UNIT 3:POPOULATION

ECOLOGY(Campbell & Reece, 2010. Chapter:53)

POPOULATION ECOLOGY

Population ecology is the study of populations in relation to environment, including environmental influences on density and distribution, age structure, and population size.

1. TERMINOLOGY A population is a group of individuals

of the same species living in the same area at the same time.

Density is the number of individuals per unit area or volume.

Dispersion is the pattern of spacing among individuals within the boundaries of the population.

TERMINOLOGYDensity is the result of an interplay between processes that add individuals to a population and those that remove individuals. Immigration is the influx of new

individuals from other areas Emigration is the movement of

individuals out of a population

POPULATION SIZE IS PRIMARILY INFLUENCED BY:

TERMINOLOGY Demography is the study of the vital

statistics of a population and how they change over time. Death rates and birth rates are of particular interest to demographers.

2. PATTERNS OF DISPERSIONEnvironmental and social factors influence spacing of individuals in a population:1. In a clumped dispersion, individuals aggregate in patches. A clumped dispersion may be influenced by resource availability and behaviour.2. A uniform dispersion is one in which individuals are evenly distributed. It may be influenced by social interactions such as territoriality3. In a random dispersion, the position of each individual is independent of other individuals.

It occurs in the absence of strong attractions or repulsions.

PATTERNS OF DISPERSION

3.Patterns of Population Growth in an Ecosystem

• Many factors affect population growth, but one factor is a species' intrinsic growth rate.

• The birth rate minus the death rate with no environmental restrictions defines a species intrinsic growth rate.

• Within an ecosystem, however, resource limits and predation also effect population growth.

There are two main patterns of population growth:

• Exponential growth/J-pattern: only one reproductive chance is given to members of the population during their entire lifespan. Once mission accomplished, they die. Many insects and annual plants reproduce in this manner.

• Logistic growth/S-pattern: members experience many reproductive events throughout their lifetime. Most vertebrates, and trees have this pattern of reproduction.

• Exponential growth/J-pattern

Lag phase: Growth is slow because population base is small.Exponential growth phase: Growth is accelerating, that is, the rate of growth itself grows.

• Exponential growth/J-pattern

Exponential growth cannot be sustained for long in any population

• Logistic growth/S-pattern:

• Logistic growth/S-pattern:

Lag phase: Growth is slow because the population base is small, organisms adapt. Exponential growth phase: Growth is accelerating, that is, many offspring born at a fast rate.Deceleration phase: The rate of population growth slows down – individuals start to die. Stable equilibrium phase: Little growth because births and deaths are about equal. Area has reached its carrying capacity.

• Logistic growth/S-pattern of Daphnia

Carrying capacity:

Carrying capacity (K) is the maximum population size the environment can support

In the logistic population growth model, the rate of increase declines as carrying capacity is reached.

4. Survival patterns/curvesSurvivorship curves can be classified into three general types:

• Type I: low death rates during early and middle life, then an increase among older age groups

• Type II: the death rate is constant over the organism’s life span

• Type III: high death rates for the young, then a slower death rate for survivors.

Survival patterns/curves

5. Factors that influence and regulate population growth

There are two general questions about regulation of population growth:• What environmental factors stop a

population from growing indefinitely?• Why do some populations show radical

fluctuations in size over time, while others remain stable?

Factors that influence and regulate population growth : density

• In density-independent populations, birth rate and death rate do not change with population density.

• In density-dependent populations, birth rates fall and death rates rise with population density.

Density-dependent populations

• The population growth in density-dependent populations are affected by many factors, such as :

competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors

INTRASPECIFIC COMPETITION FOR RESOURCES

• In crowded populations, increasing population density intensifies competition for resources and results in a lower birth rate.

• Resources like: water, shelter, food, space, access to mates, ecological niches.

TERRITORIALITY• In many vertebrates and some invertebrates,

competition for territory may limit density• Cheetahs are highly territorial, using

chemical communication to warn other cheetahs of their boundaries.

DISEASES• Population density can influence the health

and survival of organisms• In dense populations, pathogens can spread

more rapidly.

PREDATION• As a prey population builds up, predators

may feed preferentially on that species.• This will decrease the prey population size –

and later decrease the predator population size. – Predator-prey relationship (Graph)

TOXIC WASTE

• Accumulation of toxic wastes can contribute to density-dependent regulation of population size.

INTRINSIC/PHYSIOLOGICAL FACTORS

• For some populations, intrinsic (physiological) factors appear to regulate population size.

6. How to determine the size of a population

In most cases, it is impractical or impossible to count all individuals in a population.

Sampling techniques can be used to estimate densities and total population sizes

Method to determine population size can be estimated by:

Sensus taking – counting each individual

Mark-recapture method Quadrant method (will be done as an

assignment)

MARK-RECAPTURE METHOD (PETERSON METHOD)

One way to estimate the size of a population is to capture and mark individuals from the population, release them, and then resample to see what fraction of individuals carry marks.

Useful when sampling closed populations --those populations that do not change in size at all or very much during the study period

due to births, deaths, immigration, or emigration.

MARK-RECAPTURE METHOD (PETERSON METHOD)

N = estimated population size M = the number of individuals marked in the first

sample C = total number of individuals captured in 2nd

sample R = number of individuals in 2nd sample that are

marked

N = CM R

ASSUMPTIONS OF THE MARK-RECAPTURE METHOD (PETERSON

METHOD) The population is "closed", so N is constant. All animals have the same chance of getting

caught in the first sample. Marking individuals does not affect their mobility

and chance to be caught again. Animals do not lose marks between the two

sampling periods. All marks are reported on discovery in the

second sample.

7. HUMAN POPULATION The human population is no longer growing

exponentially but is still increasing rapidly. No population can grow indefinitely, and humans

are no exception. The human population increased relatively

slowly until about 1650 and then began to grow exponentially.

HUMAN POPULATION Though the global population is still growing, the

rate of growth began to slow during the 1960s

REGIONAL PATTERNS OF POPULATION CHANGE

• To maintain population stability, a regional human population can exist in one of two configurations:

• Zero population growth = High birth rate – High death rate

• Zero population growth =Low birth rate – Low death rate

• The demographic transition is the move from the first state toward the second state

REGIONAL PATTERNS OF POPULATION CHANGE

• The demographic transition is associated with an increase in the quality of health care and improved access to education, especially for women

• Most of the current global population growth is concentrated in developing countries.

SWEDEN – DEVELOPED COUNTRY MEXICO – DEVELOPING COUNTRY

POPULATION GROWTH IN SOUTH AFRICA

PROJECTIONS OF S.A.POPULATION SIZE

POPULATION GROWTH IN SOUTH AFRICA

• The Population; total in South Africa was last reported at 49991300 in 2010.

• The Population; total in South Africa was 49320150 in 2009.

• The Population; total in South Africa was reported at 48793022 in 2008.

AGE AND GENDER STRUCTURES

• One important demographic factor in present and future growth trends is a country’s age and GENDER structure

• Age structure is the relative number of individuals at each age.

• Age structure diagrams can predict a population’s growth trends

• They can illuminate social conditions and help us plan for the future.

AGE AND GENDER STRUCTURES

AGE DISTRIBUTION IN S. AFRICA

GENDER DISTRIBUTION IN S.A.

How many humans can the biosphere support?

What is the earth’s carrying capacity?

Our carrying capacity could potentially be limited by food,

space, non-renewable resources, or build-up of wastes

8. SOCIAL ORGANISATION

An organism that is highly interactive with other members of its species is said to be a social animal.

All mammals (and birds) are social to the extent that mothers and offspring bond.

A few species, notably insects (ants, bees wasps and termites) show an extreme form of sociality, involving highly organized societies, with individual organisms specialized for distinct roles.

This form of social behaviour is referred to as eusociality.

Vertebrate societies may exhibit one of more of these behaviours:

cooperative rearing of young by the group overlapping generations living in a

permanent, as opposed to seasonal, group cooperative foraging or hunting cooperative defence from predators and

competitors social learning (such as a young chimpanzee

learning by observation to use a twig to fish for termites)

SOCIAL ORGANISATION

SOCIAL ORGANISATION

SOCIAL ORGANISATION

Many herbivores (e.g. zebra) are always in herds, to outnumber the predators.

Wolves, hyena's and wild dogs – hunt in packs – guarantee a kill.

Bee’s and ants divide their daily tasks to get everything done.

SOCIAL ORGANISATION

9. COMMUNITY STRUCTURES

A biological community is an assemblage of populations of various species living close enough for potential interaction, in a specific area, at a specific time.

Community includes the producers (plants), consumers (herbivore, carnivores, omnivores) and decomposers.

COMMUNITY STRUCTURES

Ecologists call relationships between species in a community interspecific interactions

Examples are competition, predation, herbivory, and symbiosis (parasitism, mutualism, and commensalism)

Interspecific interactions can affect the survival and reproduction of each species, and the effects can be summarized as positive (+), negative (–), or no effect (0).

COMPETITION Interspecific competition (–/– interaction)

occurs when different species compete for a resource in short supply (e.g. water, food, shelter, space, light)

Strong competition can lead to competitive exclusion, local elimination of a competing species.

The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place.

COMPETITION The total of a species’ use of biotic and

abiotic resources is called the species’ ecological niche

An ecological niche can also be thought of as an organism’s ecological role

Ecologically similar species can coexist in a community if there are one or more significant differences in their niches.

Resource partitioning is differentiation of ecological niches, enabling similar species to coexist in a community

Resource partitioning example:Seven species of Anolis lizzards live close to each other, all feed on the same insects, but competition for food is reduced because they prefer different perches (niches)

PREDATION Predation (+/– interaction) refers to interaction

where one species, the predator, kills and eats the other, the prey

Some feeding adaptations of predators are claws, teeth, fangs, stingers, and poison.

Prey display various defensive adaptations. Behavioral defenses include hiding, fleeing,

forming herds or schools, self-defense, and alarm calls.

Animals also have morphological and physiological defence adaptations

Cryptic coloration, or camouflage, makes prey difficult to spot

PREDATION

HERBIVORY• Herbivory (+/– interaction) refers to an

interaction in which an herbivore eats parts of a plant or alga.

• It has led to evolution of plant mechanical and chemical defences and adaptations by herbivores.

SYMBIOSIS

• Symbiosis is a relationship where two or more species live in direct and intimate contact with one another.

• 3 TYPES: PARASITISM MUTUALISM COMMENSIALISM

PARASITISM

• In parasitism (+/– interaction), one organism, the parasite, derives nourishment (benefits), from another organism, its host, which is harmed in the process.

• Parasites that live within the body of their host are called endoparasites; parasites that live on the external surface of a host are ectoparasites

PARASITISM

MUTUALISM

• Mutualistic symbiosis, or mutualism (+/+ interaction), is an interspecific interaction that benefits both species.

• A mutualism can be: Obligate, where one species

cannot survive without the other. Facultative, where both species

can survive alone.

MUTUALISMAnemones provide the Clown Fish with protection from predators whilst Clown fish defend the Anemones from Butterfly fish who like to eat Anemones.

The flower is pollinated and the butterfly gets nectar. – both benefit

COMMENSALISM

• In commensalism (+/0 interaction), one species benefits and the other is apparently unaffected

Cattle egrets/tick birds benefits (insects) and water buffalo (not affected)

10. ECOLOGICAL SUCCESSION

• Ecological succession is the sequence of community and ecosystem changes after a disturbance.

• Primary succession occurs where no soil exists when succession begins.

• Secondary succession begins in an area where soil remains after a disturbance.

• Example of ecological succession of a glacial retreat at Glacier Bay, Alaska.

ECOLOGICAL SUCCESSION• The first inhabitants of a disturbed area are called

the pioneer community.• As more organisms inhabit the area – it reaches a

climax community – no more new comers can be accommodated.

PRIMARY SUCCESSION

SECONDARY SUCCESSION