Community and Population Ecology

Chapter 6

Good Morning!

Place your portfolio containing your paper and sources on the front table and then sign in using the red pen.

Why Should We Care about the American Alligator?

Fig. 6-1, p. 108

Core Case Study: American Alligator

Highly adaptable

Only natural predator is humans

1967 – endangered species list

Successful environmental comeback

Keystone species

6-1 How Does Species Diversity Affect the Sustainability of a Community?

Concept 6-1 Species diversity is a major component of biodiversity and tends to increase the sustainability of communities and ecosystems.

Species Diversity

Species richness combined with species evenness

Niche structure

Varies with geographic location

Species richness declines towards poles

Sustainability and Environmental Change

Inertia or persistence

Constancy

Resilience

Science Focus: Community Sustainability

No certain definition of sustainability

Do communities need high inertia and high resilience?

Communities may have one but not the other

Equilibrium is rare

Richness and Sustainability

Hypotheses• Does a community with high species richness

have greater sustainability and productivity?

• Is a species-rich community better able to recover from a disturbance?

Research suggests “yes” to both

6-2 What Roles Do Species Play in a Community?

Concept 6-2 Based on certain ecological roles they play in communities, species are described as native, nonnative, indicator, keystone, or foundation species.

Ecological Niche

Species occupy unique niches

Native species – those normally found living and thriving in a particular community Spanish moss in the south

Nonnative species – plants, animals, fungi• Spread in new, suitable niches

Purple looselife European starling African honeybee(“Killer bee”)

Nutria Salt cedar(Tamarisk)

Marine toad Water hyacinth Japanese beetle Hydrilla European wild boar(Feral pig)

Fig. 9-11a, p. 193

Deliberately Introduced Species

http://dnr.wi.gov/invasiveS/fact/loosestrife.htm

http://www.npwrc.usgs.gov/resource/plants/loosstrf/index.htm

http://www.maxshores.com/kudzu/ Kudzu

Fig. 9-12, p. 194

http://www.desertusa.com/mag98/sep/stories/kbees.html

http://www.invasivespeciesinfo.gov/animals/afrhonbee.shtml

http://aaabeeremoval.com/photogallery_africanbeeswarm.htm

Sea lamprey(attached to lake trout)

Argentina fire ant Eurasian muffleBrown tree snake Common pigeon(Rock dove)

Formosan termite Zebra mussel Asian long-hornedbeetle

Asian tiger mosquito Gypsy moth larvae

Fig. 9-11b, p. 193

Accidentally Introduced Species

Indicator Species

Early warning system – tell about harmful changes in biological communities

Birds – found everywhere; affected by habitat problems including pesticides

Butterflies – associate with various plant species becoming vulnerable to habitat loss

Amphibians – multiple reasons; complex and interacting

Case Study: Why Are Amphibians Vanishing? (1) – See latest article

Habitat loss and fragmentation

Prolonged drought

Pollution

Ultraviolet radiation

Parasites - chytrid fungi

sperm

Eggs

Sexualreproduction

Fertilized eggdevelopment Organ formation

Egg hatches

Tadpole

Tadpole develops into frog

Young frogAdult frog(3 years)

Fig. 6-3, p. 112

Life Cycle of a Frog

Case Study: Why Are Amphibians Vanishing? (2)

Viral and fungal diseases

Climate change

Overhunting

Nonnative predators and competition

Why we should care

Keystone Species

Significant role in their food web

Elimination may alter structure, function of community

Pollinators

Top predators

Foundation Species

Create habitats and ecosystems

Beavers

Elephants

Seed dispersers

http://www.morning-earth.org/Graphic-E/Interliv-Two.html great overview

http://www.naturehaven.com/elephantbottom.html - Elephant site

Science Focus: Why Should WeProtect Sharks?

Remove injured, sick animals

Many are gentle giants

Provide potential insight into cures for human diseases

Keystone species

6-3 How Do Species Interact?

Concept 6-3A Five basic species interactions – competition, predation, parasitism, mutualism, and commensalism – affect the resource use and population sizes of the species in a community.

Concept 6-3B Some species develop adaptations that allow them to reduce or avoid competition for resources with other species.

Interspecific Competition

No two species can share vital limited resources for long

Resolved by:• Migration• Shift in feeding habits or behavior• Population drop• Extinction

Intense competition leads to resource partitioning

Fig. 6-5, p. 115

Resource Partitioning of Warbler Species

Fig. 6-4, p. 114

Nu

mb

er o

f in

div

idu

als

Nu

mb

er o

f in

div

idu

als

Resource use

Resource use

Species 1 Species 2

Regionof

niche overlap

Species 1 Species 2

Resource Partitioning and Niche Specialization

Predation

Predator-prey relationship

Predators and prey both benefit – individual vs. population

Predator strategies

Prey strategies

Span worm Bombardier beetle

Viceroy butterfly mimicsmonarch butterfly

Foul-tasting monarch butterfly

Poison dart frog When touched, the snake caterpillar changes shape to look like the head of a snake

Wandering leaf insect

Hind wings of io mothresemble eyes of a much larger animal

Fig. 6-6, p. 116

How Species Avoid Predators

Parasitism

Live in or on the host http://mybloatingrelief.com/parasites/

Parasite benefits, host harmed

Parasites promote biodiversity

http://www.youtube.com/watch?v=rLtUk-W5Gpk

http://www.morning-earth.org/Graphic-E/Interliv-Two.html

Mutualism

Everybody benefit by unintentional exploitation

Nutrition and protection

Gut inhabitant mutualism

Oxpeckers and black rhinoceros

Clown fish and sea anemone

Lack of mycorrhizae fungi on juniper seedlings in sterilized soil

Examples of Mutualism

© 2006 Brooks/Cole - Thomson

Mycorrhizae fungi on juniper seedlings in normal soil

Commensalism

Benefits one with little impact on other

Bromeliad

6-4 How Do Communities Respond to Changing Environmental Conditions?

Concept 6-4A The structure and species composition of communities change in response to changing environmental conditions through a process called ecological succession.

Concept 6-4B According to the precautionary principle, we should take measures to prevent or reduce harm to human health and natural systems even if some possible cause-and-effect relationships have not been fully established scientifically.

Ecological Succession

Primary succession

Secondary succession

Disturbances create new conditions

Intermediate disturbance hypothesis

Fig. 6-9, p. 119

Small herbs and shrubs

Jack pine,black spruce,

and aspen

Balsam fir, paper birch, and white spruce climax

communityExposedrocks

Lichensand mosses

Ecological Succession

Ecological succession

1. It is an orderly process of COMMUNITY development; it normally proceeds in a predictable, orderly direction; it represents the gradual replacement of populations by others that are better adapted to the existing conditions.

2. It results from modification of the physical environment by the populations that interact to makeup the community thus, succession is community controlled; the physical factors of the environment and climate determine the pattern and the rate of change; the climate and immediate environment often set the limit as to how far development can proceed

3. The end result of succession is a stabilized ecosystem which is in balance with the climate and environment of the area; under these conditions the maximum number of organisms (biomass) and their symbiotic (nutritional) interactions are balanced or maintained with the energy available to the system.

Thus, the strategy of succession as a short term process is very much like the strategy of long-term evolutionary development of the biosphere. It results in HOMEOSTATIC balance of organisms with the physical environment WITH THE BENEFIT of achieving a means of effectively dealing with the constant changes or pertubations presented by the environment.

The Strategy of Ecosystem Development, Eugene P. Odum Science 18 April 1969: Vol. 164. no. 3877, pp. 262 - 270

Fig. 6-9, p. 119

Time

Small herbsand shrubs

Heath mat

Jack pine,black spruce,

and aspen

Balsam fir, paper birch, and white spruce climax

community

Exposedrocks

Lichensand mosses

Primary Ecological Succession

Fig. 6-10, p. 120

Annualweeds

Perennialweeds and

grasses

Shrubs and pine seedlings

Young pine forest with developing understory

of oak and hickory trees

Mature oak-hickory forest

Secondary Ecological Succession

Time

Succession’s Unpredictable Path

Successional path not always predictable toward climax community

Communities are ever-changing mosaics of different stages of succession

Continual change, not permanent equilibrium

Precautionary Principle

Lack of predictable succession and equilibrium should not prevent conservation

Ecological degradation should be avoided

Better safe than sorry

6-5 What Limits the Growth of Populations?

Concept 6-5 No population can continue to grow indefinitely because of limitations on resources and because of competition among species for those resources.

Population Distribution

Clumping – most populations Uniform dispersion Random dispersion

http://www.biology.iupui.edu/biocourses/n100/images/39dist.gif

Why Clumping?

Resources not uniformly distributed

Protection of the group

Pack living gives some predators greater success

Temporary mating or young-rearing groups

Populations Sizes Are Dynamic

Vary over timepopulation = (births + immigration) - (deaths + emigration)

Age structure• Pre-reproductive stage•Reproductive stage• Post-reproductive stage

Limits to Population Growth (1)

Biotic potential is idealized capacity for growth

Intrinsic rate of increase (r)

Nature limits population growth with resource limits and competition

Environmental resistance

Fig. 6-11, p. 121

Carrying capacity (K)

Environmentalresistance

Bioticpotential

Exponentialgrowth

Population Growth Curves

Time (t)

Po

pu

lati

on

siz

e (N

)

Limits to Population Growth (1)

Carrying capacity – biotic potential and

environmental resistance (Number of individuals of a given species that can be sustained indefinitely in a given area)

Exponential growth - logarithmic increase

Logistic growth – exponential growth followed by steady decrease over time until population size levels off. Due to population meeting environmental resistance and approaching carrying capacity

Fig. 6-12, p. 121

Logistic Growth of Sheep Population

Overshoot Carrying Capacity

Year

N

um

ber

of

shee

p (

mil

lio

ns) 2.0

1.5

1.0

.5

1800 1825 1850 1875 1900 1925

Overshoot and Dieback

Population does not transition smoothly from exponential to logistic growth

Overshoot carrying capacity of environment

Caused by reproductive time lag

Dieback, unless excess individuals switch to new resource

Exponential Growth, Overshoot and Population Crash of Reindeer

Fig. 6-13, p. 122

PopulationOvershootsCarrying Capacity

Populationcrashes

Carrying capacity

Year

Nu

mb

er o

f re

ind

eer

(mil

lio

ns)

2,000

1,500

1,000

500

01910 1920 1930 1940 1950

Different Reproductive Patterns

r-Selected species• High rate of population increase

• Opportunists

K-selected species• Competitors

• Slowly reproducing

Most species’ reproductive cycles between two extremes

Humans Not Exempt from Population Controls

Bubonic plague (14th century) – Ebola like symptoms

Famine in Ireland (1845) – led to emigration to the United States (through 1848)

AIDS – major player in population decline Technology, social, and cultural changes

extended earth’s carrying capacity for humans Expand indefinitely or reach carrying capacity?

Case Study: Exploding White-tailed Deer Populations in the United States

1900: population 500,000

1920–30s: protection measures

Today: 25–30 million white-tailed deer in U.S.

Conflicts with people living in suburbia