AP Environmental Science - Ecosystems
Ecosystem Basics
Individual: One organism (e.g., elk).
Population: A group of individuals of the same species (e.g., elk herd).
Community: All living organisms in an area.
Ecosystem: All living and nonliving things in an area (e.g., plants, animals, rocks, soil, water, air).
Biome: The plants and animals found in a given region, determined by climate (e.g., tropical rainforest).
Organism Interactions
Mutualism: A relationship that benefits both organisms (e.g., coral reef).
Competition: Organisms fighting over a resource like food or shelter, which limits population size.
Predation: One organism using another for an energy source (e.g., hunters, parasites).
Commensalism: A relationship that benefits one organism and doesn’t impact the other (e.g., birds nesting in trees).
Predation (+/-)
True predators: Carnivores that kill and eat prey for energy (e.g., leopard & giraffe).
Herbivores: Plant eaters that consume plants for energy (e.g., giraffe & tree).
Parasites: Use a host organism for energy, often without killing the host, and often living inside the host.
Examples: mosquitoes, tapeworms, sea lamprey
Parasitoids: Lay eggs inside a host organism; eggs hatch and larvae eat the host for energy.
Examples: parasitic wasps, bot fly
Symbiosis
sym = together | bio = living | osis = condition
Any close and long-term interaction between two organisms of different species.
Mutualism (+/+), commensalism (+/0), and parasitism (+/-) are all symbiotic relationships.
Mutualism Example: Coral (animals) provide reef structure & CO_2 for algae; algae provide sugars for coral to use as energy
Lichen: composite organism of fungi living with algae; algae provide sugars (energy) & fungi provides nutrients
Competition
Resource partitioning: Different species using the same resource in different ways to reduce competition. Reduces population size since there are fewer resources available & fewer organisms can survive
Temporal partitioning: Using a resource at different times, such as wolves & coyotes hunting at different times (night vs. day).
Spatial partitioning: Using different areas of a shared habitat (different length roots).
Morphological partitioning: Using different resources based on different evolved body features.
Terrestrial Biomes
Biome: the plants & animals found in a region; based on yearly temp. + precipitation (climate)
The community of organisms (plants & animals) in a biome are uniquely adapted to live in that biome
Examples: camels & cacti have water preserving traits for desert; shrubs & wildflowers store lots of energy in roots to recover quickly from fire in grasslands
Biomes are defined by average annual temperature & precipitation
Biome chart can also predict where on earth biomes are found
Tundra & Boreal = higher lat. (60^o +)
Temperate = mid lat. (30^o - 60^o)
Tropical = closer to equator
Latitude (distance from equator) determines temperature & precipitation which is why biomes exist in predictable pattern on earth
Nutrient Availability
Tropical RF = nutrient-poor soil (high temp. & rainfall → rapid decomposition of org. matter; acidic soil + high rainfall → nutrient leaching)
Boreal forest = nutrient-poor soil (low temp. & low decomp. rate of dead organic matter)
Temp. forest = nutrient-rich soil (lots of dead organic matter - leaves & warm temp/moisture for decomposition)
Plants need soil nutrients to grow, so availability determines which plants can survive in a biome
* Ex: frozen soils of tundra don’t allow nutrients in dead organic matter to be broken down by decomposers, causing:
* Low soil nutrients
* Low water availability
* Few plants survive here
Shifting Biomes
Biomes shift in location on earth as climate changes
Ex: warming climate will shift boreal forests further north as tundra permafrost soil melts & lower latitudes become too warm for aspen & spruce
Characteristics of Aquatic Biomes
Depth
Influences how much sunlight can penetrate and reach plants below the surface for photosynthesis
Temperature
Warmer water holds less dissolved O_2 so it can support fewer aq. organisms
Salinity
How much salt there is in a body of water, determines which species can survive & usability for drinking (Fresh water vs. estuary vs. ocean)
Flow
Determines which plants & organisms can survive, how much O_2 can dissolve into water
Freshwater: Rivers & Lakes
Rivers have high O_2 due to flow mixing water & air, also carry nutrient-rich sediments (deltas & flood plains = fertile soil)
Lakes = standing bodies of fresh H_2O (key drinking water source)
Littoral: shallow water w/emergent plants
Limnetic: where light can reach (photosynthesis)
No rooted plants, only phytoplankton
Profundal: too deep for sunlight (no photosynthesis)
Benthic: murky bottom where inverts (bugs) live, nutrient-rich sediments
Freshwater: Wetlands
Wetland: area with soil submerged/saturated in water for at least part of the year, but shallow enough for emergent plants
Plants living here have to be adapted to living with roots submerged in standing water (cattails, lily pads, reeds)
Benefit$ of Wetland$
Stores excess water during storms, lessening flood damage to property
Recharges groundwater by absorbing rainfall into soil
Roots of wetland plants filter pollutants from water draining through
High plant growth rates due to lots of water & nutrients (dead organic matter) in sediments
Estuaries
Estuaries: areas where rivers empty into the ocean
Mix of fresh & salt water (species adapt to this ex: mangrove trees)
High productivity (plant growth) due to nutrients in sediments deposited in estuaries by river
Salt Marsh:
Estuary hab. along coast in temperate climates
Breeding ground for many fish & shellfish species
Mangrove Swamps:
Mangrove trees with long, stilt roots stabilize shoreline & provide habitat for many species of fish & shellfish
Estuary hab. along coast of tropical climates
Coral Reef
Warm shallow waters beyond the shoreline; most diverse marine (ocean) biome on earth
Mutualistic relationship between coral (animals) & algae (plants)
Coral take CO2 out of ocean to create calcium carbonate exoskeleton (the reef) & also provide CO2 to the algae
Algae live in the reef & provide sugar (energy) to the coral through photosynthesis
Both species rely on the other:
Coral couldn’t survive without energy from algae.
Algae need the home of the reef & CO_2 from the coral
Intertidal Zone
Narrow band of coastline between high & low tide
Organisms must be adapted to survive crashing waves & direct sunlight/heat during low tide
Ex: Barnacles, sea stars, crabs that can attach themselves to rocks
Shells & tough outer skin can prevent drying out (desiccation) during low tides
Open Ocean
Low productivity per m^2 as algae & phytoplankton can only survive in photic zone
Photic zone = area where sunlight can reach (photosynthesis)
Aphotic zone (abyssal) = area too deep for sunlight
Species rely on detritus from photic zone or chemosynthetic microbes @ hydrothermal vents for energy
So large that algae & phytoplankton of ocean produce a lot of earth’s O2 & absorb a lot of atmospheric CO2
Carbon Cycle Overview
Movement of molecules that contain Carbon (CO2, glucose, CH4) between sources and sinks
Some steps are very quick (fossil fuel combustion); some are very slow (sedimentation & burial)
Leads to imbalance in which reservoirs or sinks are storing carbon
Atmosphere is key C reservoir; increasing levels of C in atm. Leads to global warming
Carbon sink: reservoir that take in more carbon than it releases
Ocean (algae & sediments), plants, soil
Carbon source: reservoir that releases more carbon than it takes in
Fossil fuel (oil, coal, nat gas) combustion
Animal ag. (cow burps & farts = CH_4)
Deforestation, releases CO_2 from trees
Photosynthesis & Cellular Respiration
Photosynthesis
Removes CO_2 from the atmosphere & converts it to glucose
Glucose = biological form of C & stored (chemical) energy in form of sugar
Done by plants & algae, phytoplankton
CO_2 sink
Cellular Respiration
Done by plants & animals to release stored energy
Uses O_2 to break glucose down & release energy
Releases CO_2 into atmosphere
CO2 source (adds CO2 to atmosphere)
Both processes are very quick
Cycle C between biosphere & atmosphere in balanced amount (no net C increase in atm.)
Ocean & Atmosphere
Direct exchange: CO_2 moves directly between atmosphere & the ocean by dissolving into & out of ocean water at the surface
Happens very quickly & in equal directions, balancing levels of CO_2 between atm. & ocean
Because of direct exchange, increasing atmospheric CO2 also increases ocean CO2, leading to ocean acidification
Algae & phytoplankton: take CO_2 out of the ocean & atmosphere through photosynthesis
Coral, mollusks and some zooplankton also take CO_2 out of the ocean to make calcium carbonate exoskeletons
Sedimentation: calcium carbonate precipitates out as sediment & settles on ocean floor
Burial: over, long, periods of time, pressure of water compresses C-containing sediments on ocean floor into sedimentary rock (limestone, sandstone) - long-term C reservoir
Burial, Extraction, & Combustion
Burial: slow, geological process that stores C in underground sinks like sedimentary rock or fossil fuels
Sediments (bits of rock, soil, organic matter) compacted into sedimentary rock by weight of overlying rock layers or water
Fossil Fuels (FF): formed from fossilized remains of organic matter into coal (ex. plants) or oil (ex. plankton). Their decomposition produces natural gas (CH_4)
Extraction & Combustion: digging up or mining FFs & burning them as energy source; releases CO_2 into atmosphere
Burial (formation of FFs) takes far longer than extraction & combustion, which means they increase concentration of CO_2 in atmosphere
Nitrogen Cycle
N = critical plant & animal nutrient
Atmosphere = main N reservoir
Movement of N-containing molecules between sources & sinks/reservoirs
Sources release N into atmosphere; sinks take N out of the atmosphere in increasing amounts
N in atmosphere exists mostly as N_2 gas, which is not useable by plants or animals
All living things need N for DNA & amino acids to make proteins
N reservoirs hold N for relatively short periods of time compared to C cycle
Ex: plants, soil, atmosphere
Nitrogen Fixation
Process of N2 gas being converted into biologically available (useable by plants) NH3 (ammonia) or NO_3 - (nitrate)
Abiotic fixation: Lightning converts N2 gas into nitrate (NO3 -) and FF combustion converts N2 gas into ammonia (NH3)
Biotic fixation: certain bacteria that live in the soil, or in symbiotic relationship with plant root nodules convert N2 into ammonia (NH3)
Rhizobacteria live in root nodules of legumes (peas, beans) & fix N for them in return for amino acids from the plant (mutualism)
NH_3 is added to synthetic fertilizer and applied to agricultural soils (where it’s converted into nitrate)
Other N Cycle Steps
Nitrification: conversion of NH4 into nitrite (NO2 -) & then nitrate (NO_3) by soil bacteria
Ammonification: soil bacteria, microbes & decomposers converting waste & dead biomass back into NH_3 and returning it to soil
Assimilation: plants & animals taking N in and incorporating it into their biomass
Plant roots take in NO3 - or NH3 from soil; animals assimilate N by eating plants or other animals
Denitrification: conversion of soil N (NO3) into nitrous oxide (N2O) gas which returns to atmosphere
Human Impacts on N Cycle
Leaching & Eutrophication: synthetic fertilizer use leads to nitrates (NO_3) leaching, or being carried out of soil by water
Nitrates runoff into local waters, causing algae blooms that block sun & kill other aquatic plants
Climate: N_2O (nitrous oxide) = greenhouse gas which warm earthʼs climate
Produced by denitrification of nitrate in agricultural soils (especially when waterlogged/over watered)
Phosphorus Cycle
P cycle is very slow compared to C/H 2O/N cycles
Movement of P atoms & molecules b/w sources & sinks/reservoirs
Rocks & sediments containing P minerals = major reservoirs
Takes a long time for P minerals to be weathered out of rocks & carried into soil/bodies of water
No gas phase of P (doesn’t enter atmosphere)
B/c it cycles so slowly, it is a limiting nutrient, meaning plant growth in ecosystems is often limited by P availability in soil/water
P is needed by all organisms for DNA, ATP (energy), bone & tooth enamel in some animals
Phosphorus Sources
Major natural source of P is weathering of rocks that contain P minerals.
Wind & rain break down rock & phosphate (PO_4-3) is released and dissolved into water; rain water carries phosphate into nearby soils & bodies of water
Synthetic (human) sources of P = mining phosphate minerals & adding to products like synthetic fertilizers & detergents/cleaners
Synthetic fertilizers containing phosphates are added to lawns or ag. Fields; runoff carries P into nearby bodies of water
Phosphates from detergents & cleaners enter bodies of water via wastewater from homes
Weathering is so slow that P is often a limiting nutrient in aquatic & terrestrial ecosystems
Assimilation & Excretion/Decomp
Just like N, P is absorbed by plant roots & assimilates into tissues; animals assimilate P by eating plants or other animals
Animal waste, plant matter & other biomass is broken down by bacteria/soil decomposers that return phosphate to soil
Phosphate doesn’t dissolve very well into water; much of it forms solid bits of phosphate that fall to the bottom as sediment (sedimentation )
P sediments can be compressed into sedimentary rock over long time periods by weight of overlying water
Assimilation & excretion/decomp form a mini-loop within P cycle just like assimilation & ammonification in N Cycle, photosynthesis & resp. in C cycle
Sedimentation & Geologic Uplift
Geological uplift = tectonic plate collision forcing up rock layers that form mountains; P cycle can start over again with weathering & release of phosphate from rock
Eutrophication (too much N & P)
B/c they’re limiting nutrients in aquatic ecosystems, extra input of N & P leads to eutrophication (excess nutrients) which fuels algae growth
Algae bloom covers surface of water, blocking sunlight & killing plants below surface
Algae eventually die-off; bacteria that break down dead algae use up O_2 in the water (b/c decomp. = aerobic process)
Can occur from fertilizer runoff, human/animal waste contamination
Lower O_2 levels (dissolved oxygen) in water kills aquatic animals, especially fish
Bacteria use up even more O_2 to decompose dead aq. animals
Creates positive feedback loop: less O2 → more dead org. → more bacterial decomposition → less O2
Hydrologic (Water) Cycle
Movement of H_2O (in different states) between sources & sinks
Ex: precipitation = atm. (gas) → land or surface water (liquid)
Energy from sun drives the H_2O cycle
State of matter (solid/liquid/gas) as well as where water is moving are key in H_2O cycle
Ex: heat from sun causes liquid water in ocean to become a gas (evaporation) in atm.
Ocean = largest water reservoir
Ice caps & groundwater are smaller reservoirs, but contain fresh, useable water for humans
Evaporation & Evapotranspiration
2 main sources of water (processes that cycle it from liquid on earth back into the atmosphere)
Transpiration: process plants use to draw groundwater from roots up to their leaves
Sometimes called “vaporization” since liquid water becomes water vapor (gas) in atm.
Leaf openings called stomata open, allowing water to evap. into atm. from leaf
Mvmnt of H2O out of leaf creates low H2O potential in leaf, pulling H_2O up from roots
Evapotranspiration: amount of H_2O that enters atm. from transpiration & evaporation combined
Both processes are driven by energy from the sun
Runoff & Infiltration
Precipitation (rain) either flows over earth’s surface into a body of water (runoff) or trickles through soil down into groundwater aquifers (infiltration)
Groundwater (aquifers) & surface waters (lakes/rivers) are important freshwater reservoirs for humans & animals
Precipitation recharges groundwater through infiltration, but only if ground is permeable (able to let water pass through)
Runoff recharges surface waters, but can also carry pollutants into water sources
Primary Productivity
units: kcal/m2/yr.
Primary Productivity: rate that solar energy is converted into organic compounds via photosynthesis over a unit of time
Also known as rate of photosynthesis of all producers in an area over a given period of time
Since photosynthesis leads to growth, you can also think of PP as the amount of plant growth in an area over a given period of time
High PP = high plant growth = lots of food & shelter for animals
Ecosystems with high PP are usually more biodiverse (more diversity of species) than ecosystems with low PP
Calculating PP
Gross Primary Productivity (GPP): The total amount of sun energy (light) that plants capture and convert to energy (glucose) through photosynthesis
Net Primary Productivity (NPP): The amount of energy (biomass) leftover for consumers after plants have used some for respiration
*Respiration loss (RL): plants use up some of the energy they generate via photosynthesis by doing cell. respiration (movement, internal transportation, etc.)NPP = GPP - RL
Ecological Efficiency
The portion of incoming solar energy that is captured by plants & converted into biomass (NPP or food available for consumers)
Generally, only 1% of all incoming sunlight is captured & converted into GPP via photosynthesis (~99% of solar energy comes in wavelengths plants can’t use for photosynthesis & is reflected by or passes through them)
Of that 1%, an average of 40% (or 0.4% of total incoming solar energy) is converted into biomass/plant growth (NPP)
Some ecosystems are more efficient (higher NPP) than others
Trends in Productivity
The more productive a biome is, the wider the diversity of animal life it can support (high. biodiv.)
Water availability, higher temperature, and nutrient availability are all factors that lead to high NPP
Shortage of any of these three factors will lead to decreased NPP
Conservation of Matter & Energy
Matter & energy are never created or destroyed; they only change forms
Ex: Tree dies & the C/N/H2O/P are returned to the soil & atmosphere
Ex: Sun rays (light energy) hit leaves & are converted into glucose (chemical energy)
1st law of thermodynamics: energy is never created or destroyed
Biogeochem. cycles demonstrate conservation of matter (C/N/H2O/P)
Food webs demonstrate conservation of energy
Ex: When a rabbit eats a leaf, the energy from the leaf (glucose) is transfered to the rabbit & stored as body tissue like fat/muscle
2nd Law of Thermodynamics
Each time energy is transferred, some of it is lost as heat
Applied to food webs: the amount of useable energy decreases as you move up the food chain (organisms use up most of it for movement, development, etc.)
10% Rule: in trophic pyramids, only about 10% of the energy from one level makes it to the next level; the other 90% is used by the organism & lost as heat
Because available energy decreases with each step up the food chain, a trophic pyramid (troph = nourishment or growth) is used to model how energy moves through an ecosystem
Trophic Levels & 10% Biomass
Producers (plants) “produce”- really convert sun’s light energy into chemical energy (glucose)
Primary Consumers: animals that eat plants (herbivores)
Secondary Consumers: animals that eat primary consumers or herbivores (aka - carnivores & omnivores)
Tertiary Consumers: animals that eat secondary consumers or carnivores & omnivores (aka - top/apex predators)
10% rule also applies to biomass (or mass of all living things at each trophic level)
Since energy is needed for growth & only 10% of energy transfers from one level to the next, only 10% of the biomass of the previous trophic level can be grown/supported by the available energy
Calculating Biomass & Energy
To calculate biomass or energy available at the next level up, move the decimal place one spot to the left (or divide by 10)
Food Web Basics
Shows how matter & energy flow through an ecosystem, from organism to organism
When one organism preys on (eats) another, the matter (C/N/H2O/P) and energy (glucose, muscle tissue, etc.) are passed on to the predator
Arrows in food webs indicate direction of energy flow (point to the org. taking in the energy)
Food Web vs. Chain
Food chains just show one, linear path of energy & matter
Food webs have at least 2 different, interconnected food chains
Webs show that organisms can exist at different trophic levels
Interactions & Trophic Cascade
Food webs show how increase or decreases in population size of a given species impact the rest of the food web
Trophic cascade: removal or addition of a top predator has a ripple effect down through lower trophic levels