Populations And Communities

Ecology Populations and Communities

Ecology  Ecology –

Is the study of the interactions between organisms and the environment

 These –

39.1

interactions

Determine both the distribution of organisms and their abundance

The environment of any organism includes  Abiotic, – – – – –

Temperature Water Sunlight Wind Rocks and soil

 Biotic, –

39.2

or nonliving components

or living components

All organisms in the environment

A –

population Is a group of individuals of a single species living in the same general area

 Density –

Is the number of individuals per unit area or volume

 Dispersion –

Is the pattern of spacing among individuals within the boundaries of the population

39.3

A – –

clumped dispersion Is one in which individuals aggregate in patches May be influenced by resource availability and behavior

(a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.

39.5

A – –

uniform dispersion Is one in which individuals are evenly distributed May be influenced by social interactions such as territoriality

(b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.

39.5

A –

random dispersion Is one in which the position of each individual is independent of other individuals

(c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

39.5

Life Tables A – –

39.6

life table Is an age-specific summary of the survival pattern of a population Is best constructed by following the fate of a cohort (group of individuals from a population)

 The

life table of Belding’s ground squirrels –

Reveals many things about this population

39.6

Life Table for Batteries

Exponential Growth  The –

J-shaped curve of exponential growth

Is characteristic of some populations that are rebounding Elephant population

8,000

39.7

6,000 4,000

2,000

0 1900

1920

1940 Year

1960

1980

The Logistic Growth Model  In –

39.7

the logistic population growth model The per capita rate of increase declines as carrying capacity is reached

The Logistic Model and Real Populations  The

–

39.7

Fits an S-shaped curve

1,000 Number of Paramecium/ml

growth of laboratory populations of paramecia

800 600 400 200 0 0

5

10 Time (days)

15

(a) A Paramecium population in the lab. The growth of Paramecium aurelia in small cultures (black dots) closely approximates logistic growth (red curve) if the experimenter maintains a constant environment.

 Some

populations overshoot K (carrying capacity) Before settling down to a relatively stable density 180 Number of Daphnia/50 ml

–

150 120 90 60 30 0 0

20

40

60

80

100

120

140

160

Time (days)

39.8

(b) A Daphnia population in the lab. The growth of a population of Daphnia in a small laboratory culture (black dots) does not correspond well to the logistic model (red curve). This population overshoots the carrying capacity of its artificial environment and then settles down to an approximately stable population size.

 Some –

populations

Fluctuate greatly around K

Number of females

80 60 40 20 0

1975

1980

1985

1990

1995

2000

Time (years)

39.8

(c) A song sparrow population in its natural habitat. The population of female song sparrows nesting on Mandarte Island, British Columbia, is periodically reduced by severe winter weather, and population growth is not well described by the logistic model.

Population Change and Population Density  In

density-independent populations Birth rate and death rate do not change with population density

–

 In

density-dependent populations

–

39.9

Birth rates fall and death rates rise with population density

Competition for Resources –

In crowded populations, increasing population density intensifies competition for resources

4.0 3.8 Average clutch size

Average number of seeds per reproducing individual (log scale)

10,000

1,000

100

3.6 3.4 3.2 3.0 2.8

0 0

10

100

Seeds planted per m2 (a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases.

0

10

20

30

40

50

60

70

80

Density of females (b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply.

39.9

Abiotic and Biotic Factors Controlling Populations Many populations regular boom-and-bust cycles

Lynx populations are dependent on the snowshoe hare population in a community

39.10

160

120

Snowshoe hare Lynx

9

Lynx population size (thousands)

Undergo

Hare population size (thousands)

–

80

6

40

3

0 1850

1875 1900 Year

1925

0

Abiotic and Biotic Factors Controlling Populations  The

accumulation of toxic wastes can contribute to the regulation of population size  If snowshoe hares are exposed to toxic waste that reduces their reproductive rate, what will happen to the lynx?

39.10

 Human

population growth has slowed after centuries of exponential increase

 No

population can grow indefinitely

The Global Human Population  The

human population increased relatively slowly until about 1650 and then began to grow exponentially

5 4 3 2 The Plague 1

39.11

8000 B.C.

4000 B.C.

3000 B.C.

2000 B.C.

1000 B.C.

0

1000 A.D.

0 2000 A.D.

Human population (billions)

6

 Though

the global population is still

growing –

The rate of growth began to slow approximately 40 years ago 2.2 2 Percent increase

1.8 1.6

2003

1.4 1.2 1 0.8 0.6 0.4 0.2

39.11

0 1950

1975

2000 Year

2025

2050

Birth or death rate per 1,000 people

50

40

30

20

10

0 1750

Sweden

Mexico

Birth rate

Birth rate

Death rate

Death rate

1800

1850

1900 Year

1950

2000

2050

Age Structure  One

important demographic factor in present and future growth trends –

Is a country’s age structure, the relative number of individuals at each age

 Age –

structure

Is commonly represented in pyramids

Rapid growth Afghanistan Male Female

8 6 4 2 0 2 4 6 8 Percent of population

Age 85+ 80–84 75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4

Slow growth United States Female Male

8 6 4 2 0 2 4 6 8 Percent of population

Age 85+ 80–84 75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4

Decrease Italy Female Male

8 6 4 2 0 2 4 6 8 Percent of population

Global Carrying Capacity  Just

how many humans can the biosphere support?

What Is a Community? A –

biological community Is an assemblage of populations of various species living close enough for potential interaction

A

community’s interactions include competition, predation, herbivory (plant/animal), symbiosis, and disease  Populations are linked by interspecific interactions –

They affect the survival and reproduction of the species engaged in the interaction

39.12

 Interspecific –

39.12

interactions

Can have differing effects on the populations involved

The Competitive Exclusion Principle  The –

39.13

competitive exclusion principle

States that two species competing for the same limiting resources cannot coexist in the same place

Ecological Niches  The –

39.13

ecological niche

Is the total of an organism’s use of the biotic and abiotic resources in its environment

Predation  Predation –

Where one species, the predator, kills and eats the other, the prey

 Feeding

include –

39.14

adaptations of predators

Claws, teeth, fangs, stingers, and poison

 Animals –

refers to an interaction

also display

A great variety of defensive adaptations

 Cryptic –

39.14

coloration, or camouflage

Makes prey difficult to spot

 Aposematic –

39.14

coloration

Warns predators to stay away from prey

 In –

Batesian mimicry A palatable or harmless species mimics an unpalatable or harmful model

(b) Green parrot snake

39.14

(a) Hawkmoth larva

 In –

Müllerian mimicry Two or more unpalatable species resemble each other

(a) Cuckoo bee

39.14

(b) Yellow jacket

Parasitism  The –

39.15

parasite

Derives its nourishment from another organism, its host, which is harmed in the process

Mutualism Is an interspecific interaction that benefits both species

39.15

Commensalism One species benefits and the other is not affected

39.15

Trophic Structure  Trophic – –

39.16

structure

Is the feeding relationships between organisms in a community Is a key factor in community dynamics

Quaternary consumers

 Food –

chains

Link the trophic levels from producers to top carnivores

Carnivore

Carnivore Tertiary consumers

Carnivore

Carnivore

Secondary consumers Carnivore

Carnivore

Primary consumers Zooplankton

Herbivore

Primary producers

39.16

Plant A terrestrial food chain

Phytoplankton A marine food chain

Food Webs A –

food web

Is a branching food chain with complex trophic interactions

Humans

Smaller toothed whales

Baleen whales

Crab-eater seals

Birds

Leopard seals

Fishes

Sperm whales

Elephant seals

Squids

Carnivorous plankton Euphausids (krill)

39.16

Copepods

Phytoplankton

Keystone Species  Keystone – –

39.17

species

Are not necessarily abundant in a community Exert strong control on a community by their ecological roles, or niches

 Field

Exhibit their role as a keystone species in intertidal communities

Number of species present

–

studies of sea stars

20

With Pisaster (control)

15 10

Without Pisaster (experimental)

5 0 1963 ´64 ´65 ´66 ´67 ´68 ´69 ´70 ´71 ´72 ´73

39.17

(a) The sea star Pisaster ochraceous feeds preferentially on mussels but will consume other invertebrates.

(b) When Pisaster was removed from an intertidal zone, mussels eventually took over the rock face and eliminated most other invertebrates and algae. In a control area from which Pisaster was not removed, there was little change in species diversity.

What Is Disturbance? A – – –

disturbance Is an event that changes a community Removes organisms from a community Alters resource availability

 Stability

39.18

 The

large-scale fire in Yellowstone National Park in 1988 –

Demonstrated that communities can often respond very rapidly to a massive disturbance

(a) Soon after fire. As this photo taken soon after the fire shows, the burn left a patchy landscape. Note the unburned trees in the distance.

(b) One year after fire. This photo of the same general area taken the following year indicates how rapidly the community began to recover. A variety of herbaceous plants, different from those in the former forest, cover the ground.

39.18

Ecological Succession  Ecological –

Is the sequence of community and ecosystem changes after a disturbance

 Primary –

succession

Occurs where no soil exists when succession begins

 Secondary –

39.19

succession

succession

Begins in an area where soil remains after a disturbance

 Retreating –

glaciers

Provide a valuable field-research opportunity on succession Canada

l.

nt

1931

1911

1900 1892

Ca s

G

1948

1879

Miles

em e

u

1879 1949 1935

1879

5

Gl .

1948 1941

ea

1907

0

Mc

. Gl

Br id

s

at Pl

1899

gg

1912

eG l.

Ri

1940

Alaska

l. rG ui M

Grand Pacific Gl.

1913 1860

Reid Gl. Johns Hopkins Gl.

1879 Glacier Bay 1830

1780

1760 Pleasant Is.

39.19 McBride glacier retreating

10

 Succession

Bay, Alaska –

on the moraines in Glacier

Follows a predictable pattern of change in vegetation and soil characteristics (a) Pioneer stage, with fireweed dominant

(b) Dryas stage

60

Soil nitrogen (g/m2)

50 40 30 20 10 0

39.19

Pioneer Dryas Alder Spruce Successional stage

(d) Nitrogen fixation by Dryas and alder increases the soil nitrogen content.

(c) Spruce stage