Ecology Exam #1

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Ecology Root Word

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"Oikos" meaning "home"

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Ecology

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the study of relationships of organisms to their environments (biotic and abiotic)

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History of Ecology

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many people thought the study was wastefull and meaningless

-who cares what plants grow on a sand dune or what insects live in the bottom of a stream?

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People payed attention to ecology when they realized...

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that a study of ecology of all life also is a study of the ecology and fate of ourselves

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Aquatic insects reflect

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the quality of water

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Dust Bowls (1930's) resulted from

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ignorance of ecological principles

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Career Opportunities

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shifted to land-use planning, environmental law, ecological consultation, etc.

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Ecology is a Science so..

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it is based on a testable hypotheses, data are gathered and analyzed, the study can be replicated, and errors can be found and corrected

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Unifying theme of Ecology

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the inter-relatedness of components of the system: affecting one thing will affect many

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environment or habitat

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the surroundings of an organism (biotic and abiotic)

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Habitats have several levels

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broad subdivisions like aquatic or terrestrial

more minute subdivisions such as microhabitats

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Microhabitat Example
Sand Darter

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a fish that is aquatic, but is found only in flowing water over sand

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Law of Tolerance

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environmental conditions vary somewhat, and a species will survive within a range of the variation

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Tolerance

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ranges differ between species, thus different habitats support different communities (wet vs. dry, cold vs. hot)

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Optimum Survival

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although a species may survive in a range, individuals are usually most successful within a smaller optimum range

success of an organism depends on where several factors intersect acceptably
-the optimum for one environmental variable may not be obtainable if another important ecological factor doesn't operate at that level

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When there are several shifts that go outside the range of tolerance:

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1) organisms may die and go extinct until it can re-invade

2)survive if a life history stage can withstand the change (insect pupae or eggs can overwinter)

3)survive if it moves to protected microhabitats (herps, bats, rodents in caves or under frost)

4)survive if it migrates (some birds and mammals and monarch butterflies)

5)survive if it can acclimate

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Acclimation

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a gradual change into new environmental conditions

ex. aquarium fish placed in a bag for transport

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Temporary Shifts

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some shifts are extreme but temporary, and may be more important that seasonal shifts because you only have to kill an organism once

ex. toxic spills

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Limiting Factors

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when several variables are importanat and present, the success of the organsims will depend on the variable present as "too little" or "too much"

similar to analogy of the "weakest link in the chain"

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Limiting Factor Example

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plants need phosphate for growth, so it is present in fertilizer

-algae in ponds or lakes are limited most by the relative lack of phosphates

-thus phosphates we put in the environment as runoff from fertilizers or phosphate detergents cause "algal blooms" which cause odors and taste changes, then die and take up O2 for decompostition which may cause fish kills

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Factors may Compensate

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ex. an organism living in cold water with low O2 may not live in warmer water unless the O2 content is higher (for metabolism)

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Synergism

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combined effects of 2 factors is greater than their sum

this can favor or exterminate populations, depending on the effect

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Ecological Indicators

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organisms with a narrow tolerance range for some factor of interest

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Valid Indicator

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one that occurs only within the condition it is meant to indicate (it has good fidelity)

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Significant Indicator

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one that is very likely to occur (not rare) if hte conditions it indicates are present (it has good constancy)

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Ecological Indicator Examples

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ex. heavy grazing in praries can be indicated by more bluestem and less ragweed, dandelion, white clover

ex. mayflies of genus Isonychia occur in clean, clear water; Hexagenia in dirtier, lesser quality water

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Use of Ecological Indicators

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identifying soil types, depth of groundwater, archaeological sites (sweet gum grove)

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Energy

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the ability to do work

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Organism without energy

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would die

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Energy is transferred through the ecosystem according to..

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the physical principles called the laws of thermodynamics

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1st Law of Thermodynamics

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energy cannot be created or destroyed, only changed in form

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2nd Law of Thermodynamics

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in the transfer of energy, some will be lost as heat

this is why we speak of effciency in cars, heat pumps, etc.

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calorie

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the unit to measure heat

(the amount of heat required to raise 1 gram of water 1 degree Celcius, starting at 14.5 degrees Celcius)

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Calorie

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=kilocalorie or 1000 calories

the unit we talk about when dieting

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Calorie Example

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if a hamburger has 300 Calories, it possesses the ability to raise the temperature of 300,000 grams of water 1 degree Celcius

a person weighing 150lbs (68,100 grams) eating the burger has the potential to raise their temperature 4.4 degrees Celcius (300,000/68,100 - assuming all your weight was water)

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Person who ate the Burger

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the energy transferred partly to heat and "burned off", or it will be stored as lipids

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Organism Energy

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energy must constantly be added into an organism

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Autotrophs

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produce their own food from inorganic materials

-most are photosynthetic
-some are chemosynthetic

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Photosynthetic Organisms

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use light energy to store chemical energy

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Chemosynthetic Organisms

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some bacteria use chemical reactions

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Photosynthesis

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puts together carbon dioxide and water to form organic molecules

6 CO2 + 6 H2O --> C6H12O6 + 6 O2
--O2 is a by product

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Autotrophs and Heterotrophs

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autotrophs store food for themselves by using solar energy, and this allows for the existence of other organisms that raid the storehouse (heterotrophs)

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Heterotrophs

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organisms that depend on autotrophs for their food (directly or indirectly)

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Respiration

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process in which complex molecules are reduced to simple ones, releasing energy tied up in molecular bonds

Heterotrophs use Respiration

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Why must there by fewer heterotrophs?

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due to the 2nd Law of Thermodynamics

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Food

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when it is taken into the body it provides the energy for life processes, but its use is not efficient

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Where does energy from food go?

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-some energy is lost as heat
-some is lost in feces and urine and sweat
-the rest is available for work

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Assimilated Energy

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energy left over and available for work

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Standard Metabolism

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energy used just to stay alive

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Homeothermic Animals SMR

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mammals and birds

the main factor affecting standard metabolic rate is size

SMR gets larger as the animal gets bigger, but not proportionately

(an animal 5x the size of another will use more energy but not 5x more)

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Unproportionate Increase due to:

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the main factor affecting it is the surface area to volume ratio

-heat loss is proportional to surface area, so bigger animals can get by using actually more but proportionately less energy

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Amount of energy used by a Homeotherm

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there must be enough to stay alive + energy to maintain constant temperature + enough for productive work (activity and reproduction)

-a homeotherm therefore needs 2-3x the energy required for standard metabolism

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Energy Subsidies

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uses of outside energy to aid an organism

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Energy Subsidies
Examples

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-gulls, vultures, hawks use energy in air currents to soar

-some freshwater organisms use energy of flowing water to bring food and eliminate waste

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Ecological Questions can

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examine proximate or ultimate factors

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Proximate Factor

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one that deals with the immediate cause:it is within the organism that you might seek and explanation

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Ultimate Factor

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deals with the greater cause: it is within the environment or population that the answer might be found

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Proximate vs. Ultimate Factor
Example

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varying hares turn white in winter and brown in summer - why?

ultimately, changing color helps in seasonal camouflage

proximately, photoperiod causes hormonal changes and thus the change to occur

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Ecotypes

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different populations which have genetic differences related to ecological constraints

-ultimate factors may vary geographically, thus different populations of a species may respond to the variation resulting in ecotypes

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Dispersal

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movement of individuals from their place of birth

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Plant Dispersal

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plants have morphological features aiding dispersal, based on the agent involved

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Plant Dispersal
Water

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seeds or fruits are buoyant and waterproof

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Plant Dispersal
Wind

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-fruits with long hair-like structures (dandelions, milkweed, cottonwood)

-fruits with wing-like structures (maple, ash, pine)

-balloon-like fruits - light and inflated so roll easily (nightshade)

-tumbleweed - plant dries, dies, rolls around in wind dropping seeds

-small size - tiny so gusts of wind carry seeds like dust

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Plant Dispersal
Animals

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Hitch a ride on mobile life forms

-fleshy fruits with hard seed - eat fruit, defecate seed later (raccoon)

-sticky seed - stick due to slimy seed, rubbed off elsewhere

-storage without recovery - invest in many seeds, some will be eaten but others buried and lost

-stick-tights - spines or hooks hold seed to a passing animal's hair, skin, etc. (cockleburs, beggar ticks, sandburs)

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Plant Dispersal
Animals
Storage without Recovery Example

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squirrels often store acorns or hickory seeds underground (in effect planting them) - if not recovered they have been dispersed

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Plant Dispersal
Explosive Projection

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upon maturity or touch a quick snap of the seed pod throws the seeds (touch-me-not)

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Plant Dispersal
No Method

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if none of the methods are used, dispersal may be limited to effects of gravity

-no morphological features, no real dispersal

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Animal Dispersal

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animals hae few morphological adaptations for dispersal because they usually are mobile

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Animal Dispersal
Morphological Adaptations
Examples

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larval stages that swim but have sessile adult stages (some hydroids, sea squirts)

some insects such as aphids and termites have winged stages which function only for dispersal considering that they are shed after dispersal is accomplished

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Animal Dispersal is effected more by:

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behavioral means related to genetics and the environment

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Animal Dispersal
Intolerance

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adults may aid dispersal by becoming intolerant of young (bobcat)

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Animal Dispersal
Crowding

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crowding may cause dispersal (emigration) in search of better habitat (lemming)

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Animal Dispersal
Genetics

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some genetic combinations may trigger dispersal (some rodent work)

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Animal Dispersal
Inbreeding

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dispersal may aid success by preventing inbreeding (often males disperse and females stay home - prairie dogs)

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Animals Dispersal
Environment Inhibiting Dispersal

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in some cases the environment may not allow dispersal

ex. in Florida scrub jays have a habitat that is so limited and so poor that young stay with parents and become helpers at the nest for the next year, where they presumably learn extra survival techniques and aid in nest success by also providing food for their siblings

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Dispersal Area

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normally within the range of the species, into newly created sections of habitat (a forest fire allows invasion of ground plants) or areas vacated by the death of previous individuals

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Range Expansion

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range expansion is dynamic, usually caused by removal of barriers or human action, or environmental change (glacial periods)

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Range Expansion Examples

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-humans brought starlings to NYC in the 1800s; since then they have dispersed through North America

-humans cut down eastern forests and coyotes moved eastward

-water separated North and South American until the plates collided and lifted a land bridge - armadillos and opossums moved north, camels moved south and across the Bering straights to Asia

-stream capture allows fishes to expand ranges

-changing climates makes range expansion dynamic: southern species move farther north if there are consecutive warm years

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Organismal Response to Habitats

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organisms respond to abiotic and biotic components of their habitats

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Thermal Relations
Heat Gain

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an organism obtains heat from solar radiation, infrared and heat radiation from surroundings, through metabolism, and by convection

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Thermal Relations
Heat Loss

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an organism loses heat by infrared and heat radiation, convection heat loss, and evaporative heat loss (sweat)

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Importance of Body Temperature

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-based on metabolic activity

-some enzymes work only in the right temperature range, thus to function you must have the right temperature (ex. feed aquarium lizards)

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Law of Q10

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for every 10 degrees Celcius increase in temperature there is a 2-3x increase in rate of chemical processes (metabolism in an organism)

vice versa

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Ectotherm

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also called a poikilotherm

an organism depends on the environment for heat energy

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Endotherm

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also called a homeotherm

an organism that warms itself using metabolism

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Winter for Ectotherm vs. Endotherm

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ectotherms have the advantage of shutting down to ride out winter, whereas endotherms must spend energy searching for a food supply to maintain metabolic heat

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Easier Life for Ectotherms?

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ectotherms would seem to have an easier life, but they are lethargic in cooler periods (like morning) - an endotherm would have the advantage of feeding on ectotherms (Dimetrodon and the Sailfin - solar heat collector)

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Ectotherm Advantages

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-energy conservative, low-power strategy

-because they don't maintain a temperature, they are not limited by the surface/volume ratio

-therefore, they can be very small (some fishes, salamanders, frogs, etc.) and can have elongate shapes with a lot of surface area (snakes, worms, etc.)

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Endotherm Advantages

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-extravagant, high-power strategy

-this strategy typically will outcompete the ectothermic strategy in the same habitat.

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Hibernation

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a special strategy in which an endotherm seasonally behaves as an ectotherm

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True Hibernators

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-they go into a deep sleep from which it is very difficult to wake (ground squirrels, woodchucks)

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Carnivoran Lethargy

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bears and other carnivores sometimes enter a deeper-than-normal sleep but they have not dropped body temperature as much and can awaken quickly

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Humidity

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water vapor in the air

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Moisture Problems

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ability of air to hold moisture becomes greater with temperature, thus a cold air mass colliding with a warm, moisture laden one results in precipitation

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The importance of the ability of air to hold moisture to organisms is...

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the comparative drying power of the habitat (it is difficult to run in August heat in Arkansas but not in Arizona)

-organisms must maintain a favorable water balance

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Xerophytes

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-grow in xeric (dry) habitats

often perennials with small, hard leaves to retain moisture when soil dries

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Xerophytes
Succulents

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ex. cacti

xerophytes in which water is stored in fleshy tissue

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Xerophytes
Phreatophytes

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have very long roots to tap into water table

ex. mesquite root system may reach down 175 feet

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Hydrophytes

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grow in water so generally there is no problem unless the pond or creek dries

primary limit for these is CO2 (not as much is dissolved in water)

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Mesophytes

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usually grow where water is not much of a problem, water conservation adaptations are minimal

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Salt Concentration

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some physically wet habitats can be physiologically dry due to salt concentration

-water is present, but salt concentration make it osmotically unavailable

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Halophytes

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adapt to obtain water in environments with high salt concentrations

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Water Balance in Animals
Gain

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-drinking
-metabolic water
(C6H12O2 + 6 O2 --> 6 CO2 + 6 H2O)
-water in food

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Water Balance in Animals
Loss

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-urine
-feces
-evaporations from skin and lungs

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Water Conservation in Xeric-adapted Animals
Behavioral

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be active at night when cooler, dig burrows that trap respiratory moisture, seek shade

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Water Conservation in Xeric-adapted Animals
Physiological

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intestine resorbs water before elimination of feces; loop of Henle in kidneys especially long to resorb water before elimination of urine

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Water Conservation in Aquatic Animals

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Main problem is when salt concentration differs between body fluids and environment

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Water Conservation in Aquatic Animals
Isotonic

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same concentrations so no problem (marine invertebrates)

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Water Conservation in Aquatic Animals
Hypertonic

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organism has higher salt concentration: can eliminate water coming in but must work to retain salts (freshwater organisms)

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Water Conservation in Aquatic Animals
Hypotonic

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organism has lower salt than environment so must excrete excess salt (marine vertebrates)

usually by salt glands on gills, beaks of marine birds and snout of reptiles

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Human View of Light

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biased view of light because we can perceive wavelengths within only part of the range (violet (short wavelength) to red (long wavelength))

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Insects, Fish and Some Birds View of Light

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can see ultraviolet wavelengths

-used by insects to find flowers

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Light's Importance

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ecologically important in photosynthesis, vitamin D production, orientation and perception of the world

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Shade Tolerance

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ability of plants to survive in reduced light

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Shade Benefits

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shade may reduce light while providing other better conditions such as wind break, increased humidity, moderate temperature

adaptation to survive low light allows use of the other favorable conditions

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Shade Tolerance Example

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think of local forests: what do you find in the understory?

dogwood, ironwood, holly, etc.

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Shade Intolerance Example

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Trees in the overstory that only occur as small trees in an opening are intolerant

hickory, walnut, sweetgum

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Photoperiod

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length of light and dark portions of a day

varies seasonally (solstice is long and short, equinox is equal)

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Photoperiod Info

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most accurate of environmental cues (temperature, rainfall, etc. are more variable)

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Short-Day and Long-Day Plants

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depend on short enough or long enough days to bloom: snowshoe rabbit may depend on shortness of days

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Effect of Photoperiod

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is more pronounced in temperate regions and is relatively insignificant in the tropics, thus other cues such as rainfall must be used

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The Actual Effect of Photoperiod

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is tied to a circadian rhythm

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Circadian Rhythm

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the cycle of responsiveness to stimuli over a 24-hour period

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Soil

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a complex system of mineral, organic, gas, water, and living components

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Soil Component Balance

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the particular balance the kind of plants that can occur in it, thus of the animals as well

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Soil Organisms

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so many tiny organisms live in the soil that, if everything except them was removed, the structure would remian the same

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Soil Forms from:

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mechanical weathering - wind and water crack parent rock

chemical weathering - pH factors causing dissolution and leaching

biological weathering - earthworms and other life move materials about, aerate or further break up and mix soil

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Soil Formation

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usually begins from the exposed surface (top), so soil develops a vertical structure called a soil profile

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Soil Profile

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can be recognized in 3 primary layers (horizons)

topsoil (A horizon), B horizon has almost no organic material and less weathered mineral material, C horizon has generally unaltered parent material

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Soil Parent Material

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determines the kins of mineral determines the kinds of minerals available which may support, or be limiting to, vegetation

the type of vegetation further affects soil formation depending on which minerals are absorbed by them

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Particle Sizes

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determine soil texture, thus its ability to hold moisture

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Silt and Clay

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small so hold moisture well, may be fertile

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Sandy Soils

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well aerated but do not hold moisture well and may be infertile

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Fire

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traditionally it has been viewed by humans as destructive (USFS and Smokey the Bear)

In natural history, it played an important role in the development and maintenance of several ecosystems, naturally started by lightening strikes

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Use of Sections of Trees

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sections of trees several hundred years old have been used to estimate fire frequency and direction due to scarring

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Surface Fires

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are "cool", may scorch tree bases, kill some stems, but mostly consumes litter and herbs

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Ground Fires

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subterranean, burns slowly often where there is a thick litter

hot, kills most plants, even burns bogs as it dries peat in front of it

worst type of fire

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Crown Fires

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in dense woody vegetation, spreads through canopy killing vegetation from ground up

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Effects of Fires

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depends on the probability of a fire occurring, thus the adaptation of plants to fire frequency

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Surface fires may kill..

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above-ground stems of herbs so these can sprout again from underground parts

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Thick-Barked Trees

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are adapted to withstand surface fires (fires relatively frequent)

-often there are several sprouts (a forest with trees with multiple trunks indicates fire)

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Plant Requirement of Fire
Pines

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for successful reproduction some pines have cones that remain on trees and do not open unless the cones are heated: because the seeds are only occasionally released the new stands are even-aged

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Plant Requirement of Fire depends on...

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predictable fire frequency

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Predictable Fire Frequency

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tends to be a function of climate

drier forests are easier to ignite by the natural source of fire - lightning strikes

most likely habitats are between cold-hot and wet-dry environments

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Predictable Fire Frequency Example
Longleaf pine

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Southeastern U.S.

-"wiregrass stage"- long needles form a protective crown with protected bud

-stays this way 3-7 years, storing energy and growing root systems

-suddenly bursts upwards 8-18 feet in 2-3 years, putting the bud out of reach of most fires

-Nature Conservancy efforts to preserve forest by preventing fire failed (fire was required to maintain it)

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Predictable Fire Frequency Example
True Prairie

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true prairie is maintained by burning each 1-3 years to kill woody growth

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Fire Management

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developed in relation to species of interest (those adapted to fire) and to its indirect effects

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Fire Effects

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-fire removes vegetation so allows more light to the ground

-fire frees inorganic nutrients for plant growth and results in shoots that are more nutritious for herbivores

-fire aids germination of seeds that germinate on bare ground

-fire-darkened soil also absorbs more heat and becomes drier, and erosion may be increased

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Populations

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made of individuals but have unique characteristics

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Individual vs. Population

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individual can be born or die once, has an age and usually one sex

populations has a sex ratio and age structure, and can be "born" or "die" several times

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A population can..

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grow through births and immigration and can decline by death or emigration

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Birth rate

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aka natality rates

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Death Rate

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aka mortality rates

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Closed Population

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(no immigration or emigration)
only these rates affect population size

b=d -stable
b>d -increasing
b<d -declining

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Life Tables

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first developed by actuaries for insurance purposes, later adapted by biologists

summarizes statistics of death and survival of a population in an age-specific manner

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Concept of a Life Table 1

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the concept assumes that you have knowledge of the entire reproduction in a specific year (a cohort), and that you can follow their survivorship until all have died

-this allows calculation of an age-specific table

-the life tabled derived is valid only for the population it examines (maybe many years ago)

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Concept of a Life Table 2

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-most survivorship and mortality data are collected based on several cohorts all alive at one time

-to be able to calculate life table variables, then, you must assume that r=0
-otherwise, the demographic variables cannot be true

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Time-Specific Life Tables

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are based on a sample collected at one time, thus representing several cohorts

if several years of data are required to have a large enough sample for analysis, the life table is a composite one

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Calculation of Variables

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most variables in a life table can be calculated from other variables, so it is important to recognize the type of data collected

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life history data

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represents a sample of the living -catch, age, release

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death history data

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a sample of the dying - find dead animals or skulls and determine the age at death

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problem with data

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trapped furbearers are killed- which type of data are they?

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death history

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used to calculate mortality rates (qx), then other variables

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life history

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used to calculate survivorship rates (lx), then other variables

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How to sampe and calculate Life Table variables

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read in notes~

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Survivorship Curves

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made by plotting the lx series (dependent variable) against the x (age) column (independent variable)

-the lx series is plotted on semilog paper (alternately, logs can be plotted)

-the resulting curve gives information about changes in survivorship through life

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Type I Survivorship Curve

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(convex) curve has high survivorship early, then most of the population dies in a relatively short time (humans in developed countries)

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Type II Survivorship Curve

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(diagonal) curve indicates a constant probability of dying - each age class is affected proportionately by mortality (some species of mammals)

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Type III Survivorship Curve

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(concave) curve indicates high juvenile mortality then better survivorship later in life (fish, insects)

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Survivorship Curves Most Species

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most species have curves that represent mixes of these hypothetical types

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Exponential Population Growth

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based on biotic potential: inherent capactiy of a species to reproduce successfully, assuming optimum conditions and thus no environmental resistance

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Exponential Population Growth aka

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intrinsic rate of natural increase (r), it is the relationship between birth and death rates under the best of conditions

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Exponential Growth Curve

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a "J-shaped" curve, with a slow start then a very rapid ascent

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Biotic Potential

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is seldom realized because there is environmental resistance and conditions are seldom optimal

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Biotic Potential varies in different species according to their life histories, depending on :

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1)number of offspring per breeding period (per litter or clutch and # of litters or clutches)

2)survival through reproductive age

3)age of first reproductive age

4)length of reproductive age

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Biotic Potential Example

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mammals - rodents depend on plants (herbivores) so must be able to respond quickly to availability of seeds or shoots

-carnivores cannot afford to respond too quickly - if the rodent populations suddenly peaked then crashed as the predator population increased, most predators would die

-within the rodents, herbivores (meadow mice) have higher r than carnivores (grasshopper mouse)

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Species with a High r

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-can invade new habitats or rebound from population crashes more quickly than those with lower r

-thus, species with high r often are found in unstable environments and species with lower r in more stable environments

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Age of First Breeding

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one of the most important factors influencing high vs. low biotic potential (r) is age of first breeding, because earlier breeders have offspring who also are reproducting before late breeders have started themselves

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Age of First Breeding Effect on Biotic Potential Example

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r varies within a species at different times as well as between species

-wolves from high-density populations produce more males (slows r) but wolves from low-density populations produce equal sexes or more females (>r)

-coyotes and bobcats may breed in their first year in low-density populations but may not breed until the 2nd or 3rd year in high-density populations

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Geographic Ranges

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geographic ranges of species approximately are equal to the area in which r is greater than or equal to 0

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Logistic Growth

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when biotic potential is approximated, the growth curve is exponential, but the environment sets limits on growth, which alters the "J-shaped" curve to a sigmoid ("S-shaped") curve

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If logistic growth is observed..

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it is the result of environmental resistance which increases with population density

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Carrying Capacity (K)

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the population size that a habitat can support

dynamic concept

-populations may overshoot K then decline and fluctuate

-lags may allow the population to grow beyond K until the effects of passing K are felt

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Allee Effect

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optimal density is above minimal density

-undercrowding may be important, especially if cooperation is important

-often regarded as when optimum success occurs at an intermediate rather than minimum density

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Allee Effect Example

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maybe Florida pather

-low density so can't find mates and mates you do find may be related (due to inbreeding depression)
both of these lead to <r

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Ecology models

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models help us understand aspects of ecology, but these are mathmatical formulations typically based on untenable assumptions

-still, they allow us to grasp some underlying principles

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Exponential Growth Model

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Represented by a differential equation

dN/dt = rN
(you can calculate r by knowing changes in N and t)

N = N e
(to get change in population size)
- r is instantaneous (such as a speedometer - instantaneous reading)
- e is the base of natural logrithms

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Logistic Growth Model

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(formig the sigmoid curve) depends on a dampening effect as the population approaches K

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

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Logistic Growth Model 2

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some populatins may have time lags before actually reacting to changes in the environment: the preceding equations assume the reaction is instantaneous

To make the logistic equation more sensitive to such effects:

equation:

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Logistic Growth Equation Variables

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t-c represents population size at an earlier time (t is present time, c is time interval required for the population to respond, lag time)

t-w represents depressing effects of crowding (approaching K) that are not felt immediately, so the depressing effects depend on the size of the population at an earlier time (w is time interval required)

c and w may or may not be the same interval

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Intrinsic Rate of Increase

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can be calculated from life table data when fecundities (# of offspring) are known per age group (m series)

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Generation Length

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(T)

length of time from birth of parents to birth of offspring

T=

these values are part of the life table

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Generation Length Notes

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x should represent the age class, not age - what if the 1st class was 0?

l series represents probabilities

equations:

Notes:


R is called net reproductive rate

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Density

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number of individual in a unit a space

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Density Stability

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densities often are rather stable (mild fluctuations), indicating some degree of natural regulation

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Natural Regulation

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for this to occur, individuals in local populations must transmit and receive information about crowding or local habitat conditions so overcrowding might be avoided

ex. birds give territorial songs

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If regulation occurs due to density

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density-dependent factors: a sort of negative feedback mechanism

-density-dependent factors may cause decrease in reproduction, increase in mortality, increase in emigration, or decrease in immigration:

b+i=d+e (stable)
b+i>d+e (increasing)
b+i<d+e (declining)

density may equilibrate to K in several ways

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Carrying Capacity

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usually determined by one or more of climate, food, and space

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Carrying Capacity Example

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if forestry practices removed dead, hollow trees, the limiting factor might be nest sites: placing nest boxes could increase K for cavity nesters

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K is Dynamic...

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depending on the time of interest

ex: K for summer when more food is available is higher than in winter

-often, K is viewed as the number that could, in a particular environment, live to be part of the next reproductive population

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Subdivision of Density-Dependent Factors
Extrinsic Factors

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factors that are outside of the organism's control

ex. predation, parasitism (host as islands), disease, interspecific competition)

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Subdivision of Density-Dependent Factors
Intrinsic Factors

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factors that are responses originating within the population

ex. intraspecific competition, immigration and emigration, physiological and behavioral responses affecting reproduction and survival (lab rat population)

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Intraspecific Competition
Exploitative (Scramble) Competition

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each individual tries to gain as much of the resource as possible (those not as able to exploit lose out)

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Intraspecific Competition
Interference (Contest) Competition

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individuals attempt to exclude others from gaining the resource

-animals may do this by being territorial

-plants may accomplish this be releasing inhibitory chemicals

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Human Population Growth

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based on technology

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Sanitation and Medical Care

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better of these decreases death rate and increases reproductive success (prematures, fertilization, etc.)

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Europe

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burgeoning Europe invaded and occupied (emigration) Africa, Australia, the Americas

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Agricultural Technology

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has increased K over hunter-gatherer levels

-however the world still is finite

-effects of supplemental feeding eventually would starve all individuals

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Agricultural Technology
Water

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even with fertilizers and genetic engineering, water still is required and we can't really change this one

-aquifers (ground water) are being over-used, are drying up, and cannot be replenished

-water wells already have to be dug deeper and deeper to reach water

-arid adapted plants with long root systems would die because the water is out of reach