Ecology: Ecosystems and Communities

• Ecology refers to the relationships between the biotic and abiotic aspects of an environment.
• Ecosystem Ecology studies how larger-scale organisms interact to cycle energy and matter.
• In ecosystems and communities, equilibrium is dynamic such that fluctuations are normal, but factors usually stay within a range that supports the success and survival of living things.
• Ecologists study the biosphere.
• Biosphere is the living part of Earth as a whole, including the hydrosphere, lithosphere, and atmosphere.
• Biomes are regions of Earth that have characteristic temperatures, levels of precipitation, and biotic communities, and can be categorized as aquatic or terrestrial.
• Ecosystem is a smaller region with a somewhat defined group of biotic and abiotic factors.
• Community is a group of interacting populations of organisms.
• Population is a group of organisms of the same species in the same place at the same time.
• Organism refers to one individual member of a species.

Ecosystem Terminology

• Organisms play different roles in their communities and ecosystems, with their role is typically defined by diet.
• Niche is the role an organism plays and the habitat it occupies.

Diet Types

• Autotrophs produce their own nutrients and support all other organisms in the community.
• Photoautotrophs make food through photosynthesis.
• Chemoautotrophs use heat and inorganic molecules to make food through chemosynthesis.
• Heterotrophs must consume other organisms to meet their needs.

Trophic Levels

• The suffix 'troph' means 'feeder'.
• Trophic level refers to an organism's position in their food chain/web, based on what they feed on or who feeds on them.
• Producers are autotrophs, typically forming the base of the food chain/web.
• Consumers are heterotrophs.
• Primary consumers eat the autotrophs and are herbivores.
• Secondary consumers eat primary consumers and are carnivores.
• Tertiary consumers eat secondary consumers and may be apex predators.
• Quaternary consumers may exist, but only in ecosystems with lots of energy, and are apex predators.
• Detritivores eat dead or decaying material and are critical for waste recycling in ecosystems such as cockroaches or millipedes.
• Decomposers break down material outside their bodies, secreting enzymes onto material and then absorbing small molecules such as fungi.
• Omnivores feed on two or more trophic levels, and can eat both animals and plants.

Ecological Models

• Models demonstrate how we believe systems work.
• Ecologists use models to track the flow of matter and energy from the abiotic environment, through the organisms in a system.
• Models are simplified versions of the natural world.

Food chains

• The simplest ecological model illustrates one organism at each trophic level, starting with producers.
• Arrows indicate the flow of matter and energy.
• Removing one organism in the chain will affect the others.
• Food chain length is limited because of thermodynamics.
• Some energy is wasted at every transfer from one trophic level to the next, lost through chemical bonds in waste products, and some is used by the organism for various activities.

Food Webs

• Include a larger number of organisms.
• These are also more accurate because they illustrate more relationships but harder to interpret/ work with.

Applications

• Tracking how energy and matter are transferred allows identification of the consequences of changes made to the environment.
• Biomagnification occurs when environmental toxins become concentrated the higher up you go in a food chain.
• Biomagnification is not to be confused with Bioaccumulation: the buildup of a contaminant in one individual over time.

Feeding

• As global populations continue to rise, feeding the world will become more challenging.
• As countries become more industrialized, the trend is toward including more meat in the diet.
• In terms of energy efficiency, more people could be fed on a plant-based diet or insects.

Ecological Pyramids

• Used to show the relative amounts of material/energy at each trophic level.
• Dimensions of each part of the pyramid are proportional to the amount of material/energy at that level.
• There are 3 types, numbers, biomass, energy

Pyramid of Numbers

• The pyramid shows the number of all the organisms at each trophic level (each may include multiple species).
• May be inverted or spindle-shaped because of how the food chain is built and the size of the base organism.
• One single large producer can support an entire food chain.
• Numerous parasites (tertiary consumers) can live on a single host.

Pyramid of Biomass

• Shows the dry mass of materials present in each trophic level.
• The pyramid may be inverted, common in aquatic environments where producers and primary consumers are small.

Pyramid of Energy

• Shows the amount of chemical energy present at each trophic level, typically in kJ or kcal.
• Always an upright pyramid because they illustrate the limit of energy transfer from one level to the next.

10% Rule

• Only 10% of the energy in one trophic level makes it to the next.
• The amount of energy transferred from one level to the next can be calculated by multiplying the energy in the 1st level by 0.10.
• Energy is used by organisms to survive, lost from organisms in the form of chemical bonds (CO2 they breathe out, urine, feces) or radiated out in the form of heat from mammals.

Ecological Feedback & Trophic Cascades

• The body has feedback and regulatory systems to remain healthy and maintain equilibrium.

Ecological feedback

• A healthy feedback system in ecology is when populations remain at the size that the environment can support (carrying capacity).
• Healthy feedback systems maintain moisture, energy and nutrient levels that fluctuate, but still support the community.
• There is biodiversity in healthy ecosystems and as many trophic levels as can be supported.
• Trophic cascades occur when an organism is removed from an ecosystem.
• These events can be similar to a series of falling dominoes.
• Such as wolves removed from Yellowstone.
• The wolves were a keystone species, where animal at the top of the food chain stabilizes everything below.
• As well as the otters from the north pacific, where when otters were removed, there was no predator to keep sea urchins in check.
• And as urchin populations exploded, they ate all the kelp.
• Kelp forests are a critical habitat for many ocean species.

Ecosystem engineers

• Animals that modify the habitat in such a way that supports other organisms in the ecosystem.
• Beavers turn rivers into rich wetlands that provide habitat for other organisms; these wetlands also filter water and enrich soil.
• Elephants prevent trees in grasslands from taking over, create channels for water in the rainy season.
• Trophic cascades can cause major problems in disturbed ecosystems BUT they also point to the most effective solutions.
• By restoring and protecting keystone species or ecosystem engineers, ecosystems can recover.

Nutrient Cycling in Terrestrial Ecosystems

• Terrestrial ecosystems are founded on the productivity of primary producers.
• Energy transfer in the system comes from the amount of light energy photoautotrophs can convert into organic matter.
• Matter, energy, and nutrients are passed up the chain as consumers eat the producers.
• Nutrients in the soil are absorbed by plants and then assimilated by consumers.

Soil

• Soil is the literal foundation of terrestrial ecosystems.
• Contains the substrate for rooting, also being a storage reservoir for nutrients plants need.

Composition of soil

• Litter is the top layer and made of organic matter like dead leaves, grasses, and feces.
• Decomposers & detritivores occupy this layer, breaking down materials & making them more accessible to plants
• Topsoil is small rocks with partially decomposed organic matter known as humus, typically dark & rich in nutrients.
• Subsoil contains more rock and less organic matter.
• Bedrock is solid rock that marks the end of the soil layer, which is often impermeable letting water sit above this layer in a reservoir.
• Soil quality influences the diversity of the plant community and productivity of an ecosystem.
• A diverse plant community dictates diversity of the animal community, providing organic molecules that heterotrophs feed on and creating micro-habitats that animals can specialize in.
• Plant communities are more niches.

Forest structure

• The forest floor provides home to decomposing matter, decomposers, detritivores, and other small organisms that rely on them, or large organisms that can't climb.
• The forest floor is cool, moist, and has plants adapted to low light conditions.
• The understory holds trunks of taller trees, shrubs, and partially shade tolerant plants, which are cooler, have some sunlight, but are free of wind.
• The canopy is where the bulk of the leaves from trees are located, with lots of fruit and light although getting water may be a challenge.
• The emergent layer makes up extra tall portions of trees, which is windy, but has intense sunlight.
• Nutrients move through ecosystems via absorption in the producers to the consumption & assimilation in consumers but also through abiotic processes.
• Some nutrients have large reservoirs (storage) in the biosphere.
• Abiotic processes with in the hydrologic cycle can help move some of these nutrients around.

The hydrologic cycle

• Precipitation – such as rain or snow
• Condensation - formation of clouds
• Evaporation -L→G
• Transpiration – evaporation from stomata
• Percolation moves through soil
• Leaching - water dissolves 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 & water flows over top & into bodies of water

Nitrogen cycle

• The cycle contains one of the most critical nutrients for plant growth: N
  • This is also an essential component of chlorophyll as well as required for making amino acids and proteins.
• Largest reservoir is N2 gas in the atmosphere but cannot be used by organisms in this form.
• Plants can absorb nitrates (NO3¯), ammonia (NH3), ammonium (NH4+), & sometimes nitrites (NO2).
• Plants & animals can also assimilate organic forms of nitrogen, like amino acids.
• Atmospheric nitrogen gas must be fixed into bio-available forms

Terminology

• Nitrogen Fixation – converting N2 gas into biologically available nitrogen.
  • Lightning can provide the energy to bind N to the atmostphere.
  • Nitrifying bacteria can also fix N.
• Nitrification - forming nitrates from other nitrogen sources
• Nitrifying bacteria can covert inorganic nitrogen into nitrates through an aerobic reaction and are often found in soil or on nodules on the roots of some plants.
• Denitrification is anaerobic
• The middle step of this process is forming nitrites from nitrates, and the end formation is of N2 gas which is no longer available.
• But denitrification is only partly of the process.
• Ammonification – formation of ammonia from other nitrogen sources like urine or feces or decomposing organic matter (proteins).
• No P is stored in the atmosphere, with it's main reservoir in sedimentary rock
• P is biologically available in the form of phosphate (PO4³¯).
• Phosphate is found in cell membranes, nucleic acids, and in calcium phosphate (in bones & shells)
• There are 2 interacting cycles that move phosphorous:
  • Short cycle - moves P around in a food chain
  • Long cycle - involves geologic activity
• Animal waste (i.e., bird & bat feces) is a rich source of P
  • Easily absorbed and assimilated by plants and then animals
• Another source of P is from the broken-down shells of marine animals.
• When this phosphorous is sunk out of the ecosystem it is referred to as sedimentation
• When sediments are compacted, the P becomes stored long-term in rock formations
  • Only large-scale tectonic activity can push the rock up in a process called uplift or upwelling and expose it.
• When rock is exposed, erosion or lichen can release the stored P so that it can be absorbed by plants such with this process called weathering
• Lichens complete this process by secreting enzymes onto the surface of rock to liberate nutrients

Law of the minimum

• The law describes the concept that the nutrient that is in the least supply is the one that provides the limitation
• Phosphorous is the most limiting nutrient in aquatic environments meaning it will restrict overall productivity and growth.
• If a phytoplankton requires 10 C, 6 N & 4 P but 30 C, 18 N & 5 P are available, only ONE phytoplankton can be produced
  • There is enough C & N for three phytoplankton, but only enough P for one
• P is a common component of fertilizer and was a common component of detergents.
• Contamination of water bodies with P often leads to a process called eutrophication.
• P is a common component of fertilizer and was a common component of detergents, where contamination of water bodies with P often leads to a process called eutrophication.

Aquatic Ecosystems

Physical Factors Affecting Aquatic Ecosystems

• Depth - determines the amount of light that will reach the soil.

  • Deeper bodies of water will have aphotic (lightless) zones that cannot rely on photosynthetic organisms in their food chain.
  • Shallow waters are photic zones, they can be highly productive given the amount of light.

• Turbidity - a measure of clarity.

  • Dirt, silt, phytoplankton, & algae can call make the water turbid
  • Turbid areas are likely to have cellular respiration (decomposition) outpace photosynthesis.
  • Measured using a secchi disk.

• Soil - regions that have light and soil are going to support more organisms & aquatic plants can root into the soil and obtain nutrients

  • These plants provide a greater diversity of habitats

• Benthic zone soil region in the aphotic zone

  • Benthos - organisms that live in this zone

• Littoral zone – where light reaches the soil (photic zone)

• Where there is only open water is the limnetic zone (photic) or the profundal zone (aphotic).

• Motion - flow rate, rapids & ripples that may make choppy water difficult for organisms to live in, also increasing the amount of dissolved gases.

• Temperature – cooler waters contain more dissolved gases that are also are more nutrient rich and productive

  • Warmer waters are more hospitable & favor reactions in organisms' bodies, but nutrients become depleted easily.

• Density - water is most dense at 4°c

• Because of this, bodies of water become stratified (layered) as different regions will have different temperatures, and therefore, different densities.

• Water at 0°C (ice) is also less dense than the less cool water, so it floats

  • Life can be supported underneath winter ice

Lakes in Temperate Zones

• Stratified because of differences in temperature and density.
• Layers are separated by a region of steep temperature change known as the thermocline. -Summer: water lies above the thermocline in the epilimnion, wheras the hypolimnion have nutrients locked at the bottom of lakes.
• Mixis or turnover occurs in the fall & spring which pushes nutrients up and around, providing nutrients to limnetic organisms & oxygen to benthic organisms
• N & P from fertilizers can runoff into aquatic ecosystems & result in eutrophication where as organisms die, their bodies settle & decompose at the bottom of the lake reducing the depth of the lake.
• A depth reduction leads to shallower lakes that are more productive, which leads to more decomposing matter.
  • Over time, lakes become shallow, murky, anaerobic & less diverse.
• Deep lakes are called oligotrophic & have oxygen rich waters but fewer phytoplankton & algae.
• Eutrophication over time is natural but excess fertilization runoff can lead to algal blooms which block out sunlight, limit productivity & reduce the amount of oxygen available.
• pH - influenced by geologic surroundings, runoff, plant life & pollutants such as sulfur compounds.
  • Narrow range can support life, otherwise low pH can be damaging to tissues.
• Dissolved Oxygen – amount of oxygen available to organisms for cellular respiration that is also influenced by motion of water, temperature & amount of producers
• Biological Oxygen Demand – amount of oxygen required by organisms, which is also higher when there is lots of decomposing material because decomposers use up oxygen fast and reduce the amount available for others
• Estrogen (mimics): compounds like bisphenol-A act as estrogens & can feminize aquatic species due to persistent exposure, especially during development from birth control pills that contaminate waterways (any medications can do this)
  • Estrogens are also compounds are small and difficult to remove so often remain in water even after it has been treated

Biological Indicators of Health

• Coliform Bacteria – water contaminated with coliforms means there is a relatively large amount of feces(bacteria) in the water because this bacteria reside in the digestive systems of animals (humans too).

  • This is indicative of larger water contamination problems

• Some aquatic Invertebrates are pollution tolerant, whereas others are pollution intolerant.

• Amphibian Indicators (frogs, salamanders, etc.) need complete gas exchange through their skin so they are very susceptible to changes in the chemical environment

  • Life stage includes aquatic & terrestrial forms – if quality of either declines, amphibians will be affected
  • Eat different foods at the larval stage than adult stage so will be influenced by materials at different points in a food chain and have External development – exposed to contaminants in the water
  • Rely on moisture – many habitats are drying up and warming up and this also makes them more prone to fungal infections

Test your knowledge of ecosystems and communities. Questions cover species interactions, ecological roles, and ecosystem dynamics. Explore topics like autotrophs, decomposers, food webs, and soil layers.