ichneumon wasps are parasitoids; females lay their eggs inside a “host”, often a caterpillar, and the caterpillar continues to eat and grow until almost full grown. By this time, the eggs of the wasp have developed into larvae, and the eventually kill the caterpillar host and emerge.
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.
Examples of Food webs involving birds and arthropods: 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.
Image:John Carrel