Biodiversity, Species Interactions, and Population Control

Chapter 5

Core Case Study: Southern Sea Otters: Are They Back from the Brink of Extinction?

Habitat Hunted: early 1900s Partial recovery

Why care

about sea otters?• Ethics• Keystone

species• Tourism dollars

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Case Study: Sea Otters Are They Back From the Brink of Extinction

(a) Southern sea otter (b) Sea Urchin (c) Kelp bed

5-1 How Do Species Interact?

Concept 5-1 Five types of species interactions—competition, predation, parasitism, mutualism, and commensalism—affect the resource use and population sizes of the species in an ecosystem.

Most Species Compete with One Another for Certain Resources

Competition the struggle among organisms, both of the same and of different species, for food, space, and other vital requirements.

Competitive exclusion principle The principle that when two species compete for the same critical resources within an environment, one of them will eventually outcompete and displace the other. The displaced species may become locally extinct, by either migration or death, or it may adapt to a sufficiently distinct niche within the environment so that it continues to coexist noncompetitively with the displacing species.

Species Interact in Five Major Ways

Interspecific Competition

Predation

Parasitism

Mutualism

Commensalism

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Interspecific competition• Competition between two

different species• For food, sunlight, water, soil,

space• One species may migrate or

shift feeding habits or face extinction

• Example-native ants and nonnative fire ants

Intraspecific competition• competition between

members of the same species

Most Consumer Species Feed on Live Organisms of Other Species

Predators may capture prey by• Pursuit

• Walking• Swimming• Flying

• Pursuit and ambush• Camouflage• Chemical warfare

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PREDATION

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Most Consumer Species Feed on Live Organisms of Other Species

Prey may avoid capture by• Camouflage• Chemical warfare• Warning coloration• Mimicry• Deceptive looks• Deceptive behavior• Swift movement• Shell

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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

Some ways prey species avoid their prey

Wandering leaf insect

Hind wings of mothresemble eyes of a much larger animal

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Parasitism, Mutualism, Commensalism

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Parasitism

• Live on or in another species• Host is harmed

• Ex. Tapeworms, ticks, fleas, mosquitoes, candiru (vampire fish)

                     

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Mutualism (benefits both species)

• Pollination mutualism (between flowering plants and animals)

• Nutritional mutualism• Lichens grow on trees• Birds/rhinos- nutrition and

protection• Clownfish/sea anemones• Inhabitant mutualism• Vast amount of organisms like

bacteria in an animal’s digestive tract

• Termites and bacteria in gut

                     

Coral Reefs- The corals get food and the

zooxanthellae (algae) get protection.

.

zooxanthellae

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Yucca’s only pollinator is the yucca moth. Hence entirely dependent on it for dispersal.

Yucca moth caterpillar’s only food is yucca seeds.

Yucca moth lives in yucca and receives shelter from plant.

Example of co evolution

Yucca and Yucca Moth

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Figure 8-10Page 155

Oxpeckers and black rhinoceros Clown fish and sea anemone

Mycorrhizae fungi on juniper seedlings in normal soil

Lack of mycorrhizae fungi on juniper seedlings in sterilized soil

Examples of Mutualism

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Commensalism• Helps one species but

does nothing for the other

Ex. Redwood sorrel grows in shade of redwood

- Humans and Eyelash Mites

                          

                                                                                       

Science Focus: Why Should We Care about Kelp Forests?

Kelp forests: biologically diverse marine habitat

Major threats to kelp forests• Sea urchins• Pollution from

water run-off• Global warming

5-2 How Can Natural Selection Reduce Competition between Species?

Concept 5-2 Some species develop adaptations that allow them to reduce or avoid competition with other species for resources.

Some Species Evolve Ways to Share Resources

Resource partitioning

Reduce niche overlap

Use shared resources at different• Times• Places• Ways

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Resource partitioning

• Evolve more specialized traits

Five species of common insect-eating warblers in the Spruce forests of Maine

5-3 What Limits the Growth of Populations?

Concept 5-3 No population can continue to grow indefinitely because of limitations on resources and because of competition among species for those resources.

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Characteristics of a PopulationCharacteristics of a Population

Population - individuals inhabiting the same area at the same time

Population Dynamics: is the study of how population change due to• Population Size - number of individuals• Population Density - population size in a certain

space at a given time• Population Dispersion - spatial pattern in habitat• Age distribution - proportion of individuals in each

age group in population

Populations Have Certain Characteristics

Changes in population characteristics due to:• Temperature• Presence of disease organisms or harmful

chemicals• Resource availability• Arrival or disappearance of competing species

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Population SizePopulation Size

Natality• Number of individuals added through reproduction• Crude Birth Rate - Births per 1000• Total Fertility Rate – Average number of children

born alive per woman in her lifetime

Mortality• Number of individuals removed through death• Crude Death Rate- Deaths per 1000

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Population DensityPopulation Density

Population Density (or ecological population density) is the amount of individuals in a population per unit habitat area• Some species exist in high densities - Mice• Some species exist in low densities - Mountain

lions

Density depends upon• social/population structure• mating relationships• time of year

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Population DispersionPopulation DispersionPopulation dispersion is the spatial pattern of distribution

There are three main classifications

Clumped: individuals are lumped into groups ex. Flocking birds or herbivore herds due to resources that are clumped or social interactions most common http://www.johndarm.clara.net/galleryphots/

Most Populations Live Together in Clumps or Patches

Why clumping?• Species tend to cluster where resources are

available• Groups have a better chance of finding clumped

resources• Protects some animals from predators• Packs allow some to get prey• Temporary groups for mating and caring for

young

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Population DispersionPopulation Dispersion

Uniform: Individuals are regularly spaced in the environment - ex. Creosote bush due to antagonism between individuals, or do to regular spacing of resources rare because resources are rarely evenly spaced

http://www.calflora.net/bloomingplants/creosotebush2.html

www.agry.purdue.edu/turf/ tips/2002/clover611.htm

Random: Individuals are randomly dispersed in the environment ex. Dandelions due to random distribution of resources in the environment, and neither positive nor negative interaction between individuals rare because these conditions are rarely met

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Age StructureAge Structure The age structure of a population is usually

shown graphically The population is usually divided up into

prereproductives, reproductives and postreproductives

The age structure of a population dictates whether is will grow, shrink, or stay the same size

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Age Structure DiagramsAge Structure Diagrams

Positive Growth Zero Growth Negative Growth (ZPG)Pyramid Shape Vertical Edges Inverted Pyramid

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Four variables influencing growth• Births• Deaths• Immigration• Emigration

Increase by birth & immigration Decrease death & emigration

Population change= (Birth + Immigration)-

(Death + Emigration)

No Population Can Grow Indefinitely: J-Curves and S-Curves (1)

Biotic potential - is the population’s capacity for growth • Low generally large animals elephant and blue whales

• High small individuals like bacteria and insects

Intrinsic rate of increase (r) is the rate of population growth with unlimited resources.

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Rapidly growing populations have four characteristics (high r)

• Reproduction early in life• Short periods between generations• Long reproductive lives• Multiple offspring each time they reproduce

• A single house fly could

total 5.6 trillion house flies

within 13 months

No Population Can Grow Indefinitely: J-Curves and S-Curves (2)

Size of populations limited by• Light• Water• Space• Nutrients• Exposure to too many competitors, predators or

infectious diseases

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Environmental ResistanceEnvironmental Resistance

Consists of all factors that act to limit the growth of a population• Abiotic Contributing Factors:

• Unfavorable light• Unfavorable Temperatures• Unfavorable chemical environment - nutrients

• Biotic Contributing Factors:• Low reproductive rate• Specialized niche• Inability to migrate or disperse• Inadequate defense mechanisms• Inability to cope with adverse conditions

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Limits on population growth

• Carrying capacity [K] determined by biotic potential & environmental resistance

• This is the # of a species’ individuals that can be sustained indefinitely in a specific space

• As a population reaches its carrying capacity, its growth rate will decrease because resources become more scarce.

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Population GrowthPopulation Growth Populations show two types of growth

• With few resource limitations• Exponential

• J-shaped curve• Growth is independent of population density

• The growth rate levels off as population reaches carrying capacity • Logistic

• S-shaped curve• Growth is not independent of population density

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Science Focus: Why Are Protected Sea Otters Making a Slow Comeback?

Low biotic potential

Prey for orcas

Cat parasites

Toxic algae blooms

PCBs and other toxins

Oil spills

When a Population Exceeds Its Habitat’s Carrying Capacity, Its Population Can Crash

Carrying capacity: not fixed

Reproductive time lag may lead to overshoot• Dieback (crash)

Damage may reduce area’s carrying capacity

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2,000

1,500

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Year

1,000

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Exponential growth, overshoot, and population crash of reindeer introduced to a small island off of SW Alaska

Carryingcapacity

Populationovershootscarryingcapacity

Populationcrashes

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Reproductive StrategiesReproductive Strategies Goal of every species is to produce as

many offspring as possible Each individual has a limited amount of

energy to put towards life and reproduction This leads to a trade-off of long life or high

reproductive rate Natural Selection has lead to two strategies

for species: r - strategists and K - strategists

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r - Strategistsr - Strategists Spend most of their

time in exponential growth

High rate of reproduction

Little parental care Minimum life Opportunist

K

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R StrategistsR Strategists

Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental

conditions High population growth rate – (r) Population size fluctuates wildly above and below

carrying capacity – (K) Generalist niche Low ability to compete Early successional species

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K - StrategistsK - Strategists

Maintain population at carrying capacity (K)

Maximize lifespan Competitor Follow a logistic

growth curve

K

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K- StrategistK- Strategist

Reproduce later in life Fewer, larger offspring High parental care and protection of offspring Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental

conditions Lower population growth rate (r) Population size fairly stable and usually close to

carrying capacity (K) Specialist niche High ability to compete Late successional species Prone to extinction

Genetic Diversity Can Affect the Size of Small Populations

Founder effect

Demographic bottleneck

Genetic drift

Inbreeding

Minimum viable population size- the number of individuals populations need for long term survival

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Effects of Genetic Variations on Population Size

Genetic diversity• 1. Founder effect

• Few individuals move to a new location and are isolated from the original population

• Limited genetic

diversity

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• 2. Demographic bottleneck• Few individuals survive a catastrophe- fire,

hurricane• Lack of genetic diversity may limit these

individuals to rebuild the population

• 3. Genetic drift• Random changes in gene

frequencies • May help or hurt survival of a

population• Some individuals may breed

more than others and their

genes may eventually dominate the gene pool of the population

• 4. Inbreeding• Members of a small population

exchange genes

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Density of a population density

Density-independent (affects population size regardless of its density)• Floods, hurricanes, fire, pesticide spraying ,

pollution) Density-dependent (greater effect as population

density increases)• Competition for resources, predation, parasitism,

disease – bubonic plague)

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Population fluctuations in nature

Stable (varies slightly above and below carrying capacity,K)

Irruptive (explode to a high level and then drastically drop - insects)

Cyclic (over a regular time period – lemmings populations rise and fall ever 3-4 years)

Irregular behavior (no pattern)

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© 2004 Brooks/Cole – Thomson Learning

Nu

mb

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f in

div

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Time

(b) Irruptive

(a) Stable

(c) Cyclic

(d) Irregular

General types of simplified population changes curves found in nature

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usa

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01845 1855 1865 1875 1885 1895 1905 1915 1925 1935

Year

Hare

Lynx

Predator – prey relationships Lynx-Hare Cycle Cyclic ever 10 years

Humans Are Not Exempt from Nature’s Population Controls

Ireland• Potato crop in 1845• 1 million people died from hunger or disease form malnutrition• 3 million migrated to other countries (mainly U.S.)

Bubonic plague• Fourteenth century• Killed a least 25 million people in European Cities

AIDS• Global epidemic• Between 1981- 2007 AIDS has killed more than 25 million

people• Claims 2.1 million a year ( average of 4 deaths per min.)

Case Study: Exploding White-Tailed Deer Population in the U.S.

1900: deer habitat destruction and uncontrolled hunting

1920s–1930s: laws to protect the deer

Current population explosion for deer• Lyme disease• Deer-vehicle accidents• Eating garden plants and shrubs

Ways to control the deer population

5-4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions?

Concept 5-4 The structure and species composition of communities and ecosystems change in response to changing environmental conditions through a process called ecological succession.

Communities and Ecosystems Change over Time: Ecological Succession

Natural ecological restoration• Primary succession is ecological succession in a

bare area that has never been occupied by a community of organisms.

• Bare rock exposed by retreating glacier, severe erosion, newly cooled lava, abandoned concrete/ highway, newly created pond

• Secondary succession is an ecological succession in an area in which natural vegetation has been removed or destroyed but the soil is not destroyed.

• forest fires, deforestation, abandoned farmland, heavily polluted streams, and land that has been damned or flooded.

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Succession = change

• 1. Primary succession• Gradual establishment of biotic community on lifeless

ground• Barren habitat

• Bare rock / retreating glacier• A newly- cooled lava• A newly formed pond

• It takes several centuries to several thousands of years for natural processes to produce fertile soil.

• Ex. Hawaii• Pioneer species (lichens, moss and microbes)

Some Ecosystems Start from Scratch: Primary Succession

No soil in a terrestrial system No bottom sediment in an aquatic system Early successional plant species, pioneer

• Bacteria, moss, lichens

Midsuccessional plant species• Herbs and shrubs

Late successional plant species• Balsam fir, paper birch, and white spruce

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Primary Succession

Glacier Retreat

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Time

Small herbsand shrubs

Heath mat

Jack pine,black spruce,

and aspen

Balsam fir,paper birch, and

white spruceclimax community

Exposedrocks

Lichensand mosses

Primary Succession

Some Ecosystems Do Not Have to Start from Scratch: Secondary Succession

Some soil remains in a terrestrial system

Some bottom sediment remains in an aquatic system

Ecosystem has been• Disturbed• Removed• Destroyed

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Time

Annualweeds

Perennialweeds and

grasses

ShrubsYoung pine forest

Mature oak-hickory forest

Secondary Succession

Some Ecosystems Do Not Have to Start from Scratch: Secondary Succession (2)

Primary and secondary succession• Tend to increase biodiversity• Increase species richness and interactions

among species

Primary and secondary succession can be interrupted by• Fires• Hurricanes• Clear-cutting of forests• Plowing of grasslands• Invasion by nonnative species

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Succession of an Aquatic Ecosystem

Aquatic ecosystem gradually increasing in sedimentation/inflow of nutrients from surrounding land areas

Slowly filling w/ silt, sand and other particles; shoreline gradually advances toward the center of the pond;

Aquatic vegetation contributing to this filling In a “classic scenario” the pond would eventually

become a wetland, then perhaps a grassland, followed by some type of forest.

Science Focus: How Do Species Replace One Another in Ecological Succession?

1. Facilitation• One species makes an area of suitable for

another species• Ex. Moss build land for grasses

2. Inhibition• Early species limit later species• Ex. Plants may release toxins

3. Tolerance• Later species are unaffected by earlier

species

Succession Doesn’t Follow a Predictable Path

Traditional view • Balance of nature and a climax community

Current view • Ever-changing mosaic of patches of vegetation• Mature late-successional ecosystems

• State of continual disturbance and change

Living Systems Are Sustained through Constant Change

Inertia, persistence• Ability of a living system to survive moderate

disturbances Resilience

• Ability of a living system to be restored through secondary succession after a moderate disturbance

Tipping point• Where any additional stress can cause the

system to change in an abrupt and usually irreversible way

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The Cats of Borneo

What happened first?

Arrange the sentence strips in chronological order

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Operation Cat Drop

One of the most bizarre events to accompany this early use of DDT occurred when it became necessary to parachute cats into remote jungle villages in what was then Burma.  The following account was taken from a source at Cornell University:

In the early 1950s, the Dayak people in Borneo suffered from malaria. The World Health Organization had a solution: they sprayed large amounts of DDT to kill the mosquitoes which carried the malaria. The mosquitoes died, the malaria declined; so far, so good. But there were side-effects. Among the first was that the roofs of people's houses began to fall down on their heads. It seemed that the DDT was also killing a parasitic wasp which had previously controlled thatch-eating caterpillars. Worse, the DDT-poisoned insects were eaten by geckoes, which were eaten by cats. The cats started to die, the rats flourished, and the people were threatened by outbreaks of sylvatic plague and typhus. To cope with these problems, which it had itself created, the World Health Organization was obliged to parachute14,000 live cats into Borneo.

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The Day they Parachuted Cats into Borneo

WHO sent DDT to Borneo. Mosquitoes were wiped out. Caterpillar numbers went up. Caterpillars ate grass roofs. Roaches stored DDT in their bodies. Lizards ate roaches and got DDT. Lizards slowed down. Cats caught lizards containing DDT. Lizards disappeared. Cats died. Rats increased. Rats brought the plague. Cats were parachuted in.