Ecosystem Dynamics and Nutrient Cycling

• Ecology is the study of relationships between biotic and abiotic components of the environment.
• Ecosystem ecology focuses on the interactions of larger-scale organisms in cycling energy and matter.
• Equilibrium in ecosystems and communities remains dynamic, with fluctuations occurring within a range that supports living organisms.
• Ecologists determine the scale at which they conduct their studies.
• The biosphere is the Earth’s living part.

Biosphere Components

• Hydrosphere
• Lithosphere
• Atmosphere
• Biomes are regions with characteristic temperatures, precipitation levels, and biotic communities.

Biome Types

• Aquatic
• Terrestrial
• An ecosystem is a smaller region containing a defined group of biotic and abiotic factors.
• A community comprises interacting populations of organisms.
• A population consists of organisms of the same species in the same location and time.
• An organism is an individual member of a species.

Ecosystem Terminology

• Organisms fulfill various roles within their communities and ecosystems.
• Diet usually defines an organism's role.
• Niche is the role an organism plays, as well as the habitat it occupies.

Diet Types

• Autotrophs produce their own nutrients and support all other organisms in the community.

Autotroph Types

• Photoautotrophs make food through photosynthesis.
• Chemoautotrophs use heat and inorganic molecules to produce food through chemosynthesis.
• Heterotrophs need to consume other organisms to meet their nutritional requirements.
• The suffix 'troph' means 'feeder'.
• Trophic level indicates an organism's position in the food chain or web, based on its diet.
• Producers, or autotrophs, form to the base of the food chain.
• Consumers are heterotrophs.

Consumer Types

• Primary consumers eat autotrophs and are herbivores.
• Secondary consumers eat primary consumers and are carnivores.
• Tertiary consumers eat secondary consumers and may be apex predators.
• Quaternary consumers exist only in ecosystems with significant energy and are apex predators.
• Detritivores consume dead or decaying material and are critical for waste recycling in ecosystems.

Detritivore Examples

• Cockroaches
• Millipedes
• Decomposers break down material outside their bodies.

Decomposer Example

• Fungi secrete enzymes onto material and then absorb small molecules.
• Omnivores feed on two or more trophic levels and consume both animals and plants.
• Models demonstrate how systems function.
• Ecologists models to track matter and energy flow from the abiotic environment through organisms within a system.
• Models are simplified versions of the natural world.
• Food chains are the simplest ecological model.
• Food chains illustrate one organism at each trophic level starting with producers.
• Arrows in food chains indicate the flow of matter and energy.
• Removing an organism from the chain will impact others.
• Food chain length is limited by thermodynamics' second law.
• Energy is lost at each transfer from one trophic level, through chemical bonds, waste products and organism activity.
• Food chains are useful and need to be interpreted.
• Ecosystem elements may be missing from food chains.
• Food webs include more organisms and illustrate relationships more accurately, making them harder to interpret.
• Tracking matter and energy transfer allows for the identifying the consequences of environmental changes.
• Biomagnification occurs when environmental toxins concentrate higher up in a food chain.
• Biomagnification should not be confused with bioaccumulation, which is the buildup of a contaminant in an individual over time.
• Feeding the population will become more challenging as populations rise.
• There is a trend toward increased meat consumption as countries industrialize.
• More people could be fed on a plant-based diet or by including insects in the diet, due to energy efficiency.
• Ecological pyramids show the relative amounts of material/energy at each trophic level.
• Dimensions of the pyramid sections correspond to the amount of material/energy at the respective level.

Types of Ecological Pyramids

• Numbers
• Biomass
• Energy
• A pyramid of numbers indicates the count of organisms at each trophic level, which may include multiple species.
• Pyramids of numbers can be inverted or spindle-shaped, based on the food chain construction and organism size at the base.
• One large producer can support an entire food chain.
• Numerous parasites can live on a single host.
• A pyramid of biomass shows the dry mass of materials in each trophic level.
• Biomass pyramids may be inverted, commonly in aquatic settings where producers and primary consumers are small.
• A pyramid of energy depicts the chemical energy at each trophic level, measured in kJ or kcal.
• Energy pyramids are always upright.
• The 10% rule says only 10% of the energy in one trophic level makes it to the next.
• Energy transfer can be calculated by multiplying the energy at the first level by 0.10 to find the energy at the next level.
• Organisms use energy to survive: finding food, water, shelter, escaping predators.
• Energy is lost as CO2, urine, and feces and is radiated as heat (mammals).
• Our bodies have regulatory systems to keep us healthy and to maintain equilibrium.
• Healthy ecological feedback systems maintain populations at a size that the environment can support (carrying capacity).
• Healthy feedback systems maintain fluctuating moisture, energy, and nutrient levels, which support the community.
• Biodiversity exists in healthy ecosystems, where many trophic levels are supported.
• Trophic cascades occur when an organism is removed from an ecosystem.
• Trophic cascades are similar to falling dominoes.
• Wolves in Yellowstone are keystone species at the top of the food chain, that support layers below.
• When otters were removed from the north pacific, sea urchin populations ate all the kelp.
• Kelp forests are critical habitats for many ocean species.
• Ecosystem engineers are animals that modify habitats to support other ecosystem organisms.

Ecosystem Engineer Examples

• Beavers turn rivers into rich wetlands that filter water and enrich soil.
• Elephants prevent trees from taking over grasslands and create water channels in the rainy season.
• Trophic cascades in disturbed ecosystems point to solutions.
• Restoring/protecting keystone species or ecosystem engineers helps ecosystems recover.
• Terrestrial ecosystems are based on primary producer productivity.
• Light energy that photoautotrophs convert drives energy transfer within an ecosystem.
• Matter, energy, and nutrients move through trophic levels as consumers eat producers.
• Plants absorb nutrients in the soil and assimilate them.
• Soil is the foundation of terrestrial ecosystems.
• Soil provides the substrate for roots and is a storage reservoir for plant nutrients.
• Litter is the top soil layer consisting of organic matter like dead leaves, grasses, and feces.
• Decomposers and detritivores in the litter layer break down materials, making nutrients accessible to plants.
• Topsoil contains small rocks with partially decomposed matter, known as humus and is rich in nutrients.
• Subsoil contains more rock and less organic matter.
• Bedrock is solid rock at the end of the soil layer and may be impermeable, allowing water accumulation above it.
• Soil quality affects plant community diversity and productivity of an ecosystem.
• Plant community dictates animal community diversity.
• Plant diversity provides organic molecules for heterotrophs to feed on and creates micro-habitats for animals to specialize in.
• Plant diversity increases the amount of niches in an ecosystem.

Forest Structure

Forest Floor

• Home to decomposing matter, decomposers, detritivores, other organisms that rely on them, or organisms that can’t climb. It is also cool and moist, with plants adapted to low light.

Understory

• Consisting of trunks of taller trees, shrubs, and shade tolerant plants it is cooler and relatively free of wind.

Canopy

• Contains most leaves from trees and plenty of fruit and light.

Emergent Layer

• Has extra tall trees with intense sunlight.
• Nutrients move through ecosystems via absorption in the producers to the consumption and assimilation in consumers but also through abiotic processes.
• Some nutrients are stored in the biosphere.
• Abiotic processes like the hydrologic cycle can help move some nutrients around.

Hydrologic Cycle Elements

• Precipitation (rain and snow)
• Condensation (cloud formation)
• Evaporation (liquid to gas)
• Transpiration (evaporation from stomata)
• Percolation (water movement through soil)
• Leaching (water dissolving nutrients)
• Watershed (land area that supplies water for a river/body of water).
• Water table (level of ground water under soil)
• Runoff/overland flow when soil is saturated and water flows over top into bodies of water.
• Nitrogen is a critical nutrient for plant growth.

Nitrogen's Role in Plants

• Chlorophyll component
• Component of amino acids and proteins
• The largest reservoir of nitrogen is N2 gas in the atmosphere, unusable until it is converted.
• Plants can absorb nitrates (NO3-), ammonia (NH3), ammonium (NH4+), & sometimes nitrites (NO2).
• Plants and animals assimilate organic nitrogen forms like amino acids.
• Atmospheric nitrogen gas needs to be fixed into bio-available forms.
• Nitrogen fixation turns N2 gas into biologically available nitrogen via lightning; it can bind N to O in the atmosphere.
• Nitrifying bacteria also fix N.
• Nitrification creates nitrates from other nitrogen sources and is similar to nitrogen fixation.
• Nitrifying bacteria convert organic nitrogen into nitrates, which can be found in aerobic reaction on the roots of plants.
• Denitrification is anaerobic.
• Denitrification forms nitrites from nitrates and N2 gas, which is no longer available,.
• Ammonification forms ammonia from other nitrogen sources like urine, feces, or decomposing organic matter (proteins).
• Phosphorous is not stored in the atmosphere, the main reservoir is sedimentary rock is phosphorus.
• Phosphorous is biologically available in the form of phosphate (PO4 3-), in cell membranes, nucleic acids, and in calcium phosphate (in bones & shells).
• Phosphorous interacts in both short and long cycles.

Phosphorous Cycles

• Short cycle - moves phosphorus around in a food chain.
• Long cycle - involves geologic activity.
• Animal waste (bird and bat feces) is a rich source of P that is absorbed and assimilated by plants and then animals.
• P also comes from broken-down shells of marine animals.
• Sedementation is when phosphorus is sunk out of the ecosystem.
• Sediments becomes stored inside rock formations.
• Uplift or upwelling occurs when tectonic activity pushes the rock to the surface.
• Weathering occurs when lichen release phosphorus to be absorbed.
• Lichens secrete enzymes onto the surface of rock to liberate nutrients.
• Law of the minimum says the least supplied nutrient will restrict productivity and growth.
• Example: A phytoplankton requires 10 C, 6 N, and 4 P, but there is 30 C, 18 N, and 5 P. The one phytoplankton can be produced because there is only enough P for one.
• Eutrophication occurs when the contamination of water bodies with phosphorus occurs.
• Phosphorus is a common component of fertilizer and was a common component of detergents.
• Depth affects light levels in aquatic ecosystems.
• Deeper bodies of water have aphotic (lightless) zones and they cannot rely on photosynthetic organisms and shallow waters are photic zones.
• Turbidity indicates water clarity, with dirt, silt, phytoplankton, and algae making the water turbid.
• Turbid areas are likely to have cellular respiration (decomposition) outpace photosynthesis and uses a secchi disk.
• Soil regions with light and soil support more organisms, aquatic plants provide a diversity of habitats.
• Benthic zone refers to the soil region in aphotic zone with the benthos organisms who live in the zone.
• Littoral zone is where soil is reached by light and limnetic zone in the open water where light is available, and profundal zone for aphotic.
• Motion in the form of rapids and ripples stir water, choppy water is difficult for growth while also increasing dissolve gases.
• Temperatures are cooler with dissolve gases so they are more produce more nutrient rich.
• Warmer waters can be hospitable however nutrients can easily be depleted.
• Density is maximized at 4°c, and water is stratified leading to different temperatures and densities.
• Stratified because of slight differences in the temperature, 0°C is less dense and under that life cannot grow.
• Temperate zones create zones because of density and temperature differences which is known as themocline.
• Water is above the thermocline in the epilimnion, which create nutrients locked in the bottom of lakes called hypolimnion in summer.
• Mixis pushes nutrients and provides them to limnetic organisms and oxygen to benthic.
• N & P from fertilizers create result in eutrophication within the system and as organisms dies will decrease depth due to decomposition.
• There are lakes that have more productivity which leads to more decomposing matter, they become shallow and murky however over time there become oligotrophic.
• Eutrophication over time leads to algal blooms and sun cannot permeate, reduces oxygen levels.
• PH is influenced through surroundings, runoff, plants and pollutants from sulfur.
• A low range is very damaging and needs a narrow range to support the water and need cellular respiration.
• Influence by motion of water, temperature is needed to be required and when decomposers use water it reduce oxygen.
• Estrogen are mimicked by birth control pills (mimic) which is difficult to remove .
• Coliform bacteria is contaminated from poop and residue from where animal reside, is indicative of waste problem which in returned is contaminated.
• Aquactic invertebrates that cause tolerance needs some type of pollution.
• Amphibian completes gas exchange through their skin which indicates the change in chemical and physical components.
• Amphibian at different food chains may be effected at larvae stage at a point in time, with moisture rely more fungal infections is possible.

Explore ecosystem keystone species and their removal impact. Discuss ecosystem engineers like beavers and their environmental modifications. Analyze the role of the litter layer and topsoil in nutrient cycling, and how plant and animal communities relate.