IB ESS Topic 2: Ecosystems and Ecology

Dichotomous Key

A guide used to identify an organism where there are two options based on different characteristics at each step. When making a dichotomous key, terms such as "big" or "small" are not useful. Comparative, quantitative descriptors and simple identification of the presence or absence of external features are most useful in keys.

Turbidity

A measure of how clear water is. Cloudy water has higher turbidity and prevents less light from reaching deeper into the body of water. A Secchi disk can be used to measure it.

Stratified Random Sampling

A method of sampling that involves the division of a population into smaller sub-groups known as strata. A proportionate number of observations is taken from each part of the population.

Carnivores

A secondary consumer that feeds only on other animals.

Biomagnification

The increase in concentration of persistent or non-biodegradable pollutants along a food chain (ie, as you go up trophic levels). Toxins such as DDT and mercury biomagnify up the food chains due to organisms at higher trophic levels eating multiple organisms from lower trophic levels.

Maximum Sustainable Yield

The largest crop or catch that can be taken from the stock of a species (eg a forest, a shoal of fish) without depleting the stock. Taken away is the increase in production of the stock while leaving the stock to reproduce again. It is often used in managing fisheries. The MSY is equivalent to the net primary productivity (NPP) or net secondary productivity (NSP) of a system.

Biotic Factors

The living components of an ecosystem that directly or indirectly affect another organism. Ex: predation, competition, symbiosis, etc.

Carrying Capacity

The maximum number of a species, or "load", that can be sustainably supported by a given area.

Tricellular Model

The model which describes 3 large convection cells moving air from the equator towards the poles in each hemisphere of the earth that explains the distribution of precipitation and temperature that influence structure and relative productivity of different terrestrial biomes.

Compensation Point

When all carbon dioxide that plants produce in respiration is used up in photosynthesis, the rates of the photosynthesis and respiration are equal and there is no net release of either oxygen or carbon dioxide. This usually occurs at dawn and dusk when light intensity is not too high. The plant is neither adding biomass nor using it up to stay alive at this point - it is just maintaining itself.

Sub-climax Community

When a biotic or abiotic factor stops succession at a stage prior to the climax community. Succession will only continue if the limiting factor is removed.

Overshoot

When a population temporarily exceeds the environment's carrying capacity.

Species Diversity

A function of the number of species and their relative abundance and can be compared using an index. There are many versions of diversity indices, but students are only expected to be able to apply and evaluate the result of the Simpson diversity index.

Population

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

Species

A group of organisms that interbreed and produce fertile offspring.

Community

A group of populations of different species living and interacting with each other in a common habitat.

Biomes

A collection of ecosystems sharing similar climatic conditions. Can be classified as aquatic, forest, grassland, desert and tundra. Climate change is altering the distribution of these. Insolation, precipitation and temperature are the main factors governing the distribution of biomes.

Omnivore

A consumer that eats both plants and animals.

Food Webs

A diagram that shows food chains linked together in an ecosystem.

Quadrat

A frame of specific size which may be divided into subsections. It is used to help count nonmotile species when studying ecosystems.

Herbivore

An organism that feeds exclusively on plants.

Mineral Cycling

A biogeochemical cycle, in which elements move through the soil, living organisms, air, and water, or through some of these. Mineral cycling increases during succession.

Biodiversity

A broad concept encompassing the total diversity of living systems, which includes the diversity of species, habitat diversity and genetic diversity. Biodiversity increases during succession and decreases during mass extinctions.

Plagioclimax

A climax community that results from human intervention. Without human intervention, a different climax community would have developed. Ex: Pasture.

Lichen

A symbiotic relationship (mutualism) between a fungus and green algae. Lichens are often used as indicators species for air pollution because they are very sensitive to it.

Mutualism

A symbiotic relationship between two or more species in which all benefit and none suffer. Classic example: Clownfish get protection from predators by living within sea anenome, while the sea anenome benefits since clownfish attract prey.

Ecosystem

A system formed by the interaction of a community of organisms with their physical environment.

Systematic Sampling

A transect is used to sample along the environmental gradient. Systematic sampling can be continuous or interrupted.

Parasitism

A type of symbiotic relationship in which one organism benefits and the other organism is harmed. Classic example: Leeches bite organisms and take their blood.

Commensalism

A type of symbiotic relationship in which one organism benefits and the other organism is not harmed nor benefitted. Classic example: Whales gives the barnacles a stable place to live, a free ride, and access to plenty of food, but the whales are not harmed or benefitted.

Belt Transect

A type of transect in which A band of chosen width (usually 0.5-1 m) is measured along the environmental gradient / zonation.

Pathogen

A virus, bacteria or other micro-organism that causes disease.

Density-Independent factors

Abiotic factors that affect a population irrespective of population density (e.g. drought).

Intraspecific Competition

Competition within a species for the same resources.

Decomposers

Bacteria and fungi that obtain their energy from dead organisms by secreting enzymes that break down the organic matter. In the nitrogen cycle, they break down organic nitrogen compounds into ammonia. In the carbon cycle, they do respiration to release carbon dioxide.

Salinity

Concentration of salts.

Limiting Factors / Environmental Resistance

Biotic and abiotic factors like food, water, habitat, and mates that slow down growth of a population as it reaches its carrying capacity (ie, prevent exponential growth of the J-curve). They can be density-dependent or density independent.

Anthropogenic

Caused by humans

Diebacks

Collapse of a J-curve or overshoot due to environmental resistance; returns the population to below the carrying capacity.

Interspecific Competition

Competition between different species for the same resource.

Line Transect

Consists of a string or measuring tape which is laid out in the direction of the environmental gradient and species touching the string or tape are recorded.

Niche

Describes the particular set of abiotic and biotic conditions and resources to which an organism or population responds.

Latitude

Distance north or south of the equator. Higher latitudes give rise to larger seasonal variations (ie, winters) that can affect productivity and influence what biomes are present.

Carbon Fixation

During photosynthesis, the removal of carbon dioxide from the air to be "fixed" into a solid organic molecule like glucose.

Pioneer Species

The first stage of an ecological succession that contains a community of species able to live in difficult conditions. Examples commonly include mosses, lichens and bacteria. Often j-strategists.

Altitude

Elevation above sea level. Higher altitudes tend to result in lower oxygen levels and colder temperatures.

Productivity

Gain in biomass or energy in a specific area in a specific amount of time.

Consumers / Heterotrophs

General term for organisms that eat other organism to obtain their food.

Predator-prey Relationships

How predator/prey populations affect each other.

Ecological Pyramids

Include pyramids of numbers, biomass and productivity and are quantitative models to understand populations and transfers of energy in a food chain or ecosystem.

Currents

Mass movements of water or air (wind) that redistribute energy.

Secondary Succession

Occurs in places where a previous community has been destroyed (e.g. after forest fires).

Simpson's Diversity Index

One way of calculating species diversity. The index provides a numerical measure of species diversity that is derived from both the number of species and their relative abundance.

Detritivore

Organisms like snails and earth worms that eat (ingest) dead plant and animal matter (detritus).

Producers / Autotrophs

Organisms that can produce their own food (i.e. glucose). The are typically plants or algae (photoautotrophs) that produce their own food using photosynthesis and form the first trophic level in a food chain. Also includes chemosynthetic organisms that produce food without sunlight.

Ecological Efficiency

Percentage of energy transferred from one trophic level to another in a food chain or web (average of 10%). Also called trophic efficiency.

S-curve

Population growth curve which shows an initial rapid growth (exponential growth) and then slows down as the carrying capacity is reached. Generally followed by k-strategists.

J-curve

Population growth curve which shows exponential growth due to abundant resources and favorable abiotic factors. Growth is initially slow then increasingly rapid, and does not slow down. Generally shown by r-strategists.

Biogeochemical Cycles

Process in which elements, chemical compounds, and other forms of matter are passed from one organism to another and from one part of the biosphere to another. Examples are the carbon cycle, nitrogen cycle, etc.

Denitrification (Denitrifying)

Process in which nitrates are converted back into nitrogen gas and returned to the atmosphere.

Predation

Process of an animal eating another animal.

Nitrogen Fixation

Process of converting nitrogen gas from the atmosphere into ammonium. Primarily done via lightning and bacteria in nature. Humans use the Haber process to fix nitrogen for fertilizer production.

Photoautotrophs

Producers that convert sunlight energy into chemical energy (ie, producing glucose) through photosynthesis. Eg: plants and green algae.

Chemoautotrophs / Chemosynthetic Organisms

Producers that use energy from chemical reactions to produce glucose. Eg: Nitrifying bacteria.

R-Strategists / r-selected species

Species that produce large numbers of offspring so they can colonize new habitats quickly and make use of short-lived resources.

K-Strategist / k-selected species

Species that tend to produce a small number of offspring that they take care of, which increases their survival rate and enables them to survive in long-term climax communities.

Fundamental Niche

The full range of conditions and resources in which a species could survive and reproduce.

Pyramid of Productivity

Refers to the flow of energy through a trophic level, indicating the rate at which that stock/storage is being generated. Pyramids of productivity for entire ecosystems over a year always show a decrease along the food chain.

Pyramid of Biomass

Represents the standing stock or storage of each trophic level, measured in units such as grams of biomass per square metre or Joules per square metre. Pyramids of biomass can sometimes be inverted because they represent the biomass present at a fixed point in time.

Continuous Sampling

Sample where the whole transect is sampled (in either a belt or line through the habitat). An example of systematic sampling.

Interrupted Sampling

Samples taken at points of equal distance along the transect. Its benefit is it takes less time than continuous sampling. An example of systematic sampling.

Pyramid of Numbers

Shows the number of organisms at each trophic level in a food chain at one time. Pyramids of numbers can sometimes display different patterns; for example, when individuals at lower trophic levels are relatively large (inverted pyramids).

Primary Succession

Succession occurring on a previously uncolonized substrate (i.e. no soils existed like newly formed islands from volcanoes).

Realized Niche

The actual conditions and resources in which a species actually exists due to biotic interactions.

Bioaccumulation

The build-up of persistent or non-biodegradable pollutants within an organism over time.

Zonation

The change in community along an environmental gradient due to factors such as changes in altitude, latitude, tidal level or distance from shore/coverage by water.

Competition

The common demand by two or more organisms for a limited supply of a resource such as food, water, light, space, mates and nesting sites.

Respiration

The conversion of glucose and oxygen into carbon dioxide and water in all living organisms, releasing energy. During respiration, large amounts of energy are dissipated as heat, increasing the entropy in the ecosystem while enabling organisms to maintain relatively low entropy and so high organization. Reaction: glucose + oxygen → carbon dioxide + water + energy (it is the opposite of photosynthesis)

Latent Heat

The energy absorbed or released during a change in state. For example, when water freezes to form ice/snow, the latent heat is released. When it melts, latent heat is absorbed.

Habitat

The environment where a species normally lives.

Climax Community

The final stage of a succession that is more or less stable and is in equilibrium. Represents the maximum possible development that a community can reach under the environmental conditions.

Abiotic Factors

The non-living, physical factors that influence the organisms and ecosystem. Examples include temperature, sunlight, pH, salinity, and precipitation.

Population Density

The number of individuals of each species per unit area.

Biosphere

The part of Earth in which life exists including land, water, and atmosphere.

Percentage Frequency

The percentage of a total number of quadrats that a species was present in.

Trophic Level

The position that an organism, or group of organisms, occupies in a food chain.

Photosynthesis

The process by which green plants convert light energy from the sun into usable chemical energy stored in organic matter. Photosynthesis produces the raw material for producing biomass. Reaction: carbon dioxide + water + energy → glucose + oxygen

Nitrification (Nitrifying)

The process by which nitrites and nitrates are produced by bacteria in the soil from ammonium.

Assimilation / Secondary Productivity

The process by which nutrients become part of the organism's body. For example, producing proteins or DNA from nitrogen compounds absorbed.

Herbivory

The process of an organism feeding on a plant.

Succession

The process of change over time in an ecosystem involving pioneer, intermediate and climax communities.

Percentage Cover

The proportion of a quadrat covered by a species, measured as a percentage.

Energy Budget

The quantities of energy entering, staying within and leaving a system (ie, an animal, population, Earth, etc)

Population Dyanmics

The study of the factors that cause changes to population sizes.

Gross Secondary Productivity (GSP)

The total energy / biomass assimilated (taken up) by consumers and is calculated by subtracting the mass of fecal loss from the mass of food eaten. GSP = food eaten - fecal loss

Gross Primary Productivity (GPP)

The total gain in energy or biomass made by photosynthetic organisms in a specific area in a specific amount of time. It is the energy fixed (or converted from light to chemical energy) by green plants during photosynthesis.

Net Secondary Productivity (NSP)

The total gain in energy or biomass per unit area per unit time by consumers after allowing for losses to respiration. It is calculated by subtracting respiratory losses (R) from GSP. NSP = GSP - R

Net Primary Productivity (NPP)

The total gain in energy or biomass per unit area per unit time by green plants after allowing for losses to respiration. This is the increase in biomass of the plant (how much it grows) and is the biomass that is potentially available to consumers (animals) that eat the plant. It is calculated by subtracting respiratory losses (R) from gross primary productivity (GPP). NPP = GPP - R

Sere

The whole sequence of communities in a succession.

Random Sampling

Used when habitat is homogenous (the same) throughout an area. A random-number generator can be used to produce coordinates.