What is Ecology? Ecology is the branch of biology that studies the relationships between organisms, their habitats, and all the living and nonliving factors involved in those habitats. Some of the topics that ecologists seek to understand and study are... Adaptations and physiological responses The cycles and movement of energy and matter Ecological succession and population dynamics The biosphere, biomes and communities
What is the Biosphere? The biosphere is the portion of the Earth that includes life. Since life is found almost everywhere on the surface of Earth, you might say the entire surface of the earth is the biosphere. More specifically, the biosphere is made up of living factors, which we call biotic factors, and nonliving factors which we call abiotic factors.
Levels of Organization in Ecology Starting with a simple organism and working our way up to the biosphere, we can see increasing levels of organization in ecology. A group of similar organisms make up a population. All of the populations of organisms in the same habitat make up a biological community. A biological community, plus the abiotic factors involved in that community make up an ecosystem.
Levels of Organization in Ecology A group of ecosystems that are found in the same climate or region make up a biome. All the biomes of the world make up the biosphere.
Ecosystem Interactions In a biological community, every organism has a specific area where it lives. This area varies in size and shape depending on the organism and it is called its habitat. For an insect a habitat may be a tree. For a lynx, wolf, bear, or wolverine a habitat may be several hundred square miles. Each organism plays a specific role in its habitat. This role is called its niche.
Community Interactions Organisms living in the same biological communities interact in different ways. When more than one organism uses a resource in a biological community, competition occurs. Competition can occur for food, shelter, water, nutrients, space, sunlight, soil, habitat etc. Another interaction that occurs in a biological community is predation. A close relationship that exists when two or more species live together is called symbiosis.
Predator-Prey Relationships The relationship between predators and prey have been studied in great detail on moose and wolves on Isle Royale National Park. Populations of lynx and hare have also been studied in detail. Isle Royale is on an island so it is a closed system. So it is an ideal location to study the link between large predators and their prey. Hare populations fluctuate in 10 year cycles. Lynx populations follow the hares.
Symbiotic Relationships There are three different types of symbiotic relationships Mutualism is when two or more organisms live closely together and they each benefit from each other in the relationship. Commensalism is when two or more organisms live closely together and one organism benefits from the other but the other organism is neither helped nor harmed.
Symbiotic Relationships Parasitism is when one organism benefits at the expense of another organism. Parasites can be either endoparasitic, like roundworms, tapeworms, flukes, and bacteria, or they can be ectoparasitic like fleas and ticks. Another type of parasitism is called brood parasitism. An example of this is the brown-headed cowbird which lays its eggs in other birds' nests. The birds then hatch and often push the other birds out of the nest.
Mutualism One of the best examples of mutualism is insect pollination in plants. The plant benefits by cross-pollination of its flowers. The insect benefits by obtaining food from pollen.
Commensalism A remoras fish attached to a shark would be an example of commensalism. The remoras receives a free ride and free meal from the scraps that the shark doesn't eat. The remoras neither help nor harm the shark.
Parasitism Head lice, mosquitos, and dog heartworms are all examples of parasites
Flow of Energy in an Ecosystem Ecologists also study the flow of energy in ecosystems. Organisms that collect energy from either the sun or inorganic substances like hydrogen sulfide are called autotrophs. Organisms that get their energy from eating other organisms are called heterotrophs. Heterotrophs that eat plants are called herbivores. Heterotrophs that eat other heterotrophs are called carnivores.
Flow of Energy in an Ecosystem Organisms that eat both plants and animals are called omnivores. Organisms that eat dead or decaying organic matter are called detritivores.
Models of Energy Flow Ecologists use models to show the flow of energy through an ecosystem. Food chains are simple models that show the flow of energy through an ecosystem. Food webs are models that show the many interconnected food chains and metabolic pathways in which energy flows through a community. More realistic model. Each step or change in a level of a food chain or food web is called a trophic level.
Ecological Pyramids Another model ecologists use to show the relative amount of energy and biomass at each trophic level is called an ecological pyramid. Biomass is the total mass of living matter. It has been estimated that for every increase in a trophic level on an ecological pyramid, there is an estimated 90% decrease in energy. Biomass at each trophic level decreases as well. The relative number of species found at each trophic level decreases as well.
Cycles in the Biosphere If mass, energy, and matter flowed in only one direction, eventually all the available mass, energy, and matter would be used up. Fortunately, mass, energy, and matter travel through cycles that make them available again to living organisms that depend on them. Essential nutrients that are crucial to all living organisms must be recycled as well. These cycles that living organisms depend on are called biogeochemical cycles.