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
Population Biology Population: A group of organisms of the same species living in the same area and interacting with one another. How Study Populations? Geographic Range Density and Distribution Growth rate Age structure Geographic Range • The area inhabited by a population • Can vary greatly depending on the species (bacteria on a rotting pumpkin vs. cod in the western Atlantic ocean from Greenland to North Carolina Density and Distribution • Population density refers to the number of individuals per unit area • Distribution refers to how individuals in a population are spaced out across the range of the population: random, uniform or clumps. Clumped Random Uniform Exponential Growth – “J” curve 1. Rapid rate of increase when resources are unlimited and optimal growing conditions are present. 2. The populations double with each generation, such that the larger the population is, the faster it grows. 3. Obviously this rate of growth cannot continue indefinitely. Number of Species over Time Logistic Growth “S” Curve 1. This type of growth grows rapidly at first resembling exponential growth, but levels off toward later stages. 2. Related to the fact that resources are limited, and as the population grows larger, it is harder for each individual to get what it needs, so growth slows. 3. Population may slow down either because of decrease in birth rate or an increase in death rate (or both) 4. Populations tend to stabilize around a specific number, although there may be slight fluctuations around that amount. Logistic Curve Carrying Capacity – the maximum number of organisms of the same species that can be supported in a specific are indefinitely. Once the carrying capacity is reached, certain factors work to keep population in check (including lack of food, overcrowding, predations, accumulation of waste) If a natural population overshoots the carrying capacity, three thing can happen: 1. It will die back to the original cc. 2. It will die back, but because of damage to the environment, cc. is lower 3. It will become extinct. Age Structure Consider especially the pre-reproductive compared to the post-reproductive years. – Very young and very old and more susceptive to disease – If there are huge numbers of young adults, the population will grow; if there are mostly elderly, the population will decline. Sex Ratios • In a monogamous species, the ratio of males to females should be about equal. • In deer for example, that is not as important, because one male often fertilizes many females. Factors that Restrict the Size of a Population Limiting Factors of Environmental Resistance Density-Dependent Limiting Factors 1. 2. 3. 4. The degree of influence depends on the size of the population. Examples: competition, predation, parasitism, stress caused by crowding, disease Seldom totally eliminate a population Some populations are self-controlling in that they have mechanisms to reduce competition – delayed maturation caused by malnutrition, migration, cannibalism. Density-Independent Limiting Factors 1. 2. 3. The degree of influence is not related to population density. Examples: pollution, habitat destruction, natural disasters, weather Usually just reduce the population below the cc. but they have the ability to totally eliminate a population Relationships Within a Population Population Biology Population: A group of organisms of the same species living in the same area and interacting with one another. Relationships Between Populations of Different Species Relationships Between Populations of Different Species A. Predator-Prey B. Competition C. Symbiosis Relationships Between Populations of Different Species: Predator- Prey • Predation is any interaction between two organisms in which one organism (the predator) consumes all or part of another organism (the prey). What actually happens in nature is that a cycle develops where at some time the prey may be abundant and the predators few. Because of the abundance of prey, the predator population grows and reduces the population of prey. This results in a reduction of predators and consequent increase of prey and the cycle continues. -Predator -Prey Competition • Competition in an interaction between two organisms that are using the same limited resource. • Competition can be within the same species (intraspecific) or between different species (interspecific). Competition Intraspecific – between the same species Interspecific – between different species Symbiosis Any relationship which two species live closely together (and at least 1 benefits) The three types are: Mutualism Commensalism Parasitism Mutualism an interaction between species in which BOTH benefit (+,+) Commensalism an interaction between species in which one benefits, and the other is not helped or harmed (+,0) Parasitism an interaction between species in which one benefits and one is harmed (+,-)