Population Ecology

• How do populations grow?

Growth = birth rates > death rates

Decline = birth rates < death rates

Zero Growth = birth rates = death rates

Population Growth Models

• Exponential Growth

• Logistic Growth

Exponential Growth Model

• J-shaped curve

• If conditions perfect, then population grows by constant factor over time = unchecked growth

Ex: You count 2 deer in 1995

1996 = 4 deer

1997 = 8 deer

1998 = 16 deer,……..

rNdt

dN

K

NrN

dt

dN1

Exponential Growth Model

• Does Exponential Growth occur in the real world?

Yes & No …. Can only occur over short-time period…..something always regulates growth (Finite resources!)

Logistic Growth Model

• S-shaped curve

• Population grows exponentially for short time & then growth is checked by a limiting factor

• carrying capacity (K): # of individuals that the environment can maintain

rNdt

dN

K

NrN

dt

dN1

Logistic Growth Model

• Does Logistic Growth occur in the real world?

Yes & No …. Population growth is limited & populations do grow to near a K … but population dynamics do not end at K

initial carrying capacity

new carrying capacity

Logistic Growth Graph

Overshooting Capacity

• Population may temporarily increase above carrying capacity

• Overshoot is usually followed by a crash; dramatic increase in deaths Reindeer on St. Matthew’s Island

Limiting Factors

• Density-Dependent Factors: food, space, water, mates

• directly related to population density

Density-dependent Effects

Limiting Factors• Density-Independent Factors: fire,

floods, wind, urbanization• unrelated to population density

Resource Consumption• United States has 4.6% of

the world’s population• Americans have a

disproportionately large effect on the world’s resources (30% of consumption)

• Per capita, Americans consume more resources and create more pollution than citizens of less developed nations– 1 American = 20-40

persons from less developed nation

Human Population Problems• Over 6 billion people alive

• About 2 billion live in poverty

• Most resources are consumed by the relatively few people in developed countries

Community Ecology

Community: grouping of all species living & interacting in the same area, includes populations of different species

Properties of Communities

1) Species Richness = # species in a comm.

2) Species Evenness = relative abundance of different species

3) Species Diversity = richness & evenness

e.g., Four species (A,B,C,D) in 2 different communities

Comm 1 – 25A 25B 25C 25D

Comm 2 – 97A 1B 1C 1D

RichnessEvennessDiversity

Properties of Communities (cont)

4) Prevalent vegetation form

- vertical profile (trees, shrubs, grasses)- determine other organisms that are present

Properties of Communities (cont)

5) Trophic Structure (feeding structure)

- who eats whom?- determine energy flow in community- determine community structure

Energy Flow in Communities

food chain: sequence of organisms linked by energy & nutrient flow

trophic level: feeding level/position of organism in food chain

Trophic Levels Producer: (autotrophs) anchor of chain;

produce all organic matter for other organisms

Primary consumer: directly consume producers = herbivores

Heterotrophs (consumers)

Secondary consumer: consume herbivores

Tertiary & Quaternary consumers: consume secondary & tertiary consumers, respectively

Trophic Levels Decomposers: (detritus feeder) consume

and convert dead material for use by producers

Food Webs food web: interconnected food chains; all

trophic interactions in community

Bioaccumulation = Biomagnification

Properties of Communities (cont)

6) Stability

- recovery from disturbance (e.g., fire)

- depends on type of community & type of disturbance

What Happens in a Community?

1) Competition: individuals contest over a resource (food, space, water, mates…) – major factor determining structure

What Happens in a Community?

Types of CompetitionA) Interspecific: competition between

different species, e.g., blue jay & chickadee compete for sunflower seed at feeder

What Happens in a Community?

Types of Competition

B) Intraspecific: competition within the same species, e.g., 2 male bobcats compete for space

Principle of Competitive Exclusion (Gause’s experiments)• Two species

which compete for same resource cannot coexist in same place at same time

• Implications = different locations or different times

• Relates directly to niche concept

Niche Concept

Niche: functional role (“occupation”) & position (spatial & temporal) of a species in its community

• Principle of Competitive Exclusion = 2 species cannot occupy the same niche

What Happens in a Community? (cont.)

2) Predation: one species consumes another species

Predator: consumer of the other speciesPrey: the food species or the species to be

consumed

Predation & Community Diversity

• Predation maintains diversity

• Paine’s experiments with sea stars (a predator)

• keystone predator: predator which reduces density of most competitive species in community – leads to > diversity

What Happens in a Community? (cont.)

3) Ecological Succession: temporal sequence of one community replacing another; predictable

Major Ecosystem Processes

1) Energy Flow = energy moves through system

2) Nutrient Cycling = chemical elements recycled in system

Energy Flow

• Solar energy – primary energy source

Of incoming solar radiation:

66% absorbed

34% reflected (albedo)

Solar Energy

• Of solar radiation absorbed:

- ~22% water cycle

- nearly all transform to heat & radiates

emissivity: relative ability of Earth to release energy (e.g., radiate heat into space; link to global warming)

Solar Energy

• Tiny amount of solar energy into photosynthesis (~1%)

photosynthesis (PNS): use solar energy to convert CO2 & H2O into sugar; by-product = O2primary production: all organic matter resulting from PNS; raw material for other organisms (gross production vs. net production)

Pyramid of Energy Flow

• Primary producers trapped about 1.2% of the solar energy that entered the ecosystem

• 6–16% passed on to next level

21

383

3,368

20,810 kilocalories/square meter/year

top carnivores

carnivores

herbivores

producers

decomposers + detritivores = 5,080

Figure 30.8aPage 544

Nutrient Cycles

What does the Law of Conservation of Matter state?

• circular flow of chemicals = recycling• Inputs & relationship to energy flow?

• Water, Carbon (C), Nitrogen (N), Phosphorus (P), Sulfur (S)

Hydrologic Cycleatmosphere

ocean land

evaporation from ocean

425,000

precipitation into ocean 385,000

evaporation from land plants (evapotranspiration)

71,000

precipitation onto land 111,000

wind-driven water vapor40,000

surface and groundwater flow 40,000

Hubbard Brook Experiment

• A watershed was experimentally stripped of vegetation

• All surface water draining from watershed was measured

• Removal of vegetation caused a six-fold increase in the calcium content of the runoff water

Hubbard Brook Experiment

losses fromdisturbed watershed

time ofdeforestation

losses fromundisturbed watershed

Global Water Crisis

• Limited amount of fresh water• Desalinization is expensive and requires large

amounts of energy• Aquifers are being depleted• Groundwater is contaminated• Sewage, agricultural runoff, and industrial

chemicals pollute rivers

Carbon Cycle

• Carbon moves through the atmosphere and food webs on its way to and from the ocean, sediments, and rocks

• Sediments and rocks are the main reservoir

diffusion between atmosphere and ocean

bicarbonate and carbonate in ocean water

marine food webs

marine sediments

combustion of fossil fuels

incorporation into sediments

death, sedimentation uplifting

sedimentation

photosynthesis aerobic respiration

Carbon Cycle: Marine

Carbon Cycle: Land

photosynthesis aerobic respirationterrestrial

rocks

soil water

land food webs

atmosphere

peat, fossil fuels

combustion of wood

deforestation

volcanic action

death, burial, compaction over geologic time

leaching, runoff

weathering

combustion of fossil fuels

Carbon in the Oceans

• Most carbon in the ocean is dissolved carbonate and bicarbonate

• Ocean currents carry dissolved carbon

Carbon in Atmosphere

• Atmospheric carbon is mainly carbon dioxide

• Carbon dioxide is added to atmosphere– Aerobic respiration, volcanic action, burning

fossil fuels

• Removed by photosynthesis

Greenhouse Effect

• Greenhouse gases impede the escape of heat from Earth’s surface

Carbon Dioxide Increase

• Carbon dioxide levels fluctuate seasonally

• The average level is steadily increasing

• Burning of fossil fuels and deforestation are contributing to the increase

Other Greenhouse Gases

• CFCs: synthetic gases used in plastics and in refrigeration

• Methane: released by natural gas production, livestock

• Nitrous oxide: released by bacteria, fertilizers, and animal wastes

Nitrogen Cycle

• Nitrogen is used in amino acids and nucleic acids

• Main reservoir is nitrogen gas in the atmosphere

Nitrogen Cycle

gaseous nitrogen in atmosphere

food webs on land

ammonia, ammonium wastes, remains nitrate

ammonification

fertilizers

uptake by autotrophs

excretion, death, decomposition

uptake by autotrophs

nitrite

nitrification

nitrificationloss by leaching

loss by denitrification

nitrogen fixation

loss by leaching

Nitrogen Fixation

• Plants cannot use nitrogen gas

• Nitrogen-fixing bacteria convert nitrogen gas into ammonia (NH3)

• Ammonia and ammonium can be taken up by plants

Human Effects

• Humans increase rate of nitrogen loss by clearing forests and grasslands

• Humans increase nitrogen in water and air by using fertilizers and by burning fossil fuels

• Too much or too little nitrogen can compromise plant health

Phosphorus Cycle

• Phosphorus is part of phospholipids and all nucleotides

• It is the most prevalent limiting factor in ecosystems

• Main reservoir is Earth’s crust; no gaseous phase

Phosphorus Cycle

GUANO

FERTILIZER

TERRESTRIAL ROCKS

LAND FOOD WEBS

DISSOLVED IN OCEAN

WATER

MARINE FOOD WEBS

MARINE SEDIMENTS

excretion

weathering

mining

agricultureuptake

by autotrophs

death, decomposition

sedimentationsettling

out leaching, runoff

weathering

uplifting

over geologic time

DISSOLVED IN SOIL WATER,

LAKES, RIVERS

uptake by

autotrophs

death, decomposition

Human Effects

• In tropical countries, clearing lands for agriculture may deplete phosphorus-poor soils

• In developed countries, phosphorus runoff is causing eutrophication of waterways

Ecosystem Management

• Optimal level of resource management

• Entire systems vs. pieces

• Goal = minimize human impacts on ecosystems so as to insure their integrity & health & therefore our health

• Manage at larger scale, e.g., Great Lakes Region Ecosystem NOT Michigan only

Biosphere

• Oceans

- cover ¾ of Earth

- Temperature & rainfall patterns (climate)

- Huge oxygen sources -- algae

- estuary: fresh water meets salt water; life-rich area

Biomes Terrestrial community of common climate

& unique species assemblages1) Tundra – permafrost

2) Boreal Forest -- conifers

3) Deciduous Forest – broad-leaves

4) Tropical Rain Forest – 70% of life

5) Tropical Savannah -- fire

6) Grassland -- treeless

7) Desert – low rainfall