Unit 8: Ecology

Interacting with the Environment Behaviour

• Endotherms are animals that generate their own body heat through metabolism. Ectotherms lack an internal mechanism to control body temperature.
• Instinct is an inborn, unlearned behavior.
• Another form of behavior is learning. Learning refers to a change in a behavior brought about by an experience
• If the mother is absent, the offspring will accept the first moving object they see as their mother. This process is known as imprinting.
• While there are different types of imprinting, including parent, sexual, and song imprinting, they all occur during a critical period—a window of time when the animal is sensitive to certain aspects of the environment.
• Habituation is another form of learning. It occurs when an animal learns not to respond to a stimulus.
• Roosters do have internal alarm clocks. Plants have them as well. These internal clocks, or cycles, are known as circadian rhythms.

How Animals Communicate

• Pheromones, are chemical signals between members of the same species that stimulate olfactory receptors and ultimately affect behavior.
• Agonistic behavior is aggressive behavior that occurs as a result of competition for food or other resources.
• Dominance hierarchies (pecking orders) occur when members in a group have established which members are the most dominant.
• Territoriality is a common behavior when food and nesting sites are in short supply.
• Altruistic behavior is defined as unselfish behavior that benefits another organism in the group at the individual’s expense because it advances the genes of the group.

Many organisms that coexist exhibit some type of symbiotic relationship

The basic types of symbiotic relationships:

1. Mutualism—in which both organisms win (for example, the lichen components)
2. Commensalism—in which one organism lives off another with no harm to the host organism (for example, the remora)
3. Parasitism—in which the organism actually harms its host

Plant Behavior

• Plants flower in response to changes in the amount of daylight and darkness they receive. This is called photoperiodism
• A tropism is a turning in response to a stimulus.
• There are three basic tropisms in plants.

1. Phototropism refers to the way plants respond to sunlight—for example, bending toward light.
2. Gravitropism refers to the way plants respond to gravity. Stems exhibit negative gravitropism (they grow up, away from the pull of gravity), whereas roots exhibit positive gravitropism (they grow downward into the earth).
3. Thigmotropism refers to the way plants respond to touch. For example, ivy grows around a post or trellis.

Ecology

• The study of interactions between living things and their environments is known as ecology.
• Biosphere: The entire part of the Earth where living things exist.
• Ecosystem: The interaction of living and nonliving things
• Community: A group of populations interacting in the same area Population: A group of individuals that belong to the same species and that are interbreeding

There are two types of primary productivity:

1. The gross productivity from photosynthesis cannot be measured because cell respiration is occurring at the same time.
2. Net productivity measures organic materials that are left over after photosynthetic organisms have taken care of their own cellular energy needs.

• Producers make their own food.
• Primary consumers (herbivores) eat producers.
• Secondary consumers (carnivores and omnivores) eat producers and primary consumers.
• Tertiary consumers eat all of the above. Decomposers break things down.
• Sometimes one organism is particularly important to an ecosystem. Species like this are called keystone species.
• In a food chain, only about 10 percent of energy is transferred from one level to the next—this is the 10% rule.
• The energy flow, biomass, and numbers of members within an ecosystem can be represented in an ecological pyramid.
• Toxins in an ecosystem are concentrated and more dangerous for animals further up the pyramid.

Simpson’s Diversity Index

Diversity Index = 1 − Σ(n/)^2

n = the total number of organisms of a particular species N = the total number of organisms of all species

Population Ecology

Population growth can be represented as the number of births minus the number of deaths divided by the size of the population.

r = (births – deaths)/N (r is the reproductive rate, and N is the population size.)

• Carrying capacity—the maximum number of individuals of a species that a habitat can support.
• The factors that limit a population are either density-independent or density-dependent.
• Exponential growth occurs when a population is in an ideal environment.
• Exponential growth occurs very quickly, resulting in a J-shaped curve.

Ecological Succession

• Ecological succession refers to the predictable procession of plant communities over a relatively short period of time (decades or centuries).
• The process of ecological succession in which no previous organisms have existed is called primary succession.
• Lichens are considered pioneer organisms.

Human Impact on the Environment

Human impact on the planet includes the following issues:

• greenhouse effect
• ozone depletion
• acid rain
• desertification
• deforestation
• pollution
• reduction in biodiversity
• introduction and spread of disease