Evolution, Ecology, and Photosynthesis: Key Concepts for Biology

Evolution

Change in allele frequencies in a population over time.

Natural Selection

Process where individuals with advantageous traits reproduce more successfully.

Adaptation

A heritable trait that increases an organism’s fitness in a given environment.

Fitness

An individual’s ability to survive and reproduce relative to others.

Mutation

Random change in DNA sequence; ultimate source of genetic variation.

Genetic Drift

Random change in allele frequencies, strongest in small populations.

Gene Flow

Movement of alleles between populations through migration or interbreeding.

Phylogenetics

Study of evolutionary relationships among species.

Clade

A group containing an ancestor and all its descendants (monophyletic group).

Homologous Trait

Trait shared by species due to shared ancestry.

Analogous Trait

Trait shared due to convergent evolution, not common ancestry.

Speciation

Formation of new species from an ancestral population.

Allopatric Speciation

Occurs when populations are geographically separated.

Sympatric Speciation

Occurs without geographic separation (often via polyploidy or niche differentiation).

Biological Species Concept

Defines species as groups that can interbreed and produce fertile offspring.

Morphological Species Concept

Defines species based on physical traits.

Phylogenetic Species Concept

Defines species as the smallest monophyletic group on a phylogeny.

Hardy-Weinberg Equilibrium

Condition where allele frequencies don’t change; no evolution occurs.

HW Equation

p² + 2pq + q² = 1 (p = dominant allele frequency; q = recessive).

Directional Selection

Favors one extreme phenotype, shifting the mean.

Stabilizing Selection

Favors intermediate phenotypes, reducing variation.

Disruptive Selection

Favors both extremes, increasing variation.

Bottleneck Effect

Drastic reduction in population size leading to loss of genetic variation.

Founder Effect

When a small number of individuals start a new population, altering allele frequencies.

Sexual Selection

Type of selection based on traits that increase mating success.

Nutrients — Elements and compounds organisms need to survive and grow.

Autotroph — Organism that produces its own food from inorganic sources.

Heterotroph — Organism that obtains energy by consuming other organisms.

Photoautotroph — Uses sunlight to make food (e.g., plants).

Chemosynthetic autotroph — Uses inorganic chemicals (e.g., H₂S, NH₄⁺) for energy.

C3 photosynthesis — Common in cool/moist conditions; prone to photorespiration.

C4 photosynthesis — Adapted to hot/sunny climates; separates carbon fixation spatially.

CAM photosynthesis — Adapted to arid climates; separates carbon fixation temporally.

Photorespiration — Process that reduces photosynthetic efficiency in C3 plants.

Müllerian mimicry — Two toxic species mimic each other.

Batesian mimicry — A harmless species mimics a harmful one.

Optimal foraging theory — Organisms maximize energy gain per unit time.

Functional response — Relationship between prey density and consumption rate.

Type I functional response — Linear increase, no handling time.

Type II functional response — Levels off due to handling time.

Type III functional response — Sigmoid curve; learning or switching prey types.

Size-selective predation — Predators prefer prey of a certain size.

Net photosynthesis — Photosynthesis rate minus respiration rate. Population — Group of individuals of the same species in a specific area.

Niche — Environmental conditions and resources required for survival and reproduction.

Fundamental niche — Full range of conditions a species could occupy.

Realized niche — Actual range due to competition or predation.

Microclimate — Localized climate conditions that differ from the surrounding area.

Distribution patterns — Clumped, random, or uniform arrangements of individuals.

Clumped distribution — Individuals aggregated in patches (most common).

Uniform distribution — Even spacing due to competition or territoriality.

Random distribution — Independent of other individuals.

Endemic species — Species restricted to a specific geographic area.

Population density — Number of individuals per unit area.

Body size-density relationship — Larger organisms tend to have lower population densities.

Island species risk — High extinction risk due to small range and population size.

Population dynamics — Changes in population size, density, and structure over time.

Dispersal — Movement of individuals that affects population density and gene flow.

Numerical response — Change in predator population due to prey density.

Metapopulation — Group of subpopulations connected by dispersal.

Subpopulation — Local population within a larger metapopulation.

Cohort — Group of individuals born at the same time.

Life table — Summarizes survival and mortality data for a population.

Static life table — Records age at death of individuals of all ages at one time.

Survivorship curve — Graph showing survival rate versus age.

Type I survivorship — High early survival (humans, elephants).

Type II survivorship — Constant survival rate (birds).

Type III survivorship — High early mortality (fish, insects).

Age distribution — Proportion of individuals in different age classes.

P. smintheus butterfly — Example of metapopulation dispersal between meadows.

Stream drift — Downstream movement of organisms during flow events.

Spate — Sudden flood that disrupts stream organisms.

Exponential growth — Population growth under unlimited resources.

Logistic growth — Growth that slows near carrying capacity (K).

Geometric growth — Growth with non-overlapping generations.

Intrinsic rate of increase (r) — Maximum growth rate under ideal conditions.

Carrying capacity (K) — Maximum sustainable population size.

Exponential growth equation — dN/dt = rN.

Logistic growth equation — dN/dt = rN(1 - N/K).

Density-dependent factor — Biotic factor (disease, predation) that intensifies with density.

Density-independent factor — Abiotic factor (weather, disasters) that affects populations regardless of density.

Realized per capita rate of increase — Actual growth rate considering current population size.

Human population distribution — Clumped globally.

Age structure diagram — Shows proportions of age groups; indicates growth trends.

Whooping crane population — Example of successful exponential recovery.

Eurasian collared dove — Example of rapid dispersal and exponential growth.

Mutualism — Both species benefit (+/+).

Parasitism — One benefits, one harmed (+/-).

Commensalism — One benefits, other unaffected (+/0).

Competition — Interaction where both are harmed (-/-).

Intraspecific competition — Among individuals of the same species.

Interspecific competition — Between different species.

Interference competition — Direct conflict over resources.

Exploitative competition — Indirect competition via shared resource use.

Tilman's experiment — Showed intraspecific competition leads to self-thinning.

Self-thinning — Decrease in plant density as individuals grow larger.

Competitive exclusion principle — No two species can occupy the same niche indefinitely.

Niche partitioning — Division of resources to reduce competition.

Lotka-Volterra model — Mathematical model describing interspecific competition.

Competition coefficient — Measures strength of one species' effect on another.

Zero net growth isocline (ZNGI) — Graph line showing combinations where population growth = 0.