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POPULATION TERMS Ecolog.2 - the study of organisms and how they interact with their environment. P_9.pulation - A group of organisms of the same species that live in the same area (and interact with each other). Population Density - The number of individuals in a population per unit of area (ex. m2) Community - a collection of interacting populations that live in the same ecosystem. (the living portion of an ecosystem) D_~ersion - The arrangement of organisms in a population within a given amount of space. (the pattern of their distribution -~ ex. clumped, random, uniform) a. clumped - Occurs when individuals tend to be grouped in clusters. The presence of of one individual increases the likelihood of finding another individual nearby. This patterncould be due to the presence of a natural resource or certain social behaviors (e.g. forming herds and colonies for mating, protection from predation, migration). Most common dispersion pattern. b.random - Occurs when the presence of one individual does not directly influence the location of any other individual. The spacing between ,individuals is unpredictable. This pattern is more common in plants, but uncommon in ~nimal populations. c. uniform - Occurs when individuals are evenly spaced within an area. The preseuce of of one individual decreases the likelthood of finding another individnal nearby. Animals may avoid each other due to territoriality or competition. Fecundity - Physically capable of sexual reproduction Fertilit~ - The actual number of offspring produced through sexual reproduction Growth Rate - The change in the size of a population over a given period of time. Biotic Potential - Refers to the fastest rate at which a specific population can grow (if there were unlimited resources) Reproductive Potential - The maximum number of offspring that members of the population can produce. (it depends upon such factors as generation time, the age at which an individual is able to reproduce, # of offspring produced, fecundity, ...) Carrying Capacity - The maximum number of individuals, of a given species, that an environment can support for the long term -~ the size of population would not negatively impact the environment. Logistic Growth - Growth rates that establish an equilibrium with environmental resources and stabilizes around the carrying capacity. (S curve - restricted growth). Exponential Growth - Growth in the size of a population in which the rate of growth increases as the size of the population increases (J curve - unrestricted growth). Overshoot- A population’s size greatly exceeds the carrying capacity of the environment. It occurs when a species encounters a new environment with a stock of unexploited resources that promotes reprodnction in the population. (these resources are being utilized at a nonrenewable rate). Overshoot often leads to the degradation of the habitat, lowering of the carrying capacity, and a catastrophic collapse of the population. Limiting Factor - A condition that restricts a population’s growth. Ex. space, food availability, lack of particular nutrient, pH, oxygen. Environmental Resistance -IncIudes all the limiting factors that tend to reduce a population’s growth rates and therefore determines the carrying capacity of an ecosystem. Environmental resistance increases as a population approaches the carrying capacity. Results in logistic growth. Dynamic Equilibrium - The state of a system when it remains unchanged because two opposing forces are proceeding at the same rate. Niche - the specific role, function, and position of an organism in an ecosystem. (the full range of physical and biological conditions in which an organism lives and how the organism uses those conditions --+ includes where it lives, what it eats, its range of environmental temperatures, ho~v it interacts with other organisms, ...) Density-Dependent Factors - The way these environmental factors regulate the growth of a population is directly related to the size of the population. .,. ex. predation, disease, parasites, food supply Density-Independent Factors - The way these enviro~maentai factors regulate the growth of a population is NOT related to the size of the population. ex. frost, drought, salinity, acidity, natural disasters (fire, flood, volcanic eruption) Interspecific Interactions - Refers to interactions between different species ex. predator-prey, mutualism, commensalisms, parasitism Intraspecific Interactions - Refers to interactions between members of the same species ex. territoriality (marking territory, bird songs, aggressive behavior competition ~2gmbiosis is a reiationship in which two different species live in ctose association. There are three main types of symbiosis. Mutualism (+/+) Relationship in which both organisms benefit from the association. Ex. lichens (fungus and alga), cows and intestinal microorganisms Commensalism (+/0) Reiationship in which one organism benefits and the other organism is neither helped nor harmed. Ex. whales mad barnacles Parasitism (+/-) Relationship in which one organism benefits and the other organism is harmed by the association. Parasites live in or on an organism and obtain their nutrition at the expense of this host. (often without killing the host) Ex. ticks and mammals, tapeworms and humans SAMPLING TECHNIQUES Researchers must consider wlai~h sampling technique would work best in particular situation, determine the sample size and the number of samples (balancing desired accuracy with the need to minimize costs, time, and effort), decide how to pick the sampling locations. Mark - Recapture Sampling - This method for estimating population size is often used for animals that tend to be highly mobile, eiusive, are frequently in areas that are hard to access (therefore you would be unlikely to encounter them when sampling the area). It.involves marking a number of individuals° returning them to the natural population, and subsequently doing a second capture (many captured the second time may not be marked). It is based on the premise that the ratio of marked animals to all animals captured the second time (recaptured) is the same as the ratio of marked animals to all animals in the population. Therefore we can use a proportion to estimate the size of the population. N=_MxC R N= Estimate of total population ’size M= Total # of animals marked on the first capture C= Total # of animals (marked and tmmarked) caught during the second capture R= # of marked animals caught during the second capture (recapture) After the first capture and before the second capture, the marked animals are given sufficient time to redistribute themselves among the natural population, but no so much time as to allow things such as mi~ation, birth rates, and death rates to alter the population size. Quadrat (Plot) Samplin~ - Tiffs method studies the organisms in plots or quadrats. It is based on the premise that organisms selected randomly will be representative of the larger population (there are statistical guidelines for.determining the minimal number of quadrats needed). It is one of the techniques commonly used for estimating the population size of plant commtmities or sessile organisms. Plot can be used to estimate things such as population size, population density, and dispersion patterns. It involves counting mad recordir~g the mtmber of different organisms in each quadrat. Population Size = Total # of individuals (o~one species) from all sampled q~aadrats X Total # of Quadrats (for one species) # of all sampled quadrats (in the ecosystem) _0uadrat - A clearly marked sample area of known size that is used during ecological studies. It can be any shape, but it is usually rectangular (sometimes circular). The size of the quadrat usually depends upon the size of the species being sampled. Populations becoming established in a new area for the first time are often termed coloniTing populations (betow, left). They may undergo a rapid exponential (logarithmic) increase in numbers as the~’e are p~enty of resources to allow a high birth rate, while the death rate is often low. Exponential growth produces a J-shaped growth curve that rises steeply as more and more Individuals contribute to the population increase. If the resources of the new habitat were endless (inexhaustible) then the population would continue to increase at an exponential being added to the population per unit time Is large. rate. However, this rarely happens in natural populations. Initially, growth may be exponentia! (or nearly so), but as the population grows, its increase will slow and it will stabilize at a leve! that can be supported by the environment (called the carrying capacity or K). This type of growth is called sigmoidal end produces the logistic growth curve (below, right). Estabgshed populations will fluctuate about K, often in a regular way (gray area on the graph below, right). Some species will have populations that vary little from this stable condition, while others may oscillate wildly. as it begins to fill up the environment. This is called Envif6nme~tal re~ist~dce Carrying capacity (K) : popu!~t!on "oversh6ots the carrying capacity. " that can be supported by the enyironment. ~ .. : I~xpenential (J) curve Exponential Logistic (S) curve As the population grows, the rate of population Increase slows, reaching an equilibrium level around the carrying capacity. Lag The population tehds to fluctuate aroufid an ’equilibrium level’. The iiuctuations are caused by variations in the birth rate and death rate as a result of the population density exceeding 9r falling below c~.r~ying capacity. ¯ " arly on, Time Time Explain why populations tend not to continue to increase exponentially in an environment: 2 Explain what is meant by environmental resistance: 3. (a) Explain what is meant by carrying capacity: Explain the impgrt~nce of carrying capacity to the growth and maintenance of population numbers: Species that expand into a new area, such as rabbits did in areas of Australia, typically show a period of rapid population growth followed by a slowing of population growth as density dependent factors become more important and the population settles around a level that can be supported by the carrying capacity of the environment. (a) Explain ~Nhy a newly introduced consumer (e.g, rabbit) would initially exhibit a period of exponential population growth: (b) Describe a likely outcome for a rabbit population after the initial rapid increase had slowed: 5. Describe the effect that introduced grazing species might have on the carrying capacity of the environment: Some mammals, particularly in highly seasonal environments, exhibit regular cycles in their population numbers. Snowshoe hares in Canada exhibit such a cycle of population fluctuation that has a periodicity of 9-11 years. Populations of lynx in the area show a similar periodicity. Contrary to. early suggestions that the lynx controlled the size of the hare population, it is now known that the fluctuations in the hare population are governed by other factors, probably the availability of palatable grasses. The fluctuations in the lynx numbers however, do appear to be the result of fluctuations in the numbers of hares (their principal food item). TMs is true of most vertebrate predator-prey systems: predators do not usually cor{trol prey populations, which tend to be regulated by other factors such as food availabifity and c~imatic facto~. Most predators have more than one prey species, although one species may be preferred. Characteristically, when one prey species becomes scarce, a predator wi!l "switch" to another available prey item. Where one prey species is the principal food item and there is limited opportunity for prey switching, fluctuations !n the prey population may closely govern predator cycles. (left) ever a ~0 ye&r pe 5d rev~a ed a that was repeated ~ve~ 10 years or so. ~he oscillations in lynx numbers closely matched those of the snowshoe hsre ’,~’ ; ¯ ,.::. # ,, system and the lynx are ve~ dependent 6n the h~res for food. Consequent y, the, lagging slightly behisd those of th6 hare. 1, (a) From the graph above, date[mine the l~g time between the population peaks of the hares and the tynx: (b) Explain why there is this time lag between the iacrease in the hare population and the response of the lynx: 2. Suggest why the lynx populations appear to be so dependent on the flqctuations on the hare: 3. (a) In terms of birth and death rates, explain how the availability of palatable food might regulate tile numbers of hares: (b) Explain how a decline in availabl~ palatable food might affect their ability to withstand predation pressure: Related activities: Predator-Prey Strateaies, Population Growth Information about the populations of rare organisms in isolated populations may, in some instances, be collected by direct measure (direct counts and measurements of all the individuals in the population), However, in most cases, populatiobs are too large to be examined directly and they must be sampled in a way that still provides information about them. Most practical exercises in population ecology involve the collection or census of living organisms, with a view to identifying the species and quantifying their abundance and other population features of interest~ Sampling techniques must be appropriate to the community being studied and the information you wish to obtain. Some of the common strategies used in ecologica! sampling, and the situations for which they are best suited, are outlined in the table below, it provides an overview of points to consider when choosing a sampling regime. One must always consider the time and equipment available, the organisms involved, and thd impact of the sampling method on the environment. Fof example, if the organisms involved are very mobile, sampling frames are not appropriate. If it is important not to disturb the organisms, observation alone must be used to gain information, Point sampling individual points are chosen an a map (using a grid reference or random numbers applied to a map grid) and the organisms are sampled at those points. Mobile organisms may be sampled using traps, nets etc. Systematic (grid) Line transects: Tape or rope marks the Line. The species occurring on the line ar~ recorded (all along the line or, more usually, at regular Intervals). Lines can be chosen randomly (left) or may follow an environmental gradient. Celt transects: A measured strip is located across the study area to highlight any transitions. Quadrats are used to sample the plants and animals at regular intervals along the belt. Plants and immobile animaIs are easily recorded. Mobile or cryptic animals need to be trapped or recorded using appropriate methods. Useful for: betermining spebies a~undance and eomr~nlt~ : composition. Lf samples are large enough, popuJ~ti0n’ characteristics e.g. age structure, rep[od~)c~ive I~.a, rar~?~ta)~’ can be determined. Considerati’o~s: Time efficient. Suitable for most organisms. Depending on method environmental disturbance is minimal. Species occur ng n low abur~dance may be missed.:’ Useful for: Well suited to determLning changes in ~0mmunity composition along an environmental gradient, Wl~en p!aced. ’ andom y, they provide a quick measure of species occurr@nce~ Considerations for line transectsi "l~me efficient. Mo~t suitable; for ptants and immobile or easLly caught animals. Disturbance o the environment can be minimized, Species occurring in Low abundance may be missed¯ : ;. : ~ well. Most suitable for plants and immobile er easily caught animals. Good chance of recording most or all spe~ied, E~fo~s should be made to minimize disturbance to the el~virddrn~nt! Quadrat sampling Sampling units or quadrats are placed randomly or in a grid pattern dn the sample area.The occurrence of organisms in these squares is noted, Plants and slow moving animals are easily recorded. Rapidly moving or cryptic animals need to be trapped or recorded using appropriate methods. Mark and recapture (capture-recapture) Animals are captured, marked, and then released. After a suitable time period, the population is resampled. The number of marked animals recaptured in a second sample is recorded as a proportion of the total. mmob e species. Population should have a finite boundary, Pe od between samplings must aLl6w ~or red!stribution Of marked animals in the population. Marking shodld ~Jresen~ li~le : 1. Explain why we sample populations: 2. Describe a sampling technique that would be appropriate for determining each of the following: (a) The percentage cover of a plant species in pasture: (b) The density and age structure of a plankton population: (c) Change in community composition from low to high altitude on a mountain: 2001-2007 ReLated acftvitles: Quadrat Sampling, Transect Sampling, Mark and Recapture Sampling Distribution and density are two interrelated properties of populations. Population density is the number of individuals per unit area (for land organisms) or voldme (for aquatic organisms). Careful observation and precise mapping can determine the distribution patterns for a species. The three basic distribution patterns are: random, clumped and uniform. In the diagram below, the circles represent individuals of the same species. It can also represent populaiions of different species. LowDensi~ ’ ’ @ O O O aoart. There are on a few individuals per unff area or vo ame (e.g. highly t~riitorial, s~olita-¢ mammal soecies High Density Clumped Distribution 0 O O Co @ Uniform Distribution found a! ow densities 1. Describe why some organisms may exhibit a clumped distribution pattern because of: (a) Resources in the environment: (b) A group social behavior: 2. Describe a social behavior found in some animals that may encourage a uniform distribution: 3. Describe the type of environment that would encourage uniform distribution: 4. Describe an example of each of the following types of distribut!on pattern: (a) Clumped: (b) Random (more or less): (c) Uniform (more or less): Related activ ties Fea ures of Popu ations ry few species show continued exponehtial growth. Population size is regulated by factors that limit popul.ation growth. The diagram below illustrates how population size can be regulated by environmental factors. Density independent factors may affect all individuals in a population equally. Some, however, may be better able to adjust to them. Density dependent factors have a greater affect when the population density is higher. They become less important when the population density is low. Directly or indirectly affect the food supply Food supply Rainfall ; Humid]~ Acidity Salinity Regardless of population densi~ thes~ factors are the same for aft individuals. The effects of these factors are influenced by ," Di~eas~ Parasites omp~tit!001 Predati0~’ ".. : Catastro : " These factors are influenced by the density of the population (Le. how crowded the population Is). : Fire. . Drought Organisms that are more crowded: I~ Compete more for resources ¯ Are more easily !ound by predators i Spread disease and parasites more readily. Tsunami¯ ¯ .... Eatthq~.ke Poor health or death Increase is mortality Change in ability to reproduce Natality is affected 1. Discuss the role of density dependent factors and density independent factors in pol~ulation regulation. In your discussion, make it clear that you understand the meaning of each of these terms: 2. Explain how an increase in population density allows disease to have a greater influence in regulating population size: 3. In cooler climates, aphids go through a huge population increase during the summer months. In autumn, population numbers decline steeply. Describe a density dependent and a density independent factor regulating the populati£n: (a) Density dependent: (b) Density independent: #;,l~t~,rl ~cfi~itle~: DensitY and Distribution