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Population Ecology G. Tyler Miller’s Living in the Environment 14th Edition Chapter 9 Key Concepts Factors affecting population size Species reproductive patterns Species survivorship patterns Conservation biology and human impacts on ecosystems Population Dynamics and Carrying Capacity Population dynamics Biotic potential (intrinsic rate of increase [r]) Environmental resistance Carrying capacity Exponential and Logistic Growth Population Density Population Distribution Clumping: Most common. Safety in numbers, social interaction, mating and caring for young, resources are clumped Uniform: Not as common. Used because of scarcity of resources Random: Quite rare. Can be hard to determine between truly random or largely “clumpy” Fig. 9-2 p. 164 What goes up must come down 1. Increases in population: through birth or immigration 2. Decreases in population: through death or emigration. Change in Population Births + Immigration Deaths + emigration Age Structure • What is expected to happen if a large % of the population is under the age of 10? Growth will remain stable, then increase in 10-20 years • What is expected to happen if a large % of the population is between the ages of 20 and 40? Growth will increase within 10 years • What is expected to happen if a large % of the population is over the age of 65? Growth will decrease • What is expected to happen if there is an equal distribution in age? Growth remain stable What stage are you? • Pre-reproductive stage: Those not through puberty; reproductively immature. • Reproductive stage: Those who are capable of reproduction • Post-reproductive stage: Organisms that are too old to reproduce. • Remember: while males are capable of reproduction longer, “survival of the fittest” can prevent them from breeding once they are too old. Abiotic • • • • • Not living Sunlight Temperature Climate Chemical environment vs. Biotic Factors • • • • • • Living factors Reproduction rates Food supply Habitat Resistance to disease Ability to adapt to change Factors Affecting Population Size Biotic potential = growth Environmental resistance = decrease Fig. 9-3 p. 166 Exponential and Logistic Growth Boom then Bust Boom then Stable Logistic Growth Population size (N) Environmental resistance Carrying capacity (K) Biotic potential Exponential growth Time (t) Going up… •Intrinsic rate of increase (r) is the rate the population would grow at if it had unlimited resources. •Can be seen as the “boom” of the population. •r species: reproduce early in life, reproduce often, have many offspring each time. Coming Down • Overshoot occurs when the population “booms” and is too great for the resources to support • Overshoot is followed by dieback, or the sudden decrease in population • Reproductive time lag: the amount of time it takes for the birth rate to fall and death rate to rise. If the time lag is too long, environmental damage can occur which further limits the carrying capacity. Population Density Effects Density-dependent controls: Limits populations that are too high. Examples: competition for food, shelter, water; disease; parasites •Density-independent controls: Decreases population regardless of size. Examples: weather, temperature, natural disasters, habitat destruction Natural Population Curves Fig. 9-7 p. 168 Who’s in control here? • Top-down control: Population is limited by the predator. • Bottom-up control: Population is limited by the food source of the prey. • Example: Hare population is controlled either by the lynx killing it (top-down) or by large numbers of hare using up their food source (bottom-up) Let’s talk about sex… • Asexual reproduction: does not require sperm/egg. Mitosis – cell splitting. Bacteria reproduce this way. Only 3% of all species use this form • Sexual reproduction: requires sperm/egg, but not necessarily intercourse/copulation • Disadvantages: – Males don’t give birth – Increased chance of genetic defect/error – Courtship and mating rituals can be complex • Advantages: (get your mind out of the gutter!) – Genetic variety/diversity – Parents can divide responsibilities What species are you? Carrying capacity Number of individuals K species; experience K selection r species; experience r selection Time Species r k • Found at bottom of population curve • Reproduce early in life • Reproduce frequently • Large numbers of offspring • Little to no parental care • Boom and bust populations • Examples: – – – – – Frogs Cockroach Dandelions Mice Most insects • Found at top of population curve • Reproduce later in life • Reproduce less frequently • Have less offspring at one time • Lower infant mortality • Logistic graph (stable at top) • Examples: – – – – Humans Elephants Whales Long-living plants (oaks, rain forest trees) The Role of Predation in Controlling Population Size Predator-prey cycles Top-down control Bottom-up control Fig. 9-8 p. 168 Reproductive Patterns and Survival Asexual reproduction r-selected species Sexual reproduction K-selected species Fig. 9-10 p. 170 Survivorship Curves 1. Early loss: high infant mortality (fish, frogs) 2. Constant loss: death rate even among all ages (song birds) 3. Late loss: low infant mortality (humans, elephants) Fig. 9-11 p. 171 Isolation isn’t best… • Problems when small, isolated populations exist. 1. Founder effect: small group is geographically isolated. May not have the genetic diversity to survive (coloring, fur cover, etc) 2. Demographic bottleneck: only a few surviving individuals may not have the genetic diversity to rebuild the population 3. Genetic drift: some individuals breed more and dominate the gene pool (wolves) 4. Inbreeding: related individuals in an area mate. Can increase genetic defects. Oops! I did it again… Past mistakes that need stopped: 1. Reducing biodiversity by destroying, fragmenting and degrading habitats 2. Reducing biodiversity by simplifying natural ecosystems (monocultures – one type) 3. Unintentionial strengthening of pest species and antibiotic resistant bacteria 4. Elimination of natural predators (wolves, cougars, buffalo, eagles) 5. Over-harvesting renewable resources 6. Interfering with natural cycles in natural 7. Over dependence on fossil fuels Human Impacts on Ecosystems Habitat degradation and fragmentation Ecosystem simplification Genetic resistance Predator elimination Introduction of non-native species Overharvesting renewable resources Interference with ecological systems Learning from Nature Dependence on Nature Interdependence Unpredictability Limited resources Recycle wastes See Connections p. 173