Lecture 18 Ecology Ecology: the study of relationships and interactions among organisms and their environment What’s involved? Predator-prey relationshipsFeeding relationships Habitats and nichesAvailability of nutrients Pollutionand habitat degradation Ecosystem: a community and its abiotic (non-living) environment Population: a group of organisms of the same species (capable of interbreeding) that live in the same area at the same time Community: a group of populations living and interacting with each other Species: a group of organisms of similar appearance and which can interbreed to produce viable offspring (offspring can live to maturity and produce their own offspring) Habitat: the physical area in which individuals of a certain species exist Biosphere: the portion of the Earth and its atmosphere that can support life; the total of all areas where living things are found, including the deep ocean and lower atmosphere

Organism Population Biosphere Community Ecosystem Many organisms make up a population Many populations make up a community Many communities make up an ecosystem Many ecosystems make up a biosphere This is where abiotic factors come into play!!!

Autotroph/producer: an organism that makes organic molecules from inorganic molecules using light or chemical energy –“self-feeder” –Photoautotrophs: undergo photosynthesis; use light energy to convert inorganic carbon (CO 2 ) into organic compounds –Chemoautotrophs: break down inorganic chemicals by chemosynthesis to form organic compounds –Examples: algae, some bacteria, plants Heterotroph/consumer: an organism which eats other organisms to obtain energy and organic molecules Example - us Detritivore: an organism which ingests dead organic material –Examples: scavengers, earthworms Saprotroph/decomposer: an organism that feeds on dead organic matter using extracellular digestion –Specialized detritivores! –Consume cellulose (plant matter) and nitrogenous wastes (i.e. poop) –Examples: fungi and bacteria

Communities and Ecosystems Food chain: a sequence of trophic relationships in which one population feeds on another. Trophic level: a step on a food chain or food web

4.1 Communities and Ecosystems Food web: a diagram that shows all of the feeding relationships in a community

Energy pyramid Fourth trophic level Third trophic level Second trophic level First trophic level Tertiary consumers Secondary consumers Primary consumers Producers

Communities and Ecosystems The Carbon Cycle

Lecture 19 Populations Population size affected by Birth rate + Death rate - Immigration + Emigration - Population Size Immigration Emigration Birth Death

Populations Sigmoid growth curve involves –Exponential phase –Transitional phase –Plateau phase Exponential Transitional Plateau

Populations Exponential growth –Unlimited –All organisms can rapidly increase their population size if there are no factors controlling their growth –Birth rate alone controls growth rate

Populations Transitional and plateau phases –The initial rapid increase in population size slows down (transitional phase) until the rate of growth is zero (plateau phase) –When r = 0, the number of individuals in the population has reached the carrying capacity—the maximum number of individuals of a species which can be sustainably supported by the environment

Populations Factors which limit population growth may be density-dependent or density-independent –Density-dependent factors Affect a larger proportion of the population as the density of individuals increases Examples: mortality due to predation or disease and intraspecific (within a species) competition –Density-independent factors Affect a proportion of the population regardless of its density Example: mortality due to natural disasters (still, if the population is denser, there will be a greater affect on the population size even though the proportion affected is independent of density)

Populations Factors which limit population growth may be extrinsic or intrinsic –Extrinsic population-limiting mechanisms Originate outside of the population and include biotic and physical factors Examples: food supply, predation, disease, weather –Intrinsic population-limiting mechanisms Originate in an organism’s anatomy, physiology, or behavior Examples… –Koalas may reabsorb a developing embryo when conditions are crowded and resources are limited –Lemmings migrate in large groups when resources are depleted –Competition for resources

Populations Ecologists often study a few individuals of a population in order to draw conclusions about the entire population Random sampling: a method used to ensure that every individual in a population has an equal chance of being selected for study –Quadrat sampling (useful for determining population size of stationary organisms like plants) –Mark-Recapture method (useful for determining population size of organisms that move around)

Populations Quadrat sampling for estimating population size (a quadrat is a square area of known size) 1.A quadrat is placed in the area to be sampled and grid lines are marked within the transect and numbered 2.Two random numbers are selected as coordinates 3.Individuals within the random square are counted and the number is recorded 4.Steps 2 and 3 are repeated as many times as possible 5.The total size of the sample area is measured 6.The mean number of plants per quadrat is calculated 7.The estimated population size is calculated using the equation below

Populations Mark-recapture method for estimating population size 1.Capture as many individuals as possible in the area to be studied 2.Mark each captured individual (without making them more camouflaged or more visible to predators—this would skew results!) 3.Release all marked individuals into habitat 4.Recapture as many individuals as possible and count how many are marked and how many are unmarked 5.Calculate the estimated population size using the Lincoln index: Estimated population size = (n 1 * n 2 ) / n 3 where n 1 = number initially caught and marked n 2 = total number caught on second capture n 3 = number of marked individuals recaptured