Chapter 14Interactions in Ecosystems

Section 14.1

Habitat and Niche

HABITATS are specific environments in which organisms live. Each habitat has characteristic biotic and abiotic

factors.

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The NICHE of an organism is the unique living arrangement defined by its habitat, food sources, time of day it is most active, and other factors. It is the role that the organism plays in the environment.

( e.g. producer, consumer, decomposer etc.)

#2

Niche• A niche includes a species’ habitat, food

sources, patterns of sleeping and activity, and many other factors specific to its way of life.

The principle of COMPETITIVE EXCLUSION states that when two species are competing for the same resources , one species will be better suited to the niche, and the other species will be pushed into another niche or become extinct.

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ECOLOGICAL EQUIVALENTS are species that occupy similar niches, but live in different geological regions.

Mantella Frog

Poison Dart Frog

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Section 14.2

Community Interactions

COMPETITION is when two organisms fight for the same resources. For example, the various species in a community that all eat grasses often compete for the same food supply.

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A Predator is an organism that kills and eats another organism.

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Predator adaptations

Predator adaptations are those changes that arise in predator species in ways that enhance their ability to catch prey. Examples are speed, agility, strength, teeth, teamwork, and camouflage.

The PREY are the organisms that are eaten by the predator.

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Prey adaptationsPrey adaptations are those

changes that arise in prey species in ways that reduce their chances of being eaten. Examples include things like speed, agility, camouflage, teamwork, spines, shells, and mimicry.

Symbiotic relationships

Symbiosis is one in which there is a close interaction between species, often with one living on or in the other.

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Mutualism

Mutualism is a form of relationship in which two organisms living in symbiosis both benefit from the relationship.

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Commensalism

Commensalism is a form of symbiotic relationship in which one of the organisms is benefited and the other is neither hurt nor helped by the relationship. True commensalisms in nature is rare, as there is usually some degree of benefit or harm for both organisms from most interactions.

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Parasitism

Parasitism is a relationship in which one organism, termed the parasite, obtains food or nutrients from another organism, the host; the parasite is benefited from the relationship, while the host is harmed.

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Section 14-3

Population Density and Distribution

Population density

Population density is the number of individuals of a particular species per unit area or volume.

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Calculating population density

Population density = number of individuals / unit area

Population dispersion is the way in which individuals of a population are spread in an area or a volume.

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Clumped dispersion is where individuals may live close together in groups in order to facilitate mating, gain protection or access food resources

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Uniform dispersion occurs when organisms live at specific distances from each other. This may be due to intraspecies competition of limited resources.

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Random dispersion occurs when individuals randomly spread out within an area or volume

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A Survivorship curve is a diagram that shows the number surviving members of a population over time.

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Section 14-4

Population Growth Patterns

Migration is the movement of organisms from one area to another

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The movement of individuals IN to an area is called

IMMIGRATION.

The movement of

individuals OUT of an

area is emigration

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Exponential growth occurs in a population which increases by a constant factor over time.

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With Logistic growth a populations begins with a period of slow growth, followed by exponential growth before leveling off.

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When a population’s size has reached the number where it can grow no more because of limiting factors, it is said to have reached its carrying capacity.

Carrying capacity is the number of individual organisms in a population the environment can maintain, or “carry” with no net increase or decrease in numbers. Birth rate and death rate become equal, and population size does not change.

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A Population crash occurs when there is a dramatic decline in the size of the population. This could be caused by disease, predators, rapid climate changes or lack of food.

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• Factors that limit a population’s growth

are called limiting factors.– Food– Space– Light– Water– Nesting sites

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Factors Affecting Population Growth

• Density-dependent factors

• Density-independent factors

• Immigration

• emigration

Density-dependent factors are those elements that limit a population more as the population density increases. An example of a density-dependent factor is the availability of food; another is communicable (contagious) disease, which is usually spread more easily in higher-density populations.

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• Density-independent factors are those that limit population growth but are unrelated to population density. Examples include climate and weather events like blizzards, storms, and droughts, and others like floods, fire, earthquake, etc. Insect populations are often especially sensitive to density-independent factors like these.

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Section 14-5

Ecological Succession

Ecological succession

• is the biotic changes that regenerate a damaged area or a previously uninhabited area.

• After a major disturbance to an area, the community may be drastically changed. Many organisms may be completely wiped out. Some species may be the first to move into or colonize the area, as after a fire.

• These colonizers may then give way to yet other species as they move in, and these later species may also be finally replaced by yet others. This particular process of community change is called ecological succession.

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The first organism to live a previously uninhabited area is

called a Pioneer species

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Primary succession is the establishment and development of an ecosystem in a area previously uninhabited area..

• Autotrophic bacteria, followed by pioneer plants, are the first to appear.

• Soil begins to develop and become richer.

• Eventually, more and more species appear in a series of communities over time.

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Secondary succession• The change that follows

after a disturbance damages an area but leaves some species and soil intact is called secondary succession.

• An example is an area of forest cleared by logging or for farming; after the disruption, species of both plants and animals recolonize the area, with a tendency for the area generally to go back toward its previous state.

• An avalanche during the winter wiped out the forest in this strip of land.

• Secondary succession is now taking place here.

• Eventually forest will return.