Populations & Communities

• A population in Biology is a group of organisms of the same species interacting in an area
• Random quadrat sampling is used to estimate the population size of sessile organisms
• The Lincoln index is used to estimate the population size of motile organisms
• Negative feedback mechanism helps control population size through density-dependent factors
• In a sigmoid population growth curve, the exponential phase shows rapid growth
• Intraspecific competition refers to competition within the same species
• A community in an ecosystem includes all interacting organisms
• Mutualism benefits both species involved
• The method of Capture-mark-release-recapture is used to estimate the population size by capturing, marking, releasing, and recapturing motile organisms
• The stationary phase of the sigmoid population growth curve is characterized by a balance between birth rates and death rates
• Carrying capacity refers to the maximum population size that an environment can sustain indefinitely.
• Interspecific competition occurs between different species
• The process of using a quadrat to estimate population size involves random sampling.
• Predator-prey relationships are an example of density-dependent control of population size
• Herbivory is a form of interaction where one organism feeds on plants.
• An example of a relationship where one species benefits and the other is harmed is Parasitism or Predation.
• Population is a group of organisms of the same species living in one area at one time, being able to reproduce within that population
• Sessile (stationary) organisms can be estimated through quadrate sampling in which a random one is chosen and counted to average the population size, or line with belt transects where samples are collected and recorded along a straight line for estimation
• Random samples are where samples of equal size holds an equal chance of being chosen as any other
• If same species live apart, could eventually develop into different species
• Sessile organisms can also include very, very, very small organisms like ants
• Quadrats in sampling are places as follows; a base line is established along each edge of the habitat. Then two random numbers are generated to decide the distance from one edge, and then down the other to land on a specific quadrat.
• Motile (moving) organisms are recorded through capture and recapture methods. For initial capture, methods include pitfall traps, pooters (aspirators), mammal traps and nets.
• In capture-recapture, animals are marked after intial capture in a way they can be recognized later but it does not hinder their survivability by making them more noticeable, capping their adaptations, etc.
• In capture-recapture [capture-mark-release-and-recapture/MRR] or the Lincoln index, usually uses rings, tags, or dabs of nail varnish or paint to mark animals.
• The population size can be estimated with the Lincoln index by taking the number of organisms first marked multiplied by the number of organisms caught the second time over the number of marked organisms in the total organisms captured the second time
• Estimated population ([n1 x n2]/ n3) where n1=# of 1st capture, n2=# of second capture and n3=# of marked in second capture
• Carrying capacity is the maximum population an environment is equipped with the resources and surroundings to support.
• When carrying capacity is reached, unless human interference is accounted for, density-dependent factors such as the availability of water or prey will decrease population numbers, decrease it, then allow it to grow again
• All environment's carrying capacity (K) cannot be exceeded (naturally)
• Negative feedback control is brought on by density dependent factors that allow a population to return to or below its carrying capacity
• Density-dependent factors are self-regulating systems where deviation from steady state is countered immediately for stability (ex. prey increase causing predator increase causing prey decrease causing predator decrease)
• Density dependent factors depends on the number of the population and allows factors to change availability where some groups are targeted/affected more.
• Density-independent factors account for factors that do not influence and are not affected by the scale or density of a population and affects all species without discrimination (ex. hurricanes, wild fires)
• Higher density in populations allow for faster spreads of diseases, higher competition over limited/finite resources and increased predation (for prey)
• Natural population growth curve is sigmoidal and has 3 stages; exponential, transition, and plateau.
• The exponential stage of the natural population growth curve is where natality and immigration outweigh mortality and emigration while good resource supply is available and limiting factors fail to limit growth
• The transition stage of the natural population growth curve is where natality and immigration still outweigh mortality and emigration but by a progressively smaller amount as time passes. Competition starts to rise and resources grow scarce
• The plateau stage of the natural population growth curve is where carrying capacity (K) is reached and mortality = natality and limiting factors are too restrictive to allow further growth in population
• Population size = (Natality + Immigration) - (Mortality + Emigration)

  P = (N+I)-(M+E)