Ecology exam 2

Evolution

Change in frequency of alleles from one generation to the next

• Is a population phenomenon

• Requires variation to exist

• Modeled mathematically

• “decent with modification”

• Talking about changes in the gene pool

• Fitness

An individual’s genetic contribution to subsequent generations

• Often measured indirectly- survival and reproduction

Where does evolution take place?

• Selection acts on individuals

• Evolution happens at the population scale

• Evolution happens because genetic variation exists in natural populations

• Variation within populations arises from:

• Genetic mutation

• Recombination

• Gene duplications

• Gene flow among pops

• Mechanisms of evolutionary change

• Mutation

• Genetic drift

• Gene flow

• Selection

Genetic drift

Random fluctuations in frequencies of alleles

Gene flow

Genetic connectivity among populations

• Can bring beneficial alleles

• Can reduce effects of selection

Selection

Any process that results in differential survival and/or reproduction among the members of a population

• Selection

• Natural selection

Favors traits that increase survival and reproduction

• Selection

• Sexual selection

Favors traits that increase reproductive success, but do not necessarily increase survival

• Selection acts on traits

• Selective agent

The thing exerting force of selection on an organism

• Selection acts on traits

• Target of selection

The feature being acted upon by the selective force

• Selective forces typically act in three general ways

• Directional selection

Favors individuals at one end of the phenotypic range

• Selective forces typically act in three general ways

• Stabilizing selection

Favors intermediates and acts against either end of extreme variation

• Birth weight

• Aposematic organisms

• Selective forces typically act in three general ways

• Disruptive selection

Favors individuals at both extremes of the phenotypic range

Strength of selection varies and can be measured

• Differences between the mean of a phenotypic distribution before and after selection, measured in units of standard deviation

• - Mean swallow mass before selection = 100g; standard deviation = 10g

• - Mean swallow mass after selection = 115g

• - = (115-100)/10 = 1.5

• Regression techniques

• Depends on heritability of trait

Selection varies over space and time

• Clines

• Selection can vary in a patchy manner

Clines

Generally continuous variation in a trait across geographic space

• Melanization

• Body size

Adaption

An inherited characteristic that enhances an organism’s survival and reproduction

• Results from selection

• Not everything is an “_____”

• - Plasticity

• - Pleiotropy can be a cause for a trait

• - Some traits are product of genetic drift

Adaptations are not perfect (evolution is not a perfecting process)

• Lack of genetic variation

• Evolutionary history

• Ecological trade-offs

Ecology can influence evolution

• Biotic and abiotic factors impose selective forces on individuals → pop. genetic change

• Selection on ecological traits can cause reproductive isolation → speciation

• Red queen hypothesis

• Coevolution

Red queen hypothesis

Organisms have to continuously evolve because their environment and interactions with other species change over time

Coevolution

Reciprocal evolution between species because of their interactions

Behavioral ecology

Study of how behavior is influenced by genetics and the environment

• Behavioral ecology

• Ecological

Does this behavior influence dist. and abundance

• Behavioral ecology

• Evolutionary

Are there fitness benefits?

• Animal behaviors can be explained at different levels:

• Proximate cause

Or how the behavior occurs

• Animal behaviors can be explained at different levels:

• Ultimate causes

Why the behavior occurs; the evolutionary and historical reasons

Behaviors reflect underlying genetic architecture

• Behaviors can be adaptations

• Also influenced by environment

sexual selection

Results from differential reproductive success due to variation among individuals in success at getting mates

• Selection for traits that increase fitness, but do not necessarily increase survival

• Breaks down into intra and inter sexual selection

Many times females are choosy about their mates

• Could be tied to gamete size

• Energy invested in reproduction

• Benefits of choosiness:

• - Good genes

• - Resources

• Arbitrary or bias

Ecological factors can affect mating decisions

• Choosiness can be altered by # of potential mates

• Quality of mates

• Availability of food

• Presence of predators

• Presence of competitors

• Visual environment

If foraging behavior is an adaptation to limited food supplies, then it must benefit survival and reproduction

• Seek to maximize energy intake

• Seek to reduce energy spent

• - Finding prey

• - Handling prey

• - Consuming/digesting prey

• Seek to reduce vulnerability

Marginal value theorem

Food availability is usually patchy and animals should forage in the most profitable patch until the rate of energy declines to a point

• Giving up time - when the point is reached

• Distance influence

• Assumptions and predictions

Foraging decisions represent trade-offs

• Predators affect foraging decisions

• Environmental factors also influence

• Dietary trade-off’s to maintain defenses

Life history

The lifetime pattern of growth, development, and reproduction for an organism

• Optimal maximizes fitness

• Life history characteristics include:

• Age and size at sexual maturity

• Amount and timing of reproduction

• - Fecundity- # of offspring per reproductive episode

• Survival and mortality rates

• Differences exist among individuals, but can look at species average

• Types of reproduction

• Asexual reproduction

• Parthenogenesis - where offspring develop from unfertilized eggs

• Clones, ramets, genets

• Types of reproduction

• Sexual reproduction

• Advantage is genetic variation

• Disadvantages…

• - Parent transmits only ½ its genes

• - Males…

• Favorable gene combinations disrupted

Complex vs. simple life cycles

• Complex life cycles have at least two stages that differ morphologically and ecologically

• Simple have direct development

Selection pressured can be different from one life stage to the next in either complex or simple life cycles

• Predation vulnerability

• - Defensive compounds

• Dispersal capability

• Dormancy

• Thermoregulation

• Timing of metamorphosis

• Parity

The # of reproductive episodes

• Semelparous

• Iteroparous

Semelparous

Reproduce only once

Iteroparous

Reproduce multiple times

• Parental Investment

• Provisioning

Amt of yolk or endosperm

• Parental Investment

• Parental care

Investment of time and energy in protecting and feeding young

• The r-K selection continuum

• r-selection

Selection for high population growth rates

• Small organisms

• Short lifespans

• Low parental investment

• Rapid development

• Most insects, small vertebrates such as mice, weedy plant species

• The r-K selection continuum

• K-selection

For slower growth

• Longer lived

• Develop slowly

• Greater investment

• Lower reproductive rates

Allocation drives trade-offs

• Energy and resources are limited

• Natural selection favors max fitness

• Energy budgets and sexual maturity

• Reproductive effort - proportion of energy devoted of reproducing

Trade-off: Lifespan and reproduction

• Survival increases age maturity

• Delay reproduction: grow faster and reach larger size - benefit?

• But reproducing early guarantees offspring

Trade-off: Size and number of offspring

• Larger offspring = smaller # of offspring

• Seen in many organisms, but not all

Trade-off: Offspring # vs. offspring survival

• As offspring # increases, the amount of care per offspring decreases → decreased survival

• Lack clutch size - Maximum number of offspring a parent can successfully raise to maturity

Trade-off: Parental care vs. parental survival

• More offspring = more work

• Parental survival decreases

Inter-specific interactions can drive changes in trade-offs between life history characteristics

Trinidadian guppy work experimentally demonstrated predation can affect life history traits

Species have geographic ranges

All the areas the species occupies

• Determined by abiotic and biotic factors

• Fundamental niche

• Multiple populations

• Species not uniformly dist.

• Small-scale variation in the environment creates geographic ranges that are composed of small patches of suitable habitat

• Endemic

• Cosmopolitan

• Niche modeling

Fundamental niche

Range of abiotic factors required by a species for its persistence

Endemic

Species that live in a single, often isolated, location

Cosmopolitan

Species with very large geographic ranges that can span several continents

Niche modeling

A model that predicts a specie’s distribution based on abiotic factors (usually)

• Where to find something

• Invasive species

• Historical geographic range

How niche modeling works 101:

• Find specimens

• Get all of the relevant data to where the species is living (climate, precipitation, temp, humidity, etc.)

• Computer calculates and creates a heat map

Population

Group of interacting individuals of the same species living in a particular area at the same time (interbreed)

• Multiple populations exist across a species distribution

• Fundamental unit of evolution

• Metapopulations

Metapopulations

Populations that are made up of groups of interacting subpopulations

• World is patchy place

• Sources

• Sinks

Sources

Pops. in high quality habitats with high growth rates

Sinks

Pops in low quality habitats where growth is low

Dispersion

The spacing of individuals with respect to one another

• Uniform

• Random

• Clumped

Uniform

Individuals spread out evenly throughout an area

• Competition for space or resources

Random

Dispersal

Clumped

Individuals are clustered in certain portions of the distribution

• Resources scarce

• Social behavior

Dispersion patterns can change over organism’s life

• Mating

• Env. Requirements

• Example: Creosote bush

• Abundance and density

• Abundance

The total number of individuals in a population that exist within a defined area

• Abundance and density

• Density

In a population, the number of individuals per unit area or volume

Mark-Recapture is one method to assess population size

Assumptions for mark-recapture

• Population size does not change during sampling period

• Each individual has an equal chance of being caught

• Marking does not harm individuals or alter their behavior

• Marks are not lost over time

Dispersal - the movement of individuals from one area to another

• Not migration!

• Movement between suitable habitats

• Colonize new areas

Population ecology

Explored how biotic and abiotic factors influence populations

• Population ecology

• What are characteristics of a population?

Density, distribution, size, and age structure of populations

• Population ecology

• Four factors affect all characteristics of a population

• Birth

• Death

• Immigration

• Emigration

One of the ecological maxims is:

“No population can increase in size forever”

• What factors affect population size?

• What can we measure?

Demographics

Is the study of the vital statistics of a population and how they change over time

• Demographics

• Vital statistics

The conditions affecting life and the maintenance of population

• Birth rates, death rates, survival

• Demographics

• Study techniques

• Life tables

• Survivorship curve

• Fecundity sched.

• Age distribution

Life table

Is a summary of how survival and reproductive rates vary with age

• Life Table

• Cohort table

Made by following a cohort through life

• Life Table

• Static life table

Survival assessed from a death assemblage

• Life Table

• Age class

A category that includes individuals of, or between, a certain age

• Life Table

• Age structure

Proportion of the population in different age classes

• Mortality and reproduction differs in each age class

Parts of a life table concerning survival

• x = the age/stage class

• n0 - # of original individuals born

• nx - # of individuals alive at age class x

• sx = survival rate: proportion of individuals that survive to next age class (=nx+1/nx)

• dx - # of individuals that die in age class x

• qx - age class specific mortality rate (= dx/nx)

• lx = survivorship: Proportion of individuals that survive from birth to age x (=nx/n0)

Survivorship curve

Plot survivorship with survivorship on Y axis and age on X axis

• Survivorship curve

• Type 1:

Most individuals survive to old age (Dall sheep, humans)

• Smaller litter

• Parental care

• Large organisms

• Long lifespan

• Survivorship curve

• Type 2:

The chance of surviving remains constant throughout the lifetime (some birds)

• Survivorship curve

• Type 3

High death rates for young; those that reach adulthood survive well (species that produce a lot of offspring)

• Lots of offspring, low parental care, high predation

Reproductive potential can also be included in life tables (sometimes reproductive tables)

• Reproductive potential differs from one age group to the next

• Fecundity= bx (in book = Fx)- Average number of female offspring a female will have at age x

• Net reproductive rate

Net reproductive rate

The total number of female offspring that we expect an average female to produce over the course of her life

• Ro >1: increase

• Ro =1: stable

• Ro <1: decrease

• Using survival and reproductive data allows us to look at reproductive rate

• Generation time (T)

The average time between the birth of one generation to birth of next gen

We can model population growth and change in age distribution over time

• # individuals that will survive to the next time period

• # offspring those survivors will produce in the next time period

Stable age distribution

When the age structure of a population does not change over time

• Occurs when survival and fecundity of each age class stays constant over time

• Sudden change in environmental factors can change birth or death rates

Population growth

Refers to how the number of individuals in a population increases or decreases over time

• Open vs. closed populations

• Growth rate = #b - #d

• Two continuously accelerating growth models

• Classic exponential

• Continuous reproduction

• Generations overlap

• Population changes in size by a constant proportion at each instant in time

• r= intrinsic growth rate

• Two continuously accelerating growth models

• Geometric

• Discrete breeding seasons

• Lambda (λ) = geometric growth rate or per capita finite rate of increase

Details: Geometric growth