Biodiversity, Species Interactions, and Population Control

Fig. 5-1a, p. 104

Southern Sea Otter

5-1 How Do Species Interact?

• The interactions between species in an ecosystem affect:• the resource use in an ecosystem and• population sizes of the species in an ecosystem.

Five types of Interactions• Interspecific Competition

• Predation

• Parasitism

• Mutualism

• Commensalism

Five types of Interactions

• Interspecific Competition• Predation

• Parasitism

• Mutualism

• Commensalism

Interspecific Competition• Species compete for limited resources like• Water• Food/Nutrients• Light• Habitat/Space

Five types of Interactions• Interspecific Competition

•Predation• Parasitism

• Mutualism

• Commensalism

Predation• Predators may capture prey by

1. Walking2. Swimming3. Flying4. Pursuit and ambush5. Camouflage6. Chemical warfare

Predator-Prey Relationships

Fig. 5-4, p. 107

Avoiding Predation• Prey may avoid capture by

1. Run, swim, fly2. Protection: shells, bark, thorns3. Camouflage4. Chemical warfare5. Warning coloration6. Mimicry7. Deceptive looks8. Deceptive behavior

Fig. 5-5b, p. 109

(b) Wandering leaf insect

Fig. 5-5c, p. 109

(c) Bombardier beetle

Fig. 5-5d, p. 109

(d) Foul-tasting monarch butterfly

Fig. 5-5e, p. 109

(e) Poison dart frog

Fig. 5-5f, p. 109

(f) Viceroy butterfly mimics monarch butterfly

Fig. 5-5g, p. 109

(g) Hind wings of Io moth resemble eyes of a much larger animal.

Fig. 5-5h, p. 109

(h) When touched, snake caterpillar changes shape to look like head of snake.

Predator and Prey Interactions Can Drive Each Other’s Evolution

• Intense natural selection pressures between predator and prey populations

• Coevolution• Interact over a long period of time• Example - Bats and moths: echolocation of bats and

sensitive hearing of moths

Coevolution: A Langohrfledermaus Bat Hunting a Moth

Fig. 5-6, p. 110

Five types of Interactions• Interspecific Competition

• Predation

•Parasitism• Mutualism

• Commensalism

Parasitism• Parasitism – species feed off other species or live on

or in them

• Parasite is usually much smaller than the host

• Parasite rarely kills the host

• Parasite-host interaction may lead to coevolution

Parasitism: Trout with Blood-Sucking Sea Lamprey

Fig. 5-7, p. 110

Parasitism: Tapeworm in Human Eye

Five types of Interactions• Interspecific Competition

• Predation

• Parasitism

•Mutualism• Commensalism

Mutualism• Mutualism – both species benefit

• Nutrition and protection relationship• Clownfish and anemone

• Gut inhabitant mutualism• Bacteria in our intestines

• Not cooperation: it’s mutual exploitation

Fig. 5-8, p. 110

Mutualism: Hummingbird and Flower

Mutualism: Oxpeckers Clean Rhinoceros; Anemones Protect and Feed Clownfish

Fig. 5-9, p. 111

Five types of Interactions• Interspecific Competition

• Predation

• Parasitism

• Mutualism

•Commensalism

Commensalism• Commensalism • One species benefits, one not

harmed

• Bromeliad (air plant) in tree

• Birds nesting in trees

What Limits the Growth of Populations?

• No population can continue to grow indefinitely because of

• limitations on resources and

• competition among species for those resources.

Most Populations Live Together in Clumps or Patches

• Population: group of interbreeding individuals of the same species

• Population distribution 1. Clumping (ex. Flocks of birds)2. Uniform dispersion3. Random dispersion

Generalized Dispersion Patterns

Fig. 5-12, p. 112

Most Populations Live Together in Clumps or Patches

• Why clumping?1. Species cluster where resources are available2. Clumps have a better chance of finding resources3. Protects some animals from predators4. Packs allow some to get prey

Population of Snow Geese

Fig. 5-11, p. 112

Population Growth and Decline• Population size governed by• Births• Deaths• Immigration• Emigration

• Population change = (births + immigration) – (deaths + emigration)

Population Growth and Decline• Age structure• Pre-reproductive age “kids”• Reproductive age “adults”• Post-reproductive age “elderly”

• Sizes of each group will drive the growth or decline of population in the future

• Example: A population with 70% of kids will most likely have a population growth spike as those kids become adults

Some Factors Can Limit Population Size

• Range of tolerance• Variations in physical and chemical environment that

impact a population’s ability to survive and reproduce• Temperature, Rain, Nutrients…

Trout Tolerance of Temperature

Fig. 5-13, p. 113

Some Factors Can Limit Population Size

• Limiting factor principle• Too much or too little of any physical or chemical

factor can limit or prevent growth of a population, even if all other factors are at or near the optimal range of tolerance

“Population can only grow as much as its scarcest resource!”

No Population Can Grow Indefinitely: J-Curves and S-Curves

• Size of populations controlled by limiting factors:• Light• Water• Space• Nutrients• Exposure to too many competitors, predators or

infectious diseases

No Population Can Grow Indefinitely: J-Curves and S-Curves

• Environmental resistance • All factors that act to limit the growth of a population

• Carrying capacity (K)• Maximum population a given habitat can sustain• Calculated by looking at the limiting factors

No Population Can Grow Indefinitely: J-Curves and S-Curves

• Exponential growth• Starts slowly, then accelerates to carrying capacity

when meets environmental resistance

• Known as “J” curve due to shape• No limiting factors yet

No Population Can Grow Indefinitely: J-Curves and S-Curves (3)

• Logistic growth• Decreased population growth rate as population size

reaches carrying capacity

Yellow line = calculated theoretical carrying capacity

Green = actual population

Logistic Growth of Sheep in Tasmania

Fig. 5-15, p. 115

When a Population Exceeds Its Habitat’s Carrying Capacity, Its Population Can Crash• A population can “briefly” exceed (overshoot) the

area’s carrying capacity due to:

• Reproductive time lag

• If it greatly overshoots the carrying capacity, the result is:

• Population crash and • Damage may reduce area’s new carrying capacity

Exponential Growth, Overshoot, and Population Crash of a Reindeer

Fig. 5-17, p. 116

Species Have Different Reproductive Patterns

• Some species

• Many, usually small, offspring• Little or no parental care• Massive deaths of offspring• Ex. Insects, bacteria, algae

Species Have Different Reproductive Patterns

• Other species

• Reproduce later in life• Small number of offspring with long life spans• Young offspring grow inside mother• Long time to maturity• Protected by parents, and potentially groups• Ex. Humans, Elephants

Under Some Circumstances Population Density Affects Population Size

• Density-dependent population controls• Predation• Parasitism• Infectious disease• Competition for resources

Several Different Types of Population Change Occur in Nature

• Stable

• Irruptive• Population surge, followed by crash

• Cyclic fluctuations, boom-and-bust cycles• Top-down population regulation• Bottom-up population regulation

• Irregular

Humans Are Not Exempt from Nature’s Population Controls

• Ireland• Potato crop in 1845

• Bubonic plague• Fourteenth century

• AIDS• Global epidemic

5-3 How Do Communities and Ecosystems Respond to Changing Environmental

Conditions?• Concept 5-3 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• Secondary succession

Some Ecosystems Start from Scratch:• Primary Succession• No soil in a terrestrial system or no bottom sediment

in an aquatic system

• Takes hundreds to thousands of years to build up soils/sediments to provide necessary nutrients

• Ex. – Bare rock after a glacier retreats

Primary Ecological Succession

Fig. 5-19, p. 119

Some Ecosystems Do Not Have to Start from Scratch

• Secondary Succession• Some soil remains in a terrestrial system or bottom

sediment remains in an aquatic system

• Ecosystem has been• Disturbed• Removed• Destroyed

• Ex – old farmland, forest fires

Natural Ecological Restoration of Disturbed Land

Fig. 5-20, p. 120

Secondary Ecological Succession in Yellowstone Following the 1998 Fire

Fig. 5-21, p. 120

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

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

• Facilitation

• Inhibition

• Tolerance

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

• Some systems have one property, but not the other: tropical rainforests

Three Big Ideas

1. Certain interactions among species affect their use of resources and their population sizes.

2. There are always limits to population growth in nature.

3. Changes in environmental conditions cause communities and ecosystems to gradually alter their species composition and population sizes (ecological succession).