Biodiversity, Species Interactions,

and Population Control

Chapter 5

Biodiversity, Species Interactions,

and Population Control

Chapter 5 Part 1: Species Interactions

Review!

What is evolution? • Change in a species over time (many

generations!) What is natural selection? • Pressures of environment ‘select’

genes that survive to produce more offspring

What is an adaptation?• Trait that improves chances for

survival and reproduction

Coevolution

The process by which two species evolve in response to changes in each other over time • Sometimes

organisms that are closely connected to one another by ecological interactions evolve together.

Coevolution: A Langohrfledermaus

Bat Hunting a Moth

Species Interact in Five Major Ways

Interspecific Competition

Predation

Parasitism

Mutualism

Commensalism

Most Species Compete with One Another for Certain Resources

Competition• When two species compete, their niches

overlap

Competitive exclusion principle – no two species can occupy exactly the same ecological niche for very long• Both species suffer harm• Migration or predation will ultimately

occur

Some Species Evolve Ways to Share Resources

Resource partitioning – species evolve to reduce niche overlap

Use shared resources at different• Times• Places• Ways

Specialist Species of Honeycreepers

Sharing the Wealth: Resource Partitioning

11

Predator or Prey?

Predation – act of one organism eating another organism• Predator –

organism that does the eating

• Prey – organism that gets eaten

Most Consumer Species Feed on Live Organisms of Other Species

Predators may capture prey by:• Walking• Swimming• Flying• Pursuit and ambush• Camouflage• Chemical warfare

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

Important lesson to remember:

If an organism is small and beautiful… it is probably poisonous.

If it is strikingly beautiful and easy to catch…it is probably deadly.

Predation: Population Control

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

• Controlled by predation

• Bottom-up population regulation • Controlled by scarcity of one or more resources

Your Turn!

Predator Prey Relationships

Video Clip

Orca Training Session• 22:42 to 31:00

Mutualism: Clownfish & sea anemone

Both organisms derive mutual benefit

Intimate and obligatory

Neither can survive for long periods without the other

Mutualism: Oxpeckers Clean Rhinoceros; Anemones Protect and Feed Clownfish

Parasitism: Tapeworm and Humans

Parasite lives on or in the host and benefits at the expense of the host

Parasitism: Tree with Parasitic Mistletoe, Trout with Blood-Sucking Sea Lampreys

Commensalism: Flatworms and horseshoe crabs

Only one member benefits• sharing space,

defense, shelter, food

Flatworms that live on the gills of horseshoe crabs obtain food from the host, but do not negatively affect the host

Commensalism: Bromiliad Roots on Tree Trunk Without Harming Tree

Your Turn!

http://www.pbs.org/wnet/nature/lessons/symbiotic-strategies/video-segments/1496/

• Ecological Relationships• Predation• Competition• Commensalism• Mutualism• Parasitism

Biodiversity, Species Interactions,

and Population Control

Chapter 5 Part 2: Population Dynamics

Populations Have Certain Characteristics

Population dynamics – study of how characteristics of a population changes in response to changes in the environmental conditions

Populations differ in• Distribution• Numbers• Age structure

Density

Number of individuals of a population in a given area

Distribution Patterns

Random Independent

of other organisms

No habitat preference

Distribution Patterns

UniformEven spacingEvidence for

intra-specific competition (among other sea otters)

Distribution Patterns

ClumpedOrganisms tend

to be togetherHabitat

preferenceBehavioral

preference such as herding

Most common!

Why clumping?

Species tend to cluster where resources are available

Protects some animals from predators

Packs allow some to get prey

Temporary groups for mating and caring for young

Populations Can Grow, Shrink, or Remain Stable

Population size governed by• Births• Deaths• Immigration• Emigration

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

emigration)

Populations Can Grow, Shrink, or Remain Stable

Age structure – number of individuals in a given age class• Pre-reproductive age• Reproductive age• Post-reproductive age

Density Dependent Limiting Factors

Operates more strongly when a population is large and overcrowdedPredation – more

prey organisms – predator numbers will increase

Density Dependent Limiting Factors

Parasitism – crowding helps parasites travel from one host to another

Crowding – higher levels of stress (direct influence on immune system)

Density Dependent Limiting Factors

Competition• Intraspecific –

members of the SAME species compete

• Interspecific – competition between DIFFERENT species

Density-Independent Limiting Factors

Will affect population regardless of its sizeNatural Disasters

Forest firesFloodsEarthquakeOil Spill

Genetic Diversity Can Affect the Size of Small Populations

Minimum viable population size – number of individuals endangered species need for long-term survival• Founder effect• Demographic bottleneck• Genetic drift• Inbreeding

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