Unit 2 - Ecosystems and ecology

Ecology

Scientific study of interactions among organisms and between organisms and their abiotic environment.

Biosphere

The global ecosystem consisting of all living organisms on Earth and the regions of lithosphere, hydrosphere, and atmosphere where life exists.

Atmosphere

The envelope of gases surrounding Earth that regulates global climate and protects organisms from solar radiation.

Hydrosphere

All water at or near Earth's surface, including oceans (97%), groundwater, ice, and atmospheric vapor.

Lithosphere

The solid, outer layer of Earth comprising the crust and rigid upper mantle, serving as the geological foundation for terrestrial life.

Environment

The physical, chemical, and biological surroundings and conditions in which an organism, population, or community lives.

Habitat

The specific environment or physical location where a species lives and finds necessary resources to survive.

Species

A group of similar organisms capable of interbreeding to produce fertile offspring.

Population

A group of individuals of the same species living in a specific area at the same time.

Community

A group of populations of different species interacting and living together in a defined area.

Ecosystem

A biological community of interacting organisms (biotic) and their physical environment (abiotic), classified into terrestrial, marine, and freshwater environments.

Biome

A collection of ecosystems sharing similar climatic conditions, thermal regimes, and precipitation patterns.

Abiotic Factors

Non-living physical and chemical components of an ecosystem that influence organisms, such as temperature, sunlight, water, pH, and salinity.

Biotic Factors

Living organisms and their biological interactions within an ecosystem, including predation, herbivory, competition, and disease.

Niche

The full range of physical and biological conditions, resources, and interactions a species requires to survive and reproduce.

Fundamental Niche

The theoretical range of physical and biological conditions in which a species could survive and reproduce in the absence of biotic competition or limiting interactions.

Realized Niche

The actual range of environmental conditions and resources a species occupies due to biotic constraints like competition and predation.

Population Density Calculation

Formula: $\text{Density} = \frac{\text{Total Individuals}}{\text{Total Area or Volume}}$. Quantifies spatial crowding. High density intensifies competition for space and food while accelerating density-dependent mortality. Low density reduces intraspecific competition but risks mate-seeking failure.

Population Change Metrics

The four dynamic metrics regulating population size: natality (birth rate), mortality (death rate), immigration (movement in), and emigration (movement out).

Carrying Capacity (K)

The maximum population size of a species that a given environment can support sustainably over a long period without degrading the habitat.

Biotic Potential

The maximum theoretical growth rate of a population under ideal environmental conditions with unlimited resources and no mortality constraints.

Environmental Resistance

The sum of all limiting factors (abiotic and biotic) that restrict population growth and prevent a population from reaching its biotic potential.

Exponential Growth (J-Curve)

A pattern of rapid population growth where the growth rate increases in direct proportion to total population size, occurring when resources are abundant.

Logistic Growth (S-Curve)

A population growth model featuring an initial lag phase, exponential growth, transitional slowing, and a final plateau at environmental carrying capacity.

Density-Dependent Factors

Limiting factors whose severity increases as population density rises, operating as negative feedback mechanisms (e.g., disease, competition, predation, resource depletion).

Density-Independent Factors

Limiting factors that alter population mortality or natality regardless of population density (e.g., weather extremes, natural disasters, volcanic eruptions).

r-Species (r-Strategists)

Opportunistic species that mature quickly, produce large numbers of small offspring, invest minimal parental care, and thrive in pioneer habitats (e.g., insects, cockroaches).

K-Species (K-Strategists)

Species that mature slowly, produce few large offspring, invest high parental care, and maintain stable populations near carrying capacity in climax communities (e.g., elephants, humans).

C-Species (C-Strategists)

Species displaying intermediate survival strategies between extreme r- and K-selected traits.

Competition

An interaction between organisms driven by a shared requirement for a limited resource such as food, space, light, or mates.

Intraspecific Competition

Competition for limited resources between members of the same species, serving as a primary driver of density-dependent population regulation.

Interspecific Competition

Competition for resources between individuals of different species, which can lead to competitive exclusion or resource partitioning.

Herbivory

An interaction where an animal consumer (herbivore) feeds on primary producers such as plants or algae.

Predation

An interaction in which one organism (predator) kills and consumes another organism (prey) for nutrition.

Pursuit and Ambush

Predation tactics involving active chasing or hidden stealth to capture prey.

Animal Defenses

Mechanisms evolved by prey to avoid predation, including camouflage, warning coloration, mechanical armor, living in groups, speed, and chemical toxins.

Symbiosis

A close, long-term physical relationship between two different biological species.

Mutualism

A symbiotic relationship where both participating species derive a biological benefit (e.g., oxpeckers and large mammals, leguminous plants and nitrogen-fixing bacteria).

Commensalism

A symbiotic relationship where one species benefits while the other remains unaffected.

Parasitism

A symbiotic relationship where one organism (parasite) lives in or on a host, deriving nutrients while causing harm.

Pathogen

A disease-causing organism, such as a virus, bacterium, or fungus, that harms its host.

Autotrophs (Producers)

Organisms that synthesize their own organic molecules from inorganic substances using external energy sources.

Photoautotrophs

Producers that utilize light energy to convert carbon dioxide and water into organic molecules via photosynthesis.

Chemoautotrophs

Producers that derive energy from inorganic chemical reactions to synthesize organic compounds in lightless environments, such as thermophilic bacteria at hydrothermal vents.

Heterotrophs (Consumers)

Organisms that obtain energy and organic nutrients by consuming other living organisms or their by-products.

Primary Consumers

Herbivores that feed directly on producers, occupying the second trophic level.

Secondary Consumers

Carnivores or omnivores that feed on primary consumers, occupying the third trophic level.

Tertiary Consumers

Apex predators or high-level carnivores that feed on secondary consumers.

Scavengers

Animals that consume dead animal carcasses killed by predators or natural causes.

Detritivores

Consumers that ingest non-living organic matter and detritus internally (e.g., earthworms).

Saprotrophs (Decomposers)

Heterotrophic fungi and bacteria that digest dead organic matter externally by secreting digestive enzymes and absorbing the products.

Trophic Level

The functional position an organism occupies within a food chain or food web.

Food Chain

A linear sequence showing the transfer of energy and matter through organisms via feeding.

Food Web

A network of interconnected food chains reflecting actual feeding relationships within a community.

First Law of Thermodynamics

The principle that energy can neither be created nor destroyed, only transformed from one form to another within an isolated system.

Second Law of Thermodynamics

The principle that every energy transfer increases the entropy of the universe, causing energy to degrade into low-grade heat.

Trophic Efficiency Calculation

Formula: Efficiency = Energy at current trophic level/Energy at previous trophic level × 100%. Measures the percentage of energy transferred between trophic levels, typically averaging 10%. High efficiency retains more energy across levels, supporting higher-tier carnivores. Low efficiency explains why terrestrial food chains rarely exceed four or five levels due to heavy entropy losses.

Bioaccumulation and Biomagnification

The accumulation of non-biodegradable toxins (e.g., DDT) within individual tissues over time, leading to increasing toxin concentration at higher trophic levels that harms apex predators.

Pyramid of Numbers

A diagram showing the total count of individual organisms at each trophic level; can be inverted if a single large producer supports many consumers.

Pyramid of Biomass

A diagram representing the total dry mass of standing crop organisms at each trophic level at a specific time (units: $\text{g m}^{-2}$); can invert in aquatic systems due to rapid phytoplankton turnover.

Pyramid of Productivity

A diagram illustrating the rate of energy flow through each trophic level over time; strictly upright due to thermodynamic laws.

Productivity

The rate at which energy or biomass is generated within an ecosystem per unit area per unit time.

Gross Productivity (GP)

The total amount of energy or biomass assimilated by organisms per unit area per unit time prior to respiratory losses.

Net Productivity (NP)

The amount of energy or biomass remaining per unit area per unit time after subtracting respiratory losses NP = GP - R.

Gross Primary Productivity (GPP)

Formula: GPP = NPP + R. GPP is the total solar energy fixed into organic matter by producers per unit area per unit time. High GPP values signal optimal growing conditions (warmth, abundant water, rich nutrients), yielding rapid biomass production as seen in tropical rainforests. Low GPP reflects harsh limiting factors such as extreme cold or severe drought in tundra or desert systems.

Net Primary Productivity (NPP)

Formula: NPP = GPP - R. The biomass remaining in producers per unit area per unit time after subtracting respiratory losses. High NPP provides a large energy base, enabling long food chains and supporting high consumer biodiversity. Low NPP restricts energy availability, creating short food chains and limiting animal biomass.

Gross Secondary Productivity (GSP)

Formula: GSP = Food Eaten - Fecal Loss. The total biomass assimilated by heterotrophs from ingested food. High GSP indicates efficient assimilation, common in carnivores digesting protein-rich meat. Low GSP stems from indigestible dietary content, such as cellulose in herbivore diets, leading to heavy fecal losses.

Net Secondary Productivity (NSP)

Formula: NSP = GSP - R. The net biomass accumulated by consumers per unit area per unit time after accounting for respiratory heat loss. High NSP reflects rapid body growth and high reproductive output. Low NSP means consumers expend nearly all assimilated energy on metabolic maintenance and thermoregulation.

Light and Dark Bottle Method

Formulas: Respiration (R) = Initial DO - Dark DO; NPP = Light DO - Initial DO; GPP = Light DO - Dark DO. Measures aquatic productivity using dissolved oxygen (DO) changes. High GPP/NPP values identify nutrient-rich photic waters. Negative NPP values indicate net oxygen consumption, signaling organic pollution or eutrophication.

Maximum Sustainable Yield (MSY)

Formula: MSY = NPP (for producers) or MSY = NSP (for consumers). The highest rate of resource harvesting that avoids long-term stock depletion. Harvesting equal to or below MSY maintains capital biomass indefinitely. Harvesting above MSY causes population collapse and system degradation.

Factors Affecting Primary Productivity

Environmental variables including solar insolation, temperature, carbon dioxide levels, water availability, nutrient supply, and herbivory rates.

Nutrient Cycle

The continuous movement and exchange of organic and inorganic matter back into the production of living organisms.

Carbon Cycle

The circulation of carbon between the atmosphere, biosphere, oceans, and geosphere via photosynthesis, respiration, combustion, and decay.

Nitrogen Cycle

The biological transformation and movement of nitrogen through atmospheric, soil, and organic reservoirs.

Nitrogen Fixation

The conversion of atmospheric nitrogen gas into plant-available nitrogen forms like ammonia or nitrates by specialized bacteria (e.g., Rhizobium) or lightning.

Nitrification

The oxidation of ammonia into nitrites and subsequently into nitrates by soil bacteria (e.g., Nitrosomonas, Nitrobacter).

Denitrification

The conversion of soil nitrates back into gaseous atmospheric nitrogen by anaerobic bacteria in waterlogged conditions.

Human Impact on Energy Flows

Alterations to global radiation budgets and energy cascades caused by greenhouse gas emissions, atmospheric aerosol pollution, deforestation, and urban development.

Human Impact on Matter Cycles

Disruptions to nutrient dynamics resulting from fossil fuel combustion, deforestation, timber harvesting, livestock waste, and synthetic fertilizer runoff causing eutrophication.

Tricellular Model

A global atmospheric circulation model comprising Hadley, Ferrel, and Polar cells that drives worldwide temperature, pressure, and rainfall patterns that dictate biome distribution.

Factors Influencing Biomes

Insolation angle, elevation (1^.C temperature drop per 100m gain), continentality, atmospheric pressure belts, seasonal axial tilt (23.5^.), and precipitation regimes.

Tropical Rainforest

Equatorial biome characterized by high solar insolation, high rainfall, constant warmth, tall multi-layered canopies, continuous productivity, and maximum species diversity.

Temperate Deciduous Forest

Mid-latitude biome experiencing four seasons, moderate rainfall, warm summers, cold winters, and seasonal leaf fall by broadleaf trees.

Taiga (Boreal Forest)

Subarctic biome dominated by cold winters, short growing seasons, low species diversity, and needle-leaved evergreen conifers.

Tundra

High-latitude or high-altitude biome marked by permafrost, low precipitation, severe cold, short growing periods, and low plant stature.

Deserts

Arid biomes receive under 50 cm of annual precipitation, are subject to extreme daily temperature swings, have nutrient-rich but water-deficient soils, and have xerophytic vegetation.

Savanna

Tropical grassland biome subject to alternating wet and dry seasons, regular fires, scattered drought-tolerant trees, and large grazing herds.

Grasslands

Semiarid interior biomes dominated by herbaceous vegetation, moderate precipitation occurring early in the growing season, and extreme seasonal temperature ranges.

Chaparral

Coastal biome dominated by dense, thorny shrubs adapted to Mediterranean climates with mild, wet winters and hot, dry, fire-prone summers.

Tropical Coral Reefs

Highly productive marine ecosystems located in warm, shallow ocean waters, characterized by structural coral diversity and complex nutrient cycling.

Hydrothermal Vents

Deep-ocean chemosynthetic ecosystems reliant on thermophilic bacteria processing chemical energy from superheated mineral fluids in complete darkness.

Zonation

Spatial variation in species composition along an environmental gradient (e.g., altitude, latitude, tidal height).

Succession

The sequential, directional change in species composition and community structure over time following substrate exposure or disturbance.

Primary Succession

Ecological development initiated on previously uncolonized, soil-free substrate such as bare rock or volcanic lava.

Pioneer Community

The initial stage of succession composed of hardy species (e.g., lichens, mosses) capable of establishing on bare substrates with high NPP and low total biomass.

Secondary Succession

Ecological recovery taking place on previously colonized substrate with intact soil following a disturbance (e.g., forest fire, abandoned farmland).

Sere (Seral Stages)

The series of intermediate ecological stages through which a community progresses during succession towards a climax state.

Climax Community

The final, stable equilibrium stage of ecological succession is characterized by complex food webs, high biomass, balanced productivity (GPP = R, NPP = 0), and mature soil structure.

Plagioclimax (Deflected Succession)

A stable community maintained below its natural climax state due to ongoing human interference such as livestock grazing, burning, or mowing.

Changes During Succession

Trends over successional time: increasing total biomass, organism size, species richness, soil depth, nutrient retention, and declining NPP relative to GPP.