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Biotic and Abiotic Influences on Ecosystems, Lecture notes of Fossil Fuels

University of North Dakota (UND)Fossil Fuels

Abiotic factors such as temperature, light, and soil can influence a species' ability to survive. Every species is able to survive within a range of each of.

Typology: Lecture notes

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2.7
Biotic and Abiotic Infl uences
on Ecosystems
What determines the size of a population and where a particular species can
and does live? Th e answer to this is important if we are to live sustainably
in our environment. Ideal biotic and abiotic conditions allow a species to
fl ourish. Other conditions may lead to a species’ decline or even extinction.
Both abiotic and biotic factors determine where a species can live. A
limiting factor is any factor that places an upper limit on the size of a
population. Limiting factors may be biotic, such as the availability of food,
or abiotic, such as access to water. Human infl uences oft en act as limiting
factors.
infl uence of abiotic Factors
Abiotic factors such as temperature, light, and soil can infl uence a species’
ability to survive. Every species is able to survive within a range of each of
these factors. Th is range is called the species’ tolerance range (Figure 1).
Near the upper and lower limits of the tolerance range, individuals
experience stress. Th is will reduce their health and their rate of growth and
reproduction. Within a species’ tolerance range is an optimal range, within
which the species is best adapted. Th e largest and healthiest populations
of a species will occur when conditons are within the optimal range. Each
species has a tolerance range for every abiotic factor.
limiting factor any factor that restricts
the size of a population
tolerance range the abiotic conditions
within which a species can survive
Some species have wide tolerance ranges, while others have much
narrower ranges. Species with broad tolerance ranges will tend to be
widely distributed and may easily invade other ecosystems. For example,
buckthorn, a small tree native to Europe, has become widespread over
much of southern and central Ontario due to its broad tolerance range.
Conversely, the showy lady’s-slipper orchid has a narrow tolerance range.
It is found only in specifi c types of wetlands.
Population size
optimum range
tolerance range
no
population
no
population
high
population
low
population
low
population
low high
highlow
Abiotic factor
0
Figure 1 Species can be successful over a range of abiotic conditions. However, they will become
stressed and will die out if conditions exceed their tolerance limits.
52 Chapter 2 • Understanding Ecosystems NEL
6646_Sci9_ch02_pp48-63.indd 52 7/17/09 12:51:01 PM
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2.7 Biotic and Abiotic Infl uences

on Ecosystems

What determines the size of a population and where a particular species can

and does live? The answer to this is important if we are to live sustainably

in our environment. Ideal biotic and abiotic conditions allow a species to

flourish. Other conditions may lead to a species’ decline or even extinction.

Both abiotic and biotic factors determine where a species can live. A

limiting factor is any factor that places an upper limit on the size of a

population. Limiting factors may be biotic, such as the availability of food,

or abiotic, such as access to water. Human influences often act as limiting

factors.

influence of abiotic Factors

Abiotic factors such as temperature, light, and soil can influence a species’

ability to survive. Every species is able to survive within a range of each of

these factors. This range is called the species’ tolerance range (Figure 1).

Near the upper and lower limits of the tolerance range, individuals

experience stress. This will reduce their health and their rate of growth and

reproduction. Within a species’ tolerance range is an optimal range, within

which the species is best adapted. The largest and healthiest populations

of a species will occur when conditons are within the optimal range. Each

species has a tolerance range for every abiotic factor.

limiting factor any factor that restricts the size of a population

tolerance range the abiotic conditions within which a species can survive

Some species have wide tolerance ranges, while others have much

narrower ranges. Species with broad tolerance ranges will tend to be

widely distributed and may easily invade other ecosystems. For example,

buckthorn, a small tree native to Europe, has become widespread over

much of southern and central Ontario due to its broad tolerance range.

Conversely, the showy lady’s-slipper orchid has a narrow tolerance range.

It is found only in specific types of wetlands.

Population size

optimum range

tolerance range

no population

no population

high populationlow population populationlow

low high

high

low

Abiotic factor

0

Figure 1 Species can be successful over a range of abiotic conditions. However, they will become stressed and will die out if conditions exceed their tolerance limits.

52 Chapter 2 • Understanding Ecosystems (^) NEL

The distribution of most terrestrial plant species is largely limited by

a combination of temperature, precipitation, and light (Figure 2). The

distribution of black spruce in North America, for example, is limited to

regions with long, cold winters and moderate precipitation (Figure 3).

Other abiotic factors, such as soil type, often have less critical roles.

Figure 3 The distribution of black spruce

C02-F19-UAOS9SB

Crowle Art Group Deborah Crowle 1st pass

Ontario Science 10 SB 0-17-635528- FN CO

Pass Approved Not Approved

Table 1 Key Abiotic Factors of Terrestrial and Aquatic Ecosystems and the Effects Human Activities Can Have on Them^ C02-F19-UAOS9SB.ai

Ecosystem Key abiotic factors Human action and result terrestrial ecosystems

light availability Clear-cutting and fire remove shade and expose the remaining organisms to much more light.

water availability Damming rivers and draining swamps and marshes change water availability. Irrigation increases water availability. nutrient availability Farming practices may increase or decrease nutrient levels in the soil.

temperature Global warming is decreasing suitable habitat for many cool-adapted species.

aquatic ecosystems

light availability Activities that increase erosion or stir up the bottom cloud the water and reduce light penetration.

nutrient availability Nutrient runoff from agriculture and urban environments increases the nutrient content of surface water and groundwater, causing algal blooms. acidity Acidic air pollution results in acid precipitation. Carbon dioxide emissions produced by the burning of fossil fuels are increasing the acidity of the oceans. temperature Industries and power plants release heated waste water into lakes and rivers, killing fish and other organisms. salinity Salting highways and long-term irrigation practices can cause salt to accumulate.

The key abiotic factors in aquatic ecosystems are salt concentration and

the availability of sunlight, oxygen, and nutrients. Light is abundant in

shallow clear water but rapidly decreases with increasing depth. Oxygen

concentration is greatest near the water’s surface because this is where

oxygen enters from the air and where most photosynthesis takes place.

Remember that oxygen is released during photosynthesis.

Nutrient availability also varies in aquatic ecosystems. Plants growing

in shallow water obtain nutrients directly from the bottom soil. In deeper

water, however, the only available nutrients are those dissolved in the water.

Table 1 summarizes some of the key abiotic factors and the human activities

that can disrupt or alter them.

Figure 2 (a) Cacti can withstand long periods of drought. If overwatered, they may die because their roots cannot survive consistently damp conditions. (b) Aquatic plants, such as water lilies, will perish quickly if the water level drops and the roots are exposed to air. (c) While both cacti and water lilies prefer exposure to full sun, bunchberries are adapted to shade.

(a) (b) (c)

NEL^ 2.7 Biotic and Abiotic Influences on Ecosystems^53

UNIT TASK Bookmark

You can apply what you learned in this section about how biotic and abiotic factors limit population size to the Unit Task described on page 156.

Carrying Capacity

As a population’s size increases, the demand for resources, such as food,

water, shelter, and space also increases. Eventually, there will not be

enough resources for each individual. Furthermore, as individuals become

more crowded, they become more susceptible to predators and diseases.

Eventually, these and other factors will result in the population reaching

the upper sustainable limit that the ecosystem can support, called the

carrying capacity.

The carrying capacity can be altered through natural or human activity

when resources are removed from or added to the ecosystem. Irrigation can

change a desert into a lush oasis because it increases the carrying capacity

of the desert (Figure 5). The loss or introduction of a species can change the

carrying capacity of the ecosystem for other species in that ecosystem. For

example, the removal of wolves by human hunters will increase the carrying

capacity of the ecosystem for moose. When new species are introduced,

they interact with the original species in many ways. As you will learn, such

introductions are among the most serious threats to natural ecosystems.

carrying capacity the maximum population size of a particular species that a given ecosystem can sustain

CHECKCHECK YOUR LEARNING

  1. Distinguish between tolerance range and optimal range. K/U
  2. List three abiotic factors important to both terrestrial and aquatic ecosystems. Explain your choices. K/U
  3. How do human actions increase the carrying capacity of some ecosystems? K/U
  4. Give some examples of each of the following: predation, competition, mutualism, parasitism, commensalism. K/U
  5. Before reading this section, which types of species–species interactions were you already familiar with? C
  6. What species–species relationship or example did you find the most interesting or unusual? C 7. Is it possible to describe abiotic factors as more or less important to an ecosystem than biotic factors? Explain your reasoning. K/U 8. Cedar waxwings are one species of bird that is adapted to withstand our cold winters. Bird watchers in Barrie provide cedar waxwings with seeds at birdfeeders during winter months. K/U^ T/I (a) Would the seeds alter the carrying capacity of the ecosystem? Explain. (b) Provide a hypothesis that explains why bird watchers have noted an increase in the falcon population in recent years.

IN SUMMARY

  • Many factors place limits on the sizes of

populations in an ecosystem.

  • Tolerance ranges describe the physical conditions

under which a species can survive.

  • The type of ecosystem that occurs in a particular

location is strongly influenced by abiotic factors

such as light, water, and temperature.

  • Species interactions include competition,

predation, mutualism, parasitism, and

commensalism.

  • Carrying capacity is the maximum population

size that an ecosystem can sustain.

Figure 5 These green circles, visible from the International Space Station, are formed by an irrigation project in Libya. Irrigation increases the carrying capacity of the desert ecosystem.

NEL^ 2.7 Biotic and Abiotic Infl uences on Ecosystems^55