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BIO205H5 Chapter : BIO205 Textbook Notes.docx

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Christoph Richter

Chapter 9 Properties of Populations What is population and how is it important to ecology A population is a group of individuals of the same species that inhabit a given areaSuggests the potential in sexually reproducing organisms for interbreeding among member of the population As such the population is a genetic unit It defines the gene pool the focus of evolutionThe population is a spatial concept requiring a defined spatial boundaryfor example the breeding of Chinook salmon inhabiting the Copper River of Alaska o Organisms may be unitary or modular o The distribution of a population describes its spatial location the area over which it occurs Distribution is based on the presence and absence of individuals and is influenced by the occurrence of suitable environmental conditions In other words distribution is a spatial boundary within which all individuals in the population reside o When the defined area of distribution encompasses all the individuals of a species total area occupied by a population the distribution describes the populations geographic range Within the geographic range of a population individuals are not distributed equally throughout the area and this range can be limited by factors such as geographic barriers ie ocean between two islands and interaction with other species ie predationcompetition Abundance whereas distribution defines the spatial extent of a population abundance defines its sizethe number of individuals in the population Abundance is a function of two factors 1 the population density and 2 the area over which the population is distributed Population density vs ecological density o Population density is the number of individuals per unit are also known as crude density or per volume o To account for patchiness ecologists often refer to ecological density the number of individuals per unit of available living space Determining Abundance o SamplingQuadrant sampling population sizemean density of units sampled x total areaCapturerecapture or markrecapture method where NTotal population nnumber of individuals in the sample Minitially marked individuals Rrecaptured marked individualsDetection observations by techniques such as vocalizations counts of animal scant seen along a length of roads traveled counts of animal tracks number of individuals crossing a certain track These counts are called indices of abundance and cannot function alone as estimates of actual density However it can show trends in abundance and comparison between different habitats Population age classes or stages prereproductive reproductive and postreproductive Chapter 10 Population Growth Population growth refers to how the number of individuals in a population increases or decreases with time Two methods of calculating population growth assuming the population dynamics are a function only of demographic processes relating to birth and deathie population is closed or immigrationemigration 7 1 Exponential growth predicts the rate of population change through time Exponential growth results in a continuously accelerating rate of population increase or decelerating rate of decrease as a function of population size owhere rbirth ratedeath rate 9 2 Geometric growth described over discrete time intervals using finite growth multiplierUnlike exponential growth this estimate of the per capita growth rate does not assume that all individuals in the population are identical This estimate does however assume that the agespecific rates of birth and death for the population are constant they do not change over time o NtN0 twhere finite multiplier rateer or rln Chapter 14 Predation Predation the consumption of one living organism by another Heterotrophs consume organic matter predators are diff from decomposers and scavengers o They feed on living organisms function as agents of mortality regulate prey populations prey populations reduceregulate growth rate of predator populations Classifications of predators excludes decomposers and scavengers includes heterotrophic organisms o Carnivores eat animal tissue o Herbivores eat plantalgal tissueeat part of the individual plant may harm the plant doesnt result in mortality o Omnivores eat both plant and animal tissues Parasites and their host organisms share an intimate relationship not seen in predators and herbivores o Parasitoid attacks preyhost by laying its eggs in hosts body egss hatch larvae feed on host and kill it dont cause immediate death Population growth equation FOR PREY POPULATION has two parts o 1 exponential model dNdtRN o 2 mortality term represent removal of pretty from the predator population o Rate at which predators eat prey increases asof prey increases o cNprey c efficiency of predation o rate of predationper capita rate of consumption of predators oof prey capturedcNpreyNpred Npred cNpreyNpred dNpreydtrNpreycNpreyNpred represents rate of change in prey population Population growth rate for PREDATOR POPULATION has two parts 1 birth rate amount of food consumed increases as with the rate at which prey is captured cNpreyNpred Birth rate befficiency with which food is converted into population growth reproductionrate of predation cNpreyNpred or bcNpreyNpred 2 mortality rate represented as dNpred d probability of mortality dNpreddtbcNpreyNpreddNpred represents rate of change in predator population These two lotkavolterra equations for predator and prey population growth function as densitydependent regulator on each other o Predators regulate growth of prey population function as source of densitydependent mortality o Prey function as source of densitydependent regulation on birthrate of predator population o low predator population prey population grows exponentially dNpreydtrNprey o high predator populationprey mortality will increase until mortality rate due to predation cNpreyNpred is equal to growth rate of prey population rNprey and net population rate growth for prey species0 dNpreddt0
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