Ecology Final Exam

Autotrophs

Primary producers that occupy the first trophic level

Primary Production

• Production of biomass, organic matter, carbon, or fixation of energy by autotrophs

• Units vary based on techniques used to measure

• Common units: Biomass, Carbon, Energy

Net Primary Production

• The amount of organic matter, carbon, or energy fixed by autotrophs after they have met their metabolic needs via respiration.

• NPP = GPP - Respiratory losses (of autotrophs)

Net Primary Productivity

Net primary production expressed as a rate over time.

Measuring Primary Productivity

1. Estimate dry biomass produced by plants over a year

2. Could also estimate C% of this biomass

3. Could also estimate energy content of this biomass

Actual evapotranspiration increases with

Increased precipitation and temperature

Actual Evapotranspiration (ET)

• Rate of water vapor lost from a system to the atmosphere typically expressed as an annual rate

• Measured in milliliters of water per year

NPP increases with increased

• Actual Evapotranspiration

• Soil fertility (sometimes across small scales)

• Grazing (to a medium level in some biomes)

Biome with high ET but low NPP

Wet and cold ecosystems, like tundras

Main limiting nutrients to NPP

Mostly Nitrogen but occasionally Phosphorus or other nutrients

Global Patterns of Marine NPP

• Highest NPP rates in areas with high nutrient availability

• Highest NPP rates found along continental margins due to runoff and upwelling

Trophic Cascade Hypothesis

• Proposed by Stephen Carpenter

• Top carnivores can have a large influence on NPP

• Involves indirect interactions

• Example:

  • Top carnivores feed on fish that feed on zooplankton.

  • Reducing plankton eating fish increases zooplankton populations

  • Large zooplankton populations reduce phytoplankton abundance, limiting NPP

Keystone Species Concept

• Robert Paine

• Certain organisms have large influences on ecosystems not proportional to their biomass

Bottom-Up Control

• Lower trophic levels control higher levels by resource restriction

• Example: Low nutrient concentrations limiting autotroph populations reduces higher trophic levels

Top-Down Control

• Higher trophic levels control lower levels through predation

• Examples: Keystone species and trophic cascade concepts

Large grazer effects on NPP in grasslands

• McNaughton

• Grassland NPP highest at medium grazing intensities due to compensatory growth, self shading, water/nutrient balance, etc.

Trophic Dynamic View of Ecosystems

• Ray Lindeman

• Organisms are grouped into trophic levels

• Energy is lost as its transferred between trophic levels, decreasing with each successive trophic level

• Often <90% of energy is lost when moving to a higher trophic level

Why most ecosystems don’t have more than five trophic levels

• There’s not enough energy in lower levels to support high trophic level species

• Ecosystems with > 5 trophic levels have high NPP

Why is primary production so important?

• Dictates the amount of energy available to consumers

• More NPP, more trophic levels

• More trophic levels and biomass in trophic levels = more species and individuals

• Areas of high NPP fix more carbon, produce more food, have higher species richness

Open System

Energy flows through the biosphere

Closed System

Nutrients Cycle through the biosphere

Volatile Nutrient Cycle

• A large pool of the nutrient exists in a gaseous state

• Carbon, Water, and Nitrogen Cycles

Sedimentary Nutrient Cycle

• No large pool of the nutrient exists in a gaseous state

• Phosphorus Cycle

Organisms affect the carbon cycle through

Photosynthesis and respiration

Gross Primary Productivity

• All of the uptake of C (or energy/biomass) by primary producers. Includes what will be lost through metabolic processes.

• Aboveground only, roots can’t photosynthesize

Soil Respiration

Respiration by soil organisms (microbes, macroinvertebrates) and plant roots

ANPP

Aboveground Net Primary Production

BNPP

Belowground Net Primary Production

Major Pools/Sinks of the Carbon cycle

• Atmosphere (mainly CO2)

• Land and food webs (producers, consumers, decomposers, detritivores)

• Peat

Nitrogen Fixation

• The conversion of N2 gas into usable forms for organisms

• Nitrogen Fixers

  • Cyanobacteria

  • Free living soil bacteria

  • Bacteria/fungi in root nodules of some plants (legumes)

• Converts N2 gas into ammonia/ammonium

• Can be fixed by lightning

Available Nitrogen

• The only forms of Nitrogen that can be taken up by plants

• Ammonia or Nitrate ions

• Animals secure their N compounds from plants or other animals

Nutrient Pools

• Store nutrients

• The amount of a particular nutrient stored in a portion or compartment of an ecosystem

Nutrient Source

A portion of the biosphere where a nutrient is released faster than it is absorbed

Nutrient Sink

A portion of the biosphere where a nutrient is absorbed faster than it is released

Nitrification

A process where bacteria converts ammonium to nitrate

Ammonification

A process where the decay of organic compounds releases N as ammonium

Denitrification

• The conversion of N into atmospheric N2

• Nitrogen escapes back into the atmospheric pool and must be fixed to re-enter the biotic pool

The Phosphorus Cycle

• A sedimentary cycle

• Large pool in marine sediments and mineral deposits

  • Enters the biotic pool by uplifting of marine sediments and erosion of mineral deposits

• Plants take up Phosphate ions

• P moves through food webs and may leech or be lost to runoff

Availability of Phosphorus to Plants

• Dependent on soil pH and concentrations of other ions

• Highest levels of dissolved phosphate occur at neutral (intermediate) pH levels

• Mycorrhizae contribute to P uptake

Decomposition

• The breakdown of organic material

• Mostly focused on plant material

  • Dead plant material referred to as ‘litter’

Mineralization

• Conversion of nutrients from complex organic forms to simpler forms that can be consumed by microbes or lost to the atmosphere

• In the case of C, microbes release CO2 via microbial respiration

• In the case of N, mineralized to forms usable by microbes and plants or lost to the atmosphere

Litter Decay Rate Determined By

1. Available moisture (ET/Precip increases decay)

2. Temperatures (Warmer temps increases decay)

3. Litter Quality (Lower lignin:N increases decay)

Litter Quality

• Higher lignin concentrations slow decay

• Higher N concentrations accelerate decay

• Lignin:N ratio is a good predictor of litter quality

  • Lower ratio = faster decay

  • Higher ratio = slower decay

Litter Decay in Deserts

• Much faster than expected, not due to lignin:N ratios

• Caused by higher UV radiation (photodegredation)

Grazing and Nutrient Cycling

• Grazers accelerate N cycle

• N more quickly returned to the soil via grazer urine

Increases in nutrient loss

• Disturbances (via runoff)

• Forest clearcutting (N loss via runoff and streamflow of nitrate)

Succession

Gradual change in plant and animal communities following a disturbance

Primary Succession

Succession on newly exposed substrates lacking viable plants or seeds

Secondary Succession

Succession that occurs following a disturbance that does not destroy/remove all the soil

Pioneer Community

The first community of organisms to colonize an area following a disturbance. Typically referring to primary succession.

Climax Community

Late successional community that remains stable until disturbed again.

Seral Community

Any successional community other than the climax community

Primary Succession at Glacier Bay

• Reiners et al

• Changes in plant diversity during succession

• Total number of plant species increased with plot age

• Species richness increased rapidly in early years of succession and more slowly during later stages

• Chronosequence approach

Glacier Bay Ecosystem Changes

• Total soil depth and depth of all soil horizons increased from pioneer community

• Organic content, moisture, and N content increased

• Total biomass, community NPP and respiration increased

• pH and P concentrations declined

Clement Mechanism of Succession

Facilitation

Connell and Slayter Mechanisms of Succession

Facilitation, Inhibition, and Tolerance

Facilitation

Pioneer species modify the environment to make it more suitable for species of later successional stages and less suitable for themselves

Inhibition

• Pioneer species modify the environment to make it less suitable for themselves and later successional species.

• Later successional species eventually dominate an area because they live longer and make conditions unsuitable for colonizers.

• Secondary “old-field” succession

Clement’s Organismal View of Succession

• AKA Discrete View

• Development of vegetation occurs in a series of stages resembling the development of an organism

• Not considered realistic

• Importance of facilitation over exaggerated and inhibition ignored

Gleason/Whittaker’s Individualistic View of Succession

• AKA Continuum View

• Groups of species coincidental

• Plant communities composed of species that are each responding to the environment based on their individual characteristics

Buckwheat Succession on NM Cinder Cones

• Facilitation

• Nearly all plants establish next to existing buckwheat plants

Landscape

Heterogenous area composed of several communities

Landscape Elements

Visually distinctive patches in an ecosystem. Patches have characteristic size, shape, position, etc.

Ohio Landscape Case Study

• Quantified patch shape by ratio of patch perimeter to perimeter of a circle with with an area equal to that patch

• S = Patch shape

  • S = 1 is a circle, Increasing patch value = less circular shape

  • Higher S value = more edge per area

• P = Patch Perimeter

• A = Area

Ecotone

Edge or boundary between contrasting plant communities

Edge Effect

• Species richness and diversity typically higher in ecotones

• Ecotones support species from both ecosystems on either side, as well as some species unique to the ecotone

Fractal Geometry

• Math quantifying structure of natural shapes

• Perimeter size depends on ruler size

  • Smaller features only appearing with smaller ruler

As Patch Size Increases

• Population size increases

• Population density decreases

Corridors

• Bridges connecting landscape patches

• Increase densities by allowing migration, mitigating fragmentation

• Example: Butterflies in South Carolina

Bajadas

• Joe McAuillife

• Sloping planes at the base of desert mountain ranges

• Complex mosaic of distinctive plant communities not explained by elevation

Why are Bajadas so diverse?

• Variability in soil textures

• Differences in water infiltration during precipitation

McAuliffe Findings

• Plant community distribution corresponding with soil age and structure

• Highest plant diversity on young soils

• Younger soils more coarse, have less calcium carbonate

• Older soils accumulate more clay

Species richness on islands increases with

• Increasing area

• Decreasing isolation (distance from source)

Equilibrium Model of Island Biogeography

• MacArthur and Wilson

• Species richness on islands is a function of immigration and extinction rates

• Immigration rate highest on new islands

• Extinction rate increases with increasing number of species on the island

Habitat Islands

• Mountaintops

• Lakes

• Marine Islands

Immigration rate on islands

• Mainly influenced by an island’s isolation, or distance to a source

• More isolation = less immigration

Extinction rate on islands

• Mainly influenced by an island’s size

• Larger islands have more resources, and lower extinction rates

Species Turnover on Islands

• The equilibrium model is always changing

• There is constant species turnover from migration and extinction, but they tend to balance out

  • Community compositions can vary greatly, but the species richness is relatively stable

Why is species richness higher at lower latitudes?

• Main Hypothesis: Due to greater land area in the tropics

• Other hypotheses

  • Uniform temperatures

  • Increased speciation

  • Favorableness

  • Environmental heterogeneity

  • Longer time since large-scale disturbance

Historical and regional influences on richness

• Tree species richness higher in East Asia

  • Lower glaciation

  • Most temperate tree species evolved here

• Tree species richness lower in Europe

  • glacial period caused more tree extinctions

  • East-West mountains a barrier to Southern migration

The Greenhouse Effect

• Proposed by Svante Arrhenius in 1895

• Longwave radiation trapped by gasses in the atmosphere, heating the earth

• Radiation enters the atmosphere as shortwave, exits as longwave

Greenhouse Gasses in order of decreasing abundance

• Water vapor (H2O)

• Carbon Dioxide (CO2)

• Methane (CH4)

• Nitrous Oxide (N2O)

• CFCs

Keeling Curve

• Charles David Keeling

• Measurements of CO2 on Mauna Loa beginning in 1985

• Shows a clear rise in CO2

• Shows annual oscillations

  • Plants pull in CO2 during the growing season

Suess Effect

• 14C a radioisotope not present in fossil fuels due to degradation

• Low amounts of 14C in the atmosphere tell us that CO2 in the atmosphere is from fossil fuels

Ice Cores

• Air bubbles trapped in ice show what the atmosphere was like when that ice formed, thousands of years ago.

• Show a correlation between periods of high temperatures and high CO2 concentrations

General Circulation Models (GCM)

• Models predicting past/future temps based on all known mechanisms

• Natural forces alone don’t explain warming, anthropogenic forces must be accounted for

Net fluxes in photosynthesis and respiration dictate

How Carbon stocks in an ecosystem will change

Positive Feedback Loops

Ecosystems that release more carbon into the atmosphere, increasing global warming

Negative Feedback Loops

Ecosystems that absorb and store carbon from the atmosphere, decreasing global warming

Stratospheric Ozone

• “good” ozone

• Natural layer of ozone built up over billions of years

• Filters much solar UV

Tropospheric Ozone

• “bad” ozone

• Result of byproducts of human emissions

Chlorofluorocarbons (CFCs)

• Stable (long-lived) man-made compounds

• Break down and release chlorine

• Chlorine destroys good O3 in the stratosphere

• Ozone depletion allows more UV-B radiation to reach earth’s surface

• Are a greenhouse gas in the troposphere

Why are we concerned about UV-Bs?

• Cancer/cataracts in humans

• Stunted growth/DNA damage in many plants

• DNA damage and reduced activity of many microbes