UNIT IV STUDY GUIDE: Ecology1. (a) Define ecology. -The study of the interactions between organisms and their environment. (b) How does a population differ from a community? -A population is a group of organisms of the same species co-occurring in time and space and a community is all of the organisms inhabiting a particular area. (c) How does a community differ from an ecosystem? -A community is all of the organisms inhabiting a particular area and anecosystem is the biotic and abiotic components of a particular environment. (d) Please provide a specific example that exists in nature of: a population, a community, an ecosystem. -Population: species of fish in a pond -Community: all the species of plants and animals in the pond -Ecosystem: all the species of plants and animals in the pond and the other factors such as the water and rocks or soil2. (a) Define demography and list several types of “vital statistics” used in demography. -The study of population vital statistics and the factors that influence these.• Population size (absolute # of individuals)• Population density ( # individuals/area or volume)• Population dispersion (how individuals are distributed in a population)(b) be able to interpret age-structure diagrams for populations. -A function of birth rate and death rate. (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 population growth: Triangle shaped• Slow growth: Rectangle shaped, but more narrow at top• ZPG: narrow base, but rectangle shapedAge Structure Diagrams1SLOW growthZPG (ZERO growth)RAPID growth3. (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 time-Shows birth rate and death rate variance-Can be used to predict the future population structure(b) be able to interpret survivorship curves. -I: low death rate when young, higher later in age-large investment of E caring for relatively few young, most survive to max lifespan -II: intermediate type curve and intermediate E investments, relatively constant death rate regardless of age -III: high death rate when young but declines for the few survivors-little or no investment of E caring for large #’s of offspring, and few survive to max lifespanThe Survivorship Curves (I, II, III)(c) Explain the concept of ‘trade-offs” with respect to life history. -All organisms have a limited amount of E to allocate to enhance their fitness (survival and reproduction). Normally, there is a trade off between the two. Any E expended to one of these needs takes away E from the other.(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 is a species specific pattern of birth, reproduction and death. • Age of 1st reproduction• Frequency of reproduction• Length of reproductive activity• Number of offspring per “brood”-Sparrow vs. Albatross:• Sparrow: less E invested in survival and more E into reproduction (Reproduce earlier, die earlier)• Albatross: More E into survival than annual reproduction. By living longer they are still able to produce enough offspring to maintain species. 4. (a) Explain what carrying capacity is. 2-K= the maximum population size a particular environment can support. (b) How does carrying capacity affect population growth? • N<K, dN/dt is positive and the population grows• N=K, dN/dt is zero and the population doesn’t grow (=ZPG, or zero pop’n growth)• N>K, dN/dt is negative and the population shrinks5. (a) Explain the difference between a population that grows exponentially as opposed to one that grows logistically. -An exponential function is under “ideal conditions” which has unlimited resources and population growth rate is maximized. -A logistic function is realistic since resources are limiting and population growth rates will decline as resources are used up as the population grows.(b) Describe the shapes of the two different growth curves. -Exponential growth is J-SHAPED and logistic growth is S-SHAPED.(c) What does the logistic equation take into account that the exponential equation does not?-Logistic takes into account that resources are not unlimited and assume growth rate changes with density, and acknowledges the carrying capacity. (d) Define the meaning of each term in the logistic growth equation. -r= overall RATE of of pop’n increase (birth rate-death rate or b – m)e) What is the difference between r and rmax? -rmax reflects the max rate of increase under “ideal conditions”6. Imagine a natural population (say a newly established small population of mice in large meadow) that is initially small in size and that will proceed to grow logistically. Describe how the rate at which this population grows changes over time as it continues to grow in a natural environment in which there are limited resources. -With logistic population growth the population growth will slow as the population reaches K, the carrying capacity, here it will level out and should keep a constant population size.7. What is the difference between density-dependent and density-independent factors that regulate population growth? Please give an example of each. -Density dependent- if a factor (birth rate, death rate) changes in response to changes in the population density. Ex.• # Of seeds decrease as density increases• # Nestlings decreases as density increases• Survival decreases as density decrease -Density independent- (birth rate, death rate) does not change with population densityEx.• Weather• Sudden catastrophes, disturbances (fire, flood)8. (a) How does a Type I survivorship curve differ from a Type III curve with respect to 3both age- specific mortality and survivorship (lifespan). -Type 1 curve: low death rate when young, higher later in age large investment of E caring for relatively few young, most survive to max lifespan-Type 3 curve: high death rate when young but then declines for the relatively few survivors, little or no investment of E caring for large #’s of
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