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Ecology of Individuals and Populations

Chapter 56

Ecology

• Ecology– “Study of how organisms relate to one

another and to their environments”– Organisms respond to the abiotic

environment where they live.

Populations and Environment

• The environment determines which organisms live in a particular climate.–Temperature–Water availability–Sunlight–Soil

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Environmental Challenge

• When environmental changes occur an individual’s response can be short or long term.

• Long term responses:– Physiological responses

• Physiology – “processes or functions in an organism or in any of its parts“

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Environmental Challenges

• Long term responses:– Morphological capabilities

• Morphology – “the form and structure of an organism considered as a whole”

• Behavioral responses

Bird Bone

Range• Population range – “area where a population occurs”• Populations aren’t static.

• Individuals move into/out of an area on purpose and by accident.

Ex. Climate change Cattle egrets, fire ants

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Environmental change Moving to better habitats

Spacing Patterns

• Spacing of individuals within a range can tell us about population structure and organism behavior.

• Populations exhibit different spacing patterns:– Random spacing– Uniform spacing– Clumped spacing

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Population Change over Time

• Survivorship– “Percent of an original population that

survives to a given age”• Survivorship curve

– Shows survival rate at different ages– Three survivorship types:

• I, II and III

Survivorship Curves

Life History

• Natural selection favors traits that maximize the number of surviving offspring left in the next generation by an individual organism– 2 factors affect this quantity

• There’s a trade-off between survivorship and reproduction.

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• Biotic potential – a species maximum growth rate – there are no limitations on the population

• Result of unchecked exponential growth is a population explosion

• All populations eventually reach some limit in their growth

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Environmental Limits to Population Growth

Population Growth Curve

• The formula below is used to calculate population sizes as they reach K (carrying capacity)

dN/dt = rN (K – N)/K

– dN/dt = rate of growth– r = rate of increase– N = number of individuals in the population– K = carrying capacity

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Environmental Limits to Population Growth

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Population Types

• There are two ‘types’ of populations based on their reproductive rates:– Opportunist or r – selected species– Competitor or K - selected species

Factors That Regulate Populations

• When resources are limited, the cost of reproduction is high. When resources are abundant, costs of reproduction are low.

• Resource availability affects life history adaptations – (whether a species will adapt to be an ‘r’ or a ‘K’ selected species).

Human Population Growth

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Factors That Negatively Regulate Populations

• Density-dependent– Factors that affect the population and

depend on population size• Density-independent

– Other factors, such as natural disasters, decrease populations size regardless of population density

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Factors That Regulate PopulationsAllee effect: “Growth rates increase with increase in population size”

Locust

Puffins

• Population Pyramid– Bar graph displaying the number of

individuals in each age category

– Can be used to determine the stability and future size of a population

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Population Pyramids

Population Pyramids