Ecology

Ecology

A. Definition The study of the interactions between organisms & organisms with their environment.

I. Introduction

B. Parameters 1. Abiotic – non-living. Like? 2. Biotic – living. Like?

C. Levels of Organization

1. ChemistrySubatomic Particles Atoms Molecules Macro - Molecules

2. BiologyTissues Organs OrganismsOrganelles Cells

Population Community Ecosystem Biome Biosphere

3. Ecology

D. Distribution of Life

1. Dispersal Limitationsa. Not all areas are accessible – geographic isolationb. Each species has an actual and a potential range

Potential range = area over which a species couldsurvive if transplanted

2. Behavior and Habitat Selectiona. Animals mainly

3. Biotic Factorsa. Diseaseb. Herbivoryc. Absence of symbiontsd. Lack of pollinatorse. Competition

4. Competitiona. Factors i. Whenever the quantity of useful matter orenergy falls below the level needed for themaximal growth of two or more organisms whichmust draw on the same supply, a contest begins. ii. The more similar the needs the greater the intensity of competition. iii. Competition from introduced species canshrink an organism’s actual range

b. Reasons? i. water ii. nutrients (minerals) iii. light iv. heat v. carbon dioxide, oxygen vi. spacevii. pollinators

Strategies????

5. Abiotic Factorsa. Limits i. Climate

Varies from place to place, season to season. Each organism has an optimum environmentneeded for maximum growth.

Temperature & annual precipitation (climate vs. weather) are the most important factors determining the distribution of organisms on a global scale (biomes).

……Thus scientists predict that climate change may radically alter the distribution of organisms/ecosystems on earth.

Fig 52.10

Effects of climate on biogeography

Climate varies with latitude because ofdifferences in the angle of sunlight (seasons) Solar radiation creates wind currents, oceancurrents, and precipitation (from evaporation)

Fig 52.4

Fig 52.3 & 5

Coriolis Effect

ii. Weather = Local climate Proximity to water, mountains E or W side of land mass S slope drier than N slope (thus different plant

communities)iii. Precipitation = Microclimate

Forest floor vs. canopy Under a log Within the litter layer

Fig. 52.13

Your ecosystem type: coastal temperate rainforest

Fig 52.6

A. General Characteristics 1. Limits Locations of the earth’s biomes due to:

a. Latitude – affects temperature, precipitation b. Positions of the continents

2. Structure One biome type may occur in differentareas of the world but different plant species but same:

a. Physiognomic structure – size; shape; types of organisms & their relation to each other & the physical Environment

b. Due to convergent evolution – similar phenotypes due to similar selection pressures over time.Similar climate, soils, disturbance patterns,…

II. Biomes

Fig. 52.9

B. Types

1. Terrestrial (figure 52.12)a. Name Tropical rainforestb. Location

Equatorial regionc. Characteristics

High average annual temp and precipitation,Lush, dense vegetation, Very diverse! Large verticalstratification due to competition for light (Canopy)

a. Name Savannab. Location

rimming Equatorial regionc. Characteristics

Grasslands with scattered trees, Large herbivores & predators, Rainy & dry season! Fire adapted

a. Name Desertb. Location

Along Tropic of Cancer and Capricorn (23.5o)c. Characteristics

< 30 cm of rain per year, High temperatures, CAM plants! Unique plants with adaptations to harshenvironment

a. Name Chapparalb. Location

Along rugged hilly salt water coasts c. Characteristics

Evergreen shrubs, Hot dry summers, mildwet winters, Fire-dependent! – seeds germinatedafter fire, roots fire-resistant

a. Name Temperate Grasslandb. Location

Along 30o N and S parallel, inlandc. Characteristics

No trees, Typically 4 seasons, Occasional fire, Fertile soils

a. Name Temperate deciduous forestb. Location

Along 30o N and S parallel coastalc. Characteristics

Deciduous trees, 4 seasons (cold winter –dormant), Open forests

a. Name Coniferous Forestb. Location

N hemisphere above 30o or elevationc. Characteristics

Evergreen trees (gymnosperms), LargestBiome on earth, 4 seasons, large amounts of snowfall

a. Name Tundrab. Location

N hemisphere or high altitudec. Characteristics

Permafrost – permanently frozen subsoil, Very cold, high winds, No trees or tall plants, 20% of land area on earth, Low annual precipitation

2. Aquatic (Figure 52.16)a. Name Fresh water, relatively still - Lakesb. Location

???c. Characteristics

Thermocline, vertical zones, turbidityvaries, oligotrophic versus eutrophic

a. Name Fresh moving water - Rivers and Streamsb. Location


Current, temperature and turbidity varies, vertical zones

a. Name Wetlandsb. Location


Temporary to semi-permanent, temperature and turbidity varies

a. Name Estuariesb. Location


Salt fluctuations, temperature, depth, andturbidity varies

a. Name Oceanicb. Location

Duh?c. Characteristics

Salt fluctuations, temperature, depth, andturbidity varies, vertical zones

Fig 52.13

A. CharacteristicsI. Introduction

Plant Population Ecology

1. Dispersiona. Patterns of Dispersion:

i. Clumped – individuals in patches (ex. due tosoil types, seed dispersal by animals)

ii. Uniform – evenly spaced due to: Competition forresources or Allelopathy – plants secrete chemicals toinhibit nearby growth iii. Random – unpredictable; position of one individualcannot be predicted from position of another.

Allelopathic plant ImpactRows of black walnut interplanted with corn in an alley cropping system

Reduced corn yield attributed to production of juglone, an allelopathic compound from black walnut, found 4.25 m (~14 ft) from trees

Rows of Leucaena interplanted with crops in an alley cropping system

Reduced the yield of wheat and turmeric but increased the yield of maize and rice

Lantana, a perennial woody weed pest in Florida citrus

Lantana roots and shoots incorporated into soil reduced germination and growth of milkweed vine, another weed

Sour orange, a widely used citrus rootstock in the past, now avoided because of susceptibility to citrus tristeza virus

Leaf extracts and volatile compounds inhibited seed germination and root growth of pigweed, bermudagrass, and lambsquarters

Red maple, swamp chestnut oak, sweet bay, and red cedar Wood extracts inhibited lettuce seed as much as or more than black walnut extracts

Eucalyptus and neem trees A spatial allelopathic relationship if wheat was grown within 5 m (~16.5 ft)

Chaste tree or box elder Leachates retarded the growth of pangolagrass, a pasture grass, but stimulated the growth of bluestem, another grass species

Mango Dried mango leaf powder completely inhibited sprouting of purple nutsedge tubers.

Tree of heaven Ailanthone, isolated from the tree of heaven, has been reported to possess non-selective postemergence herbicidal activity similar to glyphosate and paraquat

Rye, fescue, and wheat Allelopathic suppression of weeds when used as cover crops or when crop residues are retained as mulch

Broccoli Broccoli residue interferes with growth of other cruciferous crops that followJungle rice Inhibition of rice cropForage radish Cover crop residue suppression of weeds in the season following the cover cropJerusalem artichoke Residual effects on weed speciesSunflower and buckwheat Cover crop residues reduced weed pressure in fava bean crop

Clumped lupine

Uniform dispersal of sagebrush

Random trees

2. Population Sizea. Demography = study of factors that affect the growth & decline of populations

i. Increase by reproduction, immigrationii. Decrease by death, emigration

Change in Population size = (B + I) – (D + E)If B – D = 0, then zero population growth

Fig. 53.9

b. Life History = events from birth, through Reproduction, to death

i. Dormancy, germination, growth, reproduction, dispersal, death

ii. Trade-offs between investments in reproduction& survival when there are limited resources

Controls at every stage of life history

Seeds washed away, eaten, decomposedDormancy (seed bank)

Seeds rain from mature plants

seedling

growth

mature plant

reproduction

death

New resources available, perfect growing conditions, freedom from disease, competition, drought

Herbivory, disease, competition, drought, flood, freeze

3. Growth

Occurs when resources are abundant or when an importantconstraint has be removed. Ex. Recolonization after fireRepresents a doubling of the population in a specified time.

a. Patternsi. Exponential

The j-shaped curve

Time

Number of Individuals

Steady increase followed by a plateau due to ????. i. Logistical

Time


Initial population density

New population density

Logistic growth

b. Limits Biotic Potential (r)

i. Intrinsic FactorsPlenty of food, living space, and other

resources.No competitionHabitat is free of predators and pathogens.

Density & competition for resources will cause reproduction rates to decline or stabilize.

Any essential resource that is in short supply is a limiting factor on population growth.

• Food (Why?)• micro-nutrients• refuge from predators• living space• pollution-free environment

ii. Environmental resistance affects the number ofindividuals of a given species that can be sustainedindefinitely in a particular area.

K

Time


Introduction

Colonization

Naturalization

iii. Carrying Capacity (K)

The maximum population size a particular area or habitatcan support at a particular time.Is not fixed - K may decrease when a large populationdamages or depletes its own resource supply.

4. Control

i. Density Independent Control

a. Factors

ii. Density Dependent Control

5. Adaptations

a. At low density, population is limited only by intrinsic rate of growth (r) b. At high density, population is limited by carrying capacity (K) c. r versus K strategy d. Competitive, Ruderals, or Stress Tolerant

i. r - selectionDisturbance creates low-density conditions, freesresources (fire, flood, volcano)Biotic potential (r) limits population sizeAdaptations that are successful for these conditions:

– Produce large # of seeds fast– Wind dispersal of seed– Plants grow & flower quickly (annuals)– Few chemical/mechanical defenses

ii. K-selection

High density, population size close to KNot much “new” space – competition for resourcesAdaptations that are successful for these conditions:

– Perennial– Fewer, larger seeds– Defenses against herbivores, pathogens– Adaptations to shading, poor soils

K & r selected species exist together because small-scale disturbances create space (exposed soil) for r species (colonizers)

– Ex. Downed tree, badger holes, grazing disturbance

I. Background

1. Groups of organisms of different species (populations)living and interacting with each other and the habitat

A. Definition

Plant Community Ecology

B. Hypothesis of Structure 1. Question? Are plant communities a real entity in nature? Why are certain species found together? 2. Hypotheses:

a. Individualistic hypothesis - Gleason i. Species are found together in nature because theyhave similar abiotic requirements ii. No distinct boundaries between communitiesiii. Each species distributed along its tolerance range iv. Thus communities change continuously along a gradient

b. Integrated Hypothesis - Clements

i. Plant communities function as a real, integrated unit. ii. Plant species found together because of interactions with each other & the rest of the ecosystem.iii. Thus species are clustered into discrete communitieswith definite distribution boundaries.

Which is correct?

c. So? Individualistic/Continuum “more correct”, but evidence of both – some sharp boundaries due to dramatic environmental changes.

II. Characteristics of communities A. Diversity – composed of:

1. Richness – the total number of species in thecommunity

2. Evenness – the relative abundance of species in the community (some dominant, some rare)

a. Relative abundance = # individuals of species X divided by total # of individuals in the community

Which community is more diverse??

Fig 54.10

Fig. 54.10

B. Factors

a. Each species has a tolerance range – rangeof conditions under which it can survive & reproduce b. Climate – temp, moisture c. Soil – types, pH d. Latitude & Altitude

1. Abiotic

e. Disturbance i. Decrease or total elimination of the bioticcomponents of the habitat ii. Results: decrease in biomass, diversity iii. Natural events – fire, flood, volcano, avalanche iv. Human-caused – herbicides, roads, development,logging, grazing, farming, mining v. Opens resources, creating opportunities for newspecies, different composition vi. All communities have evolved with some type of disturbance, varying in type, frequency, & severity

vii. Small-scale, frequent disturbanceCreates patches within the ecosystemThus increase in diversityEx. Trees downed in wind stormCan prevent large-scale disturbance – fire!

Ex. Yellowstone fire of 1988Fire suppression in fire-dependent ecosystem

caused massive, stand-replacing fire

viii. Human Caused Example Cheatgrass – wildfire cycleOvergrazing in ecosystem that did not evolve with large herbivoresCheatgrass introductionDecrease in fire frequency (100 yr to 5 year cycle)Conversion of ecosystem with tremendous loss of DiversityThese types of problems creating mass extinctionworldwide.

2. Biotica. The plant itself

i. Can modify the environment ii. Modifications can be +, -, or neutral to the plantiii. Benefit ex: beech/oak forest creates shade

needed for other young beech & oak to grow iv. Detriment ex: pine forest creates shade but

pines need lots of light to grow (succession)

b. Other plant species i. Theory of competitive exclusion: When two species compete for the same limiting resource(occupy the same niche), the species that is lessadapted will be excluded from the community by thesuperior competitor.

If this theory is true, then actually very little competition in nature, because each plant occupies a niche.

low highLight intensity

Spec

ies A

bund

ance Species A Species B

A B C D

Resource partitioning creates niches

A B C D

Species A Species B

ii. NicheA set of conditions exploited best by only one speciesIncludes all aspects of a species’ use of biotic & abiotic resources (microclimate, rooting zone, pollinators, etc.)A species’ role in the ecosystem.

c. Other (non-plant species) i. Mutualism – both organisms benefitExamples: Mycorrhizal fungi, N-fixing bacteria in root nodulesPollinator gets nectar and plant gets pollen transferAnimals eat fruit (nutrition) and seeds are dispersedAcacia trees get defense from herbivores & ants get home, food

ii. Commensalism – one species benefits & other is not affected

Bird nests in trees, seeds stuck on animal furiii. Competition – both harmediv. Predation – one harmed, other benefits

HerbivoryPathogens

Predation or the need to keep your wits about you?

C. Controls on community structurea. Dominant species = species with the highest abundance or biomass in the community

i. Best species among all species in the community at exploiting the limiting resource

ii. Controls occurrence & distribution of other species iii. If eliminated, other species take over

Example: Douglas fir

b. Keystone species i. Control community structure by their ecological roleii. If eliminated, drastic change in community structure

or composition Example Sea otter – reduction in populations caused boom in sea urchin population, destroying kelp forests (drastic decline in diversity)

Succession

III. SuccessionA. Definition 1. Changes in community structure & composition over time following a disturbance 2. Species thriving on a site are gradually replaced by other species. 3. Species replacement continues until the composition of species becomes relatively steady under prevailing climatic conditions & disturbanceregimes (dynamic equilibrium, not climax).

B. Types1. Primary Succession

a. Characteristicsi. New area of mineral rock – no soil yet (volcano, glacierretreat)

b. Sequence: i. Lichens & mosses colonize bare rock ii. As these decay, acids weather the rock & primitive soilformsiii. Pioneer plants establish (r-selected or Stress tolerant) iv. Pioneers replaced by K-selected (Ruderal and Competitive)

c. The Nature of Pioneer Species i. Adapted to growing in habitats that cannot support most species: intense sunlight, wide swings in temperature, moisture deficits. ii. Typically small plants, short life cycles, producingan abundance of small seeds which are quickly dispersed (wind & water) iii. Can grow in N-poor soil because of their mutualistic interactions with nitrogen-fixing bacteria.

Example of primary succession: glacial retreat

Alders & cottonwoods dominate

Spruce enter forest and replace alders/cottonwoods

Hemlock slowly replace Spruce. Hemlock is “climax”

iv. FacilitationImprove the living conditions for other species, setting thestage for their own replacement. Accumulation of their wastes and remains adds volume tothe soil and enriches it with nutrients that allow other species to take hold.

2. Secondary Successiona. Characteristics i. Plant community is destroyed but soil remainswhile new soil exposed ii. Examples? abandoned farm fields, clear cuts, wind storms, fire. iii. Typical progression: small herbs & grasses shrubs trees

b. Pioneer species i. r-selected (stress tolerant) (species move in first whencompetition is low (low density). ii. Sometimes these opportunistic species (especially invasive weeds!) inhibit the growth of the native climax species changing the structure and type of climax community forever. Ex. cheatgrass

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Ecology