Ecosystems

• An ecosystem has a biotic unit and an abiotic unit; living vs. non-living
  • Biotic: organisms, community, prey/food
  • Abiotic: oxygen, nutrients, water (and the availability of all of these units)
• Limiting factors: the combination of biotic and abiotic factors which can check the size of a population
• An ecosystem is divided into:
  • Producers/Autotrophs: Plants and cyanobacteria
  • Consumers: Animals
  • Decomposers: Bacteria, fungi, microorganisms
• Ecosystems contain complexity through species stability and carrying capacity
  • Carrying Capacity: the maximum population that an ecosystem can support in the long term
    • Carrying capacity is never in stasis, but fluctuates around a given average depending on environmental factors
  • Stability prevents extinction and population die-offs; instability is induced by reducing attachments to a greater food web

Producers

• Autotrophic processes: Photosynthesis and Chemosynthesis
  • Photosynthesis converts sunlight energy into chemical energy; carbon dioxide → oxygen, and light energy → sugars (glucose); plants and cyanobacteria
  • Chemosynthesis converts chemicals (sulfur) into carbon compounds; bacteria
• Producers undergo cellular respiration, but use less glucose and oxygen than they photo/chemosynthesize
• Gross Primary Productivity (GPP): the total amount of energy converted from an inorganic form to an organic form
  • Net Primary Productivity (NPP): the amount of organic energy remaining after part of the gross primary productivity is consumed by producers to survive
    • Net productivity is determined via biomass and cells (in units of g/m^{^2} per year)
    • Tropical rainforests, marshland/estuaries, & coral reefs have the highest productivity at 2,500 g/m^2
    • Temperate evergreens follow at 1,300 g/m^2
    • Woodlands at 700 g/m^2
    • Cultivated land is around 650, but can value much higher
    • Deserts lowest at 90 g/m^2

Consumers and Decomposers

• Both are heterotrophs
  • Consumers, Detritivores, and Decomposers
• Sole heterotrophic process: cellular respiration
• Food web; primary, secondary, tertiary consumers, etc.

Energy Transfer Efficiency

• Only 10% of the total energy is net transferred across each trophic level; all of the energy is consumed, but the 90% excluded is burned in order to consume prey and maintain processes to stay alive
• This net transfer/loss includes energy obtained by decomposers

O=C=O.O>>O=C(O)C(O)C(O)C(O)C(O)C.O=O
O=C(O)C(O)C(O)C(O)C(O)C.O=O>>O=C=O.O

Ecosystem Cycles

• various methods of nutrient cycling

Carbon Cycle

• primarily in the form of a gas, CO2

1. CO2 is used in photosynthesis by producers and converted
2. Heterotrophs consume organic forms of energy which were made from CO2
3. Heterotrophs perform cellular respiration, releasing CO2

Nitrogen Cycle

• Nitrogen is the basis of proteins and DNA (nucleic acid)
• 78% of the atmosphere is stable nitrogen gas; difficult to break apart
• Nitrogen-fixing bacteria converts nitrogen into ammonia
  • Prominently performed by cyanobacteria
  • Nitrifying bacteria in soil
• Algae blooms in excess nitrogen

1. Nitrogen gas is converted by bacteria to solid ammonia
2. Ammonia is biologically assimilated into bacteria
3. Bacteria undergoes decomposition

• Two outcomes:
  1. Decomposed ammonia is taken in by plants/cycled
  2. Or ammonia is denitrified; converts back into nitrogen gas
     • Denitrifying bacteria

Phosphate/Phosphorus cycle

• Phosphorus: nutrient in the soil, uptake by plants, use in animal skeletons, genetic material, ATP

1. Phosphorus is used in photosynthesis by producers and converted into glucose
2. Heterotrophs consume glucose
3. Heterotrophs release phosphorus via cell respiration and decomposition

Water/Hydrologic Cycle

• Not a nutrient, but a major component (photosynthesis)
• Complex; ground, surface, plant components involved
• A system of flows and stores

1. Evaporation off of a body of water/source; sunlight/heat energy converts into vapor
   • Evapotranspiration in plants → evaporation
2. Vapor rises through altitude levels and cools; water molecules are dense; condensate, bind, and attract via polarity; reduces surface space
3. Cloud mass forms and cools; water droplets are pulled by gravity → precipitation as rain, hail, sleet, snow

• Multiple outcomes:
  • Plant uptake; water loss becomes transpiration
  • Surface runoff on hardscape or oversaturated surfaces
  • Infiltration into ground → groundwater

Note on Structural Levels

• Population: All of the members of one species in a given place and time
• Habitat: A location in the ecosystem in which a population lives
• Community: The collection of populations in an ecosystem at a given time
• Ecosystem: The environment and the community that lives on it
• Biosphere: Every ecosystem in a given planet; every area in which life can be supported

Characteristics of Populations

• Population characteristics change over various macroscopic variables:
  • Time, season;
  • Density, volume, area;
  • Migration, behavior;
• Measuring via the mark-recapture method
  • Equation: (Marked value * Recaptured value)/Value of recaptured marked organisms

Population Models

Distribution Patterns

• Characteristics have various patterns/models dependent on the resources in the area
• Dispersal/Distribution Patterns:
  • Clumped Dispersal: Resource availability is limited to given areas
  • Uniform Dispersal: Resource rarity (Allelopathy, competition)
  • Random Dispersal: Resource abundance

Growth Models

• Growth Models:
  • Exponential Growth: Unlimited/Infinite Growth
  • Logistic Growth: Limited Growth; Capstone/Upper limit (Mortality factors, carrying capacity)

Carrying Capacity

• Carrying Capacity: The maximum number of individuals of a population that an environment can support in the long-term at the time of observation
  • Carrying capacity is equal in terms of biomass and unequal in terms of numerical value

Mortality Models

• Mortality: The rate at which deaths are affected by limiting factors in the environment
  • Two forms: Density-dependent and density-independent mortality
  • Seasonal surplus populations will be reduced by mortality factors

Density-Dependent Mortality

• Density-Dependent Mortality: Population size ultimately affects the limiting factors of the environment and the mortality rate
  • Related to population crowding
• Compensatory Mortality: One mortality factor increases to compensate for the reduction of another mortality factor
• Examples include:
  • Predation;
  • Diseases and parasites in a population distribution;
  • Density-related accidents (weight and numbers);
  • Limited physical resources;
  • Social stresses

Density-Independent Mortality

• Density-Independent Mortality: Population size is unrelated to the limiting factors in the environment and the mortality rate
• Catastrophic events independent of population crowding
• Examples include:
  • Adverse weather;
  • Fire;
  • Flooding;
  • Certain types of accidents

Growth Rates and Growth Rate Models

• Biotic Potential: The maximum reproductive rate of a population at a given time
• Environmental Resistance: Environmental factors that limit the biotic potential of a population via increased mortality rates or decreased birth rates
• Equation: Biotic potential - environmental resistance = Carrying capacity
  • As a population approaches carrying capacity, the mortality rate increases until reaching equilibrium

Survivorship Curves

• Four types:
  • Early loss;
  • Constant loss;
  • Late loss;
  • Mix of early-late loss

Early Loss

• Early loss: High initial with a rapid dropoff/death rate that declines with age
• Trees, angiosperms

Constant Loss

• Constant loss: The mortality rate of organisms is constant across lifetime
• Birds, raptors

Late Loss

• Late loss: High initial that remains stable before rapidly dropping off in old age
• Humans, elephants

Mix of Early-Late Loss

• Mix of Early-Late Loss: Begins as early loss, then levels off, then drops off ala late loss when older

Age Structures

• Pyramidic structures
• Provides information on if a population is growing, stable, or declining
• Graphs data of numbers in pre-reproductive, reproductive, and post-reproductive stages; typically, in all three shapes/patterns, post-reproductive bars are shorter than other bars
• The smaller the pre-reproductive bar is relative to the reproductive bar, the more the population is in decline; versus. growing or stability

Birth Strategies

• How births occur in wild populations
  • Middle ground and extreme
  • r-factored or r-related birth
  • K-strategy
• r-K scale: based on two factors, r and K

Rate Selection

• r-selected
  • High birth rate, high number of offspring
  • High mortality and low recruitment
  • Low parental investment
  • High adaptability and short generation times
• Goldfish, salmon, bacteria, houseflies
  • Antibiotic resistance

Carrying Capacity Selection

• K-strategy / priority
  • Low birth rate, slow gestation period, and low number of offspring
  • Low mortality; offspring typically survive
  • High recruitment rates: offspring typically survive and develop to reproductive stage
  • High parental investment in childbirth
  • Low adaptability, long generation times: slower rates of evolutionary, genetic change
• Gorillas, whales, humans

Community-Related Definitions

• Diversity: The variety of organisms typically found in an ecosystem, location, or habitat
• Species Richness: The numerical/adjectival value of diversity
• Relative Abundance: Commonality/prevalence of a species within a given place and time
• Prevalent Forms of Vegetation: The spatially dominant plants in an area
• Stability: The ability of a habitat to rebound from disturbances and mortality factors and to resist changes upon the environment
• Trophic Structure: Food consumption and transference of energy within ecosystems
• Niche: Consists of both biotic and abiotic resources used by an organism, as well as where, when, and how they use these resources
  • Ecological vs. market niche

Community Models

• Regarding the full community

Species Interactions

Competition

• Interspecific Competition: Different species
• Intraspecific Competition: Same species
• Competition results in increased energy expenditures, so it is a large factor in natural selection
• Principle of Competitive Exclusion: Two or more species competing for the same resources at an extended length of time will cause at least one species to be detrimentally affected;
  • Three options presented to species: Redistribution/movement, adaptation, or extinction
  • Competitive exclusion results in resource partitioning

Parasitism

Commensalism

• One benefits, one is unaffected
• Horses and egrets; Whales and barnacles

Mutualism

Predator-Prey Interactions

Prey Defenses

• Prey Physical Defenses:
  • Constitutive defenses such as quills, exoskeletons, spines, etc.
  • Camouflage
  • Toxicity: Venom/Poison
    • Venomous → injection, typically neurological; used for hunting
    • Poisonous → consumption/ingestion
    • Noxious
• Fleeing

Mimicry

• Batesian Mimicry: A species imitates a toxic or noxious species’ appearance for protection
• Mullerian Mimicry: At least two species that are toxic or noxious look alike for mutual protection

Predatory Defenses

• Predatory Tactics:
  • High intelligence
  • Black-and-white vision or high cones
  • Camouflage

Co-evolution

• Pairs of species interacting frequently or closely
• Changes across one species are often reflected in changes in the other species;
  • Changes in traits across one species are a selective pressure versus the other species
• Bee-plant domation, ants and acacia
• May be mutualistic or competitive

Keystone Species

• Species which ecosystems depend on to maintain the community
  • CA: giant kelp, bats, fungi, sea otters
  • SEUS: alligators
• Keystone Predator: A predator specialization for keystone species; controls overpopulation in a community to maintain diversity
• Keystone predator disruption causes trophic cascade

Indicator Species

• Warning signs for changes/problems in an ecosystem or habitat
• Nudibranchs, stoneflies, mayflies, amphibians, pika

Ecological Succession

• Progression of chronological species development
• Primary Succession: The first time any source of life exists on the site
• Secondary Succession: New life that develops after a mortality factor destabilizes/removes the original community
• Climax Community: A stabilized community following secondary succession