Community Ecology Chapter 3

Review A community is a group of interacting populations that occupy the same place at the same time.

Reproductive strategies r – strategists Rate Small organisms Produce a lot of offspring Little parenting effort k – strategists Carrying capacity Large organisms Produce few offspring A lot of parenting effort

Limiting factors any abiotic factor or biotic factor that restricts the numbers, reproduction, or distribution of organisms temperature, nutrients, predators, fire etc. What are some limiting factors in this desert?

Range of tolerance The ability of any organism to survive when subjected to abiotic factors or biotic factors is called tolerance. Lower Limit Upper Limit Zone of physiological stress Greatest # of Species Zone of Intolerance

Species richness The number of species in the community Varies by latitude Closer to the equator = greater species richness

Disturbance Disturbances are events that change communities (the organisms or the resources available) Examples: fires, droughts, volcanic eruptions, storms

Long leaf pine forest

How does a community respond when there is a disturbance? The community experiences succession, a gradual, sequential regrowth of the species in the community.

Primary succession Occurs where life has never before existed or where life was completely wiped out. ex. On an island formed from a volcanic eruption or on bare rock NO TOPSOIL. Only biological organisms are bacteria, fungal spores, pollen strains, etc.

Primary succession

Secondary succession Occurs following the disruption of an existing community (ex. Fire, tornado, farming, etc.) Pioneer species (mainly plants) are the first species to start re-growing.

Secondary succession

Is there an endpoint to succession? A climax community is the stable mature community that results when there is little change in the composition of species cannot be predicted slow complex process that involves many factors. Ex. Weather patterns, different rates of growth of species, human activities

Succession Stages The first species to dominate is called the pioneer species Primary example: On bare rock, lichens (mutualistic relationship between fungi and algae) live and form soil. With soil available, plants can move in. With plants available, animals can move in

Succession Stages Grasses and weeds begin the process Perennial grasses and shrubs take over Softwood trees (pines) compete with shrubs for sunlight and nutrients, dominate Ends with deciduous forest community (hardwoods)

Quick Quiz Limiting Factor A ____________ restricts numbers and distributions of organisms. The range in which a organism ca survive is called ________________ _____________ are events that change communities. The first species to dominate during succession is the ________________ Range of tolerance Disturbances Pioneer species

Population Dynamics Chapter 4

Review A population is a group of organisms, all of the same species, that live in a specific area.

Population size Mark-recapture method Individuals are captured, marked, and released Researchers obtain another sample later and keep track of those already marked A formula is used to estimate the population size. Random Sampling Apply # of individuals in sample to whole area

Population Density It’s the # of individuals per unit area or volume. If pop. density is too high, it can have serious consequences for the population.

Population Density Comparison China Japan 1.3 billion people 9.6 million km2 Pop. density: 135 people/km2 126 million people 377,835 km2 Pop. Density: 325 people/km2

Dispersion Patterns Dispersion- the pattern of spacing of a population within an area due to many factors both biotic and abiotic. 1) Uniform Organisms keep their space

Dispersion patterns 2) Clumped Occurs where food or space is clumped or due to social nature of organisms 3) Random Most populations show some degree of uniformity or clumping

Population Growth Rate Birth rate – death rate = growth rate Immigration – Movement of individuals into a population Emigration – Movement out of a population When birthrate > death rate, the pop. When immigration > emigration, pop.

Exponential Growth Model (J Curve) Populations of organisms grow slowly at first and as the population grows and has more reproducing individuals, it grows faster. This is exponential growth. It is shown by a J-shaped curve.

Logistic Growth Model (S Curve) the pop. growth curve levels off and becomes an S-shaped curve. This is the Carrying Capacity

Can a population grow indefinitely? a population is limited by limiting factors, such as temperature, nutrients, predators, fire, etc. Populations with plenty of resources have more births than deaths, so they grow until the environment is “maxed out.” the population is at carrying capacity, it contains all the individuals that the environment can support.

Limiting Factors Density-dependent factors have an increasing effect as the population increases. Ex. Disease, predators, food supply, competition, crowding, parasites Density-independent factors can affect populations, regardless of their density. Ex. Volcanic eruptions, floods, pesticides

Human Population Terminology Demography is the study of human population size, distribution, birth/death rates Birthrate – the # of live births / 1000 individuals in a year Death rate - the # of deaths / 1000 individuals in a year

Human Population on Earth Pretty stable until recently… -In 1999 population was over 6 billion people -Current growth rate over 80 million per year -Expected population by 2050 is 9 billion

Percent Increase in Human Population Even though human population is The rate at which it grows has Due to diseases and voluntary population control

Decreasing growth rate Although the total human population is steadily increasing, the rate of increase itself is slowing (the peak was in the 1960s). The overall slowing is a result of several factors—increased use of birth control, better education of women in developing countries, and rising standards of living

Trends in Human Population Growth 1) Demographic Transitions The change in a population from high birth rate and death rates to low birth rates and death rates.

Trends in Human Population Growth 2) Zero Population Growth (ZPG)-occurs when births plus immigration equals deaths plus emigration. Immigration – Movement of individuals into a population Emigration – Movement out of a population Birth + immigration = Death + Emigration

Trends in Human Population Growth 3) Age Structure -the proportions of the population that are in different age levels. Wide base = rapidly growing (many young people) Fairly even Between ages = stable

Trends in Human Population Growth 4) Human Carrying Capacity All populations have a carrying capacity Family planning is a way to control our population Technology has enabled us to increase our carrying capacity, although disease and overcrowding is still a concern.