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Community Ecology, Population Ecology, and Sustainability
Chapter 6
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Why Should We Care about the American Alligator?
Overhunted Niches Ecosystem services Keystone species Endangered and threatened species Alligator farms Fig. 6-1, p. 108
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Why Should We Care about the American Alligator?
Fig. 6-1, p. 108
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Community Structure and Species Diversity
Physical appearance Edge effects Species diversity or richness Species abundance or evenness Niche structure
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Natural Capital: Types, Sizes, and Stratification of Terrestrial Plants
Tropical rain forest Coniferous forest Deciduous forest Thorn forest Thorn scrub Tall-grass prairie Short-grass prairie Desert scrub Fig. 6-2, p. 110
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Species Diversity and Ecological Stability
Many different species provide ecological stability Some exceptions Minimum threshold of species diversity Many unknowns Net primary productivity (NPP) Essential and nonessential species
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Types of Species Native Nonnative (invasive or alien) Indicator
Keystone Foundation
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Indicator Species Provide early warnings Indicator of water quality
Birds as environmental indicators Butterflies Amphibians
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Amphibians as Indicator Species
Environmentally sensitive life cycle Vulnerable eggs and skin Declining populations
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Tadpole develops into frog
Life Cycle of a Frog Adult frog (3 years) Young frog sperm Tadpole develops into frog Sexual reproduction Tadpole Eggs Fertilized egg development Egg hatches Organ formation Fig. 6-3, p. 112
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Possible Causes of Declining Amphibian Populations
Habitat loss and fragmentation Prolonged drought Pollution Increases in ultraviolet radiation Parasites Overhunting Disease Nonnative species
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Why Should We Care about Vanishing Amphibians?
Indicator of environmental health Important ecological roles of amphibians Genetic storehouse for pharmaceuticals
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Keystone Species What is a keystone?
Keystone species play critical ecological roles Pollination Top predators Dung beetles Sharks
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Why are Sharks Important?
Ecological roles of sharks Shark misconceptions Human deaths and injuries Lightning is more dangerous than sharks Shark hunting and shark fins Mercury contamination Medical research Declining populations Hunting bans: effective?
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Foundation Species Relationship to keystones species
Play important roles in shaping communities Elephants Contributions of bats and birds
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Species Interactions Interspecific competition Predation Parasitism
Mutualism Commensalism
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Species Interactions: Competition
Interspecific Competition Fundamental niches Fighting for limited resources Competition from humans
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Reducing or Avoiding Competition
Resource partitioning Role of natural selection Specialization and sharing of resources Resource partitioning of warblers
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Resource Partitioning and Niche Specialization
Number of individuals Species 1 Species 2 Region of niche overlap Resource use Number of individuals Species 1 Species 2 Resource use Fig. 6-4, p. 114
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Resource Partitioning of Warbler Species
Fig. 6-5, p. 115
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Predator and Prey Interactions
Carnivores and herbivores Predators Prey Natural selection and prey populations
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How Do Predators Increase Their Chances of Getting a Meal?
Speed Senses Camouflage and ambush Chemical warfare (venom)
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Avoiding and Defending Against Predators
Escape Senses Armor Camouflage Chemical warfare Warning coloration Mimicry Behavior strategies Safety in numbers
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How Species Avoid Predators
Span worm Bombardier beetle Viceroy butterfly mimics monarch butterfly Foul-tasting monarch butterfly Poison dart frog When touched, the snake caterpillar changes shape to look like the head of a snake Wandering leaf insect Hind wings of io moth resemble eyes of a much larger animal Fig. 6-6, p. 116
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Parasites Parasitism Hosts Inside or outside of hosts
Harmful effects on hosts Important ecological roles of parasites
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Mutualism Both species benefit Pollination
Benefits include nutrition and protection Mycorrhizae Gut inhabitant mutualism
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Oxpeckers and black rhinoceros Clown fish and sea anemone
Examples of Mutualism Oxpeckers and black rhinoceros Clown fish and sea anemone Mycorrhizae fungi on juniper seedlings in normal soil Lack of mycorrhizae fungi on juniper seedlings in sterilized soil Fig. 6-7, p. 117 © 2006 Brooks/Cole - Thomson
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Commensalism Species interaction that benefits one and has little or no effect on the other Example: Small plants growing in shade of larger plants Epiphytes
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Bromeliad Commensalism
Fig. 6-8, p. 118
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Ecological Succession: Communities in Transition
What is ecological succession? Primary succession Secondary succession
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Primary Ecological Succession
Lichens and mosses Exposed rocks Balsam fir, paper birch, and white spruce climax community Jack pine, black spruce, and aspen Heath mat Small herbs and shrubs Time Fig. 6-9, p. 119
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Secondary Ecological Succession
Mature oak-hickory forest Young pine forest with developing understory of oak and hickory trees Shrubs and pine seedlings Perennial weeds and grasses Annual weeds Time Fig. 6-10, p. 120
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How Predictable is Succession?
Climax community concept “Balance of nature” New views of equilibrium in nature Unpredictable succession Natural struggles
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Population Dynamics: Factors Affecting Population Size
Population change = (births + immigration) – (deaths + emigration) Age structure (stages) Age and population stability
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Limits on Population Growth
Biotic potential Intrinsic rate of increase (r) No indefinite population growth Environmental resistance Carrying capacity (K)
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Exponential and Logistic Population Growth
Resources control population growth Exponential growth Logistic growth
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Population Growth Curves
Environmental resistance Carrying capacity (K) Population size (N) Biotic potential Exponential growth Time (t) Fig. 6-11, p. 121
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Logistic Growth of Sheep Population
2.0 Overshoot Carrying Capacity 1.5 Number of sheep (millions) 1.0 .5 1800 1825 1850 1875 1900 1925 Year Fig. 6-12, p. 121
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When Population Size Exceeds Carrying Capacity
Switch to new resources, move or die Overshoots Reproductive time lag Population dieback or crash Famines among humans Factors controlling human carrying capacity
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Exponential Growth, Overshoot and Population Crash of Reindeer
Overshoots Carrying Capacity 2,000 Population crashes 1,500 Number of sheep (millions) 1,000 Carrying capacity 500 1910 1920 1930 1940 1950 Year Fig. 6-13, p. 122
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Reproductive Patterns
r-selected species Opportunists (mostly r-selected) Environmental impacts on opportunists K-selected species (competitors) Intermediate and variable reproductive patterns
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Positions of r-selected and K-selected Species on Population Growth Curve
Carrying capacity K K species; experience K selection Number of individuals Number of individuals r species; experience r selection Time Fig. 6-14, p. 122
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r-selected Opportunists and K-selected Species
Fig. 6-15, p. 123
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r-selected Opportunists and K-selected Species
r-Selected Species r-selected Opportunists and K-selected Species Dandelion Cockroach Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species Fig. 6-15a, p. 123
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r-selected Opportunists and K-selected Species
Elephant Saguaro Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species Fig. 6-15b, p. 123
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Characteristics of Natural and Human-Dominated Systems
Property Natural Systems Human-Dominated Systems Complexity Energy source Waste production Nutrients Net primary productivity Biologically diverse Renewable solar energy Little, if any Recycled Shared among many species Biologically simplified Mostly nonrenewable fossil fuel energy High Often lost of wasted Used, destroyed, or degraded to support human activities Fig. 6-16, p. 124
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Human Impacts on Ecosystems
Natural Capital Degradation Altering Nature to Meet Our Needs Reduction of biodiversity Increasing use of the earth's net primary productivity Increasing genetic resistance of pest species and disease causing bacteria Elimination of many natural predators Deliberate or accidental introduction of potentially harmful species into communities Using some renewable resources faster than they can be replenished Interfering with the earth's chemical cycling and energy flow processes Relying mostly on polluting fossil fuels Fig. 6-17, p. 125
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Four Principles of Sustainability
Solar Energy Population Control PRINCIPLES OF SUSTAINABILITY Nutrient Recycling Biodiversity Fig. 6-18, p. 126
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Solutions: Implications of the Principles of Sustainability
How Nature Works Lessons for Us Solutions: Implications of the Principles of Sustainability Runs on renewable solar energy. Recycles nutrients and wastes. There is little waste in nature. Uses biodiversity to maintain itself and adapt to new environmental conditions. Controls a species' population size and resource use by interactions with its environment and other species. Rely mostly on renewable solar energy. Prevent and reduce pollution and recycle and reuse resources. Preserve biodiversity by protecting ecosystem services and preventing premature extinction of species. Reduce births and wasteful resource use to prevent environmental overload and depletion and degradation of resources. Fig. 6-19, p. 126
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Lessons from Nature We are dependent on the Earth and Sun
Everything is interdependent with everything else We can never do just one thing Earth’s natural capital must be sustained Precautionary Principle Prevention is better than cure Risks must be taken
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