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
Predator
• Predation:
– occurs when one organism captures
and eats another.
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.
Ø
Human Our eyelashes
are home to tiny mites
that feast on oil
secretions and dead
skin. Without harming
us, up to 20 mites may
be living in one eyelash
follicle.
Commensalism
Ø Organism is not affected
+
+
Organism benefits
Demodicids Eyelash
mites find all they need to
survive in the tiny follicles
of eyelashes. Magnified
here 225 times, these
creatures measure 0.4
mm in length and can be
seen only with a
microscope.
Community Interactions
• Parasitism
– one organism lives on or inside another organism and
harms it.
0
Parasitism
+
_
Hornworm
caterpillar
The host hornworm
will eventually die as
its organs are
consumed
by wasp larvae.
_
Organism is not affected
0
Braconid
wasp
Braconid larvae
feed on their
host and
release
themselves
shortly before
reaching
the pupae
stage of
development.
Organism benefits
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)
Three Key Features of Populations
Density: measurement of population per unit
area or unit volume
Pop. Density = # of individuals ÷ unit of space
How Do You Affect Density?
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)
Factors That Affect Future Population Growth
Immigration
Natality
+
+
Population
Emigration
-
Mortality
Population Dispersion
Three Key Features of Populations
• Dispersion: describes the spacing of
organisms relative to each other
– Clumped
– Uniform
– Random
How Are Populations Measured?
• 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 Do Populations Grow?
•
Idealized models describe two kinds of
population growth:
1. Exponential Growth
2. Logistic Growth
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
Exponential Growth Curve - J
curve
Figure 35.3A
Logistic Growth Curve – S
curve
Factors Limiting Growth Rate
• Declining birth rate or increasing death rate
are caused by several factors including:
– Limited food supply
– The buildup of toxic wastes
– Increased disease
– Predation
“Booms” and “Busts”
Reproductive Strategies
• R Strategists
 Short life span
 Small body size
 Reproduce
quickly
 Have many
young
 Little parental
care
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
The Human Population
• 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
History of the Human
Population