© 2011 Pearson Education, Inc.

Population Ecology

&

The Conservation of Biodiversity

AP Environmental Science

Mr. GrantLesson 25

© 2011 Pearson Education, Inc.

Objectives:

• Define the terms survivorship curve, and biodiversity.

• Outline the characteristics of populations that help predict population growth.

• Assess logistic growth, carrying capacity, limiting factors, and other fundamental concepts in population ecology.

• Identify efforts and challenges involved in the conservation of biodiversity.

© 2011 Pearson Education, Inc.

Survivorship Curve: A graph that shows how the likelihood of death for members of a population varies with age.

Biodiversity: The variety of life across all levels of biological organization, including the diversity of species, their genes, their populations, and their communities.

Define the terms survivorship curve, and biodiversity.

© 2011 Pearson Education, Inc.

Outline the characteristics of populations that help predict population growth.

• Populations are characterized by population size, population density, population distribution, sex ratio, and age structure.

• Birth and death rates, as well as immigration and emigration, determine how a population will grow or decline.

© 2011 Pearson Education, Inc.

Population characteristics

• All populations show characteristics that help scientists predict their future dynamics

• Population size = the number of individual organisms present at a given time- Numbers can increase,

decrease, cycle or remain the same

© 2011 Pearson Education, Inc.

Population characteristics

• Population density = the number of individuals in a population per unit area

• Large organisms usually have low densities- They need many resources and a large area to survive

• High densities make it easier to find mates- But increase competition and vulnerability to predation- Increased transmission of diseases

• Low densities make it harder to find mates- But individuals enjoy plentiful resources and space

© 2011 Pearson Education, Inc.

Population characteristics

• Population distribution (dispersion) = spatial arrangement of organisms

• Random = haphazardly located individuals, with no pattern

• Uniform = individuals are evenly spaced - Territoriality, competition

• Clumped = arranged according to availability of resources- Most common in nature

© 2011 Pearson Education, Inc.

• Sex ratio = proportion of males to females- In monogamous species, a 1:1 sex ratio maximizes

population growth• Age distribution (structure) = the relative numbers

of organisms of each age in a population- Age structure diagrams (pyramids) = show the age

structure of populations• In species that continue growing as they age

- Older individuals reproduce more (i.e. a tree)- Experience makes older individuals better breeders

Population characteristics

© 2011 Pearson Education, Inc.

Birth and death rates

• Type I: more deaths at older ages

• Type II: equal number of deaths at all ages

• Type III: more deaths at young ages

Survivorship curves = the likelihood of death varies with age

© 2011 Pearson Education, Inc.

Four factors of population change

• Natality = births within the population • Mortality = deaths within the population• Immigration = arrival of individuals from outside the

population • Emigration = departure of individuals from the

population• Births and immigration add individuals

- Deaths and emigration remove individuals• Crude birth (death) rates: number of births (deaths) per

1000 individuals per year

© 2011 Pearson Education, Inc.

Assess logistic growth, carrying capacity, limiting factors, and other fundamental concepts of population ecology. • Populations unrestrained by limiting factors will undergo

exponential growth until they meet environmental resistance.

• Logistic growth describes the effects of density dependence; exponential growth slows as population size increases, and population size levels off at a carrying capacity.

• Carrying capacity is the maximum size a population can attain in a given environment.

• K-selection and r-selection describe theoretical extremes in how organisms can allocate growth and reproduction.

© 2011 Pearson Education, Inc.

Population growth rate

• Natural rate of population growth =(Crude birth rate) – (crude death rate)- Population change due to internal factors

• Population growth rate = (Crude birth rate + immigration rate) – (Crude death rate

+ emigration rate)- Net changes in a population’s size/1000/year

• Growth rate as a percent =- Population growth rate * 100%- Populations of different sizes can be compared

© 2011 Pearson Education, Inc.

Exponential population growth

• Exponential growth- A population increases by a

fixed percent- Graphed as a J-shaped

curve• Exponential growth cannot

be sustained indefinitely• It occurs in nature with a:

- Small population- Low competition- Ideal conditions

© 2011 Pearson Education, Inc.

Limiting factors restrain population growth

• Limiting factors = physical, chemical and biological attributes of the environment- They restrain population growth

• Environmental resistance = all limiting factors taken together- Stabilizes the population size- Space, food, water, mates, shelter, suitable breeding

sites, temperature, disease, predators- Aquatic systems: salinity, sunlight, temperature, etc.

© 2011 Pearson Education, Inc.

Carrying capacity

• Carrying capacity = the maximum population size of a species that its environment can sustain

• Limiting factors slow and stop exponential growth- An S-shaped logistic

growth curve

Many factors contribute to environmental resistance and influence a population’s growth rate and carrying capacity

© 2011 Pearson Education, Inc.

Population density impacts limiting factors

• Density-dependent factors = limiting factors whose influence is affected by population density- Increased density increases the risk of predation and

competition for mates- Results in the logistic growth curve- Larger populations have stronger environmental

resistance• Density-independent factors = limiting factors whose

influence is not affected by population density - Events such as floods, fires, and landslides

© 2011 Pearson Education, Inc.

Perfect logistic curves aren’t often found

© 2011 Pearson Education, Inc.

Carrying capacities can change

• Environments are complex and ever-changing- Changing carrying capacities

• Humans lower environmental resistance for themselves- Increasing our carrying capacity- Technologies overcome limiting factors

• By increasing carrying capacity for humans- We have reduced the carrying capacity for countless

other organisms- Calling into question our own long-term survival

© 2011 Pearson Education, Inc.

Reproductive strategies vary among species

• Biotic potential = an organism’s capacity to produce offspring

• K-selected species = species with long gestation periods and few offspring - Have a low biotic potential- Stabilize at or near carrying capacity- Good competitors

• r-selected species = species which reproduce quickly- Have a high biotic potential- Little parental care, populations fluctuate greatly

© 2011 Pearson Education, Inc.

Identify efforts and challenges involved in the conservation of biodiversity.

• Social and economic factors influence our impacts on natural systems in complex ways.

• Extensive efforts to protect and restore species and habitats will be needed to prevent further erosion of biodiversity.

© 2011 Pearson Education, Inc.

Population changes affect communities• As the population of one species declines, other species

may appear• Human development displaces other species and

threatens biodiversity• As Monteverde dried out, species disappeared

- Golden toads, harlequin frogs and more had been pushed from their cloud-forest habitat into extinction

- 20 of 50 frog species, 2 lizard species went extinct• Species from lower, drier habitats appeared

- 15 species tolerant of drier conditions had moved in

© 2011 Pearson Education, Inc.

Conserving biodiversity

• Human development, resource extraction and population pressure are speeding changes- In populations and communities

• Impacts threatening biodiversity have complex social, economic and political roots- We must understand these factors to solve problems

© 2011 Pearson Education, Inc.

Costa Rica and its environment

• Past economic and social forces still threaten Costa Rica’s species and ecological communities- Lush forests are seen as obstacles to agriculture and

for timber- The country’s population grew to 3.34 million- Pasture land increased from 12% to 33%- Forests decreased from 80% to 25%- Species were declining and becoming endangered

© 2011 Pearson Education, Inc.

Costa Rica’s species were in danger• Few people saw the need to conserve biological resources

- Until it became clear they were being rapidly lost

© 2011 Pearson Education, Inc.

Costa Rica is protecting its environment

• The privately managed 10,500 ha (26,000 acre) Monteverde Cloud Forest Reserve was founded in 1972- To protect the forest, its plants and animals

• Costa Rica created the country’s first national parks and protected areas in 1970- Centered on areas of spectacular scenery- Protecting valuable tropical dry forests, turtle nesting

beaches, coral reef systems• Government support remains strong

- Over 25% of its land is under some type of protection

© 2011 Pearson Education, Inc.

Costa Rico’s protection is paying off• Ecotourism: tourists visit protected areas

- Providing thousands of jobs and billions of dollars to local economies

• But parks are still under-protected and underfunded- Restoration is a step beyond preservation