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 isolation

b. Each species has an actual and a potential range

Potential range = area over which a species could

survive if transplanted

2. Behavior and Habitat Selectiona. Animals mainly

3. Biotic Factorsa. Disease

b. Herbivory

c. Absence of symbionts

d. Lack of pollinators

e. Competition

4. Competitiona. Factors

i. Whenever the quantity of useful matter or

energy falls below the level needed for the

maximal growth of two or more organisms which

must 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 can

shrink an organism’s actual range

b. Reasons? i. water

ii. nutrients (minerals)

iii. light

iv. heat

v. carbon dioxide, oxygen

vi. space

vii. pollinators

Strategies????

5. Abiotic Factorsa. Limits

i. Climate

Varies from place to place, season to season.

Each organism has an optimum environment

needed 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 of

differences in the angle of sunlight (seasons)

Solar radiation creates wind currents, ocean

currents, 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 rainforest

b. Location

Equatorial region

c. Characteristics

High average annual temp and precipitation,

Lush, dense vegetation, Very diverse! Large vertical

stratification due to competition for light (Canopy)

a. Name

Savanna

b. Location

rimming Equatorial region

c. Characteristics

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

a. Name

Desert

b. 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 harsh

environment

a. Name

Chapparal

b. Location

Along rugged hilly salt water coasts

c. Characteristics

Evergreen shrubs, Hot dry summers, mild

wet winters, Fire-dependent! – seeds germinated

after fire, roots fire-resistant

a. Name

Temperate Grassland

b. Location

Along 30o N and S parallel, inland

c. Characteristics

No trees, Typically 4 seasons, Occasional

fire, Fertile soils

a. Name

Temperate deciduous forest

b. Location

Along 30o N and S parallel coastal

c. Characteristics

Deciduous trees, 4 seasons (cold winter –

dormant), Open forests

a. Name

Coniferous Forest

b. Location

N hemisphere above 30o or elevation

c. Characteristics

Evergreen trees (gymnosperms), Largest

Biome on earth, 4 seasons, large amounts of snowfall

a. Name

Tundra

b. Location

N hemisphere or high altitude

c. 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 - Lakes

b. Location

???

c. Characteristics

Thermocline, vertical zones, turbidity

varies, oligotrophic versus eutrophic

a. Name

Fresh moving water - Rivers and Streams

b. Location

???

c. Characteristics

Current, temperature and turbidity varies,

vertical zones

a. Name

Wetlands

b. Location

???

c. Characteristics

Temporary to semi-permanent, temperature

and turbidity varies

a. Name

Estuaries

b. Location

???

c. Characteristics

Salt fluctuations, temperature, depth, and

turbidity varies

a. Name

Oceanic

b. Location

Duh?

c. Characteristics

Salt fluctuations, temperature, depth, and

turbidity varies, vertical zones

Fig 52.13

A. CharacteristicsI. Introduction

Plant Population Ecology

1. Dispersiona. Patterns of Dispersion:

i. Clumped – individuals in patches (ex. due to

soil types, seed dispersal by animals)

ii. Uniform – evenly spaced due to: Competition for

resources or Allelopathy – plants secrete chemicals to

inhibit nearby growth

iii. Random – unpredictable; position of one individual

cannot 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 elderLeachates 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 heavenAilanthone, isolated from the tree of heaven, has been reported to possess non-selective postemergence herbicidal activity similar to glyphosate and paraquat

Rye, fescue, and wheatAllelopathic 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, immigration

ii. 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 important

constraint has be removed.

Ex. Recolonization after fire

Represents 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

Number of

Individuals

Initial population density

New population density

Logistic growth

b. Limits Biotic Potential (r)

i. Intrinsic Factors

Plenty of food, living space, and other resources.

No competition

Habitat 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 of

individuals of a given species that can be sustained

indefinitely in a particular area.

K

Time

Number of

Individuals

Introduction

Colonization

Naturalization

iii. Carrying Capacity (K)

The maximum population size a particular area or habitat

can support at a particular time.

Is not fixed - K may decrease when a large population

damages 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 - selection

Disturbance creates low-density conditions, frees

resources (fire, flood, volcano)

Biotic potential (r) limits population size

Adaptations 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 K

Not much “new” space – competition for resources

Adaptations 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 communities

with 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 the

community

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 – range

of 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 biotic

components 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 new

species, different composition

vi. All communities have evolved with some type of

disturbance, varying in type, frequency, & severity

vii. Small-scale, frequent disturbance

Creates patches within the ecosystem

Thus increase in diversity

Ex. Trees downed in wind storm

Can prevent large-scale disturbance – fire!

Ex. Yellowstone fire of 1988

Fire 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 plant

iii. 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 less

adapted will be excluded from the community by the

superior competitor.

If this theory is true, then actually very little competition in

nature, because each plant occupies a niche.

low highLight intensity

Spe

cies

Abu

ndan

ce Species A Species B

A B C D

Resource partitioning creates niches

A B C D

Species A Species B

ii. Niche

A set of conditions exploited best by only one species

Includes 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 fur

iii. Competition – both harmed

iv. Predation – one harmed, other benefits

Herbivory

Pathogens

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 role

ii. 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 & disturbance

regimes (dynamic equilibrium, not climax).

B. Types

1. Primary Successiona. Characteristics

i. New area of mineral rock – no soil yet (volcano, glacier

retreat)

b. Sequence:

i. Lichens & mosses colonize bare rock

ii. As these decay, acids weather the rock & primitive soil

forms

iii. 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, producing

an 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 the

stage for their own replacement.

Accumulation of their wastes and remains adds volume to

the soil and enriches it with nutrients that allow other

species to take hold.

2. Secondary Successiona. Characteristics

i. Plant community is destroyed but soil remains

while 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 when

competition 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