# 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.
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 â€“ 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 â€“ p2 represents A1A1 â€“ 2pq represents A1A2 â€“ 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

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