Populations and Resources

Population Is a group of organisms of one species that lives in the same place, at the same time, and can successfully reproduce. Example: Elephants.

Dynamic characteristics of populations Size, number of individuals (N) Density (N/ area) Dispersion, Random, uniform, clumped, (appropriate scale)

Population Dispersion Patterns Random Uniform Clumped

Dynamic characteristics of populations Age distribution, proportions of young, middle-aged, old Differs in growing, stable, decreasing populations

Changes in populations Growth Decline May affect size, density, dispersion, age distribution. May be affected by size, density, dispersion, age distribution.

Changes in populations Growth Expansion of species’ populations may lead to evolution of new species Decline Shrinking species’ populations may lead to extinction Small populations Narrowly specialized species 02 June Populations.ppt

Changes in populations ΔN = +B +I –D –E +B = births (birth rate) +I = immigrants (immigration rate) – D = deaths (death rate) – E = emigrants (emigration rate) (For many [most] natural populations I and E are minimal.)

Exponential Growth Accelerating growth that produces a J-like curve when the population is graphed. Only occurs for short periods in nature Usually when the organism has a lot of resources.

Limiting Factors Exponential growth cannot be sustained in nature because no ecosystem has an unlimited supply of resources. These restrictions are called limiting factors. Abiotic limiting factors: temperature, pH, oxygen, light, hiding places Biotic limiting factors: food, etc.

Factors which can limit the growth of a population include: Predation Shortage of food*Competition Lack of water Lack of space Mating Opportunities Disease Disaster Contamination of the environment

Carrying Capacity Is the size of a population that can be supported indefinitely by the resources and services of an ecosystem. When a population is maintained at its carrying capacity, it is at an equilibrium or balance. There is an equal amount of organisms being born or moving into the ecosystem as there are dying or leaving.

Carrying Capacity “The largest number of individuals in a species that an environment can support.” 4 factors that determine carrying capacity: 1.Materials/energy 2.Food Chains 3.Competition 4.Density

Materials and Energy All populations are limited by the availability of resources: Energy (from the sun) Water Oxygen Carbon Nitrogen Other nutrients

Food Chains The Pyramids of Biomass, Energy, and Numbers demonstrate how the population of a given organism is limited by: its position in a food chain/web the population size of those populations above and below it Relationships: Producer – consumer - decomposer Predator - prey

Competition Ecosystems have limited resources. Organisms with similar needs must compete to get the resources they need. Supply versus Demand Competition occurs between: Members of the same species = Intraspecific Competition Members of different species = Interspecific Competition

Density An organisms’ need for space depends on their size, environment, and way of life. Different species have different needs for space. This need for space determines how many individuals of a given species can live in the same area at the same time. Factors affecting population size may be: 1.Density-Dependent Factors 2.Density-Independent Factors

Density Dependent Factors If population density increases, it can cause a decrease in the population. Overcrowding leads to: Increased stress = spread of disease and parasites Increased aggression = neglect of offspring Reduced access to resources, mates and habitat Increased death rate/decreased birth rate =decrease in population

Density Independent Factors Events that can decrease population size that are not related to how many individuals are in the population to begin with: Forest fire Flood Volcano Extreme weather (ex. Hurricane) Pollution

Graphing Carrying Capacity

Humans and Carrying Capacity Humans alter natural ecosystems often, causing a change to carrying capacities. Urban sprawl is the growth of relatively low- density development on the edges of urban areas. Human population in the Golden Horseshoe is expected to increase by 3.7 million between 2005 and How do we make room for all these people without affecting other ecosystems?

Easter Island Discovered by Polynesians ~ A.D Population grew to several thousand Used trees for canoes to hunt dolphins Used wood for cooking Also ate birds, eggs, vegetables Resources (trees) depleted No canoes, no dolphins Warfare over land, food resources Population fell to ~ 100 when discovered by Dutch, Easter Sunday 1722.

Ecological Niche As species go about their daily activities, they interact with other species. An ecological niche is the way an organism occupies a position in an ecosystem, including abiotic and biotic factors.

Example: brown bat Biotic niche: insects that it eats, its competitors like the nighthawk, and its predators. Abiotic niche: place for roosting and hibernation, the time of night it hunts, airspace it flies in, the temperature range it can live at.

Population Regulation Predators: organism that kills and consumes other organisms Prey: is eaten as food by a predator Bottom-Up Population regulation: a shortage of plant resource at the base of the food chain causes declines in the animals in the higher trophic levels. Top-Down Population regulation: more rabbits in a population, lead to more coyotes to eat them, then more coyotes lead to fewer rabbits.

Competition Competition occurs when 2 or more organisms compete for the same resource. Can limit size of population Can influence the ecological niche of an organism

Symbiosis Mutualism: 2 species benefit from the relationship Example: algae lives in coral. The algae gives the coral energy and the coral gives the algae protection and carbon dioxide. Commensalism: 1 species benefits while the other is unaffected. Parasitism: when an organism benefits at the expense of a different organism.