Population Ecology & The Conservation of Biodiversity

AP Environmental Science Mr. Grant Lesson 25 Population Ecology & The Conservation of Biodiversity

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.

Define the terms survivorship curve, and biodiversity. 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.

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.

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

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

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

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

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

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

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.

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

Exponential population growth Exponentialgrowth 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

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.

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

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

Perfect logistic curves aren’t often found

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

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

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.

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

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

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

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

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

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

Population Ecology & The Conservation of Biodiversity