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Transcript
AP Biology Everything You Need to Know About Ecology Essential knowledge 4.A.5: Communities are composed of populations of organisms that interact in complex ways. Topic: Population Dynamics and Ecosystem Components Ecosystem Hierarchy A biosphere is made of ecosystems (Earth). An ecosystem is made up of various communities of living (biotic) and nonliving items (abiotic). A community is made of many populations. A population is made of individuals from a species. The two forest communities above have the same species richness (four species), but the relative abundance of the four species is different between the two communities. Communities with higher species diversity are often more resistant to disruption by invasive exotic species than less diverse communities. This may be because a more varied community, consisting of many species with different ecological requirements, uses a greater diversity of the available resources. This leaves fewer resources for an intruding newcomer with specific needs. Gray Squirrel A species is a group of individuals that can breed and have viable offspring. Topic: Communities The structure of a community is measured and described in terms of species composition and species diversity. To measure species diversity of a community, two factors are used: species richness and species abundance. Species richness is a count of how many different species exist in a community. Species abundance is how many of each individual is present of the species in the community. Question: What happens to all three populations with the introduction of an invasive species (gray squirrel)? Topic: Population Growth Types Question: A population is a group of individuals of the same species. Populations may show different patterns of growth. The growth pattern depends partly on the environmental conditions under which a population lives. Exponential Growth Under ideal conditions, populations of most species can grow at exponential rates. Curve A in the figure to the right represents exponential growth. The population starts out growing slowly. As population size increases, the growth rate also increases. The larger the population becomes, the faster it grows. Logistic Growth Most populations do not live under ideal conditions. Therefore, most do not grow exponentially. Certainly, no population can keep growing exponentially for very long. Many factors may limit (slow down) growth. Often, the factors are density dependent (known as density-dependent factors). These are factors that are influential when the population becomes too large and crowded. For example, the population may start to run out of food or be poisoned by its own wastes. As a result, population growth slows and population size levels off. Curve B in the figure above represents this pattern of growth, which is called logistic growth. At what population size does growth start to slow in the logistic model of growth? That depends on the population’s carrying capacity (see figure above). The carrying capacity (K) is the largest population size that can be supported in an area without harming the environment. Population growth hits a ceiling at that size in the logistic growth model. K-Selected and r-Selected Species Species can be divided into two basic types when it comes to how their populations grow. •Species that live in stable environments are likely to be K-selected. Their population growth is controlled by density-dependent factors. Population size is generally at or near the carrying capacity. These species are represented by curve B in the figure above. Examples include rhinos and elephants. Age structure diagrams show the various ages of a population and separate male and female numbers of the population. •Species that live in unstable environments are likely to be r-selected. Their potential population growth is rapid (fast). For example, they have large numbers of offspring. However, individuals are likely to die young. Thus, population size is usually well below the carrying capacity. These species are represented by the lower part of curve A in the figure above (r is the population growth rate). Examples include roaches and rabbits. Summary •Under ideal conditions, populations can grow exponentially. •The growth rate increases as the population gets larger. •Most populations do not live under ideal conditions and grow logistically instead. •Density-dependent factors slow population growth as population size nears the carrying capacity. Question: Why does China’s age distribution diagram look this way? Question: Draw a graph of a cockroach population. How would it grow? Then, what would happen to the population with the introduction of a bird that ate the cockroach? Topic: Demographics Demography is the statistical study of populations, especially human beings. Demography encompasses the study of the size, structure, and distribution of these populations, and spatial or temporal changes in them in response to birth, migration, aging, and death. Fecundity is the ability to produce an abundance of offspring or new growth; it is a measure of fertility. Question: What is the overall trend of this data? What do the lines above the bar represent? level (Rule of 10). The other 90% is lost as heat into the environment. All food webs and chains are dependent upon primary productivity (the amount of photosynthesis done by the producers). This is measures in gross primary production. If you account for how much a plant is photosynthesizing and then respiring, this is called net primary production. Changes in regional and global climates, and in levels of carbon dioxide, can greatly influence primary production. For example, high levels of CO2 may lead to increased rates of PP. NPP = GPP - R Question: Beaked whales feed at various depths, but they defecate at the ocean’s surface. Nitrogen-rich whale feces deposited in surface waters supply nutrients for algae that are eaten by surface dwelling fish. Which of the following best predicts what would happen if the whale population decreased? (A) There would be a reduction in surface nitrogen concentration, which would cause an algal bloom. (B) The surface fish populations would decline due to reduced populations of algae. (C) The remaining whales would accumulate mutations at a faster rate. (D) The remaining whales would be forced to forage in the deepest parts of the ocean. Essential knowledge 4.A.6: Interactions among living systems and with their environment result in the movement of matter and energy. Topic: Energy Flows; Food Chains and Food Webs Primary Producer Primary Consumer Secondary Consumer Tertiary Consumer Energy flows in an ecosystem. As energy passes through each trophic level, energy is lost. Approximately 10% is efficiently harnessed at the next trophic Question: Topic: Nutrient Cycles Nutrients (matter) is recycled in an ecosystem. These biogeochemical cycles can takes years to cycle through the system. Nitrogen Cycle Video: http://studyjams.scholastic.com/studyjams/jams/science/ecosystems/nitro gen-cycle.htm Essential knowledge 4.B.3: Interactions between and within populations influence patterns of species distribution and abundance. Topic: Population Interactions Interactions between populations affect the distributions and abundance of populations. Competition, parasitism, predation, mutualism, and commensalism can affect population dynamics. And relationships among interacting populations can be characterized by positive and negative effects, and can be modeled mathematically (predator/prey, epidemiological models, invasive species). Many complex symbiotic relationships exist in an ecosystem, and feedback control systems play a role in the functioning of these ecosystems. A keystone species is a species on which other species in an ecosystem largely depend, such that if it were removed the ecosystem would change drastically. An example of such is a sea otter.’ Symbioses (Relationships) to Know -Mutualism: Both species benefit from a relationship together. Ex: oxpecker and rhino. -Obligate mutualism: organism cannot survive without the other. -Commensalism: One species benefits from the relationship, but the other does not and is not harmed. Ex: cow egrets and cows -Parasitism: One species is harmed (the host), while the other species benefits. Ex: tapeworm and humans. Carbon Cycle Video: http://studyjams.scholastic.com/studyjams/jams/science/ecosystems/carbo n-cycle.htm Question: Essential knowledge 4.B.4: Distribution of local and global ecosystems changes over time. Topic: Human Impact and the Ecosystem Human impact accelerates change at local and global levels. Logging (cutting down trees), slash and burn agriculture, urbanization, mono-cropping, infrastructure development (dams, transmission lines, roads), urban runoff (from fertilizers, pesticides, and trash) and global climate change threaten ecosystems and life on Earth. Most often, we reduce the number of species in the area, thus decreasing biodiversity. An introduced species/exotic/non-native can exploit a new niche free of predators or competitors, thus exploiting new resources. An example is the Cane Toad of Australia. And, the introduction of new diseases can devastate native species. Such examples include Dutch elm disease, potato blight, or small pox (Native Americans). Also, geological and meteorological events impact ecosystem distribution. • El Nino: During the winter in No. America, warmer water leads to increased rain leads. This causes animals to change migration routes and can cause species loss with flooding. • Continental drift: Caused significant change in presence of species due to movement of the plates. • Meteor impact on dinosaurs: Caused a mass extinction of the land dinosaurs. Topic: Ecological Succession Ecological succession is the gradual process by which ecosystems change and develop over time. Nothing remains the same and habitats are constantly changing. There are two main types of succession, primary and secondary. Primary succession is the series of community changes which occur on an entirely new habitat which has never been colonized before. For example, a newly quarried rock face or sand dunes. Secondary succession is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat. For example, after felling trees in a woodland, land clearance or a fire. For example, not all individuals in a population in a disease outbreak are equally affected; some may not show symptoms, some may have mild symptoms, or some may be naturally immune and resistant to the disease. Essential knowledge 4.C.4: The diversity of species within an ecosystem may influence the stability of the ecosystem. Natural and artificial ecosystems with fewer component parts and with little diversity among the parts are often less resilient to changes in the environment. Keystone species, producers, and essential abiotic and biotic factors contribute to maintaining the diversity of an ecosystem. The effects of keystone species on the ecosystem are disproportionate relative to their abundance in the ecosystem, and when they are removed from the ecosystem, the ecosystem often collapses. Practice FRQs Essential knowledge 4.C.3: The level of variation in a population affects population dynamics. Topic: Variation in a Population Population ability to respond to changes in the environment is affected by genetic diversity. Species and populations with little genetic diversity are at risk for extinction. A great example is the California condor. The California condor has only about 200 individuals left in its population. Condors were hunted for their feathers and also became sick when they ingested lead bullets from carrion (dead animals that were hunted). They also have intrinsic characteristics that make it more difficult to rebound their population. For example, they have low birth rates and require a large territory to live in. Because so few individuals are left, the genetic diversity of the population is low. Genetic diversity is great because it ensures the survival of the species.