Lecture 21 - Ecology PDF

Ecology Concepts 52.1; 52.4; 53.1-53.3; 54.1-54.2 Campbell. Biology. 3rd ed. Outline • 1. Areas of Ecological Research • 2. Dispersal and Distribution of Species • 3. Population Ecology • 4. Community Ecology 2. Dispersal and Distribution of Species • Species distribution is a product of evolu...

Ecology Concepts 52.1; 52.4; 53.1-53.3; 54.1-54.2 Campbell. Biology. 3rd ed. Outline • 1. Areas of Ecological Research • 2. Dispersal and Distribution of Species • 3. Population Ecology • 4. Community Ecology 2. Dispersal and Distribution of Species • Species distribution is a product of evolutionary history and ecology • Eg. Kangaroos are only found in Australia • Origin of kangaroos and their relatives is Australia (fossil records) • Geographic isolation prevented their distribution outside the continent • Within Australia, kangaroos are found in some habitats but not others • Fundamental question of ecologists: not where do species occur, but why do species occur in a certain area and what are the ecological factors (biotic and abiotic) that dictate their distribution Dispersal and Distribution • Dispersal is the movement of individuals away from an area of origin or centers of high population density • Understanding past and present dispersal of species and their evolutionary history helps to explain patterns of species distribution which is the spatial arrangement of species that have dispersed • Ecologist now use molecular evidence (fossils) to determine dispersal routes • Natural range expansion occurs as a group of organisms move over time and in response to climate variations or change • Dispersal limitations could include physical barriers (mountains) or large bodies of water (oceans) for example FIg 52.18 Range Expansion: The Adaptable Coyote Abiotic Factors affecting Dispersal • Temperature, salinity, sunlight or soil may prevent a species from living in a given area • Affect physiological functions that allow for growth and survival • Fundamental Niche = the range of abiotic conditions that allows a species to persist • Only certain plant species can persist in shade conditions (recall Topic 12 Plant Growth 2) • Only a few organisms can persist in both marine and freshwater environments (recall Salmon and smoltification Topic 3 Animal Form and Function) Temperature and Moisture • Two most important abiotic factors that limit species distribution Moisture • Recall most leeches are found in aquatic environments • Low moisture levels in deserts limit the species that can persist in that environment Temperature plays a large role in biological processes • Recall Homeostasis and set points • Recall Thermophiles • Recall ectotherms and endotherms • Plants cells may rupture if the water inside freezes Biotic Factors affect Dispersal • Predation or herbivory • Seed eating small mammals are preventing sugar maples from extending their distribution as the climate warms • Absence of pollinators • Absence of food resources • Presence of pathogens, parasites or competing species • Today, humans are often the biotic factor that increases or decreases distribution of species • Loss of habitat due to anthropogenic factors • Increase of distribution due to humans moving plants or animals around the globe FIg 52.19 The range of the cattle egret expanded along with global cattle industry 3. Population Ecology • Species = a group of organisms with similar characteristics and that are capable of interbreeding and producing viable, fertile offspring • Population = a group of individuals of a single species living in the same general area • Members of a population rely on similar resources, are influenced by similar environmental factors and typically interact and breed with one another • The boundaries and size of a population help to define it • Natural boundaries – animals on island surrounded by water • Arbitrary boundaries – defined by someone investigating the population • Population ecology looks at intraspecific interactions Density of Populations • The density of a population is the number of individuals per unit area or volume • Differences in local density provide insight into environmental associations and social interactions of individuals in a population • Rarely, the density is determined by counting all individuals in the population • Sampling a population is a more common method • Number of oak trees in several random locations in a 100 x 100 m area • Calculate the average across the sampled areas • Determine an estimation of the population and extend it to the entire area • More samples leads to a better estimation Mark Recapture Method • The Mark-Recapture technique is used to estimate the size of a population such as with animals that move around a lot • The basic idea is that you capture a small number of individuals, put a harmless mark on them, and release them back into the population. • Later, you catch another small group, and record how many have a mark. In a small population, you are more likely to recapture marked individuals, whereas in a large population, you are less likely. • Density is not static. Additions can occur through birth or immigration • Immigration = the influx of new individual into an area • Removal of individuals in a population occur through death or emigration • Emigration = the movement of individuals out of a population and into other locations Dispersion of Populations Dispersion is the pattern of spacing among individuals within the boundaries of the population • Clumped = most common dispersion in which individuals are aggregated into patches • Common in plants and fungi • Clumping in animals most often associated with mating behavior • Uniform= evenly spaced pattern of dispersion • Allelopathy in plants • Territoriality in animals • Random= position of individuals in a population is independent of other individuals • occurs in the absence of strong negative or positive interactions among individuals • Chemical or physical factors are relatively constant across a study area Demographics • The study of the vital statistics of a population and how they change over time • Life Tables summarize the survival and reproduction rates of individuals in specific age groups within a population. Cohorts are used to construct the table and researchers follow the cohort from birth until death • Ecological Cohort = a group of individuals born at the same time • The life table is built by calculating the proportion of the cohort that survives from one age group to the next. Offspring produced by each age group is also accounted for. • Survivorship Curves can be created from life table data. A plot of the proportion of individuals in a cohort that are still alive at each age. • 3 general types of survivorship curves • Type I = flat at the start and during mid-life, then drops steeply among older age groups • Common for large mammals (including humans) with few offspring that they care for • Type II = A straight line indicates a relatively constant rate of death • Type III = curve drops sharply at the start reflecting high death rates in young • Typical for organisms with high numbers of offspring but no parental care such as invertebrates • Reproductive Rates • Estimating the number of breeding females in a population • Female offspring production declines with age • Can use direct counts or mark-recapture method, or molecular tools • Eg. Collect skin samples from Female Loggerhead Turtles in a given area (198 samples over 4 years) • Create a database and genetic profile for each female • Extracted dna samples from eggshells in nests and compared sequences to data base to determine which females laid the eggs and how many offspring were being produced by each female Carrying Capacity • As population density increases, each individual has access to fewer resources • If this limited access is sustained for long periods of time, food supplies dwindle, and individuals die • There is a limit to the number of individuals that can successfully occupy a habitat = carrying capacity = K = the maximum population size that a particular environment can sustain • Limiting factors include energy, shelter, refuge from predation, nutrients, water and suitable nesting sites • Population growth is limited by crowding and resource limitations. If not enough resources available birth rates decline and death rates may increase https://researchtweet.com/carrying-capacity-definition-graph-and-examples/ 4. Community Ecology • Community interactions are classified by whether they help, hinder or have no effect on the species involved • Interspecific interactions = interactions between individuals of two different species • include competition, predation, herbivory, parasitism and mutualism and commensalism • Interactions can have either positive or negative effects on survival and reproduction • Ie, predation is positive on predator population and negative on prey population Competition • Interspecific competition is an interaction that occurs between different species when they compete for a resource • Ie, weeds growing in a garden compete with crop plants for resources • Competitive exclusion occurs when two species in community compete for a limited resource • Some individuals usually have a competitive edge for obtaining the food source for example and therefore cannot coexist in the same place permanently Ie, weeds growing in a garden compete with crop plants for resources • Ecological Niche = the specific set of biotic and abiotic resources that an organism uses in its environment • Temperature ranges that are tolerated by a specific organism for example • Resource partitioning = differentiation of niches that enables similar species to coexist • Fundamental Niche = niche potentially occupied by that species • Realized Niche = the portion of the fundamental niche that the species actually occupies Figure 52.4 Resource partitioning among Dominican Republic lizards Exploitation • Exploitation is a general term for any +/- interaction where one species benefits by feeding on another species • Predation - can be +/- interactions between two species in which one species, predator, kills and eats the other, prey • Potential prey animals have behavioral, mechanical and chemical adaptations that help to prevent them being eaten • Aposematic = warning or bright coloration which deters predators (poisonous frogs) • Cryptic coloration = camouflage which makes them difficult to see (stick insects) • Batesian mimicry = a palatable or harmless species mimics an unpalatable or harmful one (other species of butterflies resembling monarchs) • Herbivory = can be+/- interactions between two species • Animal eats a plant or algae • Herbivores have specialized adaptions such as chemical sensors on insects feet to help them determine which plants are host food sources and which are toxic • Some herbivores have specialized teeth or digestive systems adapted for processing certain plants • Plants produce toxins to deter herbivores as well as morphological adaptations including spines or thorns • Tannins are chemicals that deter herbivores • Recall resin canals of pine trees • Cinnamon, cloves, peppermint • Parasitism = can be +/- interaction • When one organisms derives its food source from a living host • Endoparasites = live within the body of the host • tapeworm • Ectoparasites = feed on external surface of host • Ticks, lice • Some parasites change the behaviour of their hosts such that it increases the probability of their survival • Parasitic spiny headed worms cause their crustacean host to leave their protective covering and move out into the open. This increases likelihood that crustacean will be eaten by a bird, the parasites secondary host Positive Interactions • When both species are positively affected by the interaction +/+ • Mutualism = symbiosis = interspecific interaction where both species benefit • Mycorrhizal fungi and plants • Rhizobia bacteria and plants • Commensalism = interspecific interaction where one species benefits and the other is not harmed • Algae living on the shells of aquatic turtles "hitchhike rides" • Cattle egrets feed on insects flushed out of the ground by grazing bison/cattle • Facilitation = species have positive effects on another without living in the direct and intimate contact of symbiosis • Common in plant ecology • Grass plants near a legume (nitrogen fixing plant) will benefit from nitrogen released into the soil • Juncus gerardi (black rush) prevents salt build up in the soil by shading the soil surface in marshes which makes the soil more hospitable for other plant species Figure 54.10 Facilitation by black rush in New England salt marshes Diversity and Trophic Structures • Species Diversity • Diversity includes both richness and abundance • Species richness = number of species present in a community • Species abundance = the proportion of each species among all individuals in the community • Obtaining data on diversity and species counts can be challenging, particularly with insects or other animals that are mobile Which forest is more diverse? Diversity and Community Stability • Ecologists manipulate species diversity in experimental plots and laboratories to examine potential benefits of diversity including productivity and stability • In plant communities, the most diverse plots typically produce the greatest amount of biomass compared to single species plots (recall facilitation) • Higher diversity communities are also more resistant to invasive species = organisms that establish outside their natural range Trophic Structure • The structure and dynamics of a community also depend on feeding relationships between organisms, also known as the trophic structure • Food chain = the transfer of food energy up the trophic levels Food Webs • • • • Food webs are interconnected and interdependent food chains Plants = primary producers Herbivores = feed on primary producers and are primary consumers Carnivores = feed on other consumers and are secondary consumers and tertiary consumers • Omnivores = species that feed at more than one trophic level Tundra Food Web Species with Large Impacts in Communities • Certain species have a large impact on the structure of an entire community • Highly abundant • Play a pivotal role in the community • Dominant species = the species that are the most abundant or collectively have the highest biomass • Exert a powerful force over the entire community • Eg sugar maples • Eg American chestnut • Keystone species are less abundant than dominant species but still exert a strong control on the community • Pivotal role or niche • Eg sea otters and sea urchins • Ecosystem engineers = species that dramatically alter their environment • Effects of ecosystem engineers on other species can be +/• Eg. beavers Bottom-Up and Top-Down Controls • Bottom up control = a lower trophic level affects the community structure of higher trophic levels by means of resource restriction • Top down control = higher trophic level influences the community structure of a lower trophic level through predation • Eg.nutrient levels control plant numbers or biomass; plants control herbivore numbers; herbivores control number of predators; • To change bottom up the structure at the lower levels must be controlled • Top down model postulates that predation controls community organization because predators control herbivores The End • Thank you • Questions? • Have a great day!