Ch 53-54 Notes

Characteristics of Populations:

  • Density

  • Distribution

  • Age Structure

  • Carrying Capacity

  • mortality rate


  • one useful sampling technique for estimating population density is the mark-recapture method

Sampling Methods:

Population Characteristics:

  • Density: # of individuals per unit of area; counts:

    • sample size estimate(sometimes possible to count individuals)

    • indirect indicators

    • mark-recapture

  • Dispersion: pattern of spacing

    • random;unpredictable, patternless spacing

    • clumped- patchy aggregation (most common in nature)(has to do with available resources, not territory)

    • uniform-even spacing(usually territorial behavior)

  • Biotic Potential (r max)

  • Exponential growth is the accelerating increase that occurs during a time when growth is unregulated

    • A J-shaped growth curve described by equation G = rN is typical of exponential growth

    • rN tends to cause the population to grow increasingly rapidly(r is difference between birth and death rates, is pop. size, therefore rN is population growth rate)

      • G = population growth rate

      • r = intrinsic rate of increase/ organism’s maximum capacity to reproduce

        • r = (birth rate - death rate) + (immigration rate - emigration rate)

      • N = population size

    • Influences that regulate pop. growth rates

      • competition

      • territoriality

      • health

      • predation

      • intrinsic factors(physiological)

      • other extrinsic factors(environmental)

    • Equation G = rN(K-N)IK describes a logistic growth curve

      • K = carrying capacity

      • (K - N)IK = accounts for leveling off of the curve

    • Logistic growth is slowed by population limiting factors

      • tends to level off at carrying capacity

Population Growth Models

  • Exponential model(blue)

    • idealized population in an unlimited environment (J-curve)

    • r selected species (r=per Capita growth rate)

  • Logistic model(red)

    • carrying capacity(K): maximum population size that a particular environment can support (S-curve); K-selected species

  • Density Controls

  • Life Tables

    • Life Tables and survivorship curves predict an individual’s statistical chance of dying or surviving during each interval in its life

    • Life tables predict how long(on average), an individual of a given age can live

  • Population ecologists have adopted this technique, construcuting life tables for various plant and animal species

    • Type 1 Survivorship: a K selected species(humans)

      • live long, few offspring (maternal care)

      • mortality is later in life

      • low rates of juvenile mortality

    • Type 2 Survivorship: intermediate (plants, lizards)

      • mortality is equal across all age groups ( probability of survivorship does not change with age)

    • Type 3 Survivorship: a r-selected species

      • mortality is high right after birth (high rate of juvenile mortality)

      • small body, no paternal care

      • high production of offspring(weeds, fish, asexual reproducers)

  • Survivorship curves plot proportion of individuals alive at each age

    • 3 types of survivorship curves reflect species differences in life

R-Selected Species(density independent selection)(high reproductivity, short lifespan)(unrelated to population size)

  • high population growth rate (r=growth rate)

  • tends to maximize r, fluctuates well below carrying capacity

  • small body

  • early maturation

  • short lifespan

  • large broods

  • little or no paternal care

  • considered as opportunistic

  • found in environments that are temporary, unpredictable, and variable

  • low survivorship; die early

  • face little competition

  • ex: weeds, dandelions, asexual reproducers

K-Selected Species(density dependent selection) (humans; low reproducitvity, high life span)

  • number of individuals is near carrying capacity (K)

    (tends to maximize population size at/near “K”

  • sensitive to population density

  • large body

  • low reproductive rate

  • produce few offspring

  • long lifespan

  • development is slow(late maturation)

  • parental care and protection of young

  • found in stable environments

  • ex: birds and mammals

Density Independent factors:

  • unrelated to population size(ex: temperature

  • affects same percentage of the population regardless of population density

  • NOT: accumulation of toxic wastes(increases and decreased with population size)

  • NOT: disease(spread increases and decreased with population size)

  • NOT: food availibilty(increases and decreased with population size)

  • NOT: Parasites(eash with which Parasites spread increases and decreased with population size)

Density Dependent factors:

  • predators

  • affects larger percentage of the population as population density increases

  • competition with individuals

  • food supply

Semelparity - (one time reproduction)

  • “Big Bang” reproduction

  • ex: agave and annual desert flowers

  • (obs. in highly variable or unpredictable environments)

Iteroparity - (repeated reproduction)

  • ex: lizards

  • (obs. in dependable environments/competition for resources are intense)

Life Histories - Follows a “cohort”

  • an organism’s life history is the series of events from birth through reproduction to death

  • Life history traits include:

    • age at which reproduction first occurs

    • frequency of reproduction

    • number of offspring

    • amount of parental care given

    • energy cost of reproduction

    • when reproduction begins, how often organism breeds, and how many offspring are produced during each reproductive episode



  • Boom-and-bust cycles of growth and decline

    • ex: population cycles of the lynx and the snowshoe hare

      • lynx is one of main predators of snowshoe hare in northern forests of Canada and Alaska

    • Intrinsic Growth Pattern

  • Human Population

    • pop. doubled 3 times in the last 3 centuries

    • Increase due to improved health and tech and decline in death rate

    • birth rate has decreased

    • growth rate: 1-2% per year

    • Zero Population growth: ZPG, number of people in specified population neither grows nor declines; number of births plus in-migrants equals the number of deaths plus out-migrants.

  • Age Structures Diagrams

    • percentage of age groups in a population; pre-reproductive, reproductive, post-reproductive

    • helps predict future growth

    • can show if population is increasing, decreasing, or constnat

    • shape matters:

      • pyramid vs tapered base (funnel)


We Study Communities by Examining these Factors:

  • Number of species present

  • abundance of each species

  • defining their niche

  • interactions (ex. Predator/prey)

  • resiliency to a disturbance (succession)

  • energy and nutrient flow(food webs and geocycles)

  • productivitie(autotrophs)

Aspects of a Community

  • composed of a variety of species and all of the abiotic factors

  • lack of precise boundary

  • involves all of the interactions that occur between each species

  • diverse and complex

  • difficult to study accuratley(many variables)

  • has obvious patterns and processes

Examples of Communities

  • hydrothermal vent

  • rotting logs

  • pond

  • tree canopy

  • intertidal zone

Interactions in a Community

  • Interspecific: interactions between populations of a different species within a community

    • less intense

  • Intraspecific: between SAME species; intense

  • Predatory/prey: adaptations and protective traits

    • mimicry

    • warning coloration

    • cryptic coloration

  • Predation: the interactions in beneficial to one species and detrimental to another(including parasitism; may involve a keystone species/predator)

  • Competition: interaction detrimental to both species

  • Commensalism: one species benefits from the interaction but the other is unaffected(or harmed)

    • ex: epiphytes and forest trees

    • pearl fish and sea cucumber

  • Mutualism: interaction is beneficial to both species, facultative, not required

    • ex: rhinos and oxpeckers, trees and fungi

    • ants and acacia(ant protects aphids eggs, feeds larva, tends them, keeps them safe, aphid supplies ant with food it secretes from its body)

    • pollination(need insectsm bads, birds, and some mice to assist them, animals eat nectar and pollen)

The Niches

  • Ecological niche: the sum total of an organism’s use of biotic and abiotic resources in its environment

  • Fundamental: the set of resources a population is theoretically capable of using under ideal conditions

  • Realized: the resources a population actually uses

    • thus, 2 species cannot coexist in a community if their niches are identical

Dominant Species in a Community

  • dominant Species in the community

  • other species are dependent on its presense

  • most successful at avoiding predation and disease

  • when removed, Major changes

  • invasive species(human introduced) are examples

    • ex: American Chestnut tree

Keystone Species:

  • maintains the species diversity in a community

  • not always the most abundant species

  • control the structure of the community

    • ex: pisaster and Mytilus, sea otters, coyote

  • Key Members of community

  • need certain limited resources

  • critical element when describing an ecosystem

Competition Evidence:

  • Resource partitioning: sympatric species consume slightly different foods or use other resources in slightly different ways

    • ex: seven species lizard(Anolis) perching sites in Dominican Republic

  • Character displacement: sympatric species tend to diverge in those characteristics that overlap

    • ex: Darwin’s finch break size on the Galapagos Islands

Predation Defense:

  • cryptic: camouflage, coloration

  • aposematic: warning, coloration

  • mimicry: superficial resemblance to another species

  • batesian: palatable/harmless species; mimics an unpalatable/harmful model

  • mullerian: 2 or more unpalatable, aposematically colored species resemble each other

Mimicry:

  • batesian: palatable(harmless) mimics the harmful model

  • mullerian: two or more unpalatable mimic each other

  • mostly a prey technique

    • optical illusions

    • looks like a predator

  • school of fish; fase eyes, filled neck and inflation

Predator Strategies:

  • Structural advantages

    • natural weapons - fangs, clws

    • flexible bodies

    • larger size

  • Ambush

    • stalk victim

    • gape and suck (fish)

    • keen eyesight

    • venom

  • Speed and Cunning

    • more intelligent than prey

    • run faster than prey

    • hunt in packs

Prey Strategies:

  • Defense Techniques

    • inflate, flee, fight back, stab, poison

  • Structural Advantages:

    • hard body coverings

    • thorns or spines

    • break away body parts

    • natural weapons

  • Chemical Warfare

    • blinding ink, poison, offensive smells and tastes

  • Camouflage

    • color change, counter-shading, disruptive patterns, mimicry(batesian, mullerian)

Species Diversity

  • Tropical rainforest/coral reefs= HIGH diversity

  • Deserts and mountain tops = LOW diversity

Determining Diversity of a Community(Biodiversity)

  • between TWO different communities OR how the diversity has changed over time

  • examine “richness” (number of species) and the “evenness” (relative population of each species)

Measuring biodiversity - Simpson index

Shannon Diversity Index


How Communities Change Over Time

  • Succession: a process of community development that involves a changing sequence of species

  • Ecological Succession: transition in species composition over ecological time

  • Primary: begun in lifeless area: no soil, perhaps volcanic activity or retreating glacier

    • ex: Lichens

  • Secondary: an existing community has been cleared by some disturbance that leaves the soil intact

Why are Disturbances Important?

  • can foster greater species diversity

  • some are important to maintain the community

    • freezing in lakes and ponds

    • fires in grasslands and chaparral

  • Fire disturbance:

    • needed for reproduction

    • for clearing out competitors

Introduced Species:

  • 6500 species introduced to U.S.

  • annual costs: billions

  • 30% are due in part to exotics

  • introduced species:

    • no natural enemies

    • can outcompete natural spcies

As Ecosystems Mature:

  • increase in diversity and pop numbers

  • increased system stability

  • increase in biomass

  • decrease in net productivity

  • greater capacity to hold nutrients