Ecology

Populations, Communities, Ecosystems

Population Growth Population: all indiv. of the same

species that live together in the same place at the same time

Demography: statistical study of populations

3 Key features of population: Population size

Tend to grow in size, b/c indiv. Have more than 1 offspring

Very small populations likely to become extinct

Population density Number of indiv in a given area Widely spaced are less likely to

reproduce Dispersion

Clumped (most common) Even Random

Population Models Models: hypothetical pop. w/key

characteristics of pop being studied Growth – more indiv. are born than

die r (rate of growth) = birth rate – death

rate Number of indiv added to pop as it

grows (ΔN) Exponential growth curve (ΔN vs.

time) Carrying capacity (K) – the pop size

that an environment can sustain Logistic model – accounts for

declining resources as pop grows As N approaches K the population

ceases to grow (birth rate = death rate)

Limiting Factors Density dependent Density independent

Strategies of Pop Growth

r-strategists Exponential growth than pop size

crashes Reproduce early in life, quick gestation Have many offspring at one time Offspring mature rapidly with little

parental care Live in changing environments Ex.

K-strategists Small pop size and slow growth Reproduce later in life, few offspring Offspring mature slowly and receive

parental care Live in stable environments Ex.

Human population Humans expanded carrying capacity of

environment Nearly 94 million people are added to the

population each year

How populations evolve

In order to understand how populations change in response to evolutionary forces, you need to understand how they evolve in the absence of these forces

Hardy-Weinberg Principle Early 1900’s scientists wondered if dominant alleles would

replace recessive alleles Mathematician GH hardy and physician Wilhelm Weinberg

independently demonstrated that dominant alleles DO NOT replace recessive alleles, frequency of alleles remains constant from one generation to the next unless evolutionary forces act upon them

Hardy-Weinberg Principle Populations do not change unless evolutionary

forces act upon them

Allele frequency: proportion of the group with a specific allele p: dominant allele q: recessive allele

Easily predict the freq of each genotype in a large, randomly mating populations Calculate freq of recessive allele Calculate the freq of dominant allele Determine the freq of heterozygotes

P2+2pq+q2 = 1 (AA)2 + 2(Aa) + (aa)2 = 1

5 Forces that cause Populations to Evolve

Mutation: ultimate source of genetic variation that makes evolution possible

Migration (Gene Flow): movement of alleles into or out of a pop

Nonrandom mating (Inbreeding): increases the proportion of homozygotes, deceases heterozygotes

Genetic Drift: in small isolated populations, allele frequencies are drastically affected by natural disasters

Natural Selection: directly changes freq of alleles

Patterns of Natural Selection Only characteristics that are

expressed can be selected for or against

Directional Selection – eliminates one extreme from a range of phenotypes and favors the other extreme

Stabilizing Selection – eliminates extremes at both ends of a range of phenotypes

Disruptive Selection – eliminates the intermediate phenotype…aids in speciation

Ecosystems Ecology: study of the interactions of

living organisms with one an other and their physical environment

Habitat: the place where a particular pop of species live

Community: many different species living together in a habitat

Ecosystem: community and physical aspects of habitat Biotic – living organisms Abiotic – physical aspects (non-living)

Biodiversity – variety of organism, genetic differences and the communities and ecosystems in which they occur

No distinct boundaries of an ecosystem

Changes in an ecosystem Physical Environment

Changes sets of colonization Volcano – creates an island Glacier recedes – new soil Eventually, organisms

colonize new habitat Succession – progression

of species replacement 10 succession: occurs on land

where nothing has grown before (pioneer species)

20 succession: occurs in a n area with previous growth (forest clearing, abandoned fields)

No 2 successions are alike!

Energy Flow

Energy flows thru Earth’s ecosystems in one direction

Producers, consumers, decomposers

Heterotrophs and autotrophs Herbivore, carnivore,

omnivore, detrivore Food chain & food web Only 10% of energy moves

to the next trophic level

Biogeochemical cycles: Water cycle

Biogeochemical cycles: substance enters living organisms, then returns to the non-living environment

Water Cycle – driven by the sun Nonliving (aquatic ecosystems)

Water vapor in atm. Condenses and precipitates to earths surface

Some water seeps into soil and becomes ground water retained by earth

Remaining water collects in lakes, rivers, and oceans where it is heated by the sun and evaporates into the atm

Living (terrestrial ecosystems) Water is taken up by plant roots Transpiration – sun heats earth

and creates wind currents which draw moisture out of leaves

Carbon Cycle 0.035% CO2 in air and dissolved

in water CO2 used by plants, algae,

bacteria to build organic molecules (photosynthesis)

CO2 returns to atm by 3 ways Cellular respiration Combustion/ burning

Carbon in wood Fossil fuels – remains of organisms

buried in sediments for thousands-millions of years (coal, oil, natural gas)

Erosion Marine organisms use dissolved CO2

to build shells (CaCO3) Shells covered with sediment – form

limestone, then erode when exposed

Nitrogen Cycle Atm 78% N2 Organisms are unable to use N2 Nitrogen Fixation: break the N2

triple bond and combines w/H to form ammonia (NH3) Occurs only in the absence of O2 Nitrogen fixing bacteria live in soil

and nodules underground Assimilation: absorption and

incorporation of nitrogen into plant and animal compounds (proteins, nuc. acids)

Ammonification: production of ammonia by bacteria during the decay of nitrogen containing organic matter Urea Dead organisms

Nitrification: production of nitrate (NO3

-)by bacteria from ammonia Denitrification: bacteria converts

nitrates into nitrogen gas

Phosphorus Cycle PO4

-3 found in rock and soil Dissolves in water and is absorbed by

plants Plants use PO4

-3 to build ATP and DNA Animals eat these plants and reuse

phosphorus When plants and animals die, bacteria in

the soil convert phosphorus in organic molecules back to PO4

-3

Phosphorus can move to other ecosystems Trapped in sediments form rock If rock is exposed, weathering

releases phosphorus Phosphorus level in freshwater is low

Prevents growth of photosynthetic algae

If added by humans (fertilizers/detergents), so much algae forms that fish and other invertebrates suffocate

Communities: How organisms interact

Coevolution: back-and-forth evolutionary adjustments between interacting members of an ecosystem

Coevolving in opposition Predation: one organism feeds on

another Parasitism: one organism feeds on

and usually lives on or in host (usually don’t kill host)

Defense Overcoming defense Competition: 2 spp use the same

resource (s) in short supply

Coevolving in Cooperation

Symbiosis: 2 or more spp living together in a close, long term association

Mutualism: both spp benefit

Commensialism: one spp benefits, the other is neither helped nor harmed

Niche Niche: the functional role a particular

spp performs in an ecosystem… multidimensional

Fundamental niche: the total niche an organism is potentially able to occupy within an ecosystem, the entire range of conditions it can tolerate

Realized niche: the part of the niche that the spp actually occupies Ex. Cape May Warbler & character

displacement Principle of competitive exclusion:

if 2 spp are competing, the spp that uses the resource more efficiently will eventually eliminate the other locally – no 2 spp can occupy the same niche

Predation can lesson competition among prey – promote biodiversity Ex. Sea stars eat bivalves

The Physical Environment

Climate depends on… The amount of E from the sun that

reaches diff parts of earth and seasonal variation in that E Equator – sun’s rays are

perpendicular Poles – rays spread out over grater

s.a. (less E) Earth’s daily rotation – prevents

build up of extreme temps 23.50 tilt – seasons further from the

equator Global pattern of atmospheric and

oceanic circulation created by unequal global distribution of solar energy Latitude Distance from ocean Elevation Position relative to mountain

ranges

Major Biological Communities Marine

Shallow water Open Sea Deep Sea

Fresh Water Strongly connected w/ terrestrial

habitat Wetlands

Lots plant growth Biomes: terrestrial communities

w/similar climate Tropical Rainforest Savanna Desert Temperate Grassland Temperate Deciduous Forest Temperate Evergreen Forest Taiga Tundra

Biome Project

You are to select a biome and research its biotic and abiotic characteristics. List and describe types of organisms you would expect to find there. Where in the world would you find this biome. And then select one of the following:

Create a 3-D shoebox model of the biome and create a new organism that is well adapted (in at least 4 ways) to its biome

Write a paper comparing and contrasting 2 biomes

Human Impact on the Environment

Acid Rain Coal burning power plants release

smoke high in sulfur Sulfur combines w/water vapor

sulfuric acid Rain & snow precipitate H2S back

to earth’s surface Northeast US has pH 3.8

Destruction of Ozone 1985 – discovered low conc of

ozone over Anatartica, now hole over the Artic too

More UV radiation to reach Earth’s surface, increase in skin cancer, cataracts, and retina cancer

Chlorofluorocarbons (CFC’s) are major cause of ozone depletion

CFC’s found in refrigerator coolant, air conditioners, aerosol propellant, foaming agents

CFS’s are banned in US

Global Warming

Excess CO2 released in atmosphere from burning fossil fuels

CO2 bonds absorb solar energy trapping heat, methane, and nitrous oxide

Greenhouse Effect: the warming of atmosphere as a result of greenhouse gases

Studies indicate direct correlation between amt of CO2 in atmosphere and temp increase over the last 130 years

Problem: rising sea level (already rose >5cm), if polar ice caps melt, sea levels would rise 150m flooding entire Atlantic Coast of N. America