BIO 323: Ecology Exam 3

community

an association of interacting species inhabiting some defined area

community structure

includes attributes such as the number of species, the relative abundance of species, and the kinds of species comprising a community

guild

a groups of organisms that all make their living in a similar way (seasonality, resource requirements, and life histories)

• ex: seed eating animals in a desert area

life form

a combination of a plant’s structure and its growth dynamics

• ex: epiphytes grow without substrate in the canapy

Preston Log-Normal Distribution

populations that demonstrate a bell-shaped/normal distribution

• most species are moderately abundant

Shannon-Weiner Diversity Index

1. species richness: the number of species in the community

2. relative abundance: the species evenness of species in communities

Rank-abundance curve

portrays the relative abundance and diversity of species within a community by plotting the relative abundance of species against their rank in abundance

• higher diversity has falter curves and lower diversity has steeper slope

• *species are ranked by the highest species abundance (species with the most number of individuals present to the species with the lowest present)

habitat heterogeneity

complex and diverse environments allow more species diversity as it allows for more niches

• mainly due to the competitive exclusion principle, which leads us to predict that coexisting species will have significantly different niches

nutrient enrichment reduces environmental complexity

as nutrient supplies increase, diversity and algae declines

• It reduces the number of limiting nutrients and light becomes the single limiting resource

• This means that only species that are most effective at competing for light will thrive in a community and species diversity will decline

• It also reduces the need for mutualistic relationships between species; especially ectomycorrhizae

intermediate disturbance hypothesis

hypothesis that predicts that intermediate levels of disturbance promote higher levels of diversity

• In lower disturbances, there is more species dominance (competition)

• In higher disturbances, there is not enough recovery time for a large number of species to survive

food web

a summary of the feeding inactions within a community based on tropic levels

strong interactions in food web

the feeding activities of a few species have a dominant influence on community structure

dominant/foundation species

species that have substantial influences on community structure as a consequence of their high biomass

• ex: coral on a coral reef

keystone species

relatively low biomass compared to their influence on the community structure

• (1) predators might keep prey populations below their carrying capacity

• (2) the potential for competitive exclusion would be low in populations kept below their carrying capacity

• (3) if keystone species reduce the likelihood of competitive exclusion, their activities would increase the number of species that could coexist in communities → increase species diversity

direct interactions

between two species, including competition, predation, herbivory, and mutualism, involve positive or negative effects of one species on another without the involvement of an intermediary species

indirect interactions

one species affects through a third, intermediary species

• includes trophic cascades, apparent competition, and indirect mutualism or commensalism

• ex: indirect commensalism: occurs when the activity of one species indirectly — through intermediary species — benefit another species without itself being helped or harmed

apparent competition

negative impacts are the result of two species sharing a predator or herbivore or by one species facilitating populations of a predator or herbivore of the second species

• Ex: if two prey species share a predator, increases in one of the prey populations may lead to increased number of the predator, which feed on and depress populations of the second prey species

primary production

production of new organic matt (biomass) by autotrophs in an ecosystem

• measured as the rate of carbon uptake by primary producers or by the amount of biomass or oxygen produced

gross primary production (GPP)

total biomass produced by all autotrophs in an ecosystem

Net primary production (NPP)

biomass left over after autotrophs have met their own energetic needs

• cellular respiration and maintenance of existing tissues

secondary production

the production of biomass by heterotrophic consumer organisms feeding on plants, animals, microbes, fungi, or detritus

• includes consumer growth, reproduction, and mortality

terrestrial NPP

;generally limited by temperature, moisture, and nutrients

• temperature: logarithmic slope because at their optimum temperature, they are most effective at photosynthesis production

• precipitation: flattens because when its raining, photosynthesis cannot occur

• AET: warmer and wetter climates have a higher AET and more primary production

• soil nutrients: plants that have access to phosphorus and nitrogen almost double their primary production rate

actual evapotranspiration (AET)

the amount of water that evaporates and transpired off a landscape; occurs when plants open their stomata to take in CO2 and release water

• increases with increased precipitation and temperature

aquatic NPP

nutrients availability is key for aquatic systems (from upwelling or breakdown of organic materials) and light availability

• add nutrients —> more biomass = more chlorophyll

• more chlorophyll —> higher rate of primary production

• ex: highest NPP rates are found along coastlines due to nutrient runoff from land and sediment distribution

biodiversity

the genetic, philosophical, anatomical, functional, and ecosystem diversity that influences ecological processes in a community, especially in primary production

bottom up controls

influences of physical and chemical factors on an ecosystem/community

• access to grazing allowed grass plants to increase their biomass as it prevents interspecific competition —> self thinning

top down controls

influences of consumers on an ecosystem/community

trophic cascade hypothesis

consumers can influence the rate of primary production in aquatic and terrestrial ecosystems

• as predators increase, prey populations decrease

• but the next trophic level population increases

• and then the next trophic level population decreases

• results in an increase, optimization, and decreases in production curve

trophic dynamics

transfer of energy from one part of an ecosystem to another

trophic level

a position in the food web and is determined by the number of transfers of energy from primary producers to that level

• First level: primary producers

• Second level: herbivores and detritivores

• Third level: carnivores feeding on herbivores and detritivores 

• Fourth level: predators that feed on carnivores

ecological efficiency

the percentage of biomass produced at a lower trophic level that is transferred to biomes produced at the next trophic level, varies from 5% to 20%

• Ecosystems with greater primary production generally support higher levels of secondary production

nutrient cycling

the use, transformation, movement, and reuse of nutrients in ecosystems

• involves the storage of chemical elements in nutrient pools, or compartments, and the flux of nutrients between pools

nutrient pools

the amount of a particular nutrient stored in a portion, or compartment, of an ecosystem

nutrient flux

the movement of nutrients between the pools of an ecosystem

nutrient sink

a part of the biosphere where a particular nutrient is released faster than it is absorbed

phosphorus cycle

• [P] marine sediments > [P] mineral deposits >>> [P] atmosphere

• Phosphorus is slowly released to terrestrial and aquatic ecosystems through the weathering of rocks (apetite - type of sedimentary rock)

  • Terrestrial plants uptake the phosphorus 

  • In aquatic ecosystems, phosphorus is washed into rivers and eventually makes it to the ocean where is finds ocean sediments

    • These are eventually transformed into phosphate-bearing sedimentary rocks that can form new land through geological uplift (tectonic plate movement)

nitrogen cycle

• nitrogen sources mainly done through nitrogen fixation, lightning, and human activity

• Major atmospheric pool in for of N2 available only to N-fixers

  • Nitrogen fixation occurs under anaerobic conditions where species oxidize sugars to obtain required energy or in high pressure and energy generated by lightning

  • Humans have also been able to increase agricultural productivity by rotating crops capable of nitrogen fixation and through the industrial fixation of N2 to NH3 fertilizer

• once nitrogen fixation is completed, it becomes available to other organisms within the ecosystem

• nitrogen can leave the organic matter pool through denitrification

carbon cycle

• Carbon moves between organisms and the atmosphere as a consequence of two reciprocal biological processes: photosynthesis and respiration

  • Photosynthesis removes carbon dioxide from the atmosphere and respiration returns carbon dioxide to the atmosphere

  • In aquatic systems, CO2 must be dissolved in water before being used by autotrophs; it enters a chemical equilibrium with bicarbonate, HCO3- and carbonate CO3. 

  • The massive burning of fossil fuels has increased the concentration of atmospheric CO2

  • Some C-cycles are rapid, some C may remain sequestered for long periods

terrestrial decomposition

the breakdown of organic matter accompanied by the release of carbon dioxide

• significantly influenced by temperature, moisture, and the chemical decomposition of both plant litter and environment

• moisture and temperature increase rates of decomposition (higher AET)

• leaves with more nitrogen (less lignin) have a faster decomposition

aquatic decomposition

the more nitrogen and less lignin in the substrate, the faster the decomposition

• nutrient spiraling also plays a role in decomposition rate and nutrient retention

nutrient spiraling

stream dynamics are better represented by a spiral