1

Community Structure and Species Diversity (8-1)

Unit Three

AP Environmental

Ch. 8

Mrs. Dow

2

Keystone species

Mutualism & Coevolution

3

Community Structure

Biological community- Biologists use 3 characteristics to describe a

biological community

1. Physical appearance– Sizes, stratification, distribution– Transition occurs around edges

Species are more vulnerable

4

mft

10

50

20

30100

Tropicalrain forest

Coniferousforest

Deciduousforest

Thornforest

Tall-grassprairie

Short-grassprairie

Desertscrub

Thornscrub

Physical appearance: generalized types, size, and stratification of

plants species in various communities

5

2. Species DiversityDef: the variety of species in an area

Two subcomponents: species richness

species evenness

6

Species Richness vs. EvennessSpecies Richness: measurement of the number of species in a given area

Species Evenness: measurement of how evenly distributed organisms are among species

Community A

Community B

species 1 25 1species 2 0 1species 3 25 1species 4 25 1species 5 25 96

7

Richness (number of species)

Relative abundance

How do we describe these differences?

Comparison of Two Communities

8

Determining Species Diversity

Scientists may want to:

* get an estimate of # of species in an

area

* compare species diversity of two communities

To be accurate, need to:

* take both species evenness and species richness into account

9

Species Diversity Indices

Shannon-Weiner (Shannon-Weaver) Index

Diversity =

(p spp 1 - ln(p spp 1)) + (p spp 2 - ln(p spp. 2) + …

(p spp N - ln(p spp. N)

Simpson Index

Diversity = 1 (pspp1)2 + (pspp2)2 + … (psppN)2

10

Why should we care about measuring

biodiversity(species diversity)?

11

Loss of biodiversity caused by:

Introduction of Habitat Destruction Exotic Species

Human-Caused Factors of Biodiversity Loss

12

Biodiversity loss caused by:

Overharvesting/ Pollution Overhunting

Human-Caused Factors of Biodiversity Loss

13

There have been 5 mass extinction events

during the history of the earth 

Extinction

Are we on the verge of a 6th?

14

– 3. Niche structure # of ecological niches, how they resemble each other or

differ from each other, and how they interact. Most species-rich environments

• Rain forest, coral reefs, deep sea, large tropical lakes

High species richness low species evenness

15

Factors affecting species diversity

Latitude (distance from equator)– Highest in tropics . . . Declines toward poles

16

Biogeographical Changes

Richness declines from equator to pole

Due to:– Evolutionary history– Climate

Fig 53.23 Bird species numbers

17

Change in species diversity @ different latitudes

Sp

ecie

s D

iver

sity

200

100

0

90ºN 60 30 0 30ºS 60

Latitude(a) Ants

18

Factors affecting species diversity

Pollution (in aquatic regions)

Habitat diversity

Habitat disturbance

NPP (Net Primary Productivity)

Time

Unpolluted

stream

Polluted

streamN

um

ber

of

dia

tom

sp

ecie

s

Number of individuals per diatom species

19

Theory of Island biogeographyRobert MacArthur and Edward O. Wilson

1960s

20

High

Low

Rat

e o

f im

mig

rati

on

or

exti

nct

ion

Equilibrium number

Immigration and extinction rates

Number of species on island

(a)

© 2004 Brooks/Cole – Thomson Learning

21

High

Low

Rat

e o

f im

mig

rati

on

or

exti

nct

ion

Small island

Effect of island size

Number of species on island

(b)

Large island

© 2004 Brooks/Cole – Thomson Learning

22

High

Low

Rat

e o

f im

mig

rati

on

or

exti

nct

ion

Far island

Effect of distance from mainland

Number of species on island

(c)

Near island

© 2004 Brooks/Cole – Thomson Learning

Immigration(near island)

Immigration(far island)

Extinction

23

Click to view animation.

Animation ( watch on CD)

Area and distance effects interaction.

24

Island speciesDetermined by . . . how fast a new species arrives

(immigration)– How fast old species becomes extinct– Size of island (larger more diversity)– Distance from mainland ( closer to mainland the

more diversity)

25

Types of Species (8-2)

Native– Those whose original home

is in the ecosystem

Nonnative– Evolved in a different

ecosystem and migrated– Also called invasive or

alien species– Example is Wild African

bees

26

Nonnative Species

Nonnative plant species are invading the nation's parks at an alarming rate, displacing native vegetation and threatening the wildlife that depend on them

At some, such as Sleeping Bear Dunes National Lakeshore in Michigan, as much as 23 percent of the ground is covered with alien species, and the rate of expansion is increasing dramatically.

27

Indicator species

Why amphibians are declining?

– Habitat loss & fragmentation

– Pollution– Increases in UV radiation– Over hunting– Increase of parasitism– Introduction of

nonnative species

– Alert to environmental changes

– Ex. Birds, amphibians, trout and butterflies (high vulnerability)

28

Keystone species– Helps determine the types and numbers of various

other organisms in a community

– Help pollinate or regulate populations– Sea otters in a kelp community– Flying foxes in tropical

forest

29

•Foundation speciesFoundation species

–Can shape communities by creating Can shape communities by creating and enhancing habitats that benefit and enhancing habitats that benefit other species other species

–Ex. Elephants uprooting trees & Ex. Elephants uprooting trees & creating openings that promote the creating openings that promote the growth of grasses that benefit growth of grasses that benefit grazing animalsgrazing animals

30

Species Interactions: Competition and Predation (8-3)

31

Interspecific competition– For food, sunlight, water,

soil, space– One species may

migrate or shift feeding habits or face extinction

– Example-native ants and nonnative fire ants

32

Resource partitioning– Evolve more specialized traits

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

33

Predators– Use pursuit– Ambush– Camouflage– Chemical warfare (venom)

Prey– Swift movement– Shell– Camouflage– Chemical to poison

34

PREDATION

35

36

37

38

39

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

40

41

42

43

44

Parasitism, Mutualism, Commensalism (8-4)

45

Parasites– Live on or in another

species– Host is harmed

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

                     

46

Parasites and Parasitoids

Parasites: draw resources from host without killing the host (at least in the short term).

Parasitoids: draw resources from the host and kill them swiftly (though not necessarily consuming them).

47

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

                     

48

Obligatory Mutualism

Obligatory: An organism can't live without the mutualism--either cannot survive or cannot reproduce. – the common pollinator systems like

bees and flowering plants– protozoans in the guts of termites– the alga in the lichen partnership

49

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.

Yucca and Yucca Moth

50

Facultative Mutualism

Facultative: This is "take it or leave it" for one or both partners

While the organism benefits when the mutualism is present, it can still survive and reproduce without it– ant mutualisms, such as ants

protecting plants from predation – ants tending aphids

51

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

52

Commensalism– Helps one species

but does nothing for the other

Ex. Redwood sorrel grows in shade of redwood

- Humans and Eyelash Mites

                          

                                                                                       

53

Ecological succession: Communities in Transition (8-5)

54

Primary Succession

Glacier Retreat

55

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

56

57

Time

Annualweeds

Perennialweeds and

grasses

ShrubsYoung pine forest

Mature oak-hickory forest

Secondary Succession

58

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)

59

– 2. Secondary successionDevelop in places with existing soil or

bottom (aquatic)Ex. Forest fires, deforestation, abandoned

farmland, heavily polluted streams, dammed or flooded land.

60

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.

61

Climax community (a.k.a. mature community)– Stable stage– Deemed the balance of nature

62

Factors affecting 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

63

Disturbance

Event that disrupts an ecosystem or community;

• Natural disturbance

•tree falls, fires, hurricanes, tornadoes, droughts, & floods

• Human–caused disturbance

•deforestation, erosion, overgrazing, plowing, pollution,mining

• Disturbance can initiate primary and/or secondary succession

64

Ecological Stability, Complexity, and Sustainability (8-6)

65

Ecological StabilityCarrying Capacity – maximum number of individuals

the environment can support

66

Ecological Stability - Stress

1. Drop in Primary Productivity

2. Increased Nutrient Losses

3. Decline or extinction of indicator species

4. Increased populations of insect pests or disease organisms

5. Decline in Species diversity

6. Presence of Contaminants

67

Inertia or persistence (ability of a system to resist being altered)

Constancy (ability of a system to keeps its #’s within resource limits)

Resilience (ability of a living system to repair damage)

Three aspects of sustainability in living systems

68

Precautionary principle

– “better safe than sorry”– When an ecosystem is deemed threatened,

stop negative affects

69

“Ecological stability or sustainability by having different species present”