Ecology

Ecology is the study of organisms in their environment. The list below outlines some important vocabulary terms for the study of ecology:

Biotic factors: living components of the environment
Abiotic factors: Nonliving part of environment
Habitat: where an organism lives (Includes biotic and abiotic factors)
Population: A group of the same organisms; a subset of a species
Community: all of the biotic factors of an environment
Ecosystem: All of the biotic and abiotic factors of an environment
Landscapes: Array of ecosystems

Visit the Chemistry of Life page for more information regarding chemical cycles within ecosystems.

Transfer of Energy in Ecosystems

Ecosystems can be mapped by the transfer of energy that occurs between organisms within them. An ecological pyramid shows the various levels of producers and consumers within the ecosystem. At the bottom of the ecological pyramid are primary producers. Primary producers use the sun to produce energy through photosynthesis. Primary consumers gain energy from the producers by consuming them. Then secondary consumers gain energy from the primary consumers, and so on with tertiary and higher level consumers. The predator at the top of the pyramid is known as the apex predator. Outside of the ecological pyramid, decomposers break down detritus and waste to recycle energy for use by primary producers.

Between each trophic level, or level within the ecological pyramid, 10% of energy is transferred from one level to the next. The 10% rule is based on the fact that with each transfer of energy, 90% of the energy is lost as waste or heat, and only 10% of the energy reaches the next level of consumers. For example, if the primary producers create 1,000 Kj of energy, the primary consumers will gain 100 Kj, the secondary consumers will gain 10 Kj, and the tertiary consumers will gain 1 Kj.

Regulation of body temperature requires a considerable amount of energy. Endotherms (warm-blooded) use energy generated by their metabolism to maintain homeostatic body temperatures. Humans and other mammals, for example, are endotherms. Ectotherms (cold blooded) are unable to maintain body temperature internally so they use behavioral characteristics like sitting in the sun or in the shade to maintain body temperature. Turtles, lizards, and many other reptiles, for example, are ectotherms.

Some organisms make energy, and others consume it. Organisms can be named based on their energy-formation characteristics. An organism that uses light for energy uses the prefix photo-, while an organism that uses molecules gains the prefix hetero-. An organism whose source of carbon is carbon dioxide gains the prefix auto-, and an organism whose source of carbon is glucose gains the prefix hetero-. Plants are photoautotrophs, while most animals are chemoheterotrophs. Plants or bacteria living near hydrothermal vents are chemoautotrophs. Photoheterotrophs are rare.

Size of Ecosystems

Ecosystems can be mapped with food chains and food webs. Food chains show the transfers of energy between producers and higher-level consumers. Food webs show an interconnected relationship between food chains that is more accurate to the integrated nature of an ecosystem. The arrows in a food chain or food web always point to the consumer/predator, showing the direction of the transfer of energy.

Growth of a population can be modeled by the equation growth = births-deaths. This assumes that immigration and emigration balance out as these factors also influence population growth. The rate of growth can be calculated with growth rate = (births-deaths)/total population size.

Many biotic and abiotic factors can limit the growth of a population. From predator-prey cycles to an increase in density which causes a lack of resources, populations cannot grow exponentially. This sort of limited growth uses the logistic growth model. K, the carrying capacity, is the maximum number of members of the species an environment can maintain. Though the carrying capacity can be temporarily exceeded, the population size will always reduce to be at or below the carrying capacity.

Disruptions of Ecosystems

Evolution can change the general layout of an ecosystem. Since mutations are random, it is impossible to predict the impact they can have on an environment.

Primary succession

When a natural disaster wipes out an ecosystem, a slow rebuilding process occurs. As new niches are available, adaptive radiation occurs and species take over the ecosystem. This generally begins with simple species such as lichen or other fast-growing plants, and over time taller and more long-term vegetation develops while animals move in as well.

Climate change

As humans change the environment, certain biomes are becoming smaller or nonexistent.

Invasive species

Invasive species are species that are purposely or accidentally released into an environment. Even if an ecosystem is crowded, the lack of a natural predator for the invasive species allows it to grow and outcompete natural species for resources.

Relationships in Ecosystems

Relationships within ecosystems range from one organism eating another to various forms of symbiosis. At its most basic level, competition occurs when two or more organisms compete for the same finite resources in an environment. Usually this takes the form of different species looking for the same food source, but competition can also occur within a species in examples such as looking for mates. In predation, one organism consumes another to gain energy. The prey is the organism that is eaten, while the predator is the organism that does the killing. Symbioses occur when two organisms live in close contact and directly influence each other’s lifestyle. There are three types of symbiosis: parasitism, mutualism, and commensalism. In parasitism, an organism relies on another organism for energy while causing that organism harm. For example, a tick is a parasite for humans because it can cause Lyme Disease. In mutualism, both of the organisms benefit. For example, clownfish clear sea anemones’ tentacles from parasites while the sea anemone provides the clownfish with a safe habitat. In commensalism, neither organism is helped or harmed. For example, the horseshoe crab flatworm lives inside the horseshoe crab’s gills but does not provide a positive or negative impact.

Mimicry is a common source of interactions between species. Batesian mimicry is when a species resembles another, more dangerous species. For example, the stripes on a non-venomous king snake resemble the stripes on a coral snake which can scare off predators. Mullerian mimicry occurs when two dangerous species adopt similar warning signals. For example, both bees and wasps have black and yellow stripes despite being distinct species.

Characteristics of Species

K Species and R species

K species, named for their stable populations near their carrying capacity (represented by K), are species that reproduce relatively few offspring with long gestation periods and slow maturation. These species, such as humans, have long life spans. Contrastingly, R species, named for their reproductive rate near maximum reproductive capacity (represented by r) have many offspring which can reproduce at a young age. These species have shorter life spans and many die before they can have offspring.

Keystone species

Within an ecosystem, a keystone species is a species that would cause the ecosystem to change significantly if it was removed. For example, the beaver builds dams in rivers that change the landscape to provide habitats for many other species. Without the beaver, the ecosystem would be very different.

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