Transcript environmental science - Clinton Community College

Chapter 6
Community Ecology,
Population Ecology,
& Sustainability
Community Structure
• Structure of a community (populations of all
species living and interacting in an area at a
particular time)
– Physical appearance: relative size, stratification &
species distribution
– Species diversity: # of different species
– Species abundance: # of individuals of each species
– Niche structure: number of niches, how they differ &
how they interact
Physical Appearance
• Differences in physical structure and
properties create transition zones between 2
ecosystems (ecotones)
– Edge effect: area between forest and grasslands
– Many animals and plants thrive “on the edge”
– Many species can become stressed in the edge
as well
Species Diversity & Abundance
• Most of the Earth’s diversity is in the rainforest,
coral reefs, deep sea & large tropical lakes
• Large amount of diversity = low number of
organisms of a particular type (abundance)
• Three major factors effect diversity
– Latitude in terrestrial communities
– Depth in aquatic zones
– Pollution in aquatic communities
Niche Structure
• Niche is analogous to its job
• Ecological niche represents the adaptations or
adaptive traits through evolution
• Fundamental niche: full potential range if there is
no competition for resources
• Realized niche: occupies only part of its
fundamental niche
– Generalist species have broad niches
– Specialized species have narrow niches
Types of Species
• Native – normally live in an ecosystem
• Non-native – (invasive or exotic) deliberately or
accidentally introduced into an ecosystem
• Indicator – serve as early warning signs for
damage or pollution of an ecosystem
• Keystone – play a critical ecological role by
effecting the type and abundance of other species
• Foundation – enhance a habitat to benefit other
species
Species Interaction
• Interspecific competition– competition between species for
food & resources
– Resource partitioning – adapt to reduce competition
(hawks & owls)
• Predation – one species (predator/hunter) lives off of
another species (prey/hunted)
• Parasitism – one species (parasite) lives on another species
(host)
• Mutualism – two species live together to benefit both
• Commensalism – one species benefits, but the other is not
harmed
Ecological Succession
• All communities and ecosystems change
constantly
• Ecological succession – gradual change in
species composition
– Primary succession: biotic communities in an
abiotic environment
– Secondary succession: biotic communities in an
biotic environment
Primary Succession
• See figure 6-9 on page 119.
• Begins in a lifeless area where there is no soil or
bottom sediment (bare rocks, parking lots, cooled
lava, etc.
• Lichens & mosses build up soils
• Early successional plant species (herbs & grasses)
grow fast & have short lives
• Mid-successional plant species (shrubs & trees)
• Late successional plant species (trees that can
tolerate shade) becomes a complex forest
community
Secondary Succession
• See figure 6-10 on page 120.
• Begins in an area that has soil and was previously
a community of organisms
• New vegetation can grow due to winds carrying
seeds, or animal droppings
• Secondary succession includes
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Abandoned cropland
Burned or cut forests
Heavily polluted streams, ponds or lakes
Land that has been dammed or flooded
Disturbances
• Changes in the environment that disrupts the
ecosystem
– Catastrophic or mild
– Natural or caused by humans
– Detrimental or beneficial
• Intermediate disturbance hypothesis predicts that
communities that experience frequent but
moderate disturbances have the most species
diversity
The Balance of Nature?
• Climax community: dominated by few
long-lived plant species and is at
equilibrium
• Ever-changing mosaic vegetation patches at
different stages of succession
• We can not predict the course of succession
toward an ideal climax community
Population Change
• Four variables
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Birth
Death
Immigration
Emigration
• Population change = (birth + immigration) –
(deaths + emigration)
Limits on Population Growth
• Biotic potential – capacity for growth
• Intrinsic rate of increase (r) – rate of growth if
there were unlimited resources
• Environmental resistance – all factors that act
together to limit growth
• Carrying capacity (K) – the result of biotic
potential and environmental resistance
• Minimum Viable Population (MVP) – certain
minimum population required to sustain its growth
Exponential vs Logistic
• Exponential growth starts small increasing
ever so rapidly (J shaped)
• Logistic growth starts slow, increases for a
time and then levels off (S shaped)
– Overshoot – an initial spike followed by a
decline in population (reproduction time log)
– Carrying capacity – population becomes a
constant (at equilibrium)
Predation In Population Control
• Top-down control: predator periodically
reduces the population of prey, which then
reduces the population of the predator,
which in turn allows the prey population to
increase again
• Bottom-up control: periodic population
crashes influence the food supply
Reproduction & Survival
• Asexual reproduction – clones of their
parents
• Sexual reproduction – requires genetic
information from 2 parents
– Provides greater genetic diversity
– Allows the males to gather food & help raise
the young
Reproductive Patterns
• K-selected species are competitors
– Many offspring each time they reproduce
– Early reproductive rate
– High potential growth rate
• R-selected species are opportunists
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Born live, mature slowly & cared for by parent
Do well in competitive situations
Low reproductive rates
Thrive best in constant environments
Human Impacts on Ecosystems
• Reduced biodiversity by destroying, fragmenting,
degrading & simplifying wildlife habitats
• Used, wasted, and destroyed an increasing
percentage of Earth’s net primary productivity
• Strengthened some populations of pests and
disease causing bacteria and viruses
• Eliminated some predators
• Deliberately or accidentally introduced non-native
species into communities
Human Impacts (cont.)
• Used some renewable resources faster than we can
replenish
• Interfere with the normal chemical cycling and
energy flows in ecosystems
• Become increasingly dependent on nonrenewable
energy sources – fossil fuels – which have a whole
host of global impacts in the extraction,
processing, consumption and disposal of waste
product generated by the use of fossil fuels
Ecosystem Stability
• Stability is maintained by constant dynamic
change
– Inertia (persistence) is the ability for organisms
to resist change
– Consistency is a restriction to change due to
limited resources
– Resiliency is the ability for organisms to
bounce back
Sustainability
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Human aspects can be controlled
Balance of resource usage
Use less and waste less
Alternatives must be utilized
“Going Green”
Strive for sustainable communities
Sustainability
• Lifestyles – we need to change
• Connections – we need to be aware of our
interdependency with everything else
• Intrusion – we need to ask ourselves what
happens when we alter nature
• Can not continue to deplete & degrade – we
need to become more sustainable in all
aspects of our lives
The Precautionary Principle
• It is important to take precaution in
activities or behavior that may be harmful to
the health of species or the environment.
• See figure 6-18 on page 126.