Chapter 50Chapter 50

An Introduction to Ecology and the Biosphere

The Scope of Ecology

• Ecology

– is the scientific study of the interactions between organisms and the environment

• These interactions

– determine both the distribution of organisms and their abundance

• Ecology

– reveals the richness of the biosphere

Figure 50.1

• Concept 50.1: Ecology is the study of interactions between organisms and the environment

• Ecology

– has a long history as a descriptive science

– is also a rigorous experimental science

Ecology and Evolutionary Biology

• Events that occur in ecological time

– affect life on the scale of evolutionary time

– ecological time (minutes, months, years)

– evolutionary time (decades, centuries, millennia, and longer)

• e.g. predator prey interactions

Organisms and the Environment

• The environment of any organism includes

– abiotic, or nonliving components

– biotic, or living components

– all the organisms living in the environment, the biota

• Environmental components

– affect the distribution and abundance of organisms

Figure 50.2

Kangaroos/km2

> 2010–205–10

1–50.1–1< 0.1Limits ofdistribution

Climate in northern Australiais hot and wet, with seasonaldrought.

Red kangaroosoccur in mostsemiarid and aridregions of theinterior, whereprecipitation isrelatively low andvariable fromyear to year.

Southeastern Australiahas a wet, cool climate.

Southern Australia hascool, moist winters andwarm, dry summers.

Tasmania

• Ecologists

– use observations and experiments to test explanations for the distribution and abundance of species

Subfields of Ecology

• Organismal ecology

– studies how an organism’s structure, physiology, and (for animals) behaviour meet the challenges posed by the environment

Figure 50.3a(a) Organismal ecology. How do humpback whales

select their calving areas?

• Population ecology

– concentrates mainly on factors that affect how many individuals of a particular species live in an area

Figure 50.3b

Population ecology.What environmentalfactors affect thereproductive rate ofdeer mice?

(b)

• Community ecology

– deals with the whole array of interacting species in a community

Figure 50.3c

(c) Community ecology.What factors influencethe diversity of speciesthat make up aparticular forest?

• Ecosystem ecology

– emphasizes energy flow and chemical cycling among the various biotic and abiotic components

Figure 50.3d

(d) Ecosystem ecology. Whatfactors control photosyntheticproductivity in a temperategrassland ecosystem?

• Landscape ecology

– deals with arrays of ecosystems and how they are arranged in a geographic region

Figure 50.3e

(e) Landscape ecology. To what extent do the trees lining the drainage channels in this landscape serve as corridors of dispersal for forest animals?

The biosphere

– is the global ecosystem, the sum of all the planet’s ecosystems

Ecology and Environmental Issues

• Ecology

– provides the scientific understanding underlying environmental issues

• Rachel Carson

– is credited with starting the modern environmental movement

Figure 50.4

• Most ecologists follow the precautionary principle regarding environmental issues

• The precautionary principle

– basically states that humans need to be concerned with how their actions affect the environment

• Concept 50.2: Interactions between organisms and the environment limit the distribution of species

• Ecologists

– have long recognized global and regional patterns of distribution of organisms within the biosphere

• Many naturalists

– began to identify broad patterns of distribution by naming biogeographic realms

Tropicof Cancer(23.5N)

Equator

Nearctic

Neotropical

Ethiopian

Oriental

Australian

Palearctic

(23.5S)Tropic ofCapricornFigure 50.5

Biogeography

• provides a good starting point for understanding what limits the geographic distribution of species

Figure 50.6

Species absentbecause

Yes

No

Dispersallimits

distribution?behaviour

limitsdistribution?

Biotic factors(other species)

limitdistribution?

Abiotic factorslimit

distribution?

Yes

No

Yes

No

Area inaccessibleor insufficient time

Habitat selectionPredation, parasitism,competition, disease

WaterOxygenSalinitypHSoil nutrients, etc.

TemperatureLightSoil structureFireMoisture, etc.

Chemicalfactors

Physicalfactors

Dispersal and Distribution

• Dispersal

– is the movement of individuals away from centers of high population density or from their area of origin

– contributes to the global distribution of organisms

New areasoccupied Year

1996

1989

1974

Natural Range Expansions

– show the influence of dispersal on distribution

– moving into areas where did not exist before

Figure 50.7

Species Transplants

• Species transplants

– include organisms that are intentionally or accidentally relocated from their original distribution

– can often disrupt the communities or ecosystems to which they have been introduced

Behaviour and Habitat Selection

• Some organisms

– do not occupy all of their potential range

• Species distribution

– may be limited by habitat selection behaviour

• does behaviour play a role in limiting distribution?

Biotic Factors

• Biotic factors that affect the distribution of organisms may include

– interactions with other species

– predation

– competition

A specific case of an herbivore limiting distribution of a food species

Figure 50.8

W. J. Fletcher tested the effects of two algae-eating animals, sea urchins and limpets, on seaweed abundance near Sydney, Australia. In areas adjacent to a control site, either the urchins, the limpets, or both were removed.EXPERIMENT

RESULTS Fletcher observed a large difference in seaweed growth between areas with and without sea urchins.

100

80

60

40

20

0

Limpet

Seaurchin Both limpets

and urchinsremoved

Onlyurchinsremoved

Only limpets removed

August1982

February1983

August1983

February1984

Control (bothurchins andlimpets present)

Sea

wee

d co

ver

(%)

Removing bothlimpets andurchins orremoving onlyurchins increasedseaweed coverdramatically.

Almost noseaweed grewin areas whereboth urchins andlimpets werepresent, or whereonly limpets wereremoved.

Removing both limpets and urchins resulted in the greatest increase of seaweed cover, indicating that bothspecies have some influence on seaweed distribution. But since removing only urchins greatly increased seaweed growth whileremoving only limpets had little effect, Fletcher concluded that sea urchins have a much greater effect than limpets in limitingseaweed distribution.

CONCLUSION

Abiotic Factors

• Abiotic factors that affect the distribution of organisms may include

– temperature

– water

– sunlight

– wind

– rocks and soil

Temperature

• Environmental temperature

– is an important factor in the distribution of organisms because of its effects on biological processes

Water

• Water availability among habitats

– is another important factor in species distribution

Sunlight

• Light intensity and quality

– can affect photosynthesis in ecosystems

• Light

– is also important to the development and behaviour of organisms sensitive to the photoperiod

Wind

• Wind

– amplifies the effects of temperature on organisms by increasing heat loss due to evaporation and convection

– can change the morphology of plants

Figure 50.9

Rocks and Soil

• Many characteristics of soil limit the distribution of plants and thus the animals that feed upon them

– physical structure

– pH

– mineral composition

Climate

• Four major abiotic components make up climate

– temperature, water, sunlight, and wind

• Climate

– is the prevailing weather conditions in a particular area

• Climate patterns can be described on two scales

– macroclimate, patterns on the global, regional, and local level

– microclimate, very fine patterns, such as those encountered by the community of organisms underneath a fallen log

Global Climate Patterns

• Earth’s global climate patterns

– are determined largely by the input of solar energy and the planet’s movement in space

• sun’s warming effect on atmosphere, land, & water establishes temperature variations, cycles of air movement, & evaporation of water that are responsible for latitudinal variations in climate

• Sunlight intensity

– plays a major part in determining the Earth’s climate patterns

Figure 50.10

Low angle of incoming sunlight

Sunlight directly overhead

Low angle of incoming sunlight

North Pole60N

30NTropic ofCancer

0 (equator)

30S

60S

Atmosphere

LALITUDINAL VARIATION IN SUNLIGHT INTENSITY

Tropic ofCapricorn

South pole

Figure 50.10

June solstice: NorthernHemisphere tilts toward sun; summer begins in Northern Hemisphere; winter begins inSouthern Hemisphere.

March equinox: Equator faces sun directly;neither pole tilts toward sun; all regions on Earthexperience 12 hours of daylight and 12 hours ofdarkness.

60N30N

0 (equator)

30S

Constant tiltof 23.5

September equinox: Equator faces sun directly; neither pole tilts toward sun; all regions on Earth experience 12 hours ofdaylight and 12 hours of darkness.

December solstice: NorthernHemisphere tilts away from sun; winter begins in Northern Hemisphere; summer begins in Southern Hemisphere.

SEASONAL VARIATION IN SUNLIGHT INTENSITY

Seasonality

• The angle of the sun

– leads to many seasonal changes in local environments

– tropics that lie between 23.5° north latitude & 23.5° south latitude

• experience greatest input & least seasonal variation in solar radiation of any region on earth

• intense solar radiation near equator initiates global circulation of air, creating precipitation and winds

• creates prevailing air currents

Descendingdry airabsorbsmoisture

Ascendingmoist airreleasesmoisture

Descendingdry airabsorbsmoisture

30 23.5 0 23.5 30Aridzone Tropics

Aridzone

60N

30N

0 (equator)

30S

60S

GLOBAL AIR CIRCULATION AND PRECIPITATION PATTERNS

• Air circulation and wind patterns

– play major parts in determining the Earth’s climate patterns

Figure 50.10

GLOBAL WIND PATTERNS

Westerlies

Northeast trades

Doldrums

Southeast trades

Westerlies

AntarcticCircle

60S

30S

0(equator)

30N

60N

ArcticCircle

Figure 50.10

Regional, Local, and Seasonal Effects on Climate

• Various features of the landscape

– contribute to local variations in climate

Bodies of Water

• Oceans and their currents, and large lakes

– moderate the climate of nearby terrestrial environments

Figure 50.11

Coolerair sinksover water.

3

Air cools athigh elevation.

2 1 Warm airover land rises.

4 Cool air over watermoves inland, replacingrising warm air over land.

• Mountains have a significant effect on

– the amount of sunlight reaching an area

– local temperature

– rainfall

Mountains

Farther inland, precipitationincreases again as the airmoves up and over highermountains. Some of the world’sdeepest snow packs occur here.

Figure 50.12

3 On the eastern side of theSierra Nevada, there is littleprecipitation. As a result ofthis rain shadow, much ofcentral Nevada is desert.

As moist air moves inoff the Pacific Ocean andencounters the westernmostmountains, it flows upward,cools at higher altitudes,and drops a large amountof water. The world’s tallesttrees, the coastal redwoods,thrive here.

12

EastPacificOcean

Winddirection

CoastRange

SierraNevada

• Lakes

– are sensitive to seasonal temperature change

– experience seasonal turnover

Lakes

Figure 50.13

In spring, as the sun melts the ice, the surface water warms to 4°Cand sinks below the cooler layers immediately below, eliminating thethermal stratification. Spring winds mix the water to great depth, bringing oxygen (O2) to the bottom waters (see graphs) andnutrients to the surface.

2

In winter, the coldest water in the lake (0°C) lies justbelow the surface ice; water is progressively warmer atdeeper levels of the lake, typically 4–5°C at the bottom.

1

In autumn, as surface water cools rapidly, it sinks below theunderlying layers, remixing the water until the surface beginsto freeze and the winter temperature profile is reestablished.

4 In summer, the lake regains a distinctive thermal profile, with warm surface water separated from cold bottom water by a narrowvertical zone of rapid temperature change, called a thermocline.

3

Winter Spring

High

Medium

Low

O2 concentration

O2 (mg/L)

Lake

dep

th (

m)

0 4 8 12

8

16

24

8

16

24

Lake

dep

th (

m) O2 (mg/L)

O2 (mg/L)

Lake

dep

th (

m)

0 4 8 12

8

16

24

O2 (mg/L)

Lake

dep

th (

m)

0 4 8 12

8

16

24Autumn Summer

4C4

44

44

4C4

44

2 0

4C4

44

44

4C

6818

2022

5Thermocline

0 4 8 12

Microclimate

Microclimate

– is determined by fine-scale differences in abiotic factors

– refer to microclimate on a forest floor or under rock

– small scale differences that influence local distributions of organisms

Long-term climate change

– climate changes can have long-term effects on the biosphere

– global warming may affect distribution of organisms

– ice ages affected distribution in past

Long-Term Climate Change

• One way to predict future global climate change

– is to look back at the changes that occurred previously

Figure 50.14

Current range

Predictedrange

Overlap

(a) 4.5C warming overnext century

(b) 6.5C warming overnext century

• Concept 50.3: Abiotic and biotic factors influence the structure and dynamics of aquatic biomes

• Varying combinations of both biotic and abiotic factors

– determine the nature of Earth’s many biomes

• Biomes

– are the major types of ecological associations that occupy broad geographic regions of land or water

Earth’s aquatic biomes

Figure 50.15

30N

Tropic of Cancer

Equator

30S

Continentalshelf

Lakes

Coral reefs

Rivers

Oceanic pelagiczone

Estuaries

Intertidal zone

Abyssal zone(below oceanicpelagic zone)

Key

Tropic ofCapricorn

• Aquatic biomes

– account for the largest part of the biosphere in terms of area

– can contain fresh or salt water

• Oceans

– salt concentration ~3%

– cover about 75% of Earth’s surface

– have an enormous impact on the biosphere

• Freshwater

– salt concentration of less than 1%

– closely linked to terrestrial biomes through which they pass

Aquatic zones

• Many aquatic biomes

– are stratified into zones or layers defined by light penetration, temperature, and depth

Marine zonation. Like lakes, the marine environment is generally classified on the basis of light penetration (photic and aphotic zones), distance from shore and water depth (intertidal, neritic, and oceanic zones), and whether it is open water (pelagic zone) or bottom (benthic and abyssal zones).

Zonation in a lake. The lake environment is generally classified on the basis of three physical criteria: light penetration (photic and aphotic zones), distance from shore and water depth (littoral and limnetic zones), and whether it is open water (pelagic zone) or bottom (benthic zone).

(a)

Littoralzone Limnetic

zone

Photiczone

Benthiczone

Aphoticzone

Pelagiczone

Intertidal zone

Neritic zone Oceanic zone

0

200 mContinentalshelf

Photic zone

Pelagic zone

Aphoticzone

Benthiczone

2,500–6,000 m

Abyssal zone(deepest regions of ocean floor)

(b)

Figure 50.16a, b