Individuals, Populations, Communities, and Ecosystems Study Notes

Biosphere: The global ecological system including all parts of Earth where life exists, from the upper atmosphere to the deep crust.
Species: A group of organisms that can interbreed and produce fertile offspring.
Taxonomy: Classification system developed by Charles Linnaeus using binomial nomenclature ( $Genus\,species$ ).
Identification Tools: Includes dichotomous keys, comparison with reference specimens, and deoxyribonucleic acid (DNA) surveys.
HL Classification: Cladistics uses clades (ancestors and all descendants) to illustrate evolutionary relationships more accurately than traditional morphology.

Niche: The particular set of abiotic (temperature, sunlight, $pH$ , salinity, dissolved oxygen, soil texture) and biotic conditions upon which an organism depends.
Fundamental Niche (HL): The entire range of conditions in which a species could potentially live.
Realized Niche (HL): The actual conditions used by a species, often restricted by competition.
Community: A collection of interacting populations within an ecosystem.
Keystone Species: Species essential for maintaining ecosystem structure and sustainability (e.g., wolves or elephants).
Population Interactions: Herbivory, predation, parasitism, mutualism, disease, and competition.

Carrying Capacity ( $CC$ ): The maximum population size of a species sustainably supported by an environment.
J-curve: Represents exponential growth without limiting factors; typical for locusts or algae.
S-curve: Represents logistic growth that plateaus at carrying capacity due to environmental resistance.
Density-Dependent Factors: Factors regulating size based on population density, including resource competition, predation, and disease.
Density-Independent Factors: Factors affecting populations regardless of density, such as climate, natural disasters, and habitat destruction.
r-strategists (HL): Adapted to unstable environments, characterized by short lifespans and high numbers of offspring with no parental care.
K-strategists (HL): Adapted to stable environments, characterized by long lifespans, few offspring, and high parental investment.

Random Sampling: Uses a numbered grid to select areas to minimize bias.
Systematic Sampling: Involves sampling at regular intervals, often using a transect line across environmental gradients.
Quadrat Sampling: Used to estimate population size for non-mobile organisms by counting individuals in a fixed area ( $0.25\,m^2$ ).
Lincoln Index: A formula used for mobile organisms via capture-mark-release-recapture:

$N = \frac{n_1 \times n_2}{m}$

Where $N$ is the total population estimate, $n_1$ is the number of animals first marked, $n_2$ is the number of animals in the second sample, and $m$ is the number of marked animals recaptured.

Ecosystem Integrity: Open systems where energy and matter enter and exit; sustainability is a natural property of balanced inputs and outputs.
Tipping Points: Thresholds where human activity (e.g., deforestation in the Amazon Rainforest) causes rapid, irreversible shifts to new equilibria.
Planetary Boundaries: A model indicating human-induced changes to biosphere integrity have passed critical thresholds.
Human Population: Growth has accelerated due to technology, medicine, and the Green Revolution; carrying capacity is difficult to assess for humans due to resource mobility and consumption patterns.
Phenology (HL): Human-induced climate change alters the timing of life cycles, such as earlier flowering, which can desynchronize interactions between species like pollinators and plants.

Question: How can natural systems be modelled, and can these models be used to predict the effects of human disturbance?
Discussion: Population dynamics such as natality (birth rates) and mortality (death rates) are critical for calculating ecosystem stability and growth trends.