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Ecology, Evolution & Marine Biology

 Ecology-the study of the distribution and abundance of organisms and the factors and interaction that determines their distribution and abundance.  Where are they, and how many”  Goal: to observe patterns, describe processes and use this information to predict, manage and control.  Ecologist use a variety of sources(observation and monitoring in the natural environment, manipulative field experiments, controlled lab experiments, and mathematical models) oMathematical models  The criterion of distribution and abundance of organisms in the natural environments  P values measure the strength of the conclusions being drawn. If P is less than 0.05, then the result is statistically significant. ̂ ̂ ̂ ̂-datum ̂-population mean ̂standard error (√ where n=population size, and σ=standard deviation)  Typically operates at the highest scales of biological organization.  Each level operates at different biological, temporal, and spatial scales  Organism-a single individual of a single species o Behaviors, environmental physiology, morphology  Population-Individuals of the same species living in the same geographical area o Factors that affect population size and composition o The populations of species vary over space and time  Methods to identify population size changes o Direct observations o View age structure(life tables and survivorship curves) type 1(human)type 2(birds)type 3(plants, fishes) o Mathematical models(view populations at fundamental levels) results from models are often general and can be applied to other systems; good for measuring populations that are difficult to observe directly  Simple population growth model o Natality, mortality, immigration and emigration drive population dynamics  Natality-number of offspring per unit time oDependent on type of organism  Mortality- the number of offspring dying per unit time o Most organisms die from predation, parasitism, disease, hazards, etc.  Immigration rate- the number of individuals moving into the area  Emigration rate- the number of individuals moving out of the area per unit time oThe importance of movements as loss and gain processes to populations is dependent on spatial and temporal scales oThe smaller the spatial/ temporal scale, typically the greater the importance of movement to population dynamics oAlso critical to population persistence o All populations have the potential for exponential growth oIn an unlimited resource environment, there are no restrictions on an organisms ability to harvest energy, grow and reproduce oIf the number of new individuals per unit time to a population in constant and if the environment is constant and resources are unlimited, positive rates of increase lead to exponential growth b-d =per capita growth rate(r) so For very short time periods some populations may grow at rates close to the intrinsic growth rate EX 1: Northern Elephant Seals hunted close to extinction, stopped hunting (habitat and resources more abundant) population increased rapidly. Recolonized and population has increased exponentially EX 2: European Rabbits introduced to Australia grew exponentially could not be contained by human means but population was briefly stunted by disease o No population can maintain exponential growth indefinitely. o Population density typically fluctuates around a constant number of individuals o As population size increases, resources become limiting for growth and reproduction o Logistic Growth model  Carrying capacity (K) - the maximum population size that an environment can support.  Varies over space and time  Crowding and resource limitation effects the population growth rate(r)  Population growth slows as its density approaches K K= maximum sustainable population K-N= how many individual environment can support (K-N)/K= fraction of K available for population growth  At large values of N, population growth is small  When population size is below K, population growth increases  When population size is near K, population growth decreases oThis model fits populations of very small organisms fairly well(insects and microorganisms) oMany populations do not stabilize at K oPredictions are only correct when environment is constant, no predators, no competition from other species oLogistic curve does not fit well because:  Each individual added to population has same negative effect on population growth  Population approaches K smoothly  Time lag between the negative effect of population size increase and when they are realized; can cause population size to overshoot and undershoot  Populations may oscillate about K  Populations are large and density is important in regulation  Any essential resource that is in short supply can limit population growth  Natural populations are a mix of density dependent and density independent factors. Over long time scales, many populations remain stable and close to K (density dependent). Short term fluctuations in populations due to density- independent factors.  Density-Dependent Control oFactors that alter per capita birth or death rates in a population are dependent on population density ex: parasitism, predation, competition can be density dependent EX: Bubonic plague; blood pathogen transmitted by flea bites. Spread easily due to clumped population  Density-Independent Control oFactors that alter per capita birth rates in a population are independent of population density ex: physical/chemical factors: weather, drought, freezes, flood and fire oEX: logging removed temperature buffer and 1995 freeze killed Monarch butterflies by the millions o Density- the number of individuals per unit area or volume  Measured by o total counts(count all individuals) o sub-sampling to estimate densities and total population size(quadrats; mark and recapture)  Indirect indicators-number of nests, fecal droppings, tracks, etc., estimates of density o Patterns in dispersion- the spacing of individuals within the geographic range of population. Change with spatial scale.  Clumped- most common; due to unequal distribution of resources and/or social behavior  Uniform- distributed based on minimum distance between individuals due to interactions between individuals  Random- distributed without regard to position of other individuals; chance dispersal or resource not limiting o Population Regulation  Stable and Unstable Population- at equilibrium the population does not change unless disturbed  Stable equilibrium (birth=death) if perturbed population will return to initial density. Stabilizing forces dampen population fluctuations; density dependent control.  Unstable equilibrium- if perturbed, population may not return to initial density. Destabilizing forces enhance population fluctuations. Inverse density dependence, with long time lags. o Metapopulation  Population is divided into discrete sub-populations which are connected by immigration and emigration  Growth and reproduction within patches, migration between patches or colonization of empty patches  Migration- local population fluctuations are dampened(increase) local population fluctuations are enhanced; increase probability of extinction(decrease) shifting mosaic of occupied and unoccupied patches(intermediate) -the probability of local colonization -the probability of local extinction -the fraction of unoccupied sited f- The fraction of sites occupied  If the immigration rate is high and the extinction rate is low the fraction of occupied sites will increase with time; if the immigration rate is low and the extinction rate is high the fraction of occupied sites will decrease with time. EX: drought decimated 3 sub-populations of bay checker spot butterflies (caterpillars fed on a metapopulation of goldfield flowers); largest population serves as a source of new colonist to recolonize formerly extinct patches.  Community- two or more populations living in the same geographical area o Interactions among organisms o Characteristics: trophic structure, species diversity, dominance, growth from structure o Individualistic hypothesis(Gleason 1926) communities are chance assemblages of species with similar abiotic requirements o Interactive hypothesis(Clements 1936) communities are assemblages of dependent closely linked species o Species diversity – species richness + species evenness  Species richness-the number of species in a community  Species evenness- the relative abundance of species in a community  Shannon-Weaver(Wiener) Diversity Index: the most commonly used index of species diversity(H) ∑ The total number of individuals contributed to the total abundance - Proportion of individuals contributed to the total abundance  Disturbance- an event that removes organisms and alters resource availability. Communities with very high or low disturbance have lower species diversity than communities with moderate disturbance oIntermediate disturbance hypothesis (Connell 1978) when disturbance is sever and frequent, community is composed of good colonizers(r-selected) with high reproductive rates. When disturbance is mild and rare, community is composed of good competitors (K-selected) Species Diversity is highest where disturbance is moderate (intermediate) in severity and frequency. Allows both colonizers(r) and competitors to coexist(K) EX :( Sousa 1979) Ellwood boulder fields (species diversity was higher when disturbance was moderate)  Communities are adapted to a specific frequency and intensity of disturbance. Example: fires; diversity is higher when fire is neither too rare not too frequent. Fire survivors (K) insulation and resprouting. Fire followers(r) serotiny and scarification  The Diversity-Stability Hypothesis(Elton 1950) o Disturbance in diverse communities is dampened by large numbers of interacting species o The effect of disturbance is less than it would be in a species poor community. Example: outbreaks of pests in agricultural plots are greater than in natural landscapes that contain more species. EX: (Tillman 1996) 11year study of 207 grassland plots that varied in species richness. Variation in community biomass was lower in plots with higher diversity. (Higher diversity increases community stability; growth of disturbance resistant species can compensate for the loss of sensitive species flowing environmental change)  Ecosystem- Comprising the community, together with its physical environment o Energy flow and cycling of nutrients among abiotic and biotic components o Features of ecosystems: open biological systems, one way flow of energy, cycling of nutrients o Inputs: energy and nutrients o Outputs: energy and nutrients o Trophic levels group species by functional similarity- defined by the number of steps through which energy passes to reach the organisms in it  Primary producers(autotrophs)  Primary consumers(eat primary producers)-herbivore, decomposers, and detritivores  Secondary consumers(eat primary consumers)  Tertiary consumers(eat secondary consumers)  Quaternary consumers(eat tertiary consumers) Most communities only have 3-5 trophic levels (because so much energy is lost) o Food chain- linear sequence of feeding interactions o Food web- multi-linkage feeding interactions o Biomass and Energy flow o Biomass-measure of weight of dry tissue(carbon) an organism contain o Energy- average of 10% of energy is transferred from one level to the next oTerrestrial systems- 3 trophic levels oAquatic systems- 4 trophic levels(nutrients high) 3 trophic levels(nutrients low) oCan make predictions based on number of trophic levels; odd numbers(resource limitation), even numbers(consumer limitation) EX: (Power 1990) river food web in the Eel River. Cages excluded top predator (steelhead trout) intermediate predators were released from predation, depressed tuft weaving grazers, algae
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