Ecology Overview

Field of EcologyStudies the distribution and abundance of organisms, interrelationships of organisms and relationship between organisms and their environmentBoth field and laboratory studies explore parameters from biosphere level to organism level

Levels of Ecological StudiesBiosphere-Global scale; zone of life from Earth’s deep crust to lower trophosphereBiomes-areas determined by climate-decades of patterns of temperature and precipitationEcosystem-the biotic community, interrelationships of populations, and relationship between the populations and environmentCommunity-the populations within an areaPopulation-all the organisms of a species within an areaOrganism- a member of a population

Major biomesTundraForestGrasslandDesertAquatic

ForestsTemperate: 75-150 cm even precip throughout year, temperatures -30 to 30 C, oak, hickory, beech, hemlock, maple, elm are plants; animals: squirrels, rabbits, birds, deer, bobcats, foxes Tropical: >200 cm/yr precip even throughout year, 20-25 C, plants: trees like mahogany, orchids, bromeliads, vines, palms, buttressed trunks shallow roots; animals: birds, bats, sm. Mammals, insects Taiga: 40-100 cm precip mostly as snow, very cold temperatures, plants: Evergreen conifers, pine, fir, and spruce, animals: woodpeckers, hawks, moose, bear, weasel, lynx, fox wolf, hares, shrews

Population EcologyStudy of population growth and regulationInfluenced by density dependent factors (competition, predation, r vs K selected species) and density independent factors (climate, habitat disruptions offering opportunities for r selected species

Density and dispersion describe populations

Density is the number of organisms of that population per unit of areaDispersion is the distribution of those organisms in that area

Dispersion patternsClumped- most common pattern; could be due to numerous factors: more suitable habitat, food source is unevenly distributed, more success when there are many individuals-pack of wolves, school of fishUniform-most unusual pattern; territoriality contributes to this pattern, or competition for resourcesRandom-if there are no competition factors or resources are relatively evenly distributed or if distribution is based on random factors-like seed dispersal by wind

Dispersion patterns

Density dependent factorsNutritional resources, increasing predationMay act to slow population growth

Density Independent factorsWeather or habitat disruptionReduce population by the same proportion whether the population is large or small

Life histories: r and K selectedLife history is the birth, reproduction and death of organisms3 factors affect the rate of increase (r ): # or reproductive periods, clutch size; maturation ageR selected: opportunistic, early maturation, large clutches of small, independent individuals, no parental care (iteroparity)K selected: equilibrium (K), few offspring, mature late, larger bodied, parental care (semelparity)

dN/dt = rmaxN((K-N)/K)

The graph of this equation shows an S-shapedcurve.

Fig. 52.11

communitiesCollection of populations and their interactions within a given areaBiogeography: distribution of species on planetSuccession: change in community structure over time2 points of view on succession: Gleasonian: change groupings of species found in same area because of same requirements for environmental factorsClementsian: community is superorganism that develops in predictable sequence over time towards the climax community in which the species best fit the environmental factors (inhibition-prevent other species from colonizing; facilitation-set up stage for colonization by next species)

Community propertiesDiversity: number of species found in a communityAbundance: number of organisms within a populationDominant vegetation-physiognomyTrophic structure: feeding pyramidstability

Adaptations to biotic factorsCoevolution: reciprocal adaptations where one species acts as a selective agent on another species who acts on first species as a selective agent (flowers and their pollinators)

Competition between and within populations

Interspecific competition: competition between species for food and habitatIntraspecific competition: competition within members of a population for food, habitat, and matesCompetitive exclusion principle: two species that compete for the same limiting resource cannot occupy the same habitatResource partitioning: feed in same area but on different food sources (various bird species on beach all have different beak lengths and feed on different food sources)Habitat: address; niche: job (function)Fundamental niche: resources an organisms could theoretically useRealized niche is resources that is actually can use as determined by biological competition and predation

PredationTrophic pyramids and predator/prey relationshipsAdaptations to increase success include development of senses, morphological changes including defenses such as claws or coloration or chemical defenses-bitter or poisonousBehavioral adaptations: hide, flee, or fightKey stone predators switch sources of prey as prey becomes less plentiful resulting in a balanced community

Other interactionsMutualism: both species benefit from the relationship (corals and zooxanthellae)Commensalism: one species benefits from the other, the second species is neither harmed nor benefited ( Spanish moss hanging in trees)Parasitism: one species benefits at the expense of another (lampreys feeding on other fish)

Community stabilityResilience is the ability of the community to retain its structure when stressed by abiotic or biotic factorsUsually diverse communities are most resilienceIf there is a limiting factor, then communities with abundant populations are more successful

EcosystemsAn ecosystem is the relationships between and among the populations and the abiotic (environmental) factors Ecosystems are characterized by their structure and functionStructure is the abiotic features like topography, and the plants and animals that make up the ecosystemFunction is the relationship between them-trophic structure, nutrient cycling, flow of energy through the ecosystem

FORCING FUNCTIONSFactor that determines the structure/function of an ecosystemHydrology: water topographylight fireNutrient cycling or availability

Range of toleranceeach pop has range of tolerance in physical and chem envindividuals may have slight differences range is usually average conditionsgenetics, age, healthtotal range and optimum range

law of toleranceThe existence, abundance, and distribution of species in an ecosystem are determined by whether the levels or one or more physical or chemical factors fall within the range tolerated by that species. LEIBIG's law of minimum

limiting factor principletoo much or too little of any abiotic factor can limit or prevent growth of a population, even if all other factors are at or near the optimum range of tolerance. 1) hydrology 2)soil 3)nutrients 4)sunlight 5) temperature 6) dissolved oxygen in aquatic systems 7) salinity

Estuaries

Swamps and marshes

Tropical rain forest

Temperate forest

Northern coniferous forest (taiga)

Savanna

Agricultural land

Woodland and shrubland

Temperate grassland

Lakes and streams

Continental shelf

Open ocean

Tundra (arctic and alpine)

Desert scrub

Extreme desert

800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800 9,600

Average net primary productivity (kcal/m2/yr)

Fig. 4.25, p. 88

structure:

1-physical appearance2-species diversity3-species abundance4-niche structure number and how differ (diversity)

Fig. 8.2, p. 174

mft

10

50

20

30100

Tropicalrain forest

Coniferousforest

Deciduousforest

Thornforest

Tall-grassprairie

Short-grassprairie

Desertscrub

Thornscrub

Population dynamics respond to

Environmental stressChanges in environmental conditions

Biotic potentialCapacity for growthIf a population is at biotic potential, it is probably colonizing new areasIntrinsic rate of increase (r ) is the rate of growth, reproductive rate, if there were unlimited resources

Growth factorsFavorable environmental conditionsHigh fecundityGeneralized nicheAdequate food supplySuitable habitatAbility to compete for resourcesAbility to protect from predation and diseases or parasitesAble to migrateAble to adapt to environmental change

Environmental resistancesUnfavorable abiotic factorsLow reproductive rateSpecialized nicheInadequate food supplyPoor or unsuitable habitatToo much competitionUnable to protect against predation and diseaseUnable to live in other habitatsInability to adapt to environmental change

Major Characteristics of a population

Size: N number of individualsDensity: number of individuals per unit spaceDispersion: spatial patternAge distribution

Types of population fluctuations

StableIrruptive (explosive)Irregular (no known pattern or etiology)Cyclic (boom and bust)

Fig. 9.7, p. 202

Nu

mb

er o

f in

div

idu

als

Time

Irruptive

Stable

Cyclic

Irregular

Types of population fluctuations

Ecosystems respond to change

succession-gradual change in species composition of given area

communitiesCollection of populations and their interactions within a given areaBiogeography: distribution of species on planetSuccession: change in community structure over time2 points of view on succession: Gleasonian: change groupings of species found in same area because of same requirements for environmental factorsClementsian: community is superorganism that develops in predictable sequence over time towards the climax community in which the species best fit the environmental factors (inhibition-prevent other species from colonizing; facilitation-set up stage for colonization by next species)

Community propertiesDiversity: number of species found in a communityAbundance: number of organisms within a populationDominant vegetation-physiognomyTrophic structure: feeding pyramidstability

Types of successionprimary from rocksecondary reestablishment of biotic communities

primary succession

1-bare rock2-lava3-abandoned highway aor parking lot4-newly created shallow pond or reservoir

Fig. 8.17, p. 190

Early SuccessionalSpecies

RabbitQuailRingneck pheasantDoveBobolinkPocket gopher

MidsuccessionalSpecies

ElkMooseDeerRuffled grouseSnowshoe hareBluebird

Late SuccessionalSpecies

TurkeyMartinHammond’sFlycatcherGray squirrel

WildernessSpecies

Grizzly bearWolfCaribouBighorn sheepCalifornia condorGreat horned owl

Ecological succession

Fig. 8.15, p. 188

Time

Small herbsand shrubs

Heath mat

Jack pine,black spruce,

and aspen

Balsam fir,paper birch, and

white spruceclimax community

Exposedrocks

Lichensand mosses

Primary succession

Fig. 8.16, p. 189

Time

Annualweeds

Perennialweeds and

grasses

ShrubsYoung pine forest

Mature oak-hickory forest

Secondary succession: temperate

Secondary successionabandoned farmlandfirepolluted areasland dammed flooded

Two schools of thought about succession

Clementsian: orderly, predictable, if there is perturbation returns to the order ends w the same species in a climax communityGleasonian: species fit the conditions, if there is perturbation, whatever species are available will determine the community, climax community could vary before and after perturbation

Adaptations to biotic factorsCoevolution: reciprocal adaptations where one species acts as a selective agent on another species who acts on first species as a selective agent (flowers and their pollinators)

Competition between and within populations

Interspecific competition: competition between species for food and habitatIntraspecific competition: competition within members of a population for food, habitat, and matesCompetitive exclusion principle: two species that compete for the same limiting resource cannot occupy the same habitatResource partitioning: feed in same area but on different food sources (various bird species on beach all have different beak lengths and feed on different food sources)Habitat: address; niche: job (function)Fundamental niche: resources an organisms could theoretically useRealized niche is resources that is actually can use as determined by biological competition and predation

PredationTrophic pyramids and predator/prey relationshipsAdaptations to increase success include development of senses, morphological changes including defenses such as claws or coloration or chemical defenses-bitter or poisonousBehavioral adaptations: hide, flee, or fightKey stone predators switch sources of prey as prey becomes less plentiful resulting in a balanced community

Other interactionsMutualism: both species benefit from the relationship (corals and zooxanthellae)Commensalism: one species benefits from the other, the second species is neither harmed nor benefited ( Spanish moss hanging in trees)Parasitism: one species benefits at the expense of another (lampreys feeding on other fish)

Community stabilityResilience is the ability of the community to retain its structure when stressed by abiotic or biotic factorsUsually diverse communities are most resilienceIf there is a limiting factor, then communities with abundant populations are more successful

EcosystemsAn ecosystem is the relationships between and among the populations and the abiotic (environmental) factors Ecosystems are characterized by their structure and functionStructure is the abiotic features like topography, and the plants and animals that make up the ecosystemFunction is the relationship between them-trophic structure, nutrient cycling, flow of energy through the ecosystem

Trophic structureTroph means to feedTrophic structure determines the flow of energy through the ecosystemThere are two main trophic pyramidsThe classic pyramid begins with autotrophs (plants) then primary consumers, secondary consumers,…. The other pyramid begins with detritus and then saprophytes and scavengers in the primary consumer level, then secondary consumers…There usually are not many levels in a feeding pyramid because at each level, most of the energy is lost and little is transferred to the upper levelsThe upper levels will be top predators who must have a large range to find sufficient food

Food Chains and Webs

Food chains are the transfers of food between trophic levelsFood webs are the interactions within a food chains There may be many different species within each level of a trophic pyramid, and their predators may also be varied leading to complex food webs

Energy FlowThe source of most energy in trophic pyramids is ultimately the sun; in webs that are not photosynthetic or have detritus that is photosynthetically based, the source of energy may be elements and compounds, like those that form the basis of the food webs of hydrothermal vents and seeps

Primary productivityPrimary productivity is the rate of conversion of light to chemical energyThis is accomplished by photosynthetic organismsNet primary productivity (NPP) is the gross primary productivity (GPP) minus the energy consumed by respiration to drive cellular processes50-90% of GPP is used by the organism leaving only a small portion as NPP

Determining primary productivityProduction and consumption of oxygen can be used to determine productivity of aquatic ecosystemsPP can be expressed as energy per unit area per unit time (kcal m-2 yr-1)Biomass is mass of dry organic material per unit area per unit time (usually expressed as live biomass, dead biomass, total biomass, and may be only aboveground biomass but usually includes rootsStanding crop is total biomass of plants per unit area per unit timeThe most productive ecosystems are tropical forests, estuaries, and coral reefs

Limiting nutrientOne that is not present in adequate amounts limiting primary productivityP, due to its slow, sedimentary cycle and N, because it is entirely bacterially mediated and is found only as a diatomic gas without bacteria are the most common limiting nutrientPollution, over fertilization by N and P and run off from feed lots, leads to primary productivity blooms in aquatic ecosystemsAs the primary producers die and decompose, the bacterial decomposition uses all the dissolved oxygen, creating “dead zones” in the waterThis combination of extensive growth at the surface preventing growth of submerged aquatic vegetation (SAV) and subsequent anoxic zones in the water is called eutrophication

Energy pyramidsEnergy flow through the ecosystem is also represented as a pyramidMost gross productivity is used by the autotrophs, leaving little energy for the primary consumersThe primary consumers are only able to convert a small percentage (4-10%) of the energy that remainsSubsequent levels of the pyramid have less energy available and consequently, there is less biomass at each level

Chemical cyclingBiogeochemical cycles look at the transformations of nutrients within ecosystems or biomesAutochthonous sources move within an ecosystem and allochthonous sources move between and within ecosystems

Carbon cyclePhotosynthesis converts carbon dioxide to small hydrocarbons-sugars Metabolism of these sugars by mitochondria as a function of cell respiration results in the production of carbon dioxideBurning of hydrocarbons releases carbon dioxide and water as products of combustionExcess carbon dioxide may be sequestered by oceans where carbon dioxide reacts with salts to form bicarbonate

http://www.globalchange.umich.edu/globalchange1/current/lectures/kling/carbon_cycle/carbon_cycle_new.html

Nitrogen cycleEvery step of the nitrogen cycle is bacterially mediatedNitrogen fixing bacteria remove nitrogen from the atmosphere by making compounds that can be used by plants in a process called ammonificationPlants use the nitrogen in amino acids, nucleic acids, and other organic moleculesAs plants or animals decompose, some bacteria release nitrogen back to the atmosphere (denitrification) or convert ammonia to nitrates (nitrification)

NO3-

IN SOIL

NITROGEN FIXATION

by industry for agriculture

FERTILIZERS

FOOD WEBS ON LAND

NH3, NH4+

IN SOIL

1. NITRIFICATION

bacteria convert NH4+ to

nitrate (NO2-)

loss by leaching

uptake by autotrophs

excretion, death,

decomposition

uptake by autotrophs

NITROGEN FIXATIONbacteria convert to ammonia

(NH3+) ; this dissolves to

form ammonium (NH4+)

loss by leaching

AMMONIFICATIONbacteria, fungi convert the

residues to NH3 , this

dissolves to form NH4+

2. NITRIFICATION

bacteria convert NO2- to

nitrate (NO3-)

DENTRIFICATIONby bacteria

NITROGENOUS WASTES, REMAINS IN SOIL

GASEOUS NITROGEN (N2)

IN ATMOSPHERE

NO2-

IN SOIL

Phosphorus cycleThis is the slowest cycle because it has no gaseous componentWeather of rock adds P to soil or water usually in the form of phosphate ions which plants can absorbHumus and oil particles can bind P keeping it available for cycling within an ecosystemIf the ecosystem is aquatic or if the P flows into an aquatic ecosystem, some P will be adsorbed in sediments and trappedThese sediments will become sedimentary rocks and the process begins with weathering of these rocks

http://dosel.botany.ufl.edu/ecologyf03/nutrientcycles.html

Phosphorous Cycle

Nutrient cycling in ecosystemsThe rate of cycling of nutrients depends on climate and precipitation and availability of the nutrientsSome ecosystems cycle C rapidly, as in deciduous forests, come cycle slowly as in fens, bogs or salt marshesTropical rain forests all of the C is tied up in the biomass, there is little reservoir of C in the soil or in litter; the litter cycles rapidly

Anthropogenic effects on nutrient availability and nutrient cycling

Agriculture adds N and P, but removes much of the biomass which incorporates that N & P; some of the fertilizers may be lost if applied where there are no buffers between fields and water sources or if applied before rainfallLogging removes biomass and nutrients and alters the amount of light that enters the forest; Hubbard Brook Forest study demonstrated that logging leads to more nutrients lost in run off since there is low biomass to slow water flow and to cycle the nutrientsEutrophication was discussed earlier

eutrophicationIf N and P are added to aquatic ecosystems, eutrophication can occurN and P, which are usually limiting nutrients of ecosystems, are now available in large quantities and the algae (phytoplankton) grows prolifically in responseThe algae blocks sunlight and contributes to the loss of submerged aquatic vegetation (SAV)As the algae decomposes, the bacteria use all the available oxygen in the water and facultative anaerobes switch to anaerobic pathways for further decompositionThe water is depleted of oxygen, anoxic water, resulting in fish kills

Eutrophication

http://www.cord.edu/faculty/landa/courses/e103w00/sessions/water/eutrophication.jpg

Eutrophication

http://www.italocorotondo.it/tequila/module2/pollution/effects_pollution.htm

Biomagnification and BioaccumulationSubstances that are synthetic or not biodegradable (e.g. pesticides, herbicides, radioactive substances) may biomagnify in an organism; DDT, a pesticide, has been found in nearly every organism testedBiomagnification is the accumulation of the substance in the tissues of an organism over its lifetime (often lipid soluble, these substances sometimes accumulate in the brain) As these organisms are consumed as part of the food chain, the toxic substances bioaccumulate; each level of the food chain has more of the substance; DDT bioaccumulated in birds of prey and prevented egg shell formation resulting in large loss of populations-endangered species

Increased levels of gases due to anthropogenic activities

Increases in some gases, such as carbon dioxide from burning of biomass and fossil fuels, contribute to changes in atmospheric chemistryThese increase the “Greenhouse effect” which leads to an increase in global temperatureIncreases in global temperature alter the pattern of precipitation and winds which changes biomes and food availability