Ecology Final

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Ecology community

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An association of interacting species inhabiting a defined area. Various scales.

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Species abundance trends

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Regular. Few species very abundant, few species very rare, most species moderately abundant. Gaussian curve, lognormal distribution.

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Preston's Veil

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Lognormal distribution is not valid for all. Some only show part of a curve due to sampling incompleteness. Limited by resources or time.

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Species richness

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Number of species in a community

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Species evenness

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Relative abundance of a species in a community

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Diversity indices -- Shannon-Weiner index

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Lowest value = 0 when only one species is present. Maximum value when all species are present in equal abundance, ln(s)

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Rank-abundance curves

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Steeper slope, less species are dominating the abundance in the community (lower evenness)

Higher richness/evenness: line extends further, shallower slope.

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What controls diversity?

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Environmental complexity positively related to diversity. More heterogeneous habitats, more possible niches.

Ex) Bird diversity increases with volume & complexity of foliage

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Paradox of the plankton

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Many species of algae in the same environment- do they still compete for the same resources? Complexity and niche differences explain this.

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Asterionella & Cyclotella example

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Niches are defined by nutrient availablity. Competitive outcomes between groups change across a range of Si:P ratios.

High Si:P: Asterionella win.

Low Si:P: Cyclotella dominates.

Intermediate ratio: Coexistence.

**Asterionella take up P faster but need more Si. Coexistence when both algae are limited by nutrients

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Diversity in plant communities

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Negative relationship between nutrient availability and diversity

Soil fertility increases, number of species inhabiting the space decreases

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Disturbances

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Events that kill, displace or damage individuals, redistribute resources and create new opportunities for new individuals to establish

Prevents competitive exclusion

**No balance to nature because the world is a dynamic system!

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Diversity and disturbance relationship

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Diversity is highest at intermediate disturbance levels.

High disturbance: only species that may colonize quickly will be present

Intermediate levels: enough time for a lot of species to colonize an area, not enough for some to out compete others

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Disturbance in the intertidal zone

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Waves may overturn boulders, resetting the colonies of species present. "Reset" the environment.

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Feeding webs

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An abstract method to graphically represent feeding interactions

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Basal species

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Primary producers. Autotrophs on the bottom of the chain

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Compartments

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Groups that interact strongly within themselves

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Trophic levels

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Position along food web (autotrophs and carnivores)

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Guilds

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Similar feeding modes and food sources

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Functional types

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Response to environment, life history, feeding

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Indirect commenaslism

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One species benefits through indirect effects of another species which is unaffected. Direct interaction through competition leads to negative effects

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Apparent competition

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Competition-like effects due to shared predators

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Keystone species

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Species that have a disproportionately large impact on communities

Ex) Elephants are the species in the savannah

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Sea otters

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Keep sea urchin levels low, reduce grazing on kelp. Recent decrease in otter populations due to hunting caused an urchin increase, collapse of kelp population

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Ecosystem ecology

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Concerned with nutrient and energy flow. Powered by sun (photoautotrophs using sun's energy to fix inorganic carbon)

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Terrestrial primary production

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controlled mainly by temperature and precipitation. Warmer temperatures = longer periods of photosynthesis possible. Higher precipitation = plants keep stomata open longer

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Law of the minimum

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Productivity will be limited by the nutrient in shortest supply

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Aquatic primary producers

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Plankton, benthic algae, vascular plants

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Compensation depth

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Positive NPP only possible at depths where photosynthesis exceed respiration

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Limiting nutrients in lake ecosystems

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Phosphorus (main limiting nutrient), nitrogen (secondary limiting element)

Nutrient loading may lead to water quality issues

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Limiting nutrients in ocean habitat

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Nitrogen and iron

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Primary production seasonality

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Peaks at different times of the year. Different seasonal rates of production occur based on temperature, light, nutrients

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Consumer control of primary production

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Bottom up: light, temperature, water, nutrients

Top-down: biotic process- predation, grazing

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Trophic cascade

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potential primary production may be determined by nutrients, but actual production may be controlled by fish-propagation of indirect consumer effects

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Limits of secondary production

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Primary production!

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Loss of energy in trophic levels

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Sloppy feeding, limited assimilation, respiration, heat production. 10% transfer efficiency. Means less energy is available in each level. Pyramid shaped energy availability!

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Nutrient pools

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Nutrients contained in ecosystem compartment

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Nutrient fluxes

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movement of nutrients among compartments

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Nutrient sinks

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part of biosphere where nutrients are lost (sediment)

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Nutrient sources

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part of biosphere from where nutrients are released

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Phosphorus cycle

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Essential component of ATP, DNA, RNA, cell membranes. No atmospheric compartment (minerals are main source). Intense cycling in marine systems. Geological processes return P to active cycling

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Nitrogen cycle

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In proteins, biomolecules. Large atmospheric pool. N2 gas not available to plants- may only used NH4+ or NO3-. Also fixed by bacteria.

Human impacts on cycle: fertilizers, fossil fuel combustion

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Carbon cycle

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Large atmospheric pool of CO2 (duh)

Enters through photosynthesis, leaves through respiration. Must dissolve in water before becoming available to aquatic primary producers. Most C in sedimentary rocks, not actively cycling. Oceans are largest pool of actively cycled C.

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Nutrient conversion

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AKA mineralization, driven by decomposition (bacteria, fungi, animal detrivores)

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Decomposition rates

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Vary among ecosystems. Moisture availability positively correlated.

Soft, high N in leaves, high temperature, soil content may cause things to decompose faster

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Nutrient cycling in aquatic systems

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Vertical mixing and stratification alter

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Invasive species

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Can change cycling and distribution patterns in invaded systems

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Disturbance

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large impact on nutrient dynamics.

Hubbard brook watershed: clear cutting increased nutrient export

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Succession

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Ecological communities and ecosystems change through time following disturbance

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Primary succession

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newly created sites "complete reset"

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Secondary succession

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only biological community is destroyed "partial reset"

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Pioneer communities

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early succession species - high growth rate, short life-span, small size, good dispersal, high r

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Climax community

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Late succession species - slow growth rate, long lived, large, slow dispersal, low r. Endpoint of succession

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Landscape

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A heterogenous area made of distinctive patches (landscape elements) organized into mosaic-like pattern

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Landscape ecology

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interdisciplinary and broad science. Relationships between spacial pattern and ecological processes over a range of scales. Effects of humans on landscapes

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Patch

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homogenous area of habitat that differs from surroundings

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Matrix

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habitat/community into which patches embedded-the most continuous habitat

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Connectivity

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Ability of interactions to occur between patches. Movement of organisms and material

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Corridors

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Strips of patch-like habitat that connects adjacent patches

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Boundaries

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vary, affecting flow of organisms, energy, matter between patches. outer edge of ecosystems

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Ecotones

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wide transition of boundaries, distinct systems. Patch size and shape affects edge/boundary habitat availability

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Scale-dependent manner

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How landscapes and their subsequent elements are defined

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Patch size/shape

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large consequences for community structure/diversity. large patches contain more individuals and more species. Positive relationship. Affect ratio of interior/edge habitat and species specializing in habitats.

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Habitat shape/size

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affects movement of organisms. Rodent movement experiment: small rodents had great movement. Average distance moved decreases as patch size increased. Proportion of individuals moving increased as patch size increased.

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Habitat shape/size cont'd

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isolated patches supported smaller populations - less immigration. Size determines persistence- most extinctions and recolonizations observed in small patches.

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Habitat corridors

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Commonly used to connect patches. Corridors allow animals to move with ease. Enables dispersal and movement

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Feeding relationships

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Habitat coupling - greater connectivity in simple lakes

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Landscape structure

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Geological forces may produce landscape feature. Difference in age affect soil structure. Soil distribution affected vegetation distribution. Different soil supports different patches of community.

Beavers, humans have large effect on landscape structure. Remove trees, create dams, flood landscape

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Isolation

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"Islands"

Negative relationship between isolation and diversity seen for montane mammals

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Hypothesis to explain latitudinal gradients in species richness

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Time since perturbation- more time for evolution, less chance of extinction

Favorableness- warmer temps, more water availability

Productivity- support more species in productive environments

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Hypothesis to explain latitudinal gradients in species richness

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Heterogeneity- higher in tropics

Area hypothesis- more land/ocean area. Pattern of area-diversity relationship