What Is a Population? All the members of a species living in the same place at the same time –a reproductive group –Refers to the group in general and also to the size of the population

Properties of Populations Size Density Dispersion

Properties of Populations Size –can be measured by Mark & recapture Sampling

Properties of Populations Density –Number of individuals in a given area –People in Luzerne County: 320,918 people / 907 sq. mi. Population density: people per sq. mi. –Whitetail deer in Pennsylvania: 1.6 million whitetail / 46,055 sq. mi. Population density: 34.7 deer per sq. mi.

Properties of Populations Dispersion –The relative distribution or arrangement of its individuals within a given amount of space –Even, clumped, or random

How Does a Population Grow? Growth rate –A change in the size of a population over a given period of time –Growth rate = birth rate minus death rate –Can be positive, negative, or zero To be zero, the average number of births must equal the average number of deaths

How Fast Can a Population Grow? Reproductive potential –Maximum number of offspring that each member of the population can produce –Limits the biotic potential (fastest rate at which the population of a species can grow) –Increases when individuals produce more offspring at one time, reproduce more often, and reproduce earlier in life

How Fast Can a Population Grow? Exponential Growth –Growth in which numbers increase by a certain factor in each successive time period –Occurs in nature only when populations have plenty of food and space, and have little or no competition or predators

What Limits Population Growth? Carrying Capacity –The maximum population that the ecosystem can support indefinitely

What Limits Population Growth? Resource Limits –A species reaches its carrying capacity when it consumes a particular natural resource at the same rate at which the ecosystem produces the resource ( LIMITING RESOURCE )

What Limits Population Growth? Competition Within a Population –Members of a population will compete with each other as the population approaches its carrying capacity –Members may compete indirectly for social dominance or for a territory

Two Types of Population Regulation Population size can be limited in ways that may or may not depend on the density of a population –Density dependent: deaths occur more quickly in a crowded population than in a sparse population Predation, disease, limited resources –Density independent: a certain proportion of a population dies regardless of the population’s density Severe weather, natural disasters

What jobs are there in your community? Select a job. Answer the following questions concerning that job: –What they do for the community –How they provide the service –What resources are used by them in providing the service –Where they live and work –The times during which they work –What other professions they are dependent upon for the functioning of their profession –What special adaptations (skills, tools, behaviors) they use or they are required to have –What other professions they compete with, if any

How Species Interact with Each Other

The unique role of a species within an ecosystem –Includes: Its physical home The environmental factors necessary for the species’ survival All the species interaction with other organisms

Habitat: location Niche: an organism’s pattern of use of its habitat (its job in an ecosystem)

Now... Imagine a forest habitat. Think of all the members of this natural community. Choose one. Think about the niche it fills using the same questions used for human jobs.

–What they do for the community –How they provide the service –What resources are used by them in providing the service –Where they live and work –The times during which they work –What other professions they are dependent upon for the functioning of their profession –What special adaptations (skills, tools, behaviors) they use or they are required to have –What other professions they compete with, if any

Your Assignment: Create a “Help Wanted” ad –Develop an ad for “recruiting” individuals into given ecological niches, using special contributions, advantages, etc., as points to highlight.

Types of Species Interaction Based on whether each species causes benefit or harm to the other species Symbiosis CommensalismMutualismParasitism PredationCompetition

Relationship in which different individuals or populations attempt to use the same limited resource Each has less access to the resource, and so is harmed Can occur both within and between species –Same species: both are occupying the same niche –Different species: niches overlap Use some of the same resources

Competition Indirect competition –Using the same resource without coming into direct contact –One insect species feeds on a certain plant during the day and another insect species feeds on the same plant at night. Adaptations to competition –Niche restriction: when each species uses less of the niche than it is capable of using

Predation Interaction between 2 organisms in which one organism, the predator, kills and feeds on the other organism, the prey Examples: –Snakes eating mice –Bats eating insects –Whales consuming krill

Symbiosis Relationship that exists when two species of organisms live in close physical contact with each other At least one of the organisms directly benefits from the association

Parasitism Relationship between 2 species in which one species, the parasite, benefits from the other species, the host, which is harmed Examples: ticks, fleas, tapeworms, mistletoe Unlike predators, parasites usually don’t kill their host

Mutualism Close relationship between 2 species in which each provides a benefit to the other Example: –Bacteria in your intestine

Commensalism Relationship in which one species benefits and the other species is neither harmed nor helped Examples: –Certain orchids and trees –Birds nesting in trees