2.1 Individuals, populations, communities, and ecosystems

Carrying Capacity

The maximum population size of a species or "load" that can be sustainably supported by a given environment. This 'maximum' is dynamic and influenced by changes in abiotic factors (e.g., climate) and biotic factors (e.g., food availability).

Density-Dependent Factors

Limiting factors (limit population growth) whose impact increases as population density rises. Examples include competition for resources, predation, and disease, which intensify in crowded populations.

Density-Independent Factors

Limiting factors (limit population growth) that affect populations regardless of their density. Examples include natural disasters (e.g., hurricanes, droughts) and extreme weather events, which limit population growth regardless of 'crowdedness' (or lack of).

Community

A group of populations of different species living and interacting with each other in the same area.

Species

A group of organisms that share common characteristics and that interbreed to produce fertile offspring.

Ecosystem

A community and the physical environment with which it interacts. It's an open system where both energy and matter can enter and exit.

Keystone Species

A single species in an ecosystem necessary for maintaining its structure and function. Examples include wolves in Yellowstone, which regulate herbivore populations, and coral in reef ecosystems, which provide habitat for a variety of marine species.

Extinction Rate

The number of species becoming extinct over a given period of time. If high, it can reduce biodiversity and disrupt ecosystem stability.

Clade

Illustrates evolutionary relationships in which all the members of a taxonomic group have evolved from a common ancestor.

Fundamental Niche

The full range of environmental spaces, habitats, and resources a species could THEORETICALLY use and operate in to survive and reproduce in an ecosystem if there weren't competitors or other limiting factors. (So, the LARGEST role/position a species could theoretically occupy in an ecosystem). E.g., All the environmental spaces, habitats, and resources a species of tree could occupy, if not prevented by another faster-growing species of tree currently using them.

Realized Niche

The ACTUAL range of environmental spaces, habitats, and resources a species USES and operates in because of biotic interactions like competition and predation. These restrict it from occupying the THEORETICAL full range it COULD use. E.g., All the environmental spaces, habitats, and resources a species of tree uses, as it's limited by another faster-growing species of tree that outcompetes it for space and resources.

Niche

The ecological role of a species in an ecosystem and the range of conditions necessary for its survival. An organism's ecological ____ depends not only on where it lives but also on what it does.

Classification

The organization of organisms into different taxa (hierarchical groups) based on shared characteristics. Taxa range from broad categories like kingdoms to specific ones like species, reflecting evolutionary relationships and traits.

Population

A group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding.

Abiotic Factor

A non-living, physical factor that may influence an organism or ecosystem; for example, temperature, sunlight, pH, salinity, precipitation.

Biotic Factor

A living, biological factor that may influence an organism or ecosystem; for example, predation, parasitism, disease, or competition.

Competition

A common demand by two or more organisms upon a limited supply of a resource; for example, food, water, light, space, mates, nesting sites. It may be intraspecific (within the same species) or interspecific (between different species).

Mutualism

A relationship between individuals of two or more species in which all benefit and none suffer. For example, bees pollinate flowers while obtaining nectar for food. Both flowers and bees benefit.

Parasitism

A relationship between two species in which one species (the ____) lives in or on another (the host), gaining all or much (in the case of a partial parasite) of its nutrients/resources from it. For example, ticks feeding on mammals, mistletoe on trees (partial parasite: still performs photosynthesis), tapeworms, etc.

Capture-Mark-Release-Recapture

A method to estimate animal population sizes by capturing, marking, releasing, and recapturing individuals to calculate population estimates. For example, this can be used to estimate fish populations in a lake.

Biosphere Integrity

The health and functioning of Earth's ecosystems, including the diversity of life, the resilience of ecosystems, and their ability to support life. It is crucial for maintaining ecosystem services. It is one of the nine planetary boundaries.

Habitat

The natural environment where a species lives, providing the conditions needed for survival, such as food, water, and shelter.

Transect Sampling

A sampling method where a line is laid across a habitat, and organisms are recorded at regular intervals to study species distribution. E.g., can be used to monitor coral reef biodiversity by putting out a line across the reef, recording the presence, abundance, and variety of marine species at set points to determine changes in ecosystem health over an area.

Quadrat

A square frame used to isolate a standard area for studying the abundance and distribution of organisms in an ecosystem. For example, counting plant species in a grassland.

Lincoln Index

A formula used to estimate population size in mark-recapture studies: N = M × S / R. For example, it can be applied to estimate wildlife populations, such as counting deer in a forest by marking and recapturing them.

Systematic Sampling

A sampling method where data is collected at regular intervals to ensure even coverage of the study area.

Random Sampling

A sampling technique where every individual in a population has an equal chance of being selected to minimize bias. This can be done by placing a grid on a map and using a random number generator to select sampling points, ensuring that the selection process avoids any systematic influence.

Logistic Growth (S-Shaped)

A population growth model that slows as it nears carrying capacity, eventually reaching steady-state equilibrium, forming an S-shaped curve.

Exponential Growth

A rapid population increase that occurs under ideal conditions, typically forming a J-shaped curve as it is unsustainable and eventually crashes (boom and bust, e.g., St. Matthews deer island).

Biosphere

The global sum of all ecosystems, encompassing all life forms and their interactions with Earth's land, water, and atmosphere (_______ = ‘Life Sphere’).

Individual

A single organism, distinct from others, capable of independent survival and functioning (E.g., a single elephant in a herd).

Genus Species

The two-part scientific naming system (e.g., Homo sapiens) used to classify organisms based on their _____ and _____. E.g., Panthera leo, (lions). The _____ name is always capitalized, and the _____ name is lowercase, with both italicized (underlined when handwritten).

Taxonomist

A scientist who classifies organisms into groups based on shared traits and establishes their biological relationships. They often use tools like dichotomous keys to identify species accurately.

Dichotomous Key

A tool for identifying organisms by following a series of choices/characteristics (e.g., leaf shape) that lead to the correct name. It is frequently used by taxonomists to accurately classify species.

Herbivory

The consumption of plants by animals, which influences plant populations and ecosystem balance. For example, deer grazing on grass.

Predation

An interaction where one organism (predator) hunts and consumes another organism (prey). E.g., wolves hunting deer.

Disease

A condition that disrupts an organism’s normal functioning, caused by pathogens, genetics, or environmental factors.

Food Web

A network of interconnected food chains showing how energy and nutrients flow through an ecosystem.

Afforestation vs. Reforestation

Planting trees on non-forested land, vs replanting trees in previously forested areas (Both aim to restore ecosystems and combat climate change.)

Invasive Species

Non-native species introduced to an ecosystem that often outcompete native species, disrupt ecosystems, and reduce biodiversity. For example, zebra mussels in North American waterways.

Trophic Cascade

An ecological process where changes in the population of one species (often a top predator) cause significant effects that ripple through the food chain, altering the entire ecosystem. For example, the reintroduction of wolves to Yellowstone National Park reduced elk populations, allowing vegetation to recover, which improved habitats for birds and beavers and stabilized water systems.