3.5: Population size and growth

Fugitive

Species that are poor at competition, and instead reproduce and disperse fast. For example, algae.

Equilibrium

Species that control their population using competition within a stable environment. Their pattern of growth is the one-step growth curve.

One step growth

Curve that represents the growth of equilibrium species. Is a sigmoid curve.

Lag

Phase of the one step growth curve where the population doesn’t increase, and then has a period of slow growth. Organisms prepare for growth with intense metabolic activity, and wait for sexual maturity and gestation.

Exponential

AKA log phase. Phase of the one step growth curve where numbers increase, slowing towards the end. This is due to most individuals being able to reproduce, and decreases due to environmental resistance.

Stationary

Phase of the one step growth curve where birth and death rates are almost equal and the curve plateus. This is not a completely still population, and it still fluctuates over the carrying capacity.

Death

Phase of the one step growth curve where the environmental resistance factors grow in significance, and the population declines. Death rates are higher than birth rates.

Carrying capacity

A populations maximum size in a given environment. Maintained using negative feedback.

Predator-prey

Relationship which causes both populations to oscillate.

Density dependent

Factors that have a greater effect if the population increases. Biotic factors, such as disease and food depletion. Lowers the population back to carrying capacity.

Density independent

Factors that have the same effect no matter the population size. Abiotic factors, such as temperature and floods.

Environmental resistance

Factors lessened to raise the population back to carrying capacity. Includes decreasing food, space and increases in toxic waste, predators, competition and disease.

Ecosystem

Interaction between a community and it’s abiotic factors.

Habitat

Ecological or environmental areas inhabited by a living organism as it provides means of survival. Can be a geographical area, but also a part of another organism.

Microhabitats

Small areas that differ from their surroundings and have features that make it suitable for a particular species, such as moth larva only feeding on the lower leaves of cabbages.

Producers

Start of food chains and trophic levels, on the base of ecological pyramids. Convert light energy from the sun to chemical energy. Includes green plants, cyanobacteria and some Protocista.

Primary consumers

Second trophic level. Eat producers. Are often herbivores.

Secondary consumers

Third trophic level. Eats primary consumers. This level, and the ones higher, are often carnivores.

Decomposers

Microbes that obtain nutrients from dead organisms and animal waste, completing the decomposition process. Saprobionts. Examples are bacteria and fungi.

Detritivores

Organisms which feed on small fragments of organic debris known as detritus. Saprobionts. Examples are earthworms, woodlice and millipedes.

Destritus

Remains of dead organisms and fallen leaves. Eaten by detritivores.

3D

Dimensional environment that has longer food chains. Includes aquatic systems and forest canopies.

Primary productivity

The rate producers convert energy into biomass.

Gross primary productivity (GPP)

The overall productivity of a plant, using energy from the sun. A majority of this is used for respiration.

Net primary productivity (NPP)

Represents the energy remaining of the GPP after respiration. This is the energy used to create biomass, which is available to primary consumers and harvested by farmers.

Secondary productivity

Occurs in heterotrophs. The rate at which consumers accumulate energy from consumed biomass in cells and tissues.

Ecological

Pyramids that show a particular feature of each trophic level, such as number, energy and biomass.

Number

Ecological pyramids that show population size. Does not account for organism size, groups juveniles and adults together, can be difficult to draw, and can be inverted.

Energy

The most accurate ecological pyramid. No chance of inversions and easy to compare communities.

Biomass

Pyramids that are linked to energy, but don’t count it exactly. Hard to accurately measure, can be inverted, overstate trophic level contributions, and does not account for differing lifespans.

Primary

Type of succesion that happens after the introduction of a species into a habitat that has never had a community, and is slower.

Sere

The overall sequence of communities overtime throughout succession.

Xerosere

A sere in a very dry environment.

Seral stage

The individual stages of succession - the sequence of different communities.

Pioneer

The first species to colonise an area, forming a community. Often lichens and algae.

Humus

Organic material composed of dead and decaying matter. Increases of its concentration in the soil can move an area up seral stages.

Climatic climax

A community which is stable, self-perpetuating and relies largely on the climate. Has high species diversity, a complex food web and is dominated by long-lived plants.

Secondary

Type of succession that recolonises an area previously occupied by a community, and happens rapidly. Depends on the conditions prior to disturbance.

Dis-climax

Human interference altering the the development of a climatic climax community, via livestock grazing, land farming and deforestation.

Heather moors

Managed to allow for grouse hunting. Every 12 years, heather shoots are burned to initiate a secondary succession, preventing them from degenerating and better accomodating grouse.

Intraspecific

Competition between members of the same species. Is density-dependent, manages carrying capacity and allows for natural selection.

Interspecific

Competition between individuals of different species. Happens over common needs, such as water, oxygen and light.

Niche

Occupying a specific place and having a particular role within a community. Describes an organism’s way of life.

Competitive exclusion

Principle developed by Grouse’s bacterial experiments, which showed two species with the same niche cannot coexist, one will outcompete the other.

Symbiosis

Association between individuals of two species. Occurs across a range of interdependence.

Facilitation

Positive interactions between species. Increasingly significant in complex communities, increases resources, and provides refuge from stress, predation and competition.

Mutualism

Type of facilitation where the interaction is beneficial to both, such as plants and pollinators.

Mycorrhizae

The symbiotic and mutualistic relationship between fungi and plant roots.

Commensalism

Type of facilitation that involves loose interactions between species, where one is benefitted and one is unaffected. An example is nurse plants making a canopy which allows seeds to germinate.

Calcium carbonate and magnesium

Incorporated into shells and exoskeletons of aquatic animals. After they die, this forms the components of chalk, limestone and marble. Makes up external skeletons of coral, which are dissolvable in acid.

Cover cropping

Usage of another plant between gaps of one plant. This covers and protects soil, as well as improving other plants. It enhances soil structure and adds organic matter to topsoil, lowering CO2 production via decomposition.

Ammonification

Part of the nitrogen cycle where proteins are converted into ammonium via decomposers in the soil, which secrete deanimases to deanimate proteins, and proteases to digest proteins.

Nitrification

Part of the nitrogen cycle where nitrites (NO2-) and nitrates (NO3-) are made and enter the soil. Aerobic conditions are required.

Pseudomonas

Bacteria needed for denitrification - the loss of nitrate from the soil. Converts nitrate to nitrogen, allowing it to enter the air. Occurs in anaerobic soils, such as waterlogged ones.

Azotobacter

Bacteria needed for nitrogen fixation in the soil. The most common form, uses the enzyme nitrogenase.

Rhizobium

Bacteria needed for nitrogen fixation to legumes. To protect the reduction reductions, leg-haemoglobin is produced to bind molecular oxygen, making the nodules pink. Both of the organisms produce chemo-attractants to find each other.

Leg

Type of haemoglobin produced by legumes to protect the reduction reactions done by Rhizobium in the root nodules. Done as they have a mutualistic relationship, and amino acids and ammonium ions enter legumes via the vascular strand.

Chemo-attractants

Secreted by Rhizobium cells and legume radicles in order to find one another. Rhizobium flagella moves towards the radicle, which grows towards them. They then invade the cortex and multiply rapidly, causing swelling which is the root nodule.

Nitrosomonas

Bacteria which converts ammonium ions (NH4+) into nitrites (NO2-) using oxidation reactions. Requires aerobic conditions.

Nitrobacter

Bacteria which converts nitrites (NO2-) into nitrates (NO3-) using oxidation reactions. Requires aerobic conditions.

Slurry

Fertiliser made from manure and water, only produced from intensive livestock practices. When pig manure is used, it must be injected due to the smell caused by proteins. Attempts are being made to adjust their feed to stop this.

Biosolids

Fertiliser made from treated human sewage - a sustainable alternative.

Green

Fertiliser composed of legumes being ploughed back into the soil due to their high nitrate content.

Oligotrophic

Have very few minerals dissolved in them - describes upland streams. Where eutrophication takes place if balance is disrupted by fertilisers.

Eutrophication

Fertilisers artificially raise the mineral concentration of lakes and rivers causing algal blooms, blocking photosynthesis, killing plants, algae dies, saprobiontic bacteria then decomposes them and consumes the oxygen, killing any oxygen-reliant bacteria. Anaerobic bacteria can then thrive on converting nitrate to nitrite.

Trophic level

A position of an organism in a food chain, presented in ecological pyramids.

Nitrogen fixation

The removal of nitrogen from the air to convert it to ammonium, difficult due to it’s strong triple bond. Can be done via Rhizobium in legumes or Azotobacter in soils. Uses nitrogenase enzyme. Requires aerobic conditions.

Nitrogenase

Enzyme used to reduce airborne nitrogen to ammonium ions during nitrogen fixation. This is then converted to organic acids, then amino acids, then bacterial proteins.

Haber

A process which converts nitrogen to fertilisers via artificial nitrogen fixation. Done to increase nitrogen in soils, often also using bacteria.

Biochemical oxygen demand (BOD)

Created by short lived algal bloom death, which are decomposed by saprotrophic fungi which require aerobic conditions. Leads to fish death.