Title: Environmental Science: Toward a Sustainable Future Richard T' Wright
1Environmental Science Toward a Sustainable
Future Richard T. Wright
Chapter 4
- Ecosystems How They Change
- PPT by Clark E. Adams
2Factors That Contribute to Ecosystem Change
- Dynamics of natural populations
- Mechanisms of population equilibrium
- Mechanisms of species adaptation
- Ecosystem response to disturbance
- Lessons to learn
3Dynamics of Natural Populations
- Population growth curves
- Biotic potential versus environmental resistance
- Density dependence and critical number
4Population
- Interbreeding
- Reproducing
- Group of individuals
- In a specified area
5Mechanisms of Population Equilibrium
- Territoriality defense of a resource against
individuals of the same species - Examples of wolves and songbirds
- Results in priority use of resources
- Limits population numbers
- Organisms that cannot acquire a territory are
prevented from breeding
6Population Dynamics
- Biotic potential ability of populations to
increase - Reproductive rate
- Migration and dispersal
- Defenses
- Coping strategies
7Recruitment Level
- Portion of population that survives
- Becomes part of the breeding population
8Environmental Resistance
- Combination of abiotic and biotic factors keeping
a population in check - Natural enemies
- Predators
- Parasites
- Competitors
- Disease
- Availability of food
- Adverse weather
9Biotic Potential and Environmental Resistance
10Population Growth Curves
11J Curve
- Growth exceeds carrying capacity
- Overgrazes
- Dies due to starvation
- Population Crashes
- Looks like letter J
- Human population resembles J curve
12S Curve
- Population held in balance
- By environmental resistance
- Natural enemies
- Looks like letter S
- Population at equilibrium
13Population Dynamics
- Environmental resistance combination of biotic
and abiotic factors that may limit population
increase - Predators, competitors, disease
- Adverse weather, limited food/nutrients
14Population Dynamics
- Factors of environmental resistance are either
- Density-independent effect does not vary with
population density e.g., adverse weather - Density-dependent effect varies with population
density e.g., infectious disease
15Density Dependence
- As density increases
- Disease transmission increases
- More dieoff from disease and parasites
- Predation increases
- Easier for predators to find when more organisms
present
16Critical Numbers
- Critical number the lowest population level for
survival and recovery
17Mechanisms of Population Equilibrium
- Predatorprey dynamics
- Competition
- Interspecific
- Intraspecific
- Introduced species
18Naturally balanced ecosystems
- Herbivores dont overgraze vegetation
- Natural enemies keep herbivore population below
overgrazing levels - Predators do not eliminate their prey
- Prey is well enough adapted so many escape
19PredatorPrey Balance Wolves and Moose
20Lessons to Be Learned about PredatorPrey Balance
- Absence of natural enemies allows a herbivore
population to exceed carrying capacity, which
results in overgrazing of the habitat. - The herbivore population subsequently crashes.
- The size of the herbivore population is
maintained so that overgrazing or other overuse
does not occur.
21PlantHerbivore Dynamics
Reindeer on St. Matthew Island
- No regulatory control (predation) on herbivores
- Went into exponential growth pattern
- Overgrazed habitat
- Massive die-off of herbivores
22Keystone Species
- A single species that maintains biotic structure
of the ecosystem - Pisaster ochraceus a starfish that feeds on
mussels, keeping them from blanketing the rocks
http//www.marine.gov/
23Competition Intraspecific
- Territoriality defense of a resource against
individuals of the same species - Examples of wolves and songbirds
- Results in priority access and use of resources
- How do wolves and songbirds establish territory?
24Introduced Species
- Introductions degrade ecosystems
- No natural predators
- Better competitors
- Take over and form monoculture
- Wiping out biodiversity of area
25Introduced species
- Other names
- Non-native
- Exotic
- Noxious weeds
- Arrived
- Accidental release
- Intentional release (carp)
- Bilge water
- With other seeds
26Examples of exotic (introduced) species
- Purple loosestrife
- Leafy spurge
- Chicory
- Queen Annes lace
- Kudzu
- Fire ants
- Japanese beetles
- Water hyacinth
- Zebra Mussels
27Introduced Species
- Rabbits in Australia (next slide)
- Chestnut blight in United States
- Japanese beetles, fire ants, gypsy moths in
United States - Water hyacinth, kudzu, spotted knapweed, purple
loosestrife (see Fig. 4-13 in text) in United
States
28Introduced Species Rabbits in Australia
- Introduced into Australia from England in 1859
- No natural enemies rabbit population exploded
- Overabundant herbivore population devastated
natural vegetation (see Fig. 4-11 in text). - Using disease as control measure why will this
procedure fail in the long term?
29Mechanisms of Species Adaptation
- Change through natural selection
- Selective pressure determines which organisms
survive and reproduce and which are eliminated.
30Recipe for Change
31The Limits of Change
- Adapt
- Move (migrate)
- Die (extinction)
32Prerequisites for Speciation
- Original population must separate into smaller
populations that do not interbreed with one
another. - List some ways this might happen.
- Separated populations must be exposed to
different selective pressures. - Example arctic and gray fox (next slide)
33Fire and Succession
- Fire climax ecosystems dependent upon fire for
maintenance of existing balance - grasslands, pine and redwood forests
- Significance for humans and where they live
- Fire suppression to protect homes
- Accumulation of dead material
- Fires more intense uncontrollable
34Ecosystem Responses to Disturbance
- Ecological succession
- Disturbance and resilience
- Evolving ecosystems
35Equilibrium Theory
- Ecosystems are stable environments in which the
biotic interactions among species determine the
structure of the communities present.
36Succession and Disturbance
- Ecological succession transition between biotic
communities - Primary no previous biotic community
- Secondary previously occupied by a community
- Aquatic transition from pond or lake to
terrestrial community
37Primary Succession
- Mosses invade an area and provide a place for
soil to accumulate. - Larger plants germinate in the new soil layer,
resulting in additional soil formation. - Eventually shrubs and trees will invade the area.
38Disturbance and Resilience
- Removes organisms
- Reduces populations
- Creates opportunities for other species to
colonize
39Fire and Succession
- Fire climax ecosystems dependent upon fire for
maintenance of existing balance - grasslands, pine and redwood forests
- Significance for humans and where they live
- Fire suppression to protect homes
- Accumulation of dead material
- Fires more intense uncontrollable
40Resilience Mechanisms after a Forest Fire
- Nutrient release to soil
- Regrowth by remnant roots and seeds
- Invasions from neighboring ecosystems
- Rapid restoration of energy flow and nutrient
cycling
41Lessons to Learn
- Managing ecosystems
- The pressure of population
42Managing Ecosystems
- Protecting and managing the natural environment
to maintain the goods and services vital to human
economy and survival.
43The Pressures of Population
- What is the carrying capacity for the human
population on Earth? - How will the human ecological footprint impact on
natures goods and services?
44Implications For Humans
- Protecting and managing the natural environment
to maintain the goods and services vital to human
economy and survival. - Establishing a balance between our own species
and the rest of the biosphere. - Human consumption of resources and subsequent
ecosystem destruction is overgrazing live
sustainably
45The Fourth Principle of Ecosystem Sustainability
- The size of the consumer population is maintained
so that overgrazing or other overuse does not
occur.
46Important Test Points
- Genetic Variation
- Gene Pools
- Adaptation
- Selective Breeding
- Biotic Potential vs. Environmental Resistance
47End of Chapter 4