Population Ecology How do populations grow Growth birth

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, ……. .

Exponential Growth Model • Does Exponential Growth occur in the real world? Yes & No …. Can only occur over shorttime 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

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

Logistic Growth Graph initial carrying capacity new carrying capacity

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 – 25 A 25 B 25 C 25 D Comm 2 – 97 A 1 B 1 C 1 D

Richness Evenness Diversity

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 Heterotrophs (consumers) Primary consumer: directly consume producers = herbivores 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 Competition A) 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 species Prey: 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 CO 2 & H 2 O into sugar; by-product = O 2 primary 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 top carnivores herbivores producers decomposers + detritivores = 5, 080 383 3, 368 20, 810 kilocalories/square meter/year Figure 30. 8 a Page 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 Cycle atmosphere wind-driven water vapor 40, 000 evaporation precipitation from ocean into ocean 425, 000 385, 000 precipitation onto land 111, 000 evaporation from land plants (evapotranspiration) 71, 000 surface and groundwater flow 40, 000 ocean land

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 from disturbed watershed time of deforestation losses from undisturbed 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 photosynthesis combustion of fossil fuels aerobic respiration marine food webs death, incorporation sedimentation into sediments uplifting sedimentation marine sediments Carbon Cycle: Marine

atmosphere combustion of fossil fuels volcanic action terrestrial rocks weathering photosynthesis aerobic combustion respiration of wood land food webs deforestation soil water leaching, runoff death, burial, compaction over geologic time Carbon Cycle: Land peat, 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 nitrogen fixation food webs on land fertilizers uptake by autotrophs ammonia, ammonium loss by leaching excretion, death, decomposition uptake by autotrophs wastes, remains nitrate ammonification nitrification nitrite loss by denitrification loss by leaching

Nitrogen Fixation • Plants cannot use nitrogen gas • Nitrogen-fixing bacteria convert nitrogen gas into ammonia (NH 3) • 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 mining FERTILIZER GUANO excretion uptake by autotrophs MARINE FOOD WEBS agriculture weathering DISSOLVED IN OCEAN WATER uptake by autotrophs weathering DISSOLVED IN SOIL WATER, LAKES, RIVERS death, decomposition sedimentation LAND FOOD WEBS death, decomposition settling out leaching, runoff uplifting MARINE SEDIMENTS over geologic time TERRESTRIAL ROCKS

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 assemblages 1) 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