Learning Goal 1Populations

The Science of Ecology

Definition –

Levels of Organization in Nature –

Features of Populations

Population Characteristics –

Population Dispersion –

Survivorship Curves –

Life History Patterns

Consist Of –

Fecundity vs Parental Care –

Reproductive Episodes –

Early vs Late Reproduction –

R and K Selected Species –

Models of Population Growth

Growth Rate –

Exponential Models –

Logistic Models –

Population Regulation

Density Dependent Factors –

Density Independent Factors –

Human Population Growth

Increased Carrying Capacity –

Population Growth and Age Structure –

Demographic Transition Model -

Ecology

Learning Goal OneAnalyze aspects of populations in terms of

life history patterns, growth models, limiting factors, and human population

trends.

What’s Wrong with This Picture?

• DefinitionEcology is the study of interactions between organisms and their environment.The environment consists of both abiotic and biotic factors.Abiotic components consist of nonbiological factors such as temperature, water, soil chemistry.Biotic componenents consist of biological factors such as plants, microorganisms, and animals.

The Science of Ecology

Levels of Organization in Nature• Organisms Individuals within a population.• Populations

Made up of individuals of the same species.

• CommunityMade up of all populations in an area.

• EcosystemsIncludes the community as well as the physical environment.

• BiosphereRefers collectively to all ecosystems on earth.

Features of Populations

• Population Characteristics

Population size refers to the total number of individuals in any given population.

Density refers to the number of individuals per unit area of habitat.

Population Dispersion• Clumped

Individuals are grouped together.• Uniform

Organisms are evenly spaced in their habitat because they repel each other.

• RandomOrganisms are distributed unpredictably. Used when the other two dispersion patterns don’t apply.

Survivorship Curves

Depict changes in survival rate.Type I

High survivorship until late in life.Type II

Relatively constant rate of mortality at all ages.Type III

High juvenile mortality followed by low mortality once a certain age or size is reached.

Life History Patterns

• Consist of:GrowthIncrease in cell number from birth to maximum size for that species.MaturationUsually refers to the point where sexual maturity is reached.ReproductionOffspring is produced to ensure the survival of the species.

Fecundity vs Parental Care• Passive Parental Care

Energy is invested in offspring before birth. ie., egg yolks, endosperm in seeds, nutrients that cross placenta

• Active Parental CareContinued parental care after birth.

• Fecundity refers to the number of offspring produced during a female’s lifetime. Organisms that produce large numbers of offspring are generally passive parents whereas low numbers of offspring receive active care.

Reproductive Episodes

• One EpisodeAll energy is devoted to one reproductive event, like the salmon and most insects.

• Several EpisodesOther species devote only some of their energy budget to reproduction so spread it out over many episodes with the rest allocated to maintenance and growth.

Early vs Late Reproduction

• Early ReproductionFavored by natural selection if adult survival rates are low as in a prey species, or adults do not increase in size as they age (they’re small).

• Late Reproduction Favored by natural

selection if sexually mature individuals have a good chance of surviving to produce more offspring.

R and K Selected Species

R-Selected Species Function well in rapidly changing environments. Usually small and produce numerous offspring often in a single reproductive event. Little or no active parental care. Most die before reaching sexual maturity so success depends on producing so many that a few are likely to survive.

• K-selected SpeciesThrive in more stable environments.Larger with longer generation times.Produce offspring repeatedly throughout their life time.Offspring receive substantial parental care.Small number of offspring.

Models of Population Growth

• Growth Rate -

Change in population size =

number of births (B) – number of deaths (D)

Normally expressed in births (b) and deaths (d) per capita (individual) during a specified time period.

B/N = b and D/N = d (N = population size)

Growth rate r= b-d

Exponential Models

Occurs when populations are exhibiting unlimited growth.

Assumes unlimited resources and no build up of toxic waste products.

Population size increases by a constant ratio.

Graphs of exponential growth are known a J curves because of their characteristic shape.

Logistic Model

•Most populations exhibit a

logistic model of growth.•Growth increases rapidly

at first then slows down as

the population gets larger.•As resources run out fewer

offspring are produced

and a population reaches

its carrying capacity, the

maximum number of

individuals that an

environment can support.•Logistic models exhibit an

S-shapedS-shaped curve.

Population Regulation

• Density Dependent Factors

Factors that have more impact as population density increases.

Intraspecific Competition

• Competition between members of the same species.• Leads to decrease in reproduction, slower growth, and

smaller adult size.• May stimulate behavioral and developmental changes as

with locusts. Some will become migratory with longer wings and more body fat so they can fly great distances.

Other Examples of Density-Dependent Factors

• Interspecific Competition

• Competition between different populations.

• Disease

Microorganisms spread quickly in denser populations.

Density-Independent Factors

• Factors that reduce population size regardless of its density.• Climate, fires, earthquakes, storms are some examples.• Density-Independent factors do not cause a population to fluctuate

around its carrying capacity the way density dependent factors do. • They reduce, but do not regulate populations.

Cycles in Population Size

Intrinsic Control:As population grows, individuals undergo hormonal changes that may cause aggressive behavior, or reduced reproduction, or lead to migrating to other areas.

Extrinsic Control:Population cycles in response to food and/or predators.

Human Population Growth• Ways Humans Increased

carrying capacity:11,000 years ago humans shifted from hunter/gather cultures to agriculture. They cultivated plants and domesticated animals and significantly alter their environment by diverting water for irrigation and building settlements.Once the energy from fossil fuels was harnessed in the mid eighteenth century food supply increased further.

• Advances in Public Health:

Reduced malnutrition, contagious diseases, and improved sanitation all reduced death rates sharply.

Population Growth and Age Structure

• Zero Growth:Equal number of people in prereproductive and reproductive age groups.

• Slow Growth:Slightly more prereproductive than reproductive population

• Rapid Growth:Broad base of prereproductive population. One third of the world’s population.

• Negative Growth:

Fewer prereproductive individuals that any other age group.

Demographic Transition Model

• Preindustrial Stage-Birth and death rates are high and population grows slowly.

• Transitional Stage-Food production rises, health and sanitation improve leading to decreasing deaths.

• Industrial Stage –Birth rate declines as more people move to cities.• Postindustrial Stage – Birth rate equals or falls below death rate

leading to ZPG or declining population growth.

Options for Limiting Population Growth

• Family planning programs that limit human population growth.

• Wait until the environment does it for us.

LG 1 Terms

1. Abiotic/Biotic Components

2. Levels of Organization in Nature

3. Population Size vs Density

4. R – Selected Species

5. K – Selected Species

6. Exponential vs Logistic Growth Model

7. Carrying Capacity

8. Density Dependent Factors

9. Density Independent Factors

10. Demographic Transition Model