Ecology

Ecology is the study of the relationship between organisms and their environment. The term was first used by Ernest Hackel in 1866. Ecology includes the study of:

• populations of the same species of organism living in the same area st the same time,
• communities of a number of species living together,
• ecosystems composed of organisms plus various abiotic factors, and
• the biosphere, all living organisms on Earth and their habitats.

A. G. Tansley was the first to recognize that plants and animals are components of a system that also includes the physical factors that affect the system as well as the various cycles, energy exchanges, etc. that take place in the system. Thus he was the first to use “ecosystem.” Ecosystems are often named for the most numerous species (for example, beech-maple) but also the areas so named also include other plants and animals. An Indicator Species is not necessarily the most numerous, but it does indicate existing conditions. For example, blueberry and/or broom sedge are indicative of acid soil, hydrangea of land slides, and thistle of overgrazing.

Environmental conditions can put selective pressure on organisms = natural selection, such that only the best fit organisms survive. These factors include water/humidity, temperature, food/nutrients, light, etc. If there is too much or not enough of a particular factor, the organism(s) cannot survive in that area.

Many of these factors occur in a cyclical pattern. For example, in the water cycle, rain lands on the ground, some of it goes into a river or lake, and from there it evaporates again, creating more water vapor in the air. Alternately, some of the water may end up in an underground aquifer and be pumped up through a well. Eventually, some of the water may be absorbed by a plant or ingested by an animal, then released when the organism dies.

rain ocean, lake, river, and ground H2O plants herbivores carnivores evaporation from all of the above rain The amount of rainfall varies with the overall local climate, season, etc., and this, in turn, causes variations in the amount of water in the soil, therefore available to the local plants and animals. The organisms, then, must be able to adjust to these variations in available water.

There are also temperature cycles, both daily and seasonal. In response to daily light-dark cycles, many organisms exhibit activity cycles of about 24 hours, thus are said to exhibit circadian rhythm. There are three kinds of circadian rhythm:

Diurnal organisms are active during the daytime.	Crepuscular organisms are active at dawn and/or dusk.	Nocturnal organisms are active during the nighttime.

Annual changes in day length due to the Earth’s revolution around the Sun, trigger a number of events in the lives of organisms, including things like bird migration, hibernation, time of flowering in many plants.

Various nutrients, minerals, and gases like CO₂, N₂, Fe⁺⁺ and even pesticides, also go through cycles. Inorganic material are often converted to organic compounds by bacteria or plants, thus such organisms are called producers. These organisms are eaten by primary consumers, or herbivores. The herbivores, in turn, are eaten by secondary (or tertiary, etc.) consumers, or carnivores. If any of these organisms dies, there is another group of organisms, the decomposers, which feed on dead or decaying organic matter. A sub-group of the decomposers are the saprophytes, mushrooms, etc, that are decomposers and were formerly considered to be “plants.” Eventually, the nutrients are released into the air or soil once again. The major elements needed by living organisms can be remembered by: C HOPKINS CaFe, Mighty good, which stands for: carbon, hydrogen, oxygen, phosphorus, potassium, iodine, nitrogen, sulfur, calcium, iron, and magnesium. Since many of these are obtained from soil, the amount in an organism’s diet can vary with the soil type.

Organisms can be found in and make up a number of types of habitats. Fresh water habitats include streams, lakes, and wetland areas including marshes (grassy wetlands), swamps (woody wetlands), and bogs. Marine areas include costal waters, open water, the bottom mud, and estuary areas (area around the mouth of a river where fresh and salt water mix in various concentrations). Terrestrial habitats include several types of forest, including both temperate and tropical forests as well as jungle, which is second growth after a rainforest has been cut, grasslands, tundra, and desert.

Pond	Ocean	Grassland	Forest

Within a given community, the make-up of that community is not static. New species arrive and are able to grow in conditions provided by present species, yet these new species further alter the environment, perhaps such that some species can no longer live there. Thus, other species eventually die off, and the community make-up changes. This is called succession. For example, a bare farm field that is left alone will first be covered by a variety of hardy weeds and grasses. These will provide enough cover that shrubs such as honeysuckle or, bramble begin to grow there. Typically, this provides enough shade and humidity that the first trees, perhaps cottonwood, are able to start growing, and this further alters the environment such that conifers like eastern redcedar can live there. Within around 50 to 100 years later, a variety of other trees such as ashes, cherry, and sassafras are growing there, but there are probably still a lot of shrubs underneath the trees. Slowly, the composition of the woods may change such that oaks and hickories are the most numerous species of trees present. Eventually, these will be replaced by beeches and sugar maples, which will attain great size and age. Typically, beeches and maples are “replaced” by more beeches and maples, thus this is said to be the climax community. Also, the tree canopy os so dense that little light can reach the forest floor, thus there are few shrubs, and the area is very open under the trees.

Bare Soil	Colonizing	Old Field	Forest

Within a community, the organisms interact with other members of the same species and with members of other species. An organism’s niche is the organism’s role and “address” and job/activities and relationships (how it fits in) within the community. Intraspecific interactions are those in which members of the same species are interacting with each other and include communication (visual, vocal, chemical/pheromone), care and protection of young (some species do, some don’t), as well as courtship and sexual competition. A special case of intraspecific relationships is social and colonial species of animals, which have dominance hierarchies which are maintained through interactions among the colony members. Interspecific interactions are relationships among organisms (animals) of different species. Some types of interspecific relationships include:

	Predation, in which a larger animal eats a smaller one. Lions eat antelope, and wolves eat deer. Spiders, like this orbweaver, capture and eat insects.
Parasitism, in which a smaller animal feeds on a larger one, often living inside it and usually weakening or killing it. Often the host is not killed outright. Because a parasite lives in/on the body of its host and needs the host to remain alive, it is usually advantageous for the parasite to not kill its host. Humans and domestic animals are occasionally infected with or bothered by tapeworms, roundworms, mosquitoes and/or leeches. A parasitoid is a parasite that eventually causes the death of its host. By the time the parasitoid undergoes metamorphosis, all of the host’s innards have been eaten. Often, insect larvae that are parasitoids of other insects eat the host’s tissues, timing things such that just as they're ready to pupate, they have eaten up the whole insides of their host, and it dies. Braconid wasps do this to tomato hornworms, and this hornworm, covered with cocoons of pupating braconids, probably has almost no body parts left inside. If you see a caterpillar like this on your tomato plants, leave it alone. The wasps will eventually hatch, mate, and lay eggs in any other tomato hornworms they can find — a good means of biological control.
	Commensalism, a relationship that is beneficial to one organism and neutral for the other. Cattle egrets follow cattle to feed on the insects stirred up by the grazing cattle.
Mutualism, a relationship between two species where both benefit. The yucca moth both pollinates and feeds on the yucca plant; acacia ants live in the thorns of, defend, and are fed by the acacia tree in which they live; and trees can’t get along without mycorrhizae living in/on their roots and absorbing food for them. Many plants and their pollinators have evolved mutualistic relationships. Butterflyweed provides food for and is pollinated by butterflies like pipevine swallowtails.

All these are types of symbiosis, a term describing any kind of relationship between two different species living and interacting together. This is a general term which includes predation, parasitism, commensalism, mutualism, etc. Often, however, symbiosis is used to mean mutualism.

		To prevent or escape attack by another organism, various organisms have developed defense mechanisms, such as camouflage, mimicry, warning coloration, and/or attack to protect themselves from other organisms of the same or a different species. The bodies of Monarch butterflies contain chemicals (from the milkweed they ate as caterpillars) that make them taste bad, and they use warning coloration to advertise this to any would-be predators.
		On the other hand, coevolution is the evolution of two species totally dependent on each other. This is an extreme case of mutualism. Examples of coevolution include things like lichens (in which the fungus and alga cannot survive without each other), acacia ants (which protect their host acacia tree and receive food and shelter from it), yucca moths (which are the only pollinators of yucca plants, while yucca seeds are the only food for their caterpillars), and a variety of cases of specific pollinators for specific plants.