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Populations and Communities


Conifers in taiga, corals in coral reefs, tall-grass species in a prairie, etc. ... Also parasitism: cuckoo/great warbler interaction. Evolution ... – PowerPoint PPT presentation

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Title: Populations and Communities

Populations and Communities
  • Biology 150-009
  • Ms. Chappell
  • September 5, 2006

Quick Review
  • Definitions
  • Ecology study of how an individual interacts
    with other individuals and physical factors of
    its surrounding environment
  • Ecosystem basic unit of study in ecology all
    biotic and abiotic factors in a given space may
    be small or large biosphere is collection of ALL
    Earths ecosystems

Quick Review
  • Abiotic portion of ecosystem
  • Resources finite supply in need of reuse, either
    in storage or transfer, with CONSTANT CYCLING
    between living (biotic) and non-living (abiotic)
    portions of ecosystems
  • Conditions effects of climate (temperature,
    precipitation, winds), altitude, etc.
  • Energy 2 laws of thermodynamics
  • Never lost or gained, merely transformed
  • Unidirectional flow (more-ordered to
    less-ordered) (entropy, or disorder, increases)
  • Sun is energy source for all of life
  • either in storage or transfer, BUT NO CYCLING

Quick Review
  • Biotic portion of ecosystem
  • Individual organism
  • Role or function of an individual is its
  • Population
  • Group of all individuals of the same
    _____________ living in a given space
  • Species
  • Community
  • Group of all populations, or species, living in a
    given space and potentially interacting

Population Size
  • Population sizes and distributions vary over time
    due to interactions
  • To understand effects of changes to ecosystems,
    population size must be known before and after an
    event or impact in order to compare
  • Direct counts
  • Estimating counts

  • Growth
  • Arithmetic (Non-living) vs. Exponential (Living)
  • Growth of living populations dependent on, or
    proportional to, starting
  • population size

Fig. 31.3
Adapted from Krogh, Table 31.1
Growth and Decline
Rate of growth increases
J curve
Exponential growth slows and then ceases
More representative of real world situations
S curve
  • Could Daphnia population growth continue
    unchecked? Can any population continue
    exponential growth? r K?

Fig. 31.5
What Is r?
  • r is the rate at which a population will grow in
    a perfect world with no external limiting
  • intrinsic rate of increase (birth rate minus
    death rate of a population over a specified time
  • Start of year 1 1000 individuals
  • 100 births/year 10 growth
  • 80 deaths/year 8 loss
  • r 2 ( 0.02)
  • (if conditions remain stable, r has prediction
    value for population)
  • Start of year 2 1020 individuals
  • End of 20 years 1480 individuals

Effects of r
Fig. 31.6
r Elephants vs. E. coli
  • Each population, or species, has a unique
    generation time that affects r
  • Usually, larger species longer generation time

Fig. 31.7
On to K
  • K the carrying capacity of an area, OR the
    maximum population density of a given species
    that a defined geographical area can sustain over
  • Populations may exceed K for brief periods of
    time, but this can not be sustained
  • (e.g., Angel Island deer population)

More rs and Ks
  • Reproductive strategy characteristic that has
    the effect of increasing the number of fertile
    offspring an organism bears
  • r-selected (opportunist) species
  • K-selected (equilibrium) species
  • Organisms employ reproductive strategies that lie
    along continuum

K-selection vs. r-selection
  • K-selected species density-dependent population
    limited by biological forces (food, disease,
    water, etc.)
  • r-selected species density-independent
    population limited by physical forces or
    conditions (frost, temperature, rain, etc.)

R-selection vs. K-selection
Fig. 31.8
Which is which?
Images from www.viarural.com.ar/...zas/paspalums
p02.jpg and www.oplin.org/tree/f...ry_shagbark/tr
r/K Connection to Survivorship
Type I Type II Type III
Fig. 31.9
Human Population
  • Survivorship curves (previous slide) based on
    life tables (predictor of survivorship at
    incremental stages days for flies, blocks of
    years for humans)

T 31.2
Population Pyramids
  • Knowing distribution of a population at various
    ages helps predict population growth

Fig. 31.10
Goal Zero Population Growth
Fig. 31.11
What type of growth curve is this? Can this type
of growth be sustained forever? Or does
environmental resistance step in to stop such
  • Exponential human population growth began in late
    1700s due to surplus food, better sanitation,
    and improved medical care
  • 10BC 1804 AD 1B 1927 2B 1974 4B 2005
  • Where will it end? 2050 12B? New predictions
    2050 8.9B due to stabilizing human population
    growth AVERAGE r is slowing

Developed vs. Developing Country
EU low fertility rate (shrinking
population) Bangladesh high rate 70 increase
in 2050 US near replacement rate BUT add in
immigration, 45 increase by 2050
  • 151 humans born per minute 149 born in
    developing countries
  • Developed country populations generally reducing
    while others are still growing at frantic pace

Which Has Greater Impact?
  • Environment assaulted by
  • Human population growth more people take up more
    space, need more resources, create more wastes,
    displace or extinguish other species
  • Resource use Inequitable resource use (i.e.,
    some of us are bigger environment pigs than

US vs. China in population size but Chinese are
catching up on emissions releases today per
capita emissions are rising
Average Americans carbon footprint HUGE compared
to persons in other countries
Fig. 31.13
Community Interactions
  • Community
  • All populations that inhabit a given area
  • More specifically, all populations in a given
    area that potentially interact
  • To study a community
  • Know the species present
  • Know relative sizes of populations
  • Know importance of different community members

Community Makeup
  • Ecological dominants one to a few species that
    predominate in an ecosystem by sheer numbers
  • Conifers in taiga, corals in coral reefs,
    tall-grass species in a prairie, etc.
  • Keystone species population size may be small,
    but great ecological impact if population absent
  • Sea stars in intertidal zones, sea otters in
    kelp-bed communities
  • Biodiversity range of species in a community
  • Negative human impacts loss of species diversity

  • Greater range higher biodiversity
  • Smaller range lower biodiversity
  • Three types of biodiversity
  • Species diversity
  • Geographical diversity
  • Genetic diversity

Fig. 31.16
Species Diversity
  • High species diversity high productivity
  • i.e., the greater the range of species in a
    community, the more biomass is created and used
    to support living members of ecosystems (more
    variation of resources?)
  • High species diversity ecosystem stability???
  • Under debate if yes, humans should rethink
    ecosystem destruction and lowered species

Types of Community Interaction
  • Competition
  • Competitive exclusion principle
  • Resource partitioning
  • Predation and parasitism
  • Evolutionary aspects
  • Mutualism and commensalism
  • Beneficial interactions
  • Coevolution between species

Habitat and Niche
  • Habitat physical surroundings in which a
    species is normally found (populations separated
    geographically still have similar habitats)
  • Niche role or function of a species in its
    surroundings (how resources are obtained,
    behaviors, competition with others)

Algae, frogs, and rabbits
Fig. 31.2
Interspecific Competition
  • Competition between two or more species
  • Niches are specific to each species, but closely
    related species often have niche overlap
  • Competition may be for space, sun, food, water,
    other resources, etc.
  • Competition may involve fighting or territorial
    disputes, but usually means being better at
    something than another competitive species

Interspecific Competition
  • Competitive Exclusion Principle no two species
    can share same VITAL resource for long (no
    long-standing competition)
  • Paramecium aurelia vs. Paramecium caudatum, kudzu
    (Puerarium) vs. everything in its path
  • Resource Partitioning allows long-term
    coexistence between competitive species
  • Warbler species and tree space for food

Interspecific Competition
P. aurelia better able to sequester resources
P. caudatum locally extinct in matter of days
Fig. 31.19
Fig. 31.17
Predation and Parasitism
  • Predation one organism feeding on parts or all
    of a second organism (lion eating a spring bok,
    vegan eating a salad, birds eating wheat grains,
  • Parasitism a variation on predation one
    organism feeding on a second organism but not
    immediately, or possibly ever, killing the second
    organism (mistletoe, bedbugs, Ascaris, etc.)
  • Also parasitism cuckoo/great warbler interaction

  • Evolution may be result of predator/prey
    (or parasite/host) interactions
  • Culling of less capable members from populations
  • Ever-changing dynamics the arms race

Evolution among Predators and Their Prey
  • One organisms predatory actions spur preys
    defensive adaptations for survival
  • No choices here no active decisions to grow
    thorns to keep out would-be herbivores or to
    develop skin poisons to thwart toad-loving
  • Blending in with surroundings - camouflage
  • Mimicry is often observed as a type of
    camouflage from potential predators

Dynamics of Predation
  • Predators attack prey but are also dependent on
    them for survival population sizes

Fig. 31.21
Dynamics of Parasitism
  • Many parasites
  • both feed upon
  • and use their
  • hosts for
  • reproduction

Image source www.dpd.cdc.gov/dpdx...loides_LifeC
Strongyloides lifecycle
Batesian Mimicry
  • Harmless species evolving to resemble a harmful
    species with WARNING colors and patterns
    harmless species less often victims of predation
    (clearwing moth and yellowjacket wasp scarlet
    king snake and coral snake)

Batesian Mimicry
Scarlet King Snake
Coral Snake - DEADLY
Image sources www.educationcentral...carletkings
nake2.jpg, www.tigerhomes.org/a...ages/coral-snak
Figure 31.24
Mullerian Mimicry
  • Different species, each with protective means
    (bitter taste or poison or sharp thorns) against
    predators evolve to look similar if predator
    learns danger of one species, learns to avoid all
    organisms that are similar
  • Less members of either protected species sustain
    injury or death from predators

Mullerian Mimicry
Bad-tasting South American Heliconius cydno and
Heliconius sapho
Fig. 31.25
Mutualism and Commensalism
  • Mutualism interaction between members of two
    different species, both members gaining from
    interaction (rhinoceros and oxpecker birds
    shrimp goby and snapping shrimp)
  • Commensalism Interaction between members of two
    different species where one organism benefits and
    the other is not helped or harmed (birds and
  • Coevolution close association over long time
    results in coevolution (bee sight/flower color)

Mutualism and Commensalism
Image source www.50birds.com/imag...inch20Nest
Fig. 31.26
  • Community change over time replacement of
    communities until stability reached
  • Example Mount St. Helens May 1980 volcanic

August 1980
Ecological succession in action -
Nature reclaiming devastation
August 1999
Fig. 31.28
Types of Succession
  • Primary succession starting state is one of
    little or no life and nutrient-lacking soil
    (Glacier Bay, AK Mount St. Helens, WA)
  • Secondary succession final state of a habitat
    has been disturbed by some force, but life and
    nutrient-rich soil remain (abandoned farm land)
  • Final, stable community of either type of
    succession is climax community

Glacier Bay, AK, 1 Succession
  • Common elements of primary succession
  • Pioneer photosynthesizing species
  • Increase in biomass, to a point
  • Investment in longer-living species
  • General increase in biodiversity
  • Facilitation of growth from older to newer
  • Competitive exclusion (sunlight)

Note Climax community very dependent on biome
Lessons from Mount St. Helens Biological legacy
species living things, or products of living
things, that survive a major ecological
Fig. 31.29
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