What Shapes an Ecosystem?

Review of Biotic and Abiotic Factors• Ecosystems are influenced by a

combination of biological and physical factors.

• Biotic factors – include all the living things with which an

organism might interact.

• Abiotic Factors – Physical, or nonliving, factors that shape

ecosystems.

Habitat and Niche

• Habitat– all aspects of the area in which an

organism lives (includes both biotic and abiotic).

– Habitats may change or disappear due to natural causes or interference by man.

Habitat and Niche

• Niche – the role or place and position a species has in

its environment.

• An ecological niche includes all of the factors that a species needs to survive, stay healthy, and reproduce.– food– abiotic conditions– behavior

Habitat and Niche

• Why do you think no two species can share the same niche.• One species is better suited to the niche

and the other will either be pushed out or become extinct.

Community Interactions

• When organisms live together in ecological communities, they interact constantly.

• Community interactions include:– Competition– Predation– Symbiosis

Community Interactions

• Competition:– occurs when two organisms fight for the

same limited resource.– Direct competition in nature often results

in a winner and a loser—with the losing organism failing to survive.

How species avoid Competition

• The distribution of these warblers avoids direct competition, because each species feeds in a different part of the tree.

Community Interactions

• Predation:– occurs when one organism captures

and eats another.

Predator

Prey

Community Interactions

• Symbiosis:– Any relationship in which two species

live closely together– Includes:

– mutualism– commensalism – parasitism

Community Interactions

• Mutualism:– both species benefit from the relationship.

Community Interactions

• Commensalism– one member of the association benefits and the other is

neither helped nor harmed.

Human Our eyelashes are home to tiny mitesthat feast on oil secretions and dead skin. Without harming us, up to 20 mites may be living in one eyelash follicle.

Demodicids Eyelash mites find all they need to survive in the tiny folliclesof eyelashes. Magnified here 225 times, these creatures measure 0.4 mm in length and can be seen only with a microscope.

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Organism benefits+

Ø

Ø Organism is not affected

Commensalism

Community Interactions

• Parasitism– one organism lives on or inside another organism and

harms it.

Organism benefits0

_

Organism is not affected

Hornworm caterpillarThe host hornworm will eventually die as its organs are consumedby wasp larvae.

Braconid waspBraconid larvae feed on their host and release themselves shortly before reachingthe pupae stage of development.

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Parasitism

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0

Ecological Succession

• Succession occurs following a disturbance in an ecosystem and regenerates or creates a community after a disturbance.– a sequence of biotic changes– damaged communities are regenerated– new communities arise in previously

uninhabited areas

Ecological Succession

• There are two types of succession.• primary succession — started by pioneer

species

Ecological Succession

• There are two types of succession.– secondary succession — started by

remaining species

Population Ecology

Population Dynamics

• Population:–All the individuals of a species

that live together in an area

• Demography:–The statistical study of

populations, allows predictions to be made about how a population will change

Population Dynamics

• Three Key Features of Populations– Size– Density– Dispersion

Three Key Features of Populations

Size: number of individuals in an area

Three Key Features of Populations

• Growth Rate: – Birth Rate (natality) - Death Rate (mortality)– How many individuals are born vs. how many

die– Birth rate (b) − death rate (d) = rate of natural

increase (r)

Density: measurement of population per unit area or unit volume

Pop. Density = # of individuals ÷ unit of space

Three Key Features of Populations

1. Immigration: movement of individuals into a population

2. Emigration: movement of individuals out of a population

3. Density-dependent factors: Biotic factors in the environment that have an increasing effect as population size increases (disease, competition, parasites)

4. Density-independent factors: Abiotic factors in the environment that affect populations regardless of their density (temperature, weather)

How Do You Affect Density?

Immigration

Emigration

Natality MortalityPopulation+

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-

-

Factors That Affect Future Population Growth

Population Dispersion

• Dispersion: describes the spacing of organisms relative to each other– Clumped– Uniform– Random

Three Key Features of Populations

• Population density = number of individuals in a given area or volume

• Count all the individuals in a population

• Estimate by sampling

• Mark-Recapture Method

How Are Populations Measured?

• Idealized models describe two kinds of population growth:

1. Exponential Growth

2. Logistic Growth

How Do Populations Grow?

Carrying Capacity

• Carrying Capacity (k): – The maximum population size that can be

supported by the available resources– There can only be as many organisms as

the environmental resources can support

Figure 35.3A

Exponential Growth Curve - J curve

Logistic Growth Curve – S curve

• Declining birth rate or increasing death rate are caused by several factors including:– Limited food supply

– The buildup of toxic wastes

– Increased disease

– Predation

Factors Limiting Growth Rate

“Booms” and “Busts”

• R Strategists Short life span Small body size Reproduce quickly Have many young Little parental care Ex: cockroaches,

weeds, bacteria

Reproductive Strategies

Reproductive Strategies

• K Strategists Long life span Large body size Reproduce slowly Have few young Provides parental

care Ex: humans,

elephants

Age Distribution

• Distribution of males and females in each age group of a population

• Used to predict future population growth

Human Population Growth

• J curve growth (exponential growth curve)• Grows at a rate of about 80 million yearly

– r =1.3%• Why doesn’t environmental resistance

take effect?– Altering their environment– Technological advances

• The cultural revolution• The agricultural revolution• The industrial-medical revolution

• Doubled three times in the last three centuries

• About 6.1 billion and may reach 9.3 billion by the year 2050

• Improved health and technology have lowered death rates

The Human Population

History of the Human Population