ecology study guide

Population

a group of organisms of the same species who live in the same area and are able to produce fertile offspring

• if two populations of the same species are geographically isolated for a long time, speciation can occur

carrying capacity and competition for limited resources

the bigger a population grows, the more resources such as water, oxygen, or food are taken from the environment

• at some point a limit is reached if a population grows too large

• the maximum size of a populations that an environment can support is the carrying capacity

limiting factors for animals

include space, food, mates, nesting sites, and water

limiting factors for plants

include light, nutrients in the soil, water, carbon dioxide, and temperature

how can population be limited?

density dependent or density independent factors

density dependent limiting factors

factors that depend on population size

• competition, predation, food disease, and parasitism

density independent limiting factors

factors that affect all populations in a similar way, not dependent on population size

• drought, wild fire, volcanic eruptions, hurricane, deforestation

negative feedback control of population size

dependent factors will cause population size to fluctuate due to negative feedback control, resulting in it staying stable over time

• this fluctuation in population size continues to occur as the population oscillates around its carrying capacity

factors affecting population growth

immigration

• increase to population size from external populations

natality

• increases to population size through reproduction

mortality

• decreases to population size as a result of death

emigration

• decreases to population size as a result of loss to external populations

population size equation

(natality + immigration) - (mortality + emigration)

population growth expression

natality + immigration > mortality + emigration

population stability equation

natality + immigration = mortality + emigration

population decline expression

natality + immigration < mortality + emigration

Exponential population growth

represented by a J-shaped curve

• occurs in populations under ideal conditions where resources are unlimited and abiotic factors are favorable

Sigmoid population growth

also called logistic growth

• represented by an S-shaped curve

• occurs in environments with a limited number of resources

Bearded vulture case study

in Switzerland, the bearded vulture became extinct during the 19th century, until repopulation efforts took off and now show a steady increase since 2006

community

a group of populations living in an area interacting with each other

• the different organisms often have complex relationships and beneficial and/or harmful interactions with each other

competition

between members of the same species in a population occurs because individuals share the same ecological niche with similar requirements for resources

cooperation

individuals may have good relationships and advantages because all individuals benefit, whereas in competition, individuals tend to be harmed

herbivory relationship

primary consumers feeding on producers. the producer may or may not be killed

• bison grazing on grasses

• aphids feeding on phloem sap from plants

• limpets feeding on algae growing on rocky shores

predation relationship

one consumer species (the predator) killing and eating another consumer species (the prey)

• anteaters feeding on ants or termites

• dingoes hunting, killing, and eating red kangaroos

• starfish eating oysters

interspecific competition relationship

two or more species using the same resource, with the amount taken by one species reducing the amount available to the other species

• ivy climbing up oak trees and competing for light

• Forda and Geoica (gall-forming aphids) competing for phloem sap on leaves of the terebinth tree

• barnacles competing for space and food on rocky shores

mutualism relationship

two species living in a close association, with both species benefitting from association

• nitrogen-fixing Rhizobium bacteria living in root nodules of plants in the Fabaceae family and exchanging materials with the plant

• mycorrhizal fungi growing into the roots of plants in the Orchidaceae family and exchanging nutrients with the orchid

• photosynthesizing zooxanthellae living in the cells of hard corals and exchanging materials with the coral

parasitism relationship

one species (the parasite) living inside, or on the outer surface of, another species (the host) and obtaining food from them. the host is harmed and the parasite benefits

• ticks living on the skin of deer and feeding by sucking blood from the deer

• the roundworm Baylisascaris living in the gut of raccoons and absorbing foods that have been digested by the raccoon

• non-photosynthesizing Cuscata plants (dodders) growing on gorse and other plan hosts, absorbing foods from the host’s sap

pathogenicity relationship

one species (the pathogen) living inside another species (the host) and causing a disease in the host

• potato blight fungus (Phytophthora) infecting potato plants

• tuberculosis bacterium (Mycobacterium tuberculosis) infecting badgers

root nodules in Fabacea

fabacea are a large plant family including species like clover, peas, beans

• many of them have a mutualistic relationship with Rhizobium bacteria, which live in root nodules grown by the plant

• the bacteria receives protection and sugars made by the plant through photosynthesis

• inside the Rhizobium absorbs N2 from the atmosphere and converts this to nitrogen molecules which the plant uses for the production of proteins

mycorrhizar in orchidaceae

the roots in most plants form an association with fungi, called mycorrhizae in soil

• the fungus absorbs nitrogen, phosphorous, and water from the soil and supplies them to the plant

• orchid seeds do not contain food reserves, so they need these nutrients

• the orchid supplies the fungus with carbon compounds from photosynthesis

zooxanthellae in hard corals

hard corals are made up of individual animals (called polyps) and photosynthetic algae (zooxanthellae)

• the algae supply the coral with glucose, amino acids, and O2 from photosynthesis, while the coral provides CO2 from cellular respiration for the algae to use in photosynthesis

predator-prey relationships as an example of density-dependent control of animal populations

when a predator kills its prey, the prey population becomes one smaller

• however, the prey population does not change much, because birth and death rates are at balance, as is the case with the predator population

• in some communities this dynamic equilibrium is not shown and instead cyclic oscillations are observed

cyclic oscillations in predator-prey relationships

sometimes, this oscillation becomes out of synch

• caused by external factors?

• red fox and mountain hare graph in Sweden — shift around 1985-1992

top-down population control

acts from a higher trophic level to a lower one

• an increase in predator number will decrease the population size of the prey

• a keystone species exerts top-down influence on its community by reducing the number of species at lower trophic levels

bottom-up population control

acts from a lower trophic level to a higher one

• a population of producers may be limited by the number of nutrients in soil or water

• the amount of seaweed available on the floor of the sea will determine the number of sea turtles feeding on them, and therefore have an impact on the consumers higher up the food chain

allelopathy and secretion of antibiotics

some organisms have developed special ways to deter potential competitors from their ecological niche. these chemical interactions can help shape the dynamic of an ecosystem and have important implications in both natural ecosystems and medical applications

production of antibiotics

many fungi produce antibiotic substances like Penicillin which prevent the growth of bacteria

allelopathy

the release of chemicals as secondary metabolites or toxins by plants, which are given off into the soil to prevent nearby competitive plants to grow in the same area

resource competition

competitive exclusion does not allow two species to occupy the same ecological niche indefinitely

• invasive species compete for resources with endemic species and often cause them to occupy smaller niches, decline in population size, or become entirely extinct

endemic species

species which occur naturally in an ecological niche in an area

• density-dependent factors usually naturally control and regulate the population size

invasive species

species that were introduced by humans, deliberately or accidentally

• their population can grow quickly due to the absence of natural predators that would control them in their native habitat

estimation of population size by random sampling

it would be impossible to count organisms in a habitat by hand

• instead we count a sample from a small area and multiply this by the total area of the habitat

• this gives an estimate of the total population

• two common sampling methods

  • quadrant sampling

  • line or belt transects

random quadrant sampling for sessile organisms

randomly selects a few quadrants in an area to sample

• eliminates bias which may influence your measurements

capture-recapture methods

capture a sample of population, mark the caught sample, release them, capture a second sample, count and record the number of marked/unmarked individuals

methods of capture

• pitfall traps

• pouters (aspirators)

• mammal traps

• nets

tests for interspecific competition

to find out if two species are associated with each other a chi-squared test can be performed

• quadrant sampling to record the presence or absence of more than one species is recorded in every quadrant during sampling of a habitat

H0

two species are distributed independently

H1

two species are associated

positive association

species found in the same habitat

• predator/prey

• herbivore/plant

• symbiosis

negative association

species occur separately in differing habitats (e.g. due to competition)

no association

species occur as frequently apart as together

ecosystems as open systems

energy and matter can both be exchanged

closed systems

only energy can be exchanged

• like a terrarium

sunlight as the principal source of energy

• is the initial source of energy that sustains most ecosystems, as it is needed to produce glucose in photosynthesis

• plants, eukaryotic algae, and cyanobacteria carry out photosynthesis and are referred to as producers or autotrophs

• heterotrophs use the sunlight indirectly as they are feeding on autotrophs and are therefore still dependent on it

autotrophs

organisms that use external energy sources to synthesize carbon compounds from inorganic substances

photoautotrophs

make organic compounds using energy derived from the sun

chemoautotrophs

make organic compounds using energy from the oxidation of chemicals

supply of energy from the sun in caves

energy in caves is produced by chemoautotroph bacteria through chemical reactions with sulfides, methane, or other inorganic materials (iron, magnesium, etc) as substrates

supply of energy from the sun in water

in marine and freshwater ecosystems light must pass through water to reach producers

• transmission is not 100% and only shorter wavelengths will penetrate further in pure water, which is why the sea often appears blue

heterotrophs

organisms which take in and digest organic compounds (carbohydrates, lipids, proteins) from other organisms to assimilate and use them to produce energy or build large complex carbon compounds

flow of chemical energy through food chains

energy enters as light, flows as nutrients through the food chains and usually leaves as heat

• a food chain shows the flow of energy through a sequence of organisms, each of which feeds on the previous one

• producers are the first organism; the subsequent ones are consumers

recycling nutrients

a good example of an interaction between biotic and abiotic factors within an environment

• nutrients are absorbed from the environment, used by living organisms, and then returned to the environment

  • this process can be conceptualized as a cycle

• examples of recycled nutrients include carbon, nitrogen, and phosphorus

food web

represents the complexity of feeding relationships by showing interacting and interconnecting food chains and the many consumers there are

supply of energy to decomposers as carbon compounds

decomposers recycle all the nutrients in a cycle, like fungi, bacteria, insects, and earthworms

• decomposers are supplied with energy from carbon compounds in dead organic matter such as feces, shed exoskeletons of an insect or reptile, dead plant material such as fallen leaves

consumers

ingest organic matter which is living or recently killed

detritivores

ingest non-living organic matter, like earthworms or dung beetles

saprotrophs

feeds on non-living matter by secreting enzymes and absorbing products

energy between trophic levels

this which moves between is indicated in the units of energy (in J or kJ) per unit area per unit time kJ/year/m²

• around 90% of energy is lost between trophic levels, leaving about 10% of energy being passed on to the next level

energy pyramids

• a pyramid of energy can be used to show the amount of energy gained per year by each trophic level in an ecosystem

• must consider the following

  • amounts of energy per unit area and per year

  • pyramids of energy should be stepped, not triangular

  • producers should be the lowest horizontal bar

  • bars should be labelled producer, primary producer, secondary producer, etc.

  • if a suitable scale is used, the lengths of each bar is proportional to the amount of energy that it shows

incomplete consumption

the caterpillar does not eat the entire tree, but only the leaves

• predators usually don’t eat boned or hair

incomplete digestion

not all food ingested and digested are also absorbed

• what cannot be digested is excreted as feces

cellular respiration

substrates such as carbohydrates or proteins are oxidized to CO2 and H2O with energy being released in the form of heat

heat loss to the environment

much of this in both autotrophs and heterotrophs is due to conversion of chemical energy to heat in cell respiration

• heat cannot be recycled and is lost from ecosystems

biomass

the total mass of a group of organisms within one trophic level, consists of the cells and tissues of those organisms

• diminishes between trophic levels because some molecules along the food chain are lost (H2O in transpiration, CO2, excretion, etc) so they cannot participate in accumulating biomass

primary production of carbon compounds

production in ecosystems is the accumulation of carbon compounds in the form of biomass

• when organisms grow, biomass accumulates

gross primary productivity

the total biomass of carbon compounds made in plants by photosynthesis

net primary productivity

is GPP minus the biomass lost due to respiration of the plant and which the available to consumers

• different biomes in the world show different net primary productivity

ecosystems as carbon sinks and carbon sources

aerobic respiration by autotrophs is dependent on atmospheric oxygen produced by photosynthesis, and photosynthesis is dependent on atmospheric carbon dioxide produced by respiration by heterotrophs

constructing carbon cycle diagrams

• carbon is one of the main elements found in all organic molecules including carbohydrates, proteins, and lipids

• carbon is moved between these four pools by a variety of biological, geological, or industrial processes called fluxes

• carbon is found in pools, which is an inorganic or organic supply or carbon

  • biosphere

  • hydrosphere

  • atmosphere

  • sediments

release of CO2 by the combustion of biomass, peat, coal, oil and natural gas

biomass, peat, coal, oil, and natural gas form big carbon sinks

• when these carbon supplies burn as a fuel in complete combustion (with sufficient oxygen) carbon dioxide and water is released

release of CO2 by combustion

although wild forest fires by lightning or spontaneous ignition of coal supplies sometimes can lead naturally to the combustion of large fuel supplies, the majority of carbon dioxide emission from combustion originates from the burning of fossil fuels by humans

analysis of the keeling curve

carbon dioxide data from the last 100 years has been collected experimentally at the observatory in Mauna Loa, Hawaii, and the Keeling Curve (named after Charles Keeling) has become an important diagnostic tool for climate analysis

• the annual rhythm shows that the carbon dioxide concentration is lower in the summer months and higher in the winter months

  • what could be the explanation for this pattern?

Recycling of all chemical elements

• carbon, hydrogen, and oxygen are needed to make carbohydrates, lipids, and other carbon containing compounds

• nitrogen and phosphorus are also needed to make many of these compounds

• autotrophs obtain their inorganic nutrients from the abiotic environment (air, rock, soil) including carbon and nitrogen

• heterotrophs obtain these elements from the food they eat, but also from the abiotic environment (sodium, potassium, calcium)

anthropogenic causes of climate change

the earth’s atmosphere acts as a greenhouse, in that gases such as methane or carbon dioxide absorb long-wave radiation (infrared radiation) upon reflection from the earth’s surface

• without the greenhouse effect, the temperature on earth would be below zero celsius

• the most significant greenhouse gases are carbon dioxide and methane

CO2 as an anthropogenic cause of climate change

while cell respiration and some natural forest fires naturally release CO2 into the atmosphere, the enhanced greenhouse effect is caused by combustion of fossil fuels in internal combustion engines and biomass (coal power plants, etc), forest fires and deforestation

melting permafrost

releases methane through methanogens in swamps and waterlogged soils, as well as landfill sites where organic wastes have been dumped

methane from cows!

methanogenic bacteria in the guts of ruminants release methane during excessive cattle farming

water cycle as a heat sink

water, including atmospheric water vapor, can do this

• the water cycle is accelerated by changes in the heat content of the atmosphere (caused by an increase of greenhouse gases)

positive feedback loops in climate change

• release of carbon dioxide from deep ocean

• increases in absorption of solar radiation due to loss of reflective snow and ice

• accelerating rates of decomposition of peat and previously undecomposed organic matter in permafrost

• release of methane from melting permafrost

• increases in droughts and forest fires

tipping point

refers to the critical threshold where a system undergoes significant and potentially irreversible changes due to small disturbances

change from net carbon accumulation to net loss in boreal forests as an example of a tipping point

boreal forests in the northern areas of the world (alaska, canada, russia) are important carbon sinks, as the cold temperatures slow down cellular respiration of detritus and other organisms, while photosynthesis captures CO2 in tree biomass

• climate change has brought these forests to a tipping point, in where they might turn from carbon sinks to carbon sources

landfast ice and sea ice melting lead to polar habitat change

antarctic landfast ice is ice which is “fastened” to the shore

• animals such as the emperor penguin and polar bears use it for hunting, nesting sites, and breeding grounds

• melting of landfast ice has many negative consequences

• one such species affected by these changes is the emperor penguin, which faces the risk of losing its critical breeding grounds due to the premature breakup of landfast ice in the Antarctic

• walruses are large marine mammals which rest on practice while they feed out of the ocean in shallow waters

changes in ocean currents altering the timing and extent of nutrient upwelling

warmer, less salty water is less dense and floats on top of denser, colder, saltier water

• different laters mix as heat slowly seeps deeper into the ocean by the action of the current, winds, and tides

  • this is called upwelling

• warmer oceans will decrease the strength of these upwellings and can influence weather patterns around the world

poleward and upslope range shifts of temperature species

climate change is leading to warmer temperatures at each elevation. species whose habitat is on mountains migrate upslope to find the optimal climate

• the combination of higher maximum temperatures in summertime and lengthened growing season has increased the frequency of droughts

• based on predictions and modeling, lower elevations and southern latitudes will no longer provide the cool, wet habitats preferred by some species like sugar maple and hemlock, as well as other northern american tree species

threats to coral reefs and potential ecosystem collapse

• reef-building corals are largely composed of calcium carbonate

  • marine organisms take dissolved carbon in the form of CO2 of HCO3 ions out of the water and use some of it to make their carbonate shells

  • the organisms that build coral reefs are called coral polyps, and they combine Ca²+ from the sea with carbon to form molecules of CaCO3

  • this molecule is the basis of the coral reef, and it is sturdy like rock

• higher concentrations of dissolved CO2 cause ocean acidification

• coral bleaching is caused by the loss of symbiotic algae (zooxanthella) from the tissue of the corals as a result of pollution of increased water temperatures

biological carbon sequestration

defined as the capture and storage of carbon through geological (peat formation) and biological (photosynthesis, biomass storage) processes

afforestation

involves planting trees in areas where they do not currently exist

• a number of countries have committed to achieving numerical goals for planting as an initiative to reverse desertification and to enhance carbon sequestration

forest regeneration

aka reforestation

• is the restocking of forests that have been depleted through clearcutting

• usually this is achieved through planting seedlings in the form of monocultures of trees, which are commercially meaningful

restoring peatlands

requires the restoration of water levels, blocking drainage, and re-establishing native species such as sphagnum moss

• peat is a partially decayed organic matter that comes from unique waterlogged ecosystems such as bogs, muskegs, and moors

• it is commercially useful, as it serves as fuel, domestic heating, fertilizer, and gardening soil

• globally, these wetlands form the world’s largest carbon sinks

stability

refers to the ability to maintain or support systems and processes continuously over time

steady conditions

with a continuous supply of rainfall and sunlight, combined with warm temperatures have ensured stability for many ecosystems

requirements for stability in ecosystems

• steady supply of energy

• absence of disruptions which would interfere with sustainability

• nutrient cycling without leakages

• high genetic diversity so populations can survive selection pressures

• climatic variables within tolerance limits

disruptions

• erosion

• poaching and selective removal

• eutrophication

• plastic pollution