community and population ecology
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Community and Population Ecology. Chapter 6. American Alligator. American Alligator: community structure. Highly adaptable – around for nearly 200 million years - PowerPoint PPT PresentationTRANSCRIPT
Community and Population Ecology
Chapter 6
American Alligator
American Alligator: community structure
• Highly adaptable – around for nearly 200 million years
• Keystone species - A species whose loss from an ecosystem would cause a greater than average change in diversity or abundance of other species, community structure or ecosystem process.– Gator holes – fresh water/food supplies, refuges– Nest mounds – nesting/feeding sites for herons &
egrets– Balance predator populations
• Only natural predator is humans• 1967 – endangered species list – 90% decimated• Successful environmental comeback
Affect of Species Diversity on the Sustainability of a Community
Species diversity increases the sustainability of communities and ecosystems.
Species Diversity• Species richness combined with species
evenness• Niche structure• Varies with geographic location• Species richness declines towards poles
Species Diversity• Species richness combined with
species evenness determines diversity of an ecosystem– Tropical Rainforest vs. Coniferous Forest
Species Diversity: communities
• Niche structure determines diversity– The number
and types of similar and different niches along with how the organisms within them interact
• For example – stream macroinvertebrates
Species Diversity: communities• Niche structure determines diversity
– The number and types of similar and different niches along with how the organisms within them interact
• For example – stream macroinvertebrates
Species Diversity: communities• Diversity varies with geographic location
(richness declines towards poles)Bird species richness in the Western Hemisphere (Hawkins et al. 2006).
Sustainability and Environmental Change• Certain factors allow living systems to
maintain stability/sustainability (equilibrium)
• Inertia or persistence – ability to resist disturbance– Tropical rainforests (high), grasslands (low)
• Constancy - ability to maintain population size within limits– Endemic species vs. invasive
• Resilience – ability to recover– Tropical rainforests (low), grasslands (high)
Equilibrium: Area and Distance Effects
Animations/species_equilibrium.html
Richness and Sustainability
• Richness tends towards sustainability, productivity and better recovery– Not all of the ‘eggs are in one basket’– NPP seems to peak with at least 10-
40 producers (difficult to distinguish ‘most important’)
Roles of Species in a CommunityBased on ecological roles, species
are described as:native
endemicnonnativeindicator
keystone or foundation species
Ecological Niche• Niche = unique role• Native/endemic species =
normal• Nonnative species =
invasives, aliens– Spread in new, suitable niches– Also – most crops and feedstocks– Can reduce native populations
(Africanized honeybees)– Lack predators, disease and
competition
Indicator Species• Early warning system for the health of
an ecosystem– Trout - absence means low DO
Vanishing Amphibians: indicator species• 33%
threatened, 43% declining with no clear-cut reason– Habitat loss
and fragmentation (drain/fill)
– Prolonged drought
(breeding sites)– Pollution
(pesticides)– Ultraviolet
radiation (ozone loss/egg damage)
– Parasites (increased susceptibility)
– Viral and fungal diseases (skin)
– Climate change– Overhunting
– Nonnative predators and competition
Vanishing Amphibians• Why we should care
– Indicates there is something wrong
– Skin – pharmaceuticals – painkillers, antibiotics• Phantasmal poison frog – painkiller ,
Epibatidine, that doesn’t have the side effects of morphine, but 200x stronger
Life Cycle of Typical Frog
Frogs Galore
Videos/Frogs_Galore.mov
Keystone Species• Significant role in
their food web
• Elimination may alter structure, function of community
• Pollinators
• Top predators – Grey Wolf in Yellowstone
Keystone Species: Dung Beetle
Fig. 6-3, p. 110
Remove dungAerate soilNutrient recycling
Sharks – garbage men of the sea• Keystone species• Remove injured, sick animals• Many are non-threatening• Provide potential insight into
cures for human diseases (immune system function)
Foundation Species• Create habitats and ecosystems
– Beavers• Create wetlands
– Elephants• Push over trees, allow grasses &
nutrient cycling– Seed dispersers
• Bats’ & birds’ droppings
Species InteractionCompetition, predation,
parasitism, mutualism, and commensalism – affect resource use and population sizes of the species in a community.
Adaptations allow some species to reduce or avoid competition.
Interspecific Competition• No two species can share vital limited resources for long
• Resolved by:– Migration– Shift in feeding habits or behavior– Population drop (Gause’s Paramecium
Experiment)– Extinction
• Intense competition leads to resource partitioning
Animations/gause_v2.html
Resource Partitioning in Warblers
Species Interaction• Predator-prey relationships – food
webs– Predators and prey both benefit –
individual vs. population (weak, sick, aged, least fit)
• Predator strategies– Herbivores simply walk, fly or swim– carnivores (pursuit/ambush –
camouflage, poison)
Predator Avoidance: camouflage
• Prey strategies - Hard shell, speed, smell, spines, etc.
Fig. 6-5cd, p. 113
Predator Avoidance: chemical warfare, warning coloration
Fig. 6-5ef, p. 113
Predator Avoidance: chemical warfare, warning coloration, mimicry
Fig. 6-5gh, p. 113
Predator Avoidance: deceptive looks, deceptive behavior
Species Interaction: Symbiosis
Symbiosis: Parasitism• Live in or on the host
– Parasite benefits, host harmed• Parasites promote biodiversity –
pick off weak, aged, sick, keep population size low and allows other species to move in.
Tomato horn worm and Braconid Wasp
Cowbird
Symbiosis: Mutualism• Everybody benefits• Nutrition and protection• Gut inhabitant mutualism
– Humans and termites (enzymes for biofuels)
Symbiosis: Commensalism• Benefits one with little
impact on other• Epiphytes• Bird nests
Review: How Species Interact
Animations/species_interactions.html
Communities Respond to Changing Environmental
ConditionsEcological succession – The change in
community structure and composition due to changing environmental conditions.
Precautionary principle – Measures taken to prevent or reduce harm even if cause-and-effect relationships have not been fully established scientifically.
• Primary succession– gradual establishment of community
in lifeless areas– “Bare” – no soil– 100s to 1,000s of years to establish
fertile soil• Secondary succession
– More common– Not “bare”– Has soil
Succession
Animations/succession.html
• Disturbances create new conditions– Eliminates species– Opens new niches, increases richness
• Intermediate disturbance hypothesis– frequent/moderate disturbances results
in increased species richness
Ecological Succession
Succession’s Unpredictable Path – Intermediate Disturbance Hypothesis
• Doesn’t always arrive at a climax community– Ever-changing mosaics of different stages– Continual change, not permanent
equilibrium – Results in highest level of diversity
Precautionary Principle
• Lack of predictable outcome should not prevent conservation– Consider health of
ecosystem & humans
Population Growth• Populations differ
– Number– Distribution– Age structure
• No population can continue to grow indefinitely– Limiting factors– Competition
Population Dispersion/Distribution
Clumping• Clumped Resources
• Protection
• Hunting success
• Mating or young-rearing
Populations Sizes Are Dynamic
• Vary over timepopulation = (births + immigration) - (deaths
+ emigration)
Populations Sizes Are Dynamic
• Changes in Age structure– Pre-reproductive stage– Reproductive stage– Post-reproductive stage
Video: Bonus for a Baby
Videos/Bonus_for_a_Baby.mov
Limits to Population Growth
• Biotic potential is idealized capacity for growth
• Intrinsic rate of increase (r)
• Nature limits population growth with resource limits and competition
• Environmental resistance = limiting factors
Limits to Population Growth• Carrying capacity – biotic
potential and environmental resistance
– Exponential growth – unrestricted
– Logistic growth – restricted
Exponential and Logistic Growth
Rule of 70 = 70/r = years for doublingr = growth rate
Caused by reproductive time lag
Animations/exponential_mice.html
White-tailed Deer• Today: 25–30 million white-tailed deer
in U.S.• Conflicts with people living in suburbia
Overshoot and Population Crash of Reindeer introduced to Bering Sea Island of St. Paul
Different Reproductive Patterns• r-Selected species– High rate of increase, little parental
care– Opportunists– Do better when opportunities arise,
exponential• K-selected species
– Competitors– Slowly reproducing, parental care– Do better when near carrying
capacity, logisitic
• Most species’ cycle between two extremes
Where each does well on the Sigmoid Growth Curve
Humans Not Exempt from Population Controls• Bubonic plague (14th century)
• Famine in Ireland (1845)• AIDS• Technology, social, and cultural changes increase K• Expand indefinitely or reach carrying capacity?
Videos/World_AIDS_Day.mov
Number of deaths due to AIDS globally
2000—2004Millions
Number of deathsdue toAIDS
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
2000 2001 2002 2003 2004
This bar indicates the range around the estimate.