Unit 8: Ecology Practice Flashcards

Ecology and Levels of Organization

• Ecology Definition: The study of interactions between living things and their environments.

• The Biosphere: The entire part of Earth where living things exist.

• Ecosystem: The interaction of living (biotic) and nonliving (abiotic) components in a specific area.

• Community: A group of populations of different species interacting in the same area.

• Population: A group of individuals of the same species living in the same area at the same time who are capable of interbreeding.

• Exam Focus: Typical Question Patterns     - Identify the correct ecological level (population vs. community vs. ecosystem) from a scenario.     - Explain how both biotic and abiotic components define an ecosystem.

• Exam Focus: Common Mistakes     - Using ‘community’ and ‘ecosystem’ interchangeably (ecosystem includes abiotic factors; community does not).     - Forgetting that a population is a single species in one area and time period, with potential interbreeding.

Organisms and Their Responses to the Environment

• Scale of Ecology: Ecology starts at the smallest scale where organisms must sense and respond to conditions to improve fitness.

• Abiotic Factors: Nonliving conditions include temperature, water availability, $pH$, salinity, light, and nutrient levels.

• Biotic Factors: Living influences include predators, competitors, pathogens, and potential mates.

• Natural Selection: Favors traits that help an organism match responses to challenges and opportunities encountered regularly.

• The Three-Step Response Loop:     1. Stimulus: A change in internal or external conditions (e.g., light intensity, chemical signals, dehydration).     2. Detection and Processing: Receptors and signaling pathways detect the change and transmit information.     3. Response: Behavior, physiology, or development shifts to improve survival or reproduction. This applies to both animals and plants (even without nervous systems).

• Thermoregulation:     - Endotherms: Generate most body heat internally through metabolism; maintain stable internal temperatures despite external changes.     - Ectotherms: Lack strong internal heat-generating mechanisms; body temperature is influenced by environment. They rely on behaviors like basking or seeking shade.

Animal Behavioral Responses

• Behavior: Any observable action an organism performs. Key behaviors affect survival/reproduction: finding food, avoiding predators, selecting habitat, attracting mates, and caring for offspring.

• Orientation Behaviors:     - Taxis: Directed movement toward or away from a stimulus (e.g., positive phototaxis in moths toward light; negative chemotaxis in bacteria away from toxins). Movement is guided relative to the source.     - Kinesis: Nondirectional movement that changes speed or turning rate based on conditions (e.g., a pill bug moving faster in dry areas to leave them sooner). The organism does not steer toward a target.

• Innate vs. Learned Behavior:     - Innate Behavior (Instinct): Genetically programmed patterns occurring without experience (reflexes, fixed action patterns).     - Learned Behavior: Modified by experience; a change in behavior brought about by experience.     - Imprinting: Young animals form strong behavioral attachments during a critical period (a limited window of sensitivity). If a mother is absent, offspring may accept the first moving object seen.     - Habituation: Learning not to respond to a repeated, harmless stimulus.

• Biological Clocks: Circadian rhythms are internal daily cycles (biological clocks) seen in animals (roosters) and plants (stomatal opening, gene expression).

Communication and Social Behaviors

• Signal: A trait affecting another organism’s behavior or physiology, often benefiting the sender.

• Chemical Communication (Pheromones): Signals between members of the same species stimulating olfactory receptors to affect mating, alarm, or trail following.

• Visual and Auditory Signals: Used for mate attraction, territory defense, or deterring rivals.

• Social Interactions:     - Agonistic Behavior: Aggressive behavior resulting from competition for resources.     - Dominance Hierarchies: Pecking orders established to reduce constant fighting by making outcomes predictable.     - Territoriality: Defending space to increase resource access, though it carries energy and injury costs.     - Cooperative Behaviors: Group hunting or alarm calling that increase inclusive fitness.     - Altruistic Behavior: Unselfish behavior benefiting others at individual expense to advance group genes (often relatives). Evolution occurs when net effect on reproductive success is beneficial.

Plant Responses to the Environment

• Mechanisms: Use signaling pathways and differential growth rather than relocation.

• Tropisms: Directional growth responses.     - Phototropism: Growth toward light (shoots).     - Gravitropism: Stems show negative gravitropism (grow up); roots show positive gravitropism (grow down).     - Thigmotropism: Growth in response to touch (vines on a trellis).

• Hormonal Control: Auxin redistributes to create unequal growth. In shoots, higher auxin promotes cell elongation on the shaded side, bending the shoot toward light.

• Photoperiodism: Flowering and developmental timing based on changes in daylight and darkness.

• Stomata and Water Balance: Guard cells control openings for $CO_2$ uptake vs. water loss (transpiration). They change turgor pressure via ion movement/osmosis. During drought, stomata close to save water, limiting photosynthesis.

• Acclimation vs. Adaptation:     - Acclimation: Reversible change within an individual's lifetime (e.g., more red blood cells at high altitude).     - Adaptation: Heritable trait shaped by natural selection across generations.

Energy, Matter, and Ecosystem Dynamics

• Energy Flow: Enters as sunlight, captured by producers, flows through food webs, and is lost as heat.

• Matter Cycling: Atoms (carbon, nitrogen, phosphorus) cycle between organisms and the environment.

• Ecosystem Structure:     - Primary Producers (Autotrophs): Convert inorganic carbon ($CO_2$) into organic molecules via photosynthesis or chemosynthesis.     - Consumers (Heterotrophs): Primary (herbivores), Secondary (carnivores/omnivores), Tertiary (top predators).     - Decomposers/Detritivores: Break down dead matter, releasing nutrients; essential for preventing nutrient lock-up.

• Trophic Levels: Feeding positions. Food chains show single pathways; food webs show interconnected pathways.

• The 10% Rule: Approximately $10\%$ of energy at one trophic level becomes biomass at the next. Inefficiency is due to metabolism, movement, and thermoregulation.

• Ecological Pyramids:     - Energy Pyramid: Shows available energy; always narrows upward.     - Biomass Pyramid: Mass of living organic matter; can be inverted in aquatic systems (phytoplankton).     - Pyramid of Numbers: Individual counts; may be inverted if a single large producer supports many consumers.

• Toxins: Become more concentrated at higher trophic levels because predators eat many contaminated prey.

Primary Productivity and Nutrient Cycling

• Gross Primary Productivity (GPP): Total rate of photosynthesis (total energy captured).

• Net Primary Productivity (NPP): Organic material left after producers meet their own respiratory needs. Formula: $NPP = GPP - R$, where $R$ is respiration.

• Worked Example: If a grassland has $GPP = 2000$ units and $R = 1200$ units, then $NPP = 2000 - 1200 = 800$ units available as new plant biomass.

• The Carbon Cycle: Photosynthesis removes $CO_2$; respiration, decomposition, and combustion return it. $CO_2$ is a greenhouse gas.

• The Nitrogen Cycle:     - Nitrogen Fixation: Atmospheric nitrogen to ammonia (bacteria).     - Nitrification: Ammonia to nitrite to nitrate.     - Assimilation: Inorganic nitrogen into organic molecules.     - Ammonification: Organic nitrogen to ammonia during decay.     - Denitrification: Nitrate back to nitrogen gas.

• The Phosphorus Cycle: Cycles through rocks/soil/water; no gaseous phase. Limiting in freshwater; vital for $ATP$ and nucleic acids.

• Limiting Factors: Resources (light, $N$, $P$) that restrict growth. Adding a limiting nutrient can cause rapid growth cascades.

Population Ecology

• Population Size: Total number of individuals ($N$).

• Density: Individuals per unit area/volume.

• Dispersion: Clumped (common), Uniform (territorial), or Random (rare).

• Growth Models:     - Exponential Growth: Abundant resources; J-shaped curve. Rate: $\frac{dN}{dt} = rN$.     - Logistic Growth: Resources limited; S-shaped curve leveling at carrying capacity ($K$). Rate: $\frac{dN}{dt} = rN\left(1 - \frac{N}{K}\right)$.     - Intrinsic Rate of Increase ($r$): Summarized as $\frac{\text{births} - \text{deaths}}{N}$.

• Survivorship Curves:     - Type I: High survival until old age (mammals).     - Type II: Constant death rate (birds).     - Type III: High juvenile mortality (fish, plants).

• Age Structure Diagrams: Wide base suggests rapid future growth; narrow base suggests decline. Explain population momentum (continued growth after birth rate drops).

Density Regulation and Life History

• Density-Dependent Factors: Intensify as density rises (competition, predation, disease, waste, social stress). Mechanism: crowding increases transmission or competition.

• Density-Independent Factors: Affect populations regardless of density (weather, floods, fire).

• Life History Strategies: Continuum from ‘fast’ (many offspring, little care) to ‘slow’ (few offspring, high care).

Community Ecology and Diversity

• Ecological Niche: Full range of resource use. Fundamental niche (potential) vs. Realized niche (actual use due to constraints).

• Competition: Competitive exclusion principle states two species cannot occupy the same niche indefinitely. Coexistence requires resource partitioning.

• Symbiosis:     - Mutualism: Both benefit ($+/+$).     - Commensalism: One benefits, other unaffected ($+/0$).     - Parasitism: One benefits, one harmed ($+/-$).

• Keystone Species: Disproportionately large effect on structure relative to abundance.

• Trophic Cascade: Ripple effects across levels (e.g., loss of sea otters leads to urchin overgrowth and kelp loss).

• Ecological Succession:     - Primary: No soil initially (volcanic rock); lichens are pioneers.     - Secondary: Soil intact (after fire).

• Biodiversity Metrics:     - Species Richness: Number of species.     - Species Evenness: Distribution of individuals among species.     - Simpson’s Diversity Index: $D = 1 - \sum\left(\frac{n}{N}\right)^2$. Higher values indicate greater diversity.

• Island Biogeography: Richness depends on island size (larger = more species) and distance from source (closer = more immigration).

Disruptions and Human Impact

• Eutrophication: Nutrient enrichment ($N, P$) Leading to:     1. Fertilizer runoff.     2. Algal bloom.     3. Algae die and decompose.     4. Decomposers consume oxygen ($hypoxia$).     5. Massive die-off of aerobic organisms.

• Toxins:     - Bioaccumulation: Toxin increase within one individual over time.     - Biomagnification: Toxin increase across trophic levels.

• Habitat Fragmentation: Creates isolated patches; increases edge effects (higher light/wind/predation at boundaries) and reduces gene flow.

• Conservation: Strategies include corridors for connectivity and restoration ecology to reestablish natives.