EcologyEcology

An Introduction and Population Growth

An Introduction and Population Growth

EcologyEcology

• Ecology – is the science that deals with the interrelationships among living things and their environment.

• The science deals with words like ecosystem, community and population

• Ecology – is the science that deals with the interrelationships among living things and their environment.

• The science deals with words like ecosystem, community and population

EcologyEcology

• Let’s recall the definitions of these words.– Ecosystem – a complex, interrelated network of

living organisms and their nonliving surroundings.

– Community – interacting populations.– Population – consists of all the members of a

particular species.– Individual – is the single organism.

• Let’s recall the definitions of these words.– Ecosystem – a complex, interrelated network of

living organisms and their nonliving surroundings.

– Community – interacting populations.– Population – consists of all the members of a

particular species.– Individual – is the single organism.

EcologyEcology

• When studying ecology we are studying the environment, but it is important to specify what parts of the environment.– Abiotic – non-living

component

– Biotic – living component

• When studying ecology we are studying the environment, but it is important to specify what parts of the environment.– Abiotic – non-living

component

– Biotic – living component

PopulationsPopulations

• Studies have shown that many populations remain stable over time but there are examples of growth and decline.

• The factors that control this are:– Births, deaths, and

migration

• Studies have shown that many populations remain stable over time but there are examples of growth and decline.

• The factors that control this are:– Births, deaths, and

migration

PopulationsPopulations

• Organisms can join a population through:– Immigration (migration in)– Birth

• Oganisms can leave a population through:– Emigration (migration out)– Death

• Organisms can join a population through:– Immigration (migration in)– Birth

• Oganisms can leave a population through:– Emigration (migration out)– Death

PopulationsPopulations

• Thus simply a populations change can be difined as:– Population Change = (births-deaths) +

(immigrants-emigrants)

• Because generally migration plays a minor roll in population size whe can discuss the factors determining ultimate size of the population without them

• Thus simply a populations change can be difined as:– Population Change = (births-deaths) +

(immigrants-emigrants)

• Because generally migration plays a minor roll in population size whe can discuss the factors determining ultimate size of the population without them

PopulationsPopulations

• This final size is the result of a balance between two major opposing factors– Biotic Potential – or the maximum rate at which

the population could increase, assuming ideal conditions allowing a maximum birth rate and minimum death rate.

– Environmental Resistence – all living and non living environmental factors working against providing these ideal conditions

• This final size is the result of a balance between two major opposing factors– Biotic Potential – or the maximum rate at which

the population could increase, assuming ideal conditions allowing a maximum birth rate and minimum death rate.

– Environmental Resistence – all living and non living environmental factors working against providing these ideal conditions

PopulationsPopulations

• Population size is a function of birth rate, death rate, and the number of individuals in the original poplulation.– Growth Rate = Birth Rate – Death Rate

• Births per 1000

• Deaths per 1000

• Growth Rate

• Eg.

• Population size is a function of birth rate, death rate, and the number of individuals in the original poplulation.– Growth Rate = Birth Rate – Death Rate

• Births per 1000

• Deaths per 1000

• Growth Rate

• Eg.

PopulationsPopulations

• Population growth can then be defined as– r or growth rate * N or

number of original ind.

• If growth rate is constant this equation become exponential.

• Population growth can then be defined as– r or growth rate * N or

number of original ind.

• If growth rate is constant this equation become exponential.

PopulationsPopulations

• Exponential Growth – the populations grows (during a given time period) by a fixed percentage of its size at the beginning of that time period.

• Eg. Arithmatic v. Exponential

• J - curve

• Exponential Growth – the populations grows (during a given time period) by a fixed percentage of its size at the beginning of that time period.

• Eg. Arithmatic v. Exponential

• J - curve

Human Population GrowthHuman Population Growth

PopulationsPopulations

• Some of the factors affecting the biotic potential of a particular species are (+,-) Eg.

1. The age at which the average individual first reproduces

2. The average frequency with which reproduction occurs

3. The average number of offspring produced each time

4. The reproductive life span of the average organism

5. The average death rate under ideal conditions

• Some of the factors affecting the biotic potential of a particular species are (+,-) Eg.

1. The age at which the average individual first reproduces

2. The average frequency with which reproduction occurs

3. The average number of offspring produced each time

4. The reproductive life span of the average organism

5. The average death rate under ideal conditions

PopulationsPopulations

• Exponential growth can often lead to boom and bust cycles.– What could cause these boom and bust cycles?

– Exotic Species?

• Exponential growth can often lead to boom and bust cycles.– What could cause these boom and bust cycles?

– Exotic Species?

PopulationsPopulations

• Exponential growth carries with it the seeds of its own destruction.– Increase competition– Predators– Parasites and disease– Stress

• S-curves – around equilibriums

• Exponential growth carries with it the seeds of its own destruction.– Increase competition– Predators– Parasites and disease– Stress

• S-curves – around equilibriums

PopulationsPopulations

• Populations ussually stabalize at or below their carrying capacity.

• Carrying capacity – is the maximum size of a given population of organisms that a particular area can support indefinitely.

• Populations ussually stabalize at or below their carrying capacity.

• Carrying capacity – is the maximum size of a given population of organisms that a particular area can support indefinitely.

PopulationsPopulations

• The carrying capacity is controlled mainly by two types of resources:

1. Renewable resources, such as nutrients, water, and light, that are replenished by natural processes

2. Nonrenewable resources – such as suitable nesting or denning areas

• The carrying capacity is controlled mainly by two types of resources:

1. Renewable resources, such as nutrients, water, and light, that are replenished by natural processes

2. Nonrenewable resources – such as suitable nesting or denning areas

PopulationsPopulations

• Organisms will die if demads on renewable resources such as food, water,a dn light are too high

• Organisms will die if demads on renewable resources such as food, water,a dn light are too high

PopulationsPopulations

• In nature, environmental resistance maintains populations at or below the carrying capacity of the environment. This is done through two factors

1. Density-independent – factors limiting population size regardless of the density

2. Density-dependent – factors increasingly effective as the population density increases

• In nature, environmental resistance maintains populations at or below the carrying capacity of the environment. This is done through two factors

1. Density-independent – factors limiting population size regardless of the density

2. Density-dependent – factors increasingly effective as the population density increases

PopulationsPopulations

• Density Independent Factors– Natural Events (hurricanes, droughts, floods

and fire)– Weather (seasonal reproduction limit)

• Not reaching carrying capacity• Boom and bust cycles

– Human Activities• Pesticides and pollutants• Habitat destruction

• Density Independent Factors– Natural Events (hurricanes, droughts, floods

and fire)– Weather (seasonal reproduction limit)

• Not reaching carrying capacity• Boom and bust cycles

– Human Activities• Pesticides and pollutants• Habitat destruction

PopulationsPopulations

• Density Dependent Factors which affect long lived species the most– Predation– Competition with in the species or with

members of other species– Parasitism

• Density Dependent Factors which affect long lived species the most– Predation– Competition with in the species or with

members of other species– Parasitism

Density Dependent FactorsDensity Dependent Factors

• Predators and Parasites– Both of these processes involve one organism

feeding on another and harming it in the process (not necessarily in the case of parasitism)

– Predator – Prey– Parasite – Host

• Predators and Parasites– Both of these processes involve one organism

feeding on another and harming it in the process (not necessarily in the case of parasitism)

– Predator – Prey– Parasite – Host

Density Dependent FactorsDensity Dependent Factors

• Increase Prey?• Increase Predator?• Population Cycles?

• Increase Prey?• Increase Predator?• Population Cycles?

Density Dependent FactorsDensity Dependent Factors

• Parasites slow work?• Limitted mobility?• Population density?• Effect predation also?

• Parasites slow work?• Limitted mobility?• Population density?• Effect predation also?

Competition for ResourcesCompetition for Resources

• Competition – the interaction among individuals who attempt to utilize a limited resource, limits population size in a density-dependent manner

• Competition – the interaction among individuals who attempt to utilize a limited resource, limits population size in a density-dependent manner

Competition for ResourcesCompetition for Resources

• Interspecific competition?• Intraspecific competition?• Scramble competition? (seed dispersal)• Contest competition? (social and chemical

interations, territory)

• Interspecific competition?• Intraspecific competition?• Scramble competition? (seed dispersal)• Contest competition? (social and chemical

interations, territory)

Distribution of PopulationsDistribution of Populations

• Clumped• Uniform• Random

• Clumped• Uniform• Random