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How fast do populations grow? • Populations of organisms, do not experience linear growth. Rather, the graph of a growing population starts out slowly, then begins to resemble a J-shaped curve. 1 Population Ecology Human Population Growth The study of human population size, density, distribution, movement, and birth and death rates is demography. 2 Population Dynamics • Under normal conditions, with limiting factors, populations show an S-shaped curve as they approach the carrying capacity of the environment where they live. 4 Trends in Human Population Growth Population trends can be altered by events such as disease and war. Human population growth is not the same in all countries. 6 Age Structure A population’s age structure is the number of males and females in each of three age groups: pre-reproductive stage, reproductive stage, and post- reproductive stage. 7 Zero Population Growth (ZPG) occurs when the birthrate equals the death rate. The age structure eventually should be more balanced with numbers at prereproductive, reproductive, and postreproductive ages being approximately equal. 8 9 Carrying capacity • The number of organisms of one species that an environment can support indefinitely is its carrying capacity. Click image to view movie. • When a population overshoots the carrying capacity, then limiting factors may come into effect. 10 Section 4.1 Summary – pages 91-99 Carrying capacity • Deaths begin to exceed births and the population falls below carrying capacity. Critical miminum number- the number below which the species is destined for extinction. Carrying capacity It is different for each organism. A variety of population growth patterns, also called its life-history pattern are possible in nature. 11 Rapid life-history patterns • Rapid life-history patterns are common among organisms from changeable or unpredictable environments. • Rapid life-history organisms have • a small body size • mature rapidly • reproduce early • have a short life span. 12 Slow life-history patterns • Slow life-history organisms • live in more stable environments • reproduce and mature slowly, and are longlived. • They maintain population sizes at or near carrying capacity. 13 Density factors and population growth • How organisms are dispersed can be important. • Three patterns of dispersal are random, clumped, and uniform. Random Clumped Uniform 14 Density factors and population growth • Density-dependent factors include disease, competition, predators, parasites, and food Density-independent factors can affect all populations, regardless of their density. • Most density-independent factors are abiotic factors, such as temperature, storms, and major habitat disruption. 15 Predation affects population size Number of organisms(in thousands) Lynx and Hare Pelts Sold to the Hudson’s Bay Company Hare Lynx Times (in years) •Competition •is a density-dependent factor. •When a population increases and the demand for resources exceeds the supply, the population size decreases. 16 Doubling time • Doubling time is the time needed for a population to double in size. • 70 divided by % growth = doubling time • a 3.5% growth rate represents a doubling time of 20 years. 17 Age structure Population Distribution Per Age Range for Several Countries Stable growth Rapid growth Male Slow growth Reproductive years Age Female Population (percent of total for each country) 18 Where is biodiversity found? • Tropical regions contain two-thirds of all land species on Earth. • The more energy (sunlight) generally, the more organisms live there. 19 Biodiversity brings stability • the loss may have consequences for other living things in the area. • Biodiversity can bring stability to an ecosystem. • A pest could easily destroy all the corn in a farmer’s field, but it would be far more difficult for a single type of insect or disease to destroy all individuals of a plant species in a rain forest. 20 Section 5.1 Summary – pages 111-120 Biodiversity- Importance to people • Humans depend on other organisms for • Food • medicine. • Agriculture (source of genetic material) • aesthetic Section 5.1 Summary – pages21 111-120 Loss of Biodiversity • Extinction is the disappearance of a species when the last of its members dies. • Extinction is a natural process and Earth has experienced several mass extinctions during its history. 22 Section 5.1 Summary – pages 111-120 Loss of Biodiversity • A species is endangered species when extinction is possible. • threatened species-is likely to become endangered 23 Habitat loss • One of the biggest reasons for decline in biodiversity is habitat loss. 24 Habitat fragmentation • . 25 Habitat fragmentation Habitat fragmentation is the Habitat fragmentation has been separation of found to contribute to: wilderness • increased extinction of local species areas from other • changes in overall biodiversity wilderness • new opportunities for invasions by areas unwanted or exotic species. • increased risk of fire • disruption of ecological processes. 26 Habitat fragmentation • The smaller the fragment, the less biodiversity the area can support. • Geographic isolation can lead to genetic isolation (causes inbreeding). • makes it difficult for species to reestablish themselves in an area. 27 Edge and size • The edge of a habitat or ecosystem is where one habitat or ecosystem meets another. • The different conditions along the boundaries of an ecosystem are called edge effects. • Different organisms might live along the edge of a forest instead of in the interior of the forest. 28 Habitat • the damage to a habitat degradation by pollution • Pollutants -including volcanic eruptions and forest fires. • Acid precipitation—rain 29 Exotic species • People sometimes introduce a new species into an ecosystem, either intentionally or unintentionally. • These species can cause problems for the native species. Kudzu •Graph compares the number of native vs. alien species in FL. 30 Conservation biology is the study and implementation of methods to protect biodiversity. • Preserving habitats •Establishing parks and other protected regions has been an effective way to preserve ecosystems and the communities of species that live in them. Saguaro National Park, Arizona 31 Legal protections of species The US Endangered Species Act (ESA) is Federal legislation that aims to conserve the ecosystems upon which endangered and threatened species depend. The ESA was signed into law by President Nixon in December, 1973. The ESA protects plant and animal species and is jointly administered by the US Fish & Wildlife Service and NOAA Fisheries. Its aim is twofold: to provide protection for species that are in danger of extinction and to conserve the habitats on which those species depend. Organisms placed on the list are provided critical resources and their habitats are protected. Any activity that endangers them, even on private land is prohibited. • This law made it illegal to harm any species (catch, dig up, move, kill, or use parts of the organism) on the endangered or threatened species lists. 32 Habitat corridors • Research shows that separate wildlife populations may be resulting in inbreeding •Habitat corridors are protected strips of land that allow the migration of organisms from one wilderness area to another 33 • Reintroduction programs • release organisms into where they once lived. • The most successful are when organisms are taken in the wild and transported to a suitable habitat • Animals kept in captivity may lose the necessary behaviors to survive and reproduce in the wild. 34 Captivity • Some species no longer exist in the wild, but a small number of individual organisms is maintained by humans. Protecting plant species seeds can be cooled and stored for long periods of time in a seed banks Reintroduction is possible if needed in the future 35