Chapter # 11 – Population Regulation (pg. 223 – 237)

Chapter #11 – Population Regulation(pg. 223 – 237)


11.1 – The Environment Functions to Limit Population Growth.

The Logistic Model of Population Growth

dNdt

= r N( k – N )k

(1 – )dNdt

= r N Nkor

Population DynamicsLogistic Growth

• Environmental Resistance can reduce the reproductive rate and average life span and increase the death rate of young.

• As Environmental Resistance increases, population growth slows and eventually stops, likely near (k).

Carrying CapacityFinite Resources?

Source: Bolen and Robinson (1999) Wildlife Ecology and Management

Carrying Capacity (k): The abundance (size) of a species’ population that a habitat can support for a specified period of time (an upper limit).

Environmental

Resistance ? Finite Resources ?

Source: Bolen and Robinson (1999) Wildlife Ecology and Management

Environmental Resistance: The limitinginfluences ofenvironmental factorson the numbers ofindividuals in acommunity.

11.2 – Population Regulation Involves Density-Dependence.

As population density increases, individuals compete for space, energy, and nutrients.

At carrying capacity, each individual's share of resources is just enough to allow it to replace itself in the next generation.

At carrying capacity the birth rate (b) = death rate (d).

Carrying capacity (k) is determined by the continuous availability of resources.


• Environmental Resistance (ER) can be classified into two broad categories:

– Density-independent factors

– Density-dependent factors

Environmental Resistance (ER)

A factor that causes higher mortality or reduced birth rates as a population becomes more dense is referred to as a density-dependent factor.

Environmental Resistance (ER)

•Density-dependent factors become more effective as population density increases.

• Exert negative feedback effect on population size.

Density-Dependence

Density-Dependence (DD)

Population Density

Per CapitaBirth Rate

High

LowHighLow

“A factor that causeshigher mortality orreduced birth rates as a population becomes more dense” (Bolen & Robinson)

-disease, food supply, -predation, and -territorial behavior

Density-Dependence

• Predation- involves a predator killing a prey organism to consume.

• Predators exert density-dependent controls on a population.– Increased prey availability can

increase birth rates and/ordecrease death rates of predators.•Prey population losses will increase.

Population DynamicsPopulation Cycles

Population RegulationPopulation Cycles

Prey Switching and Availability - Interactions

11.3 – Competition Results when Resources Are Limited.

Describes the interaction among individuals who attempt to utilize a resource that is limited relative to the demand for it.

Competition intensifies as populations grow and near carrying

capacity.

For two organisms to compete, they must share the same resource(s).


Competition may be divided into two groups based on the species identity of the

competitors:

– Interspecific competition is between individuals of different species.

– Intraspecific competition is between individuals of the same species.

Competition for Resources

11.3 – Competition Results when Resources Are Limited.

Competition may also be divided into two types based on the nature of the interaction:

– Scramble (exploitative) competition is a free-for-all scramble as individuals try to beat others to a limited pool of resources.

– Contest (interference) competition involves social or chemical interactions that limit a competitor’s access to resources.


Competition may also be divided into two types based on the nature of the interaction:

– Scramble (exploitative) competition is a free-for-all scramble as individuals try to beat others to a limited pool of resources (direct or indirect – respond to depressed resource levels).

– Contest (interference) competition involves social or chemical interactions that limit a competitor’s access to resources (direct interaction).


•Density-independent factors limit populations regardless of their density–Examples: climate, weather, floods, fires, pesticide use, pollutants, and overhunting.

Density-Independence

No associationwith populationdensity – they acton a populationindependent ofdensity

- e.g., weather (floods, hurricanes)fires, earthquakes, volcanoes

Density-Independence (DI)

Density-Independence

Population Density

Per CapitaBirth Rate

11.4 – Intraspecific Competition Affects Growth and Development.

As populations density increases toward a level of insufficiency (per unit for basal metabolism), individuals can reduce food intake.

Reduced food intake slows individual growth.

Reduce growth can lead to reduced reproductive output and success.

Thus, there is an inverse relationship between density and rate of body growth.


11.4 – Intraspecific Competition Affects Growth and Development.


11.5 – Intraspecific Competition Can Reduce Reproduction.


11.6 – High Density Is Stressful to Individuals.


As population density increases, space becomes restricted. Aggressive behavior (competition for space) becomes more frequent.

Increased crowding and social contact can cause stress, triggering hormonal changes that restrict reproduction and growth.

Increased stress may also lead to immune system suppression and increased frequency of disease.

Thus, there may be reduced births and increased deaths.

Chapter #11 – Population Regulation

The Chitty Hypothesis

11.6,7 – The Chitty hypothesis depends upon having two types of individuals in the population. One is tolerant of having other individuals close by (ie, tolerant of high densities) and has a low reproductive rate. The second type is intolerant and tends to disperse from the population under conditions of high density. They also have a higher reproductive rate than the tolerant individuals.

Increasing phase Population size increases.

Peak phase Competition between animals increases (for food, mates, shelter...)

Tolerant individuals stay but they have a low reproductive rate compared to dispersers.

Intolerant individuals (dispersers) leave and colonize neighboring (often marginal) areas.

Declining phase Population size starts to decrease because of emigration of dispersers and low reproductive rate of tolerant individuals that remain.

Low density phase Animals space themselves out

Competition between animals decreases

Increasing phase Dispersers remaining in the population (or born into the population) increase in relative frequency because of their higher reproductive rate

Population size increases (back to step #1)

Home Range: an area in which an animal normally lives and is not necessarily associated with any type of aggressive behavior. Dominance hierarchy may exist among individuals with overlapping home ranges.

Territory: a defended, more or less fixed and exclusive area maintained by an individual or social unit occupying it.


11.8,9 – Social Behavior May Function to Limit Populations. Territoriality Can Function to Regulate Growth.


11.8,9 – Social Behavior May Function to Limit Populations. Territoriality Can Function to Regulate Growth (limit access).


11.10 – Plants Preempt Space and Resources – Are They “Territorial”?

Preventing root invasion can be a form of competition.

Big Sagebrush(Artemisa tridentata)


11.11 – Density-Independent Factors Can Influence Population Growth.


11.11 – Density-Independent Factors Can Influence Population Growth.

• The abundance of a population at any given time is the result of complex interactions between density-independent and density-dependent forms ofenvironmental resistance.

Ultimately . . . .

Next Time . . . .

Interspecific Competition

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Chapter # 11 – Population Regulation (pg. 223 – 237)