Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Source–sink dynamics wikipedia , lookup
Storage effect wikipedia , lookup
Two-child policy wikipedia , lookup
Molecular ecology wikipedia , lookup
Human overpopulation wikipedia , lookup
World population wikipedia , lookup
The Population Bomb wikipedia , lookup
Population Biology Population size: the number of organisms in a population (N) Biotic Potential: highest rate of reproduction under ideal conditions. -populations very rarely reach their biotic potential, because conditions are not perfect all of the time. Under perfect conditions, a population will continue to increase indefinitely. -unlimited resources, such as food and water, unlimited space, all waste is removed so that it does not build up, etc. The human population shows this pattern (so far) . Why? Population Numbers Unlimited Population 600 500 400 300 200 100 0 1 2 3 4 5 6 7 8 Time This is an example of an EXPONENTIAL growth curve. 9 Carrying Capacity: the number of individuals that a given environment can support. Ex: Number of lions in the African plains, or the number of zebras at carrying capacity, birth rate is equal to the death rate. Population Numbers Normal Population Growth 300 250 200 150 100 50 0 Carrying Capacity 1 2 3 4 5 6 7 8 Time This is an example of a LOGISTIC growth curve. 9 Environmental Resistance: the sum of limiting factors facing a population. Ex: water requirements, space, need for food, competition, lack of mates. They all add up to the Environmental Resistance, which holds numbers down Limiting Factors: -control population size and growth -can change depending on environmental conditions. Ex: rain after a long drought Population Density: the number of organisms per unit area, or volume. Limiting Factors can be Density Dependent (related to the density of the population), or Density Independent (does not matter what the density of the population is) Ex: flood/storm (DI) vs levels of disease (DD). Density Dependent Factors 1)Predation: size of prey population is held down by predators, size of predator population is dependent on size of prey population. Number of Individuals Population Relationships 30 20 Foxes 10 Rabbits 0 1 2 3 4 5 Time in Years 6 7 2) Disease: Disease spreads more rapidly through a dense population, populations can be reduced by disease 3) Food/water resources: the higher the density of organisms, the faster the food and water supply will be used up. 4) Space for nesting: High density populations will have a high level of competition for the best areas to raise young. Interspecific and Intraspecific Competition: Interspecific: competition between different populations. Ex: lions vs. hyenas Intraspecific: within a population. Ex: lions vs. lions Both types are Density Dependent Dispersion and Competition Dispersion is the pattern of distribution the individuals within a population take. Random: Individuals are placed by chance, or by self determination. Ex: trees in a forest, a coral reef. Even Distribution: Individuals are evenly spaced, located at regular intervals. Usually occurs because of intraspecific competition. Ex: Competition between pine trees for sunlight Clumped Distribution: Individuals are bunched together in clusters, for protection, reproduction, or because of narrow habitat tolerances. Ex: schools of fish, flocks of birds, clumps of one type of plant within a forest. Population Growth Patterns 1) Rapidly growing populations: Many species, such as insects, plants, and fungi are found in rapidly changing environments. Such species are called r-strategists r-strategists populations grow exponentially when environmental conditions allow them to reproduce. When conditions worsen, the population size drops quickly. R-strategists use the strategy of creating many offspring, but spending little energy and time on each individual. Many offspring, little input EX: Dandelions: Lots of seeds, blown by the wind, no care at all. Blue Crabs: Eggs are released by the thousands, but no energy is spent on the young. Population R-Strategist Population Growth 1 2 3 Years 4 5 2) Slowly Growing Populations Organisms that grow slowly often have small population sizes. These organisms are called k-strategists, because their population is usually below the carrying capacity (K). k-strategists have fewer young, but spend more time and energy on each individual. K-strategists grow slowly, have a longer life span, and are less susceptible to environmental change. Many endangered k-strategists are in trouble because they are being hunted in numbers that cannot be supported. Examples: Sharks Gorillas Tigers Lions Population K-strategist Population Growth 1 2 3 Years 4 5 Summary of R vs. K strategists R: Mature rapidly Short-lived K: Mature Slowly Long-lived Have many offspring Few offspring at a time Invest little energy in young Care for their young Boom or Bust population More stable population