BSC 2011 UNIT IV STUDY GUIDE: Ecology 1. (a) Define ecology. Ecology: the study of the interactions between organisms & their environmentIn ecology, one asks: What factors influence the distribution and abundance of organisms? - What is causing this observed pattern?Population ecology: Concerned with the characteristics of a population, such as its growth rate (size, density), age structure, sex ratio, and how these characteristics change in response to ecological and evolutionary pressures. - What factors affect population size, age structure, and distribution through space and time? “the study of population growth”- Why study: better manage crop and livestock populations, for better pest control, to better manage populations of endangered species, & to better understand human population growth & management. Community ecology: How do interactions between populations of different species that live in the same area affect the structure and organization of a community?Ecosystem ecology: What are the interactions between a biotic community in an area and its abiotic (physical) environment? How do nutrients & energy flow through communities in an ecosystem?(b) How does a population differ from a community? Population: is a group of organisms of the same species co-occurring in time & space.Community: is all the organisms inhabiting a particular area, all the species. The community consists of multiple populations of different species. (c) How does a community differ from an ecosystem? Ecosystem: is the biotic & abiotic components of a particular environment.- Biotic components: living components (all the organisms in a particular environment)- Predation (interactions between different species), competition (interactions within a species), density, disease, parasitism (type of predation)- Abiotic components: nonliving components and physical factors- Physical: temperature, humidity, light, wind, soil/substrate structure, fire, topography/physical structure- Chemical: water, oxygen, pH, salinity, minerals, nutrientsThe community is all of the species and organisms, the ecosystem is the interactions in the community and the nonliving and chemical factors.(d) Please provide a specific example that exists in nature of: a population, a community, an ecosystem. Population: Rabbits in the desertCommunity: A desert community consists of: rabbits, coyotes, snakes, birds, mice and such plants as cacti, brush ect. Ecosystem: Coral reef: the biotic is the species of fish and corals; the abiotic is the salinity of the water, pH, what minerals and nutrients are there, oxygen levels, physical structure of the coral reef, the amount of light, temperature of the water, etc.2. (a)Define demography and list several types of “vital statistics” used in demography. Demography: the study of population’s vital statistics and the factors that influence these. Vital statistics: are a tool to study population growth1. Population size - absolute number of individuals2. Population density - number of individuals/ area or volume3. Population dispersion - how individuals are distributed in a population 4. Population sex ratio - male/female; even or skewed5. Population age structure - the distribution of different age classes in a population- Even: everything is the same age (e.g. trees in a planted garden)- Mixed: different ages in a population (e.g. tress in a natural forest)(b) Be able to interpret age-structure diagrams for populations. Age-structure: of a population is a function of birth rate & death rate, and these vary with age.(c) Discuss the appearance of an age-structure diagram for a population that is growing rapidly, as opposed to one that is actually decreasing in size or experiencing ZPG (zero-population-growth). Rapid growth: majority are of child-bearing age; diagram has a broad base (Afghanistan)Slow growth: relatively even distribution of ages, percent of the population starts to decrease after age 50 (United States)No growth: most are past child-bearing age “zero population growth” (ZPG): diagram has a narrow base (Italy)3. (a) What is a cohort? What can a person learn from a “life table” and a “reproductive table” that has been constructed for a particular population of some species? Cohort: a group of individuals born at the same timeLife table: an age-specific summary of survival for a population; obtained by following acohort through life.- Shows how birth rate and death rate varies with age- A life table is a demographic tool to predict future population structure (b) Be able to interpret survivorship curves. Survivorship curves: survival as a function of age; depicts how survival varies with age- Not always clear-cut for many speciesType 1: humans and other large mammals- Low death rate when young, higher late in age- Few young; most survive to maximum lifespan- High E investment Type 2: birds, small mammals, some lizards- Intermediate-type curve and intermediate E investments- Relatively constant death rate regardless of age at any age- Cause of death unrelated to ageType 3: trees, marine inverts, fish- High death rate when young, but then declines for the relatively few survivors - Little or no investment of E caring for large #'s of offspring(c) Explain the concept of ‘trade-offs” with respect to life history. An organism has a limited amount of E (energy) to allocate to enhance its “fitness” (survival and reproduction). Tradeoff: any E expended to one of these needs takes E away from other functions; usually a trade-off between survival & reproduction.- Therefore, E allocation takes on a complex cost/benefit ratio to the organism. - Characteristic patterns of energy allocation evolve over time for a speciesSpecies evolve different life history strategies to maximize fitness- Semelparity: “big bang” reproduction; reproduce once and die, usually many offspring with low chance of survival- Often an adaptive response to a variable environment- Salmon, century plants, many annuals: dandelions- Iteroparity: repeated reproduction throughout life usually fewer offspring/brood but higher survival - An adaptation to a more stable environment- Most mammals(d) Explain what a species’ “life history” refers to and provide an example of two species that have different or “contrasting” life- history strategies, describing how they differ. Life history: a species-specific pattern of birth, reproduction and death; use demographic data to compile a
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