Ecology
Terms
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- Life Table
- Summary of how survival and reproductive rates vary with the age of the organisms.
- Sx
- Age specific survival rate: The chance that an individual at age x will survive to be age x+1. Sx=Nx+1/Nx
- Lx
- Proportion of Survivorship: individuals that survive from birth to age x. Lx=Nx/No
- Fx
- Fecundity: Average number of offspring produced by a female while she is of age x.
- Nx
- Number of individuals alive at age x.
- x
- Age.
- Cohort life table
- The fate of a group of individuals born during the same time period (a cohort) is followed from birth to death.
- Static life table
- Survival and reproduction of individuals of different ages during a single time period are recorded.
- Survivorship curve
- Survivorship (Lx) date are used to plot the number of individuals from a hypothetical cohort that will survive to reach different ages.
- Type One Survivorship Curve
- Newborns, juveniles, and young adults all have high survival rates. Death rates don't begin to increase greatly until old age.
- Type Two Survivorship Curve
- Individuals experience a constant chance of surviving from one age to the next throughout their lives.
- Type Three Survivorship Curve
- Individuals die at a very high rate when they are young, but those that reach adulthood survive well later in life.
- Age Structure
- Proportions of the population in each age class.
- No*So=
- Number of individuals that will survive to the next time period
- No*So(Surviving individuals at age x) *Fx(Fecundity at age x)
- The number of newborns those survivors will produce in the next time period.
- Lambda
- Nt+1/Nt
- Stable age distribution
- When the age structure of a population does not change from one year to the next.
- Geometric growth
- Population of a species changes in size by a constant proportion from one discrete time period to the next. (hourly, daily, yearly) Forms a J shaped graph.
- Nt+1=Lambda*Nt or Nt+Lambda^t*No
- Geometric growth
- Exponential Growth Equations
- dn/Dt=rN N(t)=N(0)ert
- Exponential Growth
- Population of a species with continuous reproduction changes in size by a constant proportion at each instant in time.
- r
- A constant rate. Provides a measure of how rapidly a population can grow. Also known as exponential population growth rate or intrinsic rate of increase.
- dN/dt
- Represents the rate of change in population size at each instant in time.
- N
- Current population size.
- Lambda=e^r or r=ln*lambda
- Compare results of discrete and continuous time growth models.
- e
- Constant: 2.718. Use e^x on calculators.
- Life history
- Record of events and landmarks relating to its growth, development, reproduction, and survival.
- Life History Strategy
- Overall pattern in the timing and nature of life history events averaged across all the individuals in the species.
- Phenotypic Plasticity
- A single genotype may produce different phenotypes for a particular trait under different environmental conditions.
- Morphs
- Produces discrete types with few or no intermediates. Polyphenism. (metamorphosis)
- Polyphenism
- A single genotype produces multiple, discrete phenotypes. (Morphs)
- Allocation
- Relative amounts of energy or resources that an organism devotes to different tasks
- Allometry
- Differential growth of body parts that results in a change in shape or proportion with size.
- Isogamy
- Equal-sized gametes
- Anisogamy
- Different types of gametes that are different sizes.
- Complex life cycle
- Life cycle in which there are at least two distinct stages that differ in their habitat, physiology, or morphology.
- Direct development
- Go directly from fertilized egg to juvenile without passing through a larval stage
- Sporophyte
- produces haploid spores that disperse and grow into gametophytes.
- Gametophyte
- Produces haploid gametes that combine in fertilization to form zygotes that grow into sporophytes.
- Alternation of generations
- Going from sporophyte to gametophyte and back again.
- Semelparous Species
- Reproduce only once in a lifetime.
- Iteroparous Species
- Capable of reproducing multiple times.
- r-selection
- Refers to selection for high population growth rates. Occurs in environments where population density is low.
- k-selection
- Slower rates of increase in populations that are at or approaching L, carrying capacity or population size limit for the environment.
- K
- Carrying capacity.
- Stress
- Any external abiotic factor that limits growth.
- Quadrat
- Sampling area (or volume) of any size or shape, such as a 1 m^2 circular plot to count small plants.
- Grime's Triangular Model
- Plant success is limited by stress and disturbance. Categorized plant life histories within a triangle whose axes measure the degree of competition, disturbance, and stress.
- Competitive plants
- Under conditions of low stress and disturbance: superior in their ability to acquire light, minerals, water, and space should have a selective advantage.
- Stress-tolerant plants
- Become dominant in areas of high stress and low disturbance. Slow growth rates, evergreen foliage, absence of phenotypic plasticity, slow rates of water and nutrient use, and low palatability to herbivores.
- Ruderals
- Best in high disturbance and low stress. Short life spans, rapid growth rates, heavy investment in seed production, and seeds that can survive in the ground for long periods until conditions are right for rapid germination and growth.
- Senescence
- A decline in the fitness of an organism with age as result of physiological deterioration.
- Endosperm
- Nutrient-rich material that sustains the developing embryo and often the young seedling.
- Diapause
- State of suspended animation or dormancy in which an organism can survive unfavorable conditions.
- Ontogenetic Niche
- A size or state specific ecological role. Coined by Wener and Gilliam.
- Sequential hermaphroditism
- Changes sex during the course of life cycle.
- Distribution
- The geographic area where individuals in a species are present.
- Abundance
- The number of individuals in a species that are found in a given area.
- Genet
- A grove of genetically identical aspen trees is actually a single individual. Members of a genet are often physiologically independent of one another and may in fact compete for resources.
- Ramets
- Actually or potentially independent members of a genet.
- Disturbance
- An event that kills or damages some individuals and thereby creates opportunities for other individuals to grow and reproduce.
- Dispersal limitation
- Prevent species from reaching areas of suitable habitat.
- Geographic range
- Entire geographic region over which that species is found.
- Cooperative breeding
- Younger birds postpone breeding and instead help their parents raise offspring by performing such activities as nest building, feeding the young, defending the territory, and mobbing predators.
- Absolute population size
- Actual abundance. Can be estimated with area-based counts, mark-recapture methods, and niche modeling.
- Mark-recapture
- Methods often used to estimate the abundance of mobile organisms.
- M
- Marked individuals from total population.
- C
- Number caught the second time. Ex) A population was marked (M). They went out again and caught 15 more (C), but only 4 were recaptured (R)
- Equation to estimate total number in a population
- N=(M*C)/R
- Ecological Niche
- The physical and biological conditions that the species needs to grow, survive, and reproduce.
- Niche Model
- Predictive tool that models the environmental conditions occupied by a species based on the conditions at localities it is known to occupy.
- Birth, death, immigration, and emigration equation
- Nt+1 = Nt+B-D+I-E
- B
- Births
- D
- Deaths
- I
- Immigrants
- Population Fluctuations
- The size rises and falls over time. Fluctuations can occur as increases or decreases in abundance from an overall mean value.
- Population Cycles
- Alternating periods of high and low abundance occur nearly constant intervals of time.
- Delayed Density Dependence
- Delays in the effect that density has on population size. Can contribute to population fluctuations.
- Damped oscillations
- Deviations from the carrying capacity gradually get smaller over time.
- Stable limit cycle
- The population exhibits a cycle in which it fluctuates indefinitely about the carrying capacity (K)
- Genetic Drift
- The process by which chance events influence which alleles are passed onto the next generation.
- Inbreeding
- Mating between related individuals.
- Demographic Stochasticity
- Chance survival and reproduction of individuals. Can result in outcomes that differ from what we expect.
- Allee Effects
- When population growth rate (r or lambda) decreases as the population density decreases, perhaps due to difficulty finding mates at low population densities.
- Environmental Stochasticity
- Refers to erratic or unpredictable changes in the environment.
- Natural catastrophes
- Eliminate or reduce size of populations that otherwise would seem large enough to be at little risk.
- Extinction and colonization equation
- dp/dt=cp(c-p)-ep
- p
- Proportion of habitat patches that are occupied at time t.
- Habitat fragmentation
- Cause a species to have a metapopulation structure where it did not have one before.
- Bottom-up Control
- Occurs when the abundance of a population is limited by nutrient supply or by the availability of food organisms.
- Top-down control
- Occurs when the abundance of a population is limited by predators.
- Population limitation
- Any ecological force that affects abundance (density-independent as well as density-dependent)
- Population regulation
- Density-dependent ecological forces that keep population abundances within upper and lower limits.
- Why are smaller populations vulnerable to the effects of genetic drift?
- 1) Loss of genetic variability reduces ability to respond to future environmental conditions. 2)Genetic drift can cause harmful alleles to occur at high frequencies. 3)Small populations show a high frequency of inbreeding.
- Metapopulation dynamics
- Study of conditions in which extinction and establishment are in balance.
- Why complex life cycles?
- Small offspring may experience the environment very differently than the larger parents. - e.g., a tadpole is more strongly affected by surface tension and viscosity than an adult frog, or predation environment differs Parents and offspring can be subject
- Population
- All individuals of the same species occupying the same space at the same time
- Natural Selection
- acts at the level of the individual (survival and reproduction through differential reproductive success of phenotypic variants), but causes changes (evolution) at the level of the population
- demes
- small subpopulations with high probability of inter-breeding & random mating – panmixia (Hardy- Weinberg Equilibrium likely)
- Assumptions: Hardy-Weinberg Equilibrium
- Emphasis on Gene Frequencies, Not Individuals ⬢ Random mating ⬢ Infinite population size ⬢ No mutation ⬢ No natural selection ⬢ No gene flow Allele & genotype frequencies do not vary once population is at equilibrium
- Randomly Mating Population Equation
- p2 + 2pq + q2 = 1 – p2 represents A1A1 – 2pq represents A1A2 – q2 represents A2A2
- Measuring Genetic Variation
- Different measures of genetic variation depend on level of genetic analysis: phenotypic differences (polygenic), proteins (amino acids differ), DNA (nucleotide differences)
- Relaxing Assumptions of Hardy-Weinberg Equilibrium
- ⬢ Small population -- chance events & genetic drift, inbreeding more likely ⬢ Natural selection -- bias in genotype/ phenotype that reproduces ⬢ Mutation -- introducing significant new alleles? ⬢ Non-random mating -- sexual selection & mate choice ⬢ Gene flow -- new alleles or altered genotype frequencies from new individuals