Principles of Ecology Practice Flashcards

Introduction to Ecology and Historical Definitions

• Etymology of Ecology: The term ‘ecology’ was first used by Ernest Haeckel in 1869. It is derived from two Greek words: ‘Oikos’ meaning ‘home’ and ‘logous’ meaning to study. It can be interpreted as the study of the ‘home life’ of living organisms or the households of the planet Earth.

• Historical Definitions:

  • Odum: Defined ecology as the study of the structure and function of nature or the study of ecosystems.

  • Haeckel: Defined it as the total relationship of an animal to both its organic and inorganic environment.

  • Charles Elton of England: Defined it as the study of scientific natural history.

  • Andrewartha of Australia: Defined ecology as the study concerned with the distribution of organisms.

  • Clematis: Defined ecology as a science of community.

  • Begon, Harper, and Townsend: Jointly defined it as the description, explanation, and prediction of individuals, populations, and communities in space and time.

  • Krebs: Defined ecology as the scientific study of interactions which determine the distribution and abundance of organisms.

• Modern Common Definition: The scientific study of the distribution and abundance of organisms and how these properties are affected by interactions between organisms and their living (biotic) and non-living (abiotic) environments.

Multi-disciplinary Nature and Organizational Levels

• Holistic Science: Ecology is a multi-disciplinary and holistic science that overarches older disciplines like biology.

• Levels of Organization: It focuses on the higher levels of the organization of life, specifically:

  • Organisms

  • Populations

  • Communities

  • Ecosystems

  • Biosphere

• Scope: It deals with these levels and their functional processes within their natural environments.

Branches and Sub-disciplines of Ecology

• Primary Divisions:

  • Autecology: Also known as population ecology; deals with the dynamics of species and populations and their interactions with the environment.

  • Synecology: A sub-discipline focused on the distribution, abundance, demography, and interactions between coexisting populations (e.g., forest ecology, grassland ecology, desert ecology, marine ecology, and limnology).

• Recently Emerged Branches:

  • Palaeoecology: The study of organisms and their habitats in the geological past.

  • Conservation Ecology: The application of ecological principles for resource management, sustainable yields, and reducing species extinction risks.

  • Resource Ecology: Management of renewable and non-renewable resources.

  • Pollution Ecology: Study of problems associated with the movement of pollutants.

  • Chemical Ecology: Investigates chemical interactions between organisms.

• Taxonomic Divisions: Ecology can also be split into Plant Ecology and Animal Ecology. Plant ecology is further subdivided by the ecosystem studied (e.g., desert or forest ecology).

Abiotic Environmental Factors: Resources and Physical Limits

• Definition of Environmental Factors: Components of the environment (living and non-living) that have a direct or indirect influence on organisms.

• Abiotic Factors: Non-living components including temperature, light, water, gases, wind, soil, and physiographic factors (altitude, slope, aspect).

• Physical Resources vs. Physical Factors:

  • Physical Resources: Essential factors organisms need to stay alive. Plants need sunlight, water, $CO_2$, nutrients, and soil. Animals need $O_2$, water, and nutrients. Absence of these leads to death (absolute factors).

  • Physical Factors: Abiotic factors that limit the quality of life or comfort but do not necessarily cause immediate death (e.g., pH, salinity, temperature).

• Limiting Factors: Abiotic factors become limiting when they determine the presence or absence of a species.

  • Law of the Minimum (Justus Von Liebig, 1840): Optimization of growth is limited by the single factor in shortest supply, even if others are abundant.

  • Law of Tolerance (Victor Shelford, 1913): Organisms require physical factors within specific upper and lower tolerance limits.

The Influence of Temperature on Biological Systems

• Physiological Impact: Temperature influences enzymes, which work best at intermediate ranges to retain shape and flexibility. Extreme temperatures reduce the rate of photosynthesis.

• Tolerance Classifications:

  • Eurythermal: Organisms with a wide temperature tolerance.

  • Stenothermal: Organisms with a narrow temperature tolerance.

• Animal Classifications:

  • Ectothermic (‘cold-blooded’ or poikilothermic): Body temperature regulated by the environment.

  • Endothermic (‘warm-blooded’ or homothermic): Internal regulation of body temperature.

• Effect on Plants:

  • Opening of flowers: Occurs during specific day or night periods.

  • Vernalization: Seeds of biennials (e.g., carrots) requiring cold periods in spring or summer to germinate.

  • Chilling requirements: Peach and plum seeds must be exposed to cold to ensure they don't germinate in autumn.

  • Dormancy: Deciduous trees lose leaves in winter; buds are protected against cold.

  • Frost: A major determinant of plant distribution; many tissues cannot survive freezing/thawing.

Sunlight, Photoperiodism, and Ecosystem Responses

• Energy Source: Sunlight is the ultimate energy source for photosynthesis. Chlorophyll is the dominant pigment. Red rays ($600-750\,nm$) induce greater tissue elongation.

• Photoperiodism: The relative duration of daylight and darkness affecting physiology.

  • Short-day plants: Flower when light is less than a critical duration (< 14\,hours). Examples: Nicotiana, Chrysanthemum, and Xanthium.

  • Long-day plants: Flower when nights are shorter than a critical length. Examples: Spinach, wheat, barley, clover, and radish.

  • Day-neutral plants: Bloom regardless of photoperiod.

• Transpiration: Intense light increases transpiration; dehydration can disrupt colloidal structures and impair enzymes.

• Animal and Aquatic Effects: Light affects breeding, development (fish/silkworms), and locomotion. In aquatic systems, light quality and intensity determine the distribution of photosynthetic organisms.

• Light Response Types:

  • Phototropism: Directional growth (e.g., stems grow toward light - positive; roots grow away - negative).

  • Phototaxis: Whole-organism movement toward or away from a light source.

  • Photokinesis: Variation in the intensity of locomotory activity based on light intensity, not direction.

  • Photonasty: Movement of plant parts in response to light where the direction of the stimulus does not dictate the direction of movement.

Water Availability and Adaptations in Plants and Animals

• Plant Classification:

  • Hydrophytes: Grow in water or waterlogged areas.

  • Mesophytes: Grow in areas with moderate water.

  • Xerophytes: Grow in dry/desert areas.

• Xerophyte Adaptations: Sunken stomata, reversed stomatal rhythms, thick cuticles, small/no leaves, and water-storage tissues.

• Animal Adaptations to Desiccation:

  • Structural: Chitinous skeletons (insects), scales (reptiles), feathers (birds), hair (mammals).

  • Physiological: Reduced sweat glands, tolerance to water loss (e.g., camels).

  • Atmospheric Absorption: Some insects absorb water vapor from coastal fog (e.g., Namib desert).

Atmospheric Gases, Wind, and Edaphic (Soil) Factors

• Gases:

  • Oxygen ($O_2$): Used for respiration.

  • Carbon Dioxide ($CO_2$): Used for photosynthesis.

  • Nitrogen ($N_2$): Obtained by plants via bacteria, algae, or lightning.

• Wind: Transports water vapor, assists in pollination and seed dispersal, causes soil erosion, and increases evaporation/heat loss.

• Soil Texture:

  • Clay: Microscopic particles; holds much water/nutrients but poorly aerated/cold.

  • Sand: Larger particles; low nutrient/water retention but well-aerated.

  • Loam: Mixture of sand and clay; ideal for plants (aerated, moisture-retaining, nutrient-rich).

• Soil Water Types:

  • Hygroscopic: Thin film around particles.

  • Capillary: Held in small spaces (primary source for plants).

  • Gravitational: Drains downward through soil.

• Soil pH: Affects mineral availability. Acidic (pH < 7) suits Azaleas/ferns. Alkaline (pH > 7) suits Lucerne/xerophytes.

Physiographic Factors and Periodic Disturbances

• Physiography: Altitude, slope, and aspect.

  • Altitude: As it increases, air temperature drops, solar radiation absorption reduces, and wind strength increases. Lower soil temperatures reduce root water/mineral absorption.

• Disturbances: Fire, hurricanes, typhoons, and volcanic eruptions devastate communities, leading to Succession.

Biotic Factors: Trophic Roles and Interactions

• Producers (Autotrophs):

  • Photosynthesis: Conversion of sunlight, $CO_2$, and water into carbohydrates and $O_2$.

  • Chemosynthesis: Conversion of inorganic compounds to nutrients (specialized bacteria).

• Consumers (Heterotrophs):

  • Primary/Secondary Consumers: Feed on living tissue.

  • Detritivores: Feed on dead matter (Detritus).

  • Detritus feeders: Consume waste directly.

  • Decomposers: Break down complex organic matter into simpler molecules.

• Specific Interactions:

  • Predator: Uses another organism as energy/matter.

  • Parasite: Gets food from a host.

  • Prey: Energy source for predator.

  • Symbiont: Aids the organism in obtaining matter/energy.

  • Competitor: Reduces the ability of an organism to harvest resources.

• The 90% Energy Rule: Approximately $90\,\%$ of energy is lost at each higher trophic level. Humans can save energy by ‘eating lower on the food chain’ (closer to producers).

Periodicity, Circadian Rhythms, and Seasonality

• Diel Change (Day/Night):

  • Dawn: Transition to activity for birds, bees, butterflies.

  • Dusk: Activity for water lilies (folding), moths, foxes, owls.

• Circadian Rhythms: Internal rhythmic activities of approximately $24\,hours$.

  • Free-running: Internal rhythm without external cues.

  • Entrainment: Use of light/temp to synchronize the internal rhythm to the environmental $24\,hour$ cycle.

• Seasonality:

  • Migration: Triggered by spring/autumn.

  • Dormancy: Torpor (reptiles), winter sleep (bears), hibernation (collecting fat before winter dormancy), and aestivation (dormancy during warm/dry conditions).

• Reproduction:

  • Ephemerals: Desert plants blooming quickly after rain.

  • Seasonal Anestrus: Ewes in the Northern Hemisphere stop cycling during spring/summer due to day length.

Population Ecology: Density, Age Structure, and Sex Ratio

• Population: Group of same-species individuals breeding in a particular space (Populus = people).

• Attributes: Density, birth/death rates, immigration/emigration, age structure, and sex ratio.

• Age Structure Categories:

  • Animals: Pre-reproductive, reproductive, and post-reproductive. Insects use eggs, pupae, and larvae.

  • Plants: Size classes ($height$, $diameter$) are often better than age because dominant trees exclude younger individuals.

  • Plant Problem: The seed bank (seeds are of a different age than the plants they become).

• Sex Ratio: Usually $1:1$.

  • Primary: At conception ($1:1$).

  • Secondary: At birth (often weighted toward males in mammals).

  • Later shift: Swings toward females in older age groups in humans; remains male-weighted in birds.

Population Growth Models: Exponential and Logistic

• Exponential Growth Model: Occurs in unlimited environments.

  • Equation: $dN/dt = r_{max}N$

  • Population at time t: $N_t = N_0e^{r_{max}t}$

  • Symbols: $N_t$ = number at time $t$, $N_0$ = initial number, $e$ = base of natural log, $r_{max}$ = intrinsic rate of increase, $t$ = time.

• Logistic Growth Model: Occurs as resources are depleted; results in a sigmoidal (S-shaped) curve.

  • Equation: $dN/dt = r_{max}N(1 - N/K)$

  • Growth Phases:

  1. Positive acceleration (establishment): Slow initial growth.

  2. Logarithmic phase: Rapid growth.

  3. Negative acceleration: Slowing as $N$ approaches $K$.

  4. Stable equilibrium: $N = K$.

• Comparison: Logistic growth is highest when $N = K/2$.

Resource Limitation and Carrying Capacity

• Carrying Capacity (K): The population size that an environment can support where birth rates equal death rates ($growth = 0$).

• Density Dependence: As $N$ increases, competition for resources increases, decreasing natality and increasing mortality.

  • Density-Independent: Factors where influence does not change with population density.

Survivorship Curves and Reproductive Strategies

• Survivorship Curves:

  • Type I: High juvenile survival, long life (e.g., humans).

  • Type II: Constant death rate throughout life (e.g., squirrels, many reptiles, American robins).

  • Type III: High juvenile mortality (e.g., plants, oysters, sea urchins).

• Evolutionary Strategies:

  • K-selection: Competitive species in stable environments, low reproduction rate, high parental care, long lifespan (e.g., humans).

  • r-selection: Rapidly growing (J-curve), high reproduction rate, small body size, early maturity, no parental care, good colonizers (e.g., bacteria).

Population Regulation and Competitive Interactions

• Competition: Happens when a resource is in short supply.

  • Intraspecific: Between individuals of the same species.

  • Interspecific: Between different species.

• Gause’s Principle: Competitive exclusion principle; two species competing for the same limiting resource cannot coexist long-term.

• Mechanisms of Competition:

  • Interference: Direct aggressive interaction (e.g., preventing establishment).

  • Exploitation: Indirect interaction through a shared limiting resource.

  • Apparent: Indirect interaction where two species share a predator; if species A increases, the predator population increases and hunts more of species B.

Direct and Indirect Interspecific Competition

• Lotka-Volterra Competition Model: Derived from the logistic equation to describe two-species interactions.

  • Species 1: $dN_1/dt = r_1N_1(K_1 - N_1 - \alpha N_2) / K_1$

  • Species 2: $dN_2/dt = r_2N_2(K_2 - N_2 - \beta N_1) / K_2$

  • Constants: $\alpha$ and $\beta$ are conversion factors (competition coefficients) expressing individuals of one species in units of the other.

• Economic Outcomes:

  1. Both coexist.

  2. Species 1 becomes extinct.

  3. Species 2 becomes extinct.

• Intraspecific Strategies:

  • Scramble: Resources shared equally; in extreme cases, none get enough to survive/reproduce.

  • Contest: Some individuals claim enough resources, denying others; maintains numerical constancy.

Predation Models and Functional Types

• Types of Predation:

  • Parasitoidism: Weak attacks strong (e.g., larvae consuming a living host).

  • Carnivory: Consumption of animals.

  • Cannibalism: Predator and prey are the same species.

  • Herbivory: Grazing/browsing plants; can kill plants if seeds or the whole plant are eaten.

  • Parasitism: Lives on or in a host for nutrition.

• Lotka-Volterra Predation Equations:

  • Prey: $dN_1/dt = r_1N_1 - PN_1N_2$

  • Predator: $dN_2/dt = dN_1N_2 - qN_2$

  • Symbols: $P$ = coefficient of predation, $q$ = mortality rate of predator, $N_1N_2$ = probability of encounter.

Categorization of Population Interactions

• Positive Interactions: Increase survival ability.

  • Commensalism: One benefits ($+$), other unaffected ($0$). E.g., epiphytes, bird nests in trees.

  • Mutualism: Both benefit ($+/+$).

  • Symbiotic: Obligatory/permanent (e.g., Mycorrhizae, lichens).

  • Non-symbiotic: Live apart but dependent (e.g., fig trees and wasps).

  • Facultative: Non-obligatory.

• Negative Interactions: Limit population densities.

  • Parasitism: One benefits ($+$), other harmed ($-$-).\n - **Microparasites**: Viruses, bacteria (short duration).\n - **Macroparasites**: Flatworms, ticks, etc. (long generation time).\n - **Ectoparasites**: On the surface. **Endoparasites**: Inside the body.\n - **Amensalism**: One harmed (-$-$), other unaffected ($0$).

• Neutralism: Neither affects the other ($0/0$).

Human Population Dynamics and Historical Growth

• Historical Milestones:

  • $10,000\,BC$: $5-10\,million$

  • $1\,AD$: $170\,million$

  • $1800$: $1\,billion$

  • $1930$: $2\,billion$ ($130\,years$ to double)

  • $1960$: $3\,billion$ ($30\,years$ to add a billion)

  • $1975$: $4\,billion$ ($15\,years$ to add a billion)

  • $1987$: $5\,billion$ ($12\,years$ to add a billion)

  • $1999$: $6\,billion$ ($12\,years$ to add a billion)

• Recent Trends: Growth rate was near zero for much of human history. The modern era began in the $1700s$. Growth peaked at $2.0\,\%$ in the mid-1960s and fell to $1.4\,\%$ by $2005$.

• Industrial Revolution: Growth occurred because death rates fell (not rising birth rates) due to improved farming, transportation, and public health.

The Demographic Transition Model

• Transition Components: $Growth = (Births - Deaths) + (Immigration - Emigration)$.

• Stages:

  • Stage 1: High birth and high death rates; little growth.

  • Stage 2: Death rates fall due to better living standards; birth rates remain high. High population growth.

  • Stage 3: Fertility falls; population growth slows.

• Regional Differences: Mortality revolution in less developed countries occurred post-WWII through medical technology. Their growth reached $2.5\,\%$ in the 1960s.

• Age Pyramids:

  • Expanding: Triangular; many young individuals (Developing countries).

  • Stable: Bell-shaped; reproductive groups equal pre-reproductive.

  • Diminishing: Pre-reproductive group is the smallest (e.g., Sweden).

Community Ecology Structure and Species Diversity

• Community: Collection of populations interacting directly or indirectly.

• Biological Structure:

  • Species Richness: Number of taxonomic groups present.

  • Relative Abundance: Proportional individuals of each species.

  • Evenness: Measures variation in relative abundance; less variation means more ‘even’.

• Diversity Estimates: $1.75\,million$ living species described; estimates for Earth range from $3-50\,million$.

• Dominants: Single or few species that predominate numerically or through biomass/activity.

Interactions and Dominance in Ecological Communities

• Types of Interaction:

  • Direct: Predation, competition, parasitism, mutualism.

  • Diffuse: Cumulative effect of small interactions.

  • Indirect: Mediated by a third species.

• Indirect Interaction Examples:

  • Keystone Predation: Predator consumes dominant competitor, allowing weak competitors to coexist (e.g., Pisaster starfish).

  • Apparent Competition: Mimics competition outcome but results from a shared predator or parasite.

• Keystone Species: Those with a disproportionate effect relative to abundance (e.g., corals building reefs that serve as habitat).

Vertical Stratification and Horizontal Community Structure

• Terrestrial Stratification:

  • Canopy: Primary site of energy fixation.

  • Understory, Shrub Layer, Herb/Ground Layer, Forest Floor.

• Aquatic Stratification: Gradient of light, temperature, and oxygen.

• Horizontal Structure: Patchiness across the landscape driven by soil, moisture, and slope. Influences animal dispersal and foraging.

Ecological Succession: Primary, Secondary, and Climax

• Succession: Temporal change in community structure.

• Sere: A sequence of communities ($grass \rightarrow shrub \rightarrow forest$); each is a seral stage.

• Primary Succession: Begins on sites previously without life (e.g., rock outcrops, dunes, glacial till). H.C. Cowles (1899) studied sand dunes at Lake Michigan.

• Secondary Succession: Occurs on previously vegetated sites following a disturbance (e.g., abandoned farmland).

• Climax Community: The endpoint which results in a stable equilibrium with the physical environment.

Ecosystem Concept: Structure and Function

• Ecosystem: Functional system of complementary relationships, energy transfer, and matter circulation.

• Structure: Autotrophs (energy capture), Heterotrophs (consumers/decomposers), and Inorganic/Dead Organic Matter.

• Functional Processes: Energy transfer between trophic levels and nutrient cycling between abiotic and biotic components.

• Disturbance: Fire, floods, and human actions make ecosystems shifting patterns on the landscape rather than permanent entities.

Ecosystem Productivity: NPP, GPP, and NEP

• Gross Primary Productivity (GPP): Total energy fixed via photosynthesis/chemosynthesis.

• Net Primary Productivity (NPP): $GPP - Producer\,Respiration$. NPP limits secondary productivity.

• Net Ecosystem Productivity (NEP): Rate of energy production stored in live matter. Negative NEP means respiration exceeds production (common in old forests).

• Measurement:

  • Terrestrial: Calculated as dry weight ($\Delta B = NPP - G - L$ where $G$ is herbivory and $L$ is mortality).

  • Aquatic: Measured via $O_2$ production in light/dark bottles. Light bottle = NPP; Dark bottle = respiration.

  • Calorimetry: Measures useful energy by burning tissue to detect temperature change.

Secondary Productivity and Trophic Efficiencies

• Net Secondary Production: $Assimilation - Maintenance\,Respiration$.

• Efficiencies:

  • Assimilation Efficiency: $Assimilation / Gross\,Assimilation$.

  • Secondary Production Efficiency: $Net\,Secondary\,Production / Assimilation$. Higher in ectotherms than endotherms due to lower basal metabolic rates.

  • Consumption Efficiency: $Gross\,Assimilation\,of\,trophic\,level\,n / Net\,Productivity\,of\,trophic\,level\,n-1$.

Trophic Structure, Food Chains, and Food Webs

• Trophic Hierarchy:

  1. Primary Producers (Autotrophs)

  2. Primary Consumers (Herbivores)

  3. Secondary/Tertiary Consumers (Predators)

• Food Chains: Grazing (source: living tissue) vs. Detritus (source: dead matter). Detritus chain is the major path in terrestrial/littoral systems.

• Food Webs: Complex meshed food chains involving omnivores.

• Ecological Pyramids:

  • Pyramid of Numbers: Numbers at lower levels are usually highest (Charles Elton).

  • Pyramid of Biomass: Total weight of standing crop; can be inverted in aquatic systems where turnover is high.

  • Energy Pyramid: Always broadest at the base (Second Law of Thermodynamics).

Laws of Thermodynamics and Energy Flow

• First Law: Energy is neither created nor destroyed, only transformed.

• Second Law: Energy transfer results in loss as heat/waste, increasing entropy. Trophic links are generally limited to $3-5$ because of this loss.

Biogeochemical Cycles: Carbon, Nitrogen, Sulfur, and Phosphorus

• Carbon Cycle: $CO_2$ assimilation by plants. In water, DIC (dissolved inorganic carbon) exists as $CO_2$, bicarbonate ($HCO_3^-$), or carbonate ($CO_3^{2-}$) based on pH (pH < 4.3 is gas, > 8.3 is carbonate).

• Nitrogen Cycle:

  • Fixation: $N_2 \rightarrow NH_3$ (Biological by bacteria/cyanobacteria; needs $160\,kcal\,mol^{-1}$) or Nitrates via lightning.

  • Mineralization/Ammonification: Organic $N \rightarrow NH_3$ (protein breakdown).

  • Nitrification: $NH_3 \rightarrow NO_2^-$ (Nitrosomonas) and $NO_2^- \rightarrow NO_3^-$ (Nitrobacter).

  • Denitrification: $NO_3^- \rightarrow N_2$ (Pseudomonas/fungi under anaerobic conditions).

• Sulfur Cycle: Long-term sedimentary phase in rocks/fossil fuels. Gaseous phase includes $H_2S$, $SO_2$, and Dimethylsulfide (DMS). DMS from phytoplankton is the largest atmospheric sulfur emission.

• Phosphorus Cycle: No significant atmospheric component. Source is the mineral apatite. Limited in aquatic systems; runoff causes algal blooms. Fractions include POP (particulate organic), DIP (dissolved inorganic), and DOP (dissolved organic).

Environmental Change and Global Warming

• Definition: Change in statistical properties of climate over decades. Synonymous with global warming.

• Natural Causes:

  • Plate Tectonics: Changes land/ocean geometry.

  • Orbital Variations (Milankovitch): Eccentricity, tilt, and precession.

  • Solar Output: variations in intensity.

  • Volcanism: Release of $CO_2$ and particulates.

• Human (Anthropogenic) Causes: Greenhouse gas emissions ($CO_2$, methane, ozone, CFCs, nitrous oxide). Humans generate $130\,times$ the amount of $CO_2$ of all volcanoes.

• Evidence: Ice cores (Antarctic), tree rings (Dendroclimatology), pollen analysis (Palynology), beetle remains, and sea-level rise measurements.

• Greenhouse Effect: Solar input is $342\,W\,m^{-2}$. $107\,W\,m^{-2}$ is reflected (Albedo). Earth absorbs $168\,W\,m^{-2}$ and must reradiate it as long-wave infrared radiation.

• Current Stats: Global surface temperature increased $0.74 \pm 0.18\,^{\circ}C$ in the 20th century. Projections suggest a further $1.1$ to $6.4\,^{\circ}C$ rise in the 21st century. The Kyoto Protocol aims to stabilize concentrations.