Animal Ecology - BIOS 275 - Lecture 7

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Ecosystem Ecology: Cycling, Succession and Biogeography

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Announcements

• Review Session - Friday 2 -3 pm
• Review Session - Monday 5 - ?
• Final Exam March 14, 2:30 pm

• Nutrients, unlike energy, remain within ecosystems where they continually cycle between the biotic and abiotic environment
• Assimlatory processes - transformations that changes elements into biological forms
• Dissimaltory processes - transformations that involve taking organic forms to inorganic forms
• redox reactions - energy releasing oxidation is coupled with energy requiring reduction

Compartment Models of Ecosystems

Food web is a compartment model of a biological community

Biochemical transformations result in the exchange of nutrients between biotic and abiotic compartments

Available nutrient compartment

• organic materials - living systems and detritus
• inorganic materials - soil, water, air, sediments

Unavailable nutrient compartment

• organic materials - peat, coal, oil
• inorganic materials - limestone, phosphates

The Carbon Cycle

Disruption of the Carbon Cycle

• Rapid buildup of CO₂ due to burning of fossil fuels
• Reduction of forests reducing CO₂ uptake potential
• Methanogenesis - the production of methane by living organisms contributing to greenhouse effect

The Nitrogen Cycle

• Molecular atmospheric nitrogen is the ultimate source - requires nitrogen fixation
• N₂ + 3H₂ ---> 2NH₃ Azobacter, Cyanobacteria, Rhizobium in legumes, actinomycetes
• lightening - high pressure an temperature
• only way for N to enter biological systems
• Ammonification - protein degredation
• Proteins ---> Amino Acids ---> NH₃
• almost all animals

• Important for Amino acids and nucleic acids
• Nitrification - oxidation of NH₃ to NO₃^-
• are oxidation - energy releasing reactions
• NH₃ + O₂ ----> NO₂^- Nitrosomonas, Nitrosococcus
• NO₂^- + O₂ ----> NO₃^- Nitrobacter, Nitrococcus
• Denitrification - the reduction of NO₃^- to N₂
• NO₃^- ----> NO₂^- ----> NO ----> N₂O ----> N₂ Psuedomonas

Disruptions of the Nitrogen Cycle

• Emission of NO from wood and fossil fuels combustion:
• N₂O + H₂O ----> Nitric Acid = Acid Rain
• Nitrous oxide is a greenhouse gas
• cattle and bacterial action
• Depleting soil nitrogen levels by harvesting nitrogen rich crops
• Nutrient loading
• runoff - non-point source pollution
• sewage - point source pollution

The Phosphorous Cycle

• Energetics, genetics, structure
• Nucleic acids, cell membranes, and ATP
• frequently in short supply
• sedimentary cycle - no atmospheric component
• much in chemical forms not available in plants

Disruption of the Phosphorus Cycle

• Mining of phosphorus for fertilizer
• Nutrient loading
• point source - sewage tratment
• non-point source - agricultural runoff

Factors affecting Nutrient Cycling

Abiotic

• increasing temperature increases cycling
• increasing moisture increases cycling
• increasing lignin or cellulose decreases cycling

Biotic

• increased biological activity increases cycling
• differential abilities of nutrient fixation and use

Human disturbance

• point source - nutrient input from specific sources
• sewage treatment, industrial effluent
• non-point source - nutrient input from the landscape
• agriculture, logging, development

Succession

• The change in the species composition and abundance over time in a particular habitat
• is there a consistent pattern among habitats in the types and numbers of species that invade a particular area

• Allogenic succession - species composition changes in response to changes in the physical environment

e.g climate change

• autogenic succession - species composition changes in response to the organisms that have already been present

e.g. trees shading and killing understory plants that require high sunlight

• primary succession - invasion by living organisms into newly formed habitats

- lava flows, glacial moraines, volcanic islands, sand dunes

- pioneer communities

• secondary succession - invasion after a disturbance, some living organisms and organic matter are already present

- following hurricanes, tornadoes, clearcuts, bulldozers

Succession of Soils and Nutrients

• Successional processes build up soil nutrients and organic matter
• nutrient build up takes much longer in areas of primary succession
• the biomass accumulation model

- describes the transformation of a forest ecosystem following distrubance

Disturbance and Succession

• Intermediate disturbance hypothesis - as disturbance increase in areas the diversity increases
• the habitat becomes a mosaic of different patches in different succession stages with an intermediate level of disturbance

Autogenic Succession Mechanisms

1) facilitation - an earlier species alters or 'paves the way' for the next successional species

• e.g. colonists that change soil composition allowing other species to invade
• lichens, grasses, conifers

2) inhibition - one species prevents the growth or invasion of another species

• e.g. allelopathy
• salt bush, pine trees

Autogenic Succession Mechanisms

3) Tolerance - modification of the habitat by one species does not affect the growth or recruitment of subsequent species

• e.g. many species of late successional species trees can all invade a particular habitat
• maple, hickory, oak, ash, poplar, can all survive in established forest

Successional Outcomes

1) replacement - over time species composition changes, different species groups replacing one another

• old fields reverting to forest

2) coexistence - several species arriving in a community at different times and persisting

• rocky intertidal where larval recruitment varies throughout the year, however many of the species manage to settle and establish

3) climax community

• - a community whose species number remain relatively stable over long periods of time

Community Stability

• Stability - the absence of change - lack of disturbance
• Resistance - the ability of a community to maintain structure in the face of disturbance
• Resilience - the ability to bounce back after disturbance - quickly returns to former state

Biogeography

• the study of past and present distribution of individual species and communities

Biogeographic provinces - the result of continental drift

• - the continual movement of the land masses that has occurred during earth's history
• - supported by geological and biological data
• - distribution of some species can be explained by continental drift
• - lungfishes, many plant species, many dinosaur fossils

Island Biogeography

The equilibrium model of island biogeography - MacArthur and Wilson 1967

• based on the species area relationship
• As area size increases, the number of species increases
• islands have a characteristic immigration rate - the number of new individuals arriving per unit time
• islands also have a characteristic extinction rate that describes the number of species going extinct
• an equilibrium point is reached where the extinction rate equals the immigration rate

Changing the Size of the Island

• Decreasing the size of the island will result in increasing the extinction rate and decreasing the immigration rate
• This will result in shifting the equilibrium point to the left
• decreasing the number of species

Changing the Distance from the Mainland

• Decreasing the distance of the island from the mainland will result in increasing the immigration rate
• This will result in shifting the equilibrium point to the right
• increasing the number of species on the island

Landscape Ecology and Fragmented Habitats

• Landscape - a heterogeneous area composed of several ecosystems
• landscape elements - the patches of different ecosystems
• landscape structure - size, shape and spacing of different ecosystems in the landscape
• geometry important relative to the organism that use different elements
• the biology of the organism determines the length of the ruler

Populations in Fragmented Habitats

• Species occur is spatially isolated patches
• metapopulations - a group of subpopulations living in spatially isolated patches
• How do subdivided populations change movement patterns, colonization rates, genetic structure, extinction probabilities?

Biogeography and Conservation

• The same principles that apply to islands can apply to fragmented habitats
• How large an area needs to be preserved to ensure natural levels of diversity found in intact habitats?
• Is it better to save several smaller patches or one large patch

1) data from Galapagos - large island Isabella - 344 species; 3 smaller islands support 609 species

2) grizzly bear populations between 50-90 individuals requires between 10,000 and 13,500 km² to survive 100 years

One Possible Solution

• Corridors between islands
• paseo panthero - establish a corridor that would allow animals to move from South America to Canada
• panther, grizzly bear, wolves
• preserves need to be large enough to avoid edge effects in the core
• Corridors must be large enough to allow core species to move between preserves
• Buffer zones - area around the core where impact is low

Edge Effects

• Microclimatological effects
• light penetration, temperature, soil nutrients
• species mixing - exotics
• introduced species, native invaders
• cowbirds
• edge effects can penetrate up to 5 km

Designing Nature Preserves

• Representative of the native ecosystem

• Maintain viable populations
• Maintain viable evolutionary and ecological processes
• Maintain landscapes
• within the context of the land, the ability to reflect both long and short term environmental change
• ESA vs. Ecosystem approach

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