Read at https://sciencing.com/abiotic-biotic-factors-ecosystems-7146052.html 

The abiotic factors in an ecosystem include all the nonliving elements of the ecosystem. Air, soil or substrate, water, light, salinity and temperature all impact the living elements of an ecosystem. Specific abiotic factor examples and how they may affect the biotic portions of the ecosystem include:

Air: In a terrestrial environment, air surrounds the biotic factors; in an aquatic environment, the biotic factors are surrounded by water. Changes in the chemical composition of the air, like air pollution from cars or factories, impacts everything that breathes the air. Some organisms are more sensitive to changes in the air. For aquatic organisms, both the chemical composition of the air and water but also the quantity of air and water impact anything living in the water. For example, when algal blooms become excessive, the algae reduce the oxygen in the water, and many fish suffocate.

Soil or Substrate: Most plants need soil for nutrients and to hold themselves in place with their roots. Plants in areas with nutrient-poor soils often have adaptations to compensate, like the insect-capturing Cobra Lily and Venus Fly-trap. Soil or substrate also impact animals, such as the filter-feeding nudibranchs whose gills would be clogged if the substrate suddenly included fine particles of sand and silt.

Water: Water is essential for life on Earth. Water is essential to the chemical reactions within living organisms, is one of the key components for photosynthesis and is the placeholder in cells. Water also serves as a living environment for aquatic creatures. As such, changes in quantity and quality of water impact living systems. Water also has mass, creating pressure in aquatic environments. Water's ability to hold temperature moderates temperature changes within its mass and in nearby areas. For example, heat from the equator moved to higher latitudes by ocean currents results in milder climates for the affected areas. Differences in rainfall mean the difference between desert and forest biomes. Clouds can even be the controlling factor in some ecosystems, such as the cloud forests of the tropics where plants draw their moisture from the air.

Light: Lack of light in the deeper ocean prevents photosynthesis, meaning that the majority of life in the ocean lives near the surface. Differences in daylight hours impact temperatures at the equator and the poles. The day-night rhythm of light impacts life patterns, including reproduction, for many plants and animals.

Salinity: Animals in the ocean are adapted to the salinity, using a salt renal gland to control the salt content of their bodies. Plants in high-salinity environments also have internal mechanisms to remove the salt. Other living creatures without these mechanisms die from too much salt in their environment. The Dead Sea and Great Salt Lake are two examples of environments where salinity has reached levels that challenge most living organisms.

Temperature: Most organisms require a relatively stable temperature range. Mammals even have internal mechanisms to control their body temperature. Temperature changes, especially extreme and sudden changes, that go beyond an organism's tolerance will harm or kill the organism. Temperature changes can be natural, due to sunspots, weather-pattern shifts or ocean up-welling, or can be artificial, as with cooling-tower outfall, released water from dams or the concrete effect (concrete absorbing heat).

Abiotic vs Biotic Factors

A major difference between biotic and abiotic factors is that a change in any of the abiotic factors impacts the biotic factors, but changes in the biotic factors don't necessarily result in changes to the abiotic factors. For example, increasing or decreasing salinity in a body of water may kill all the inhabitants in and around the water (except maybe bacteria). The loss of the biota of the body of water doesn't necessarily change the salinity of the water, however.

Abiotic factors therefore play a large part in determining where different organisms can live.

High biodiversity is linked to latitude and climate. The species richness (abundance of species / unit area) increases from polar regions to the equator, with highest at the tropics. Over 50% of earth's species live in the tropics. This is due to more stable climate, warmer temperatures, high rainfall, higher level of plant growth. 

Changes to environmental conditions (abiotic factors) on Earth have resulted from events such as Ice Ages and from processes such as tectonic plate movements.

Feeding types

Read at https://courses.lumenlearning.com/boundless-biology/chapter/ecology-of-ecosystems/ 

Species form  a web of feeding interdependencies within an ecosystem.  An ecosystem is a community of living organisms in conjunction with the nonliving components of their environment, interacting as a system. These biotic and abiotic components are linked together through nutrient cycles and energy flows 

Producers

Producers are organisms that are able to produce their own organic food. Producers are also called autotrophs. The term autotroph comes from the Greek words autos meaning 'self' and trophe meaning 'nourishing'. So autotroph means 'self-feeding'.

Consumers

Organisms which cannot produce their own food need to eat other organisms to get food. These organisms are  consumers. All animals are consumers as they cannot produce their own food. Consumers are also called heterotrophs. The term heterotroph comes from the Greek words heteros meaning 'different' and trophe meaning 'nourishing'. So heterotroph means 'different-feeding' or feeding on different things.

• Animals that eat plants are primary consumers. (Primary means first.)

• Animals that eat primary consumers are called secondary consumers.

• Animals that eat the secondary consumers (mostly predators) are the tertiary consumers.

Decomposers

Read at https://courses.lumenlearning.com/boundless-biology/chapter/ecology-of-ecosystems/ 

Decomposers are organisms that break down dead or decaying organisms, and in doing so, they carry out the  process of decomposition of complex materials to simpler components. Decomposers are heterotrophic and consumers, meaning that they cannot make their own food. They rely on organic substrates to get their energy, carbon and nutrients for growth and development .

When fungi and other decomposers break down dead material, they help to return nutrients (eg nitrates) to the soil in a form that plants can use.

Energy transfer

Read at https://courses.lumenlearning.com/boundless-biology/chapter/ecology-of-ecosystems/ 

The flow of energy from the sun to different organisms in an ecosystem is very important as it supports all the life process of living organisms. 

Energy is vital for organisms to carry out their life processes. All energy comes from the sun. Plants trap sunlight energy during photosynthesis and convert it to chemical potential energy in food compounds, which are available to animals. Herbivores get energy directly from plants, but carnivores and omnivores eat animals for energy. This energy transfer is shown by food chains.

• The arrows in a food web travel from the prey to the predator instead of the other way around. It may seem counter-intuitive, but the arrows in a food web or food chain point in the direction the energy is flowing.

Read at https://courses.lumenlearning.com/boundless-biology/chapter/ecology-of-ecosystems/ 

Each of the consumer levels  (primary, secondary, etc) in a food chain is called a trophic level. The organism uses up to 90% of its food energy itself for its life processes. Only about 10% of the energy goes into new body cells and is available to the next animal when it gets eaten. This loss of energy at each trophic level can be shown by an energy pyramid. 

An organism can occupy different trophic levels, depending on the food web. Assigning organisms to trophic levels isn't always clear-cut. For instance, humans are omnivores, meaning they can eat both plants and animals. So they may be considered both primary and secondary (or even higher!) consumers. Decomposers occupy all trophic levels.

Food Webs

Read at https://courses.lumenlearning.com/boundless-biology/chapter/ecology-of-ecosystems/ 

Consumers have different sources of food in an ecosystem and do not only rely on only one species for their food. If we put all the food chains within an ecosystem together, then we end up with many interconnected food chains. This is  a food web. A food web is very useful to show the many different feeding relationships between different species within an ecosystem .

Read at https://ib.bioninja.com.au/options/option-c-ecology-and-conser/c5-population-ecology/population-sampling.html 

A population is all the individuals of a given species living in the same area at the same time. Populations are fluid and are subject to continual change in numbers through natality, mortality, immigration and emigration.

Population Growth

Two types of population growth patterns may occur depending on specific environmental conditions:

• An exponential growth pattern (J curve) occurs in an ideal, unlimited environment

• A logistic growth pattern (S curve) occurs when environmental pressures slow the rate of growth

Exponential Growth

• Exponential population growth will occur in an ideal environment where resources are unlimited

• In such an environment there will be no competition to place limits on a geometric rate of growth

• Initially population growth will be slow as there is a shortage of reproducing individuals that may be widely dispersed

• As population numbers increase the rate of growth similarly increases, resulting in an exponential (J-shaped) curve

• This maximal growth rate for a given population is known as its biotic potential

• Exponential growth can be seen in populations that are very small or in regions that are newly colonised by a species

Logistic Growth

Read at https://ib.bioninja.com.au/options/option-c-ecology-and-conser/c5-population-ecology/population-growth.html 

• Logistic population growth will occur when population numbers begin to approach a finite carrying capacity

• The carrying capacity is the maximum number of a species that can be sustainably supported by the environment

• As a population approaches the carrying capacity, environmental resistance occurs, slowing the rate of growth

• This results in a sigmoidal (S-shaped) growth curve that plateaus at the carrying capacity (denoted by κ)

• Logistic growth will eventually be seen in any stable population occupying a fixed geographic space

Many factors affect population size and density, and prevent initial or continued exponential population growth

Density dependent environmental factors are influenced by the relative size of a population; density independent factors are not.

Population sampling

Read at https://ib.bioninja.com.au/options/option-c-ecology-and-conser/c5-population-ecology/population-sampling.html 

•  involves identifying individual numbers in small areas and then extrapolating to estimate population totals

• Sampled areas must be chosen randomly to avoid selection bias causing a misrepresentation of the population size

• The more samples that are taken (and the larger the sampling area), the more accurate population estimates are likely to be

Different sampling techniques are used to estimate population sizes for non-motile (sessile) and motile species

• Motile species can be sampled using the capture-mark-release-recapture method (with estimates based on the Lincoln index)

• Non-motile species can be sampled using quadrats (measurements can include direct counts, percentage cover or frequency) and/or transects

1. The capture-mark-release recapture method

- a means of estimating the population size of a motile species

• An area is defined and marked off, then a selection of individuals is captured, counted, marked and released (n1)

• Marking must not be easily removable or adversely affect the animal’s survival prospects

• After sufficient time has passed to allow marked individuals to reintegrate in the population, a second capture is made (n2)

• In this second capture, both unmarked individuals and marked individuals (n3) are counted

• Based on the three values generated (n1 ; n2 ; n3), an estimated population size is derived using the Lincoln Index

Read at https://ib.bioninja.com.au/options/option-c-ecology-and-conser/c5-population-ecology/population-sampling.html 

The Lincoln index is used to estimate population size based on the capture-mark-release-recapture method

• Lincoln Index:  Estimated Population 

= (n1 × n2) ÷ n3

The Lincoln index requires that the following assumptions are true:

• That all individuals in a given area have an equal chance of being captured (sampling must be random)

• That marked individuals will be randomly distributed after release (n1 cannot be allowed to influence n3)

• That marking individuals will not affect the mortality or natality of the population

The accuracy of the Lincoln index can be improved by a number of means:

• Increasing the size of the capture samples (larger samples will be more representative, but also more difficult to collect)

• Taking repeated samples in order to determine a statistical average

2. The Point Sampling Method

Point sampling involves counting organisms only at selected points, selected randomly or regularly/ It can be used to determine the range of organisms that live in an area and how many there are. Point sampling is quick, but runs the risk of missing organisms occurring in small numbers.

3. The Quadrat Sampling Method

Read at https://ib.bioninja.com.au/standard-level/topic-4-ecology/41-species-communities-and/chi-squared-test.html 

The number and variety of species within a given environment can be determined using quadrat sampling

• A quadrat is a rectangular frame of known dimensions that can be used to establish population densities

  • Quadrats are placed inside a defined area in either a random arrangement or according to a design (e.g. belted transect)

  • The number of individuals of a given species is either counted or estimated via percentage coverage

  • The sampling process is repeated many times in order to gain a representative data set

Quadrat sampling is not an effective method for counting motile organisms – it is used for counting plants and sessile animals

• In each quadrat, the presence or absence of each species is identified

• This allows for the number of quadrats where both species were present to be compared against the total number of quadrats

Earth has witnessed five major mass extinctions, when more than 75% of species disappeared across a short period of time. Palaeontologists spot them when species go missing from the global fossil record. We don’t always know what caused them, but most had something to do with rapid climate change.

Biologists warn that we’re in and causing the sixth major mass extinction. 

Read https://www.theguardian.com/environment/2017/jul/10/earths-sixth-mass-extinction-event-already-underway-scientists-warn 

(Ref: The five extinction events https://cosmosmagazine.com/palaeontology/big-five-extinctions)

1. End Ordovician, 444 million years ago, 86% of species lost

This extinction, over about a million years, was probably caused by a short, severe ice age that lowered sea levels. This was possibly triggered by the uplift of the Appalachian Mountains, the newly exposed silicate rock drawing CO2 out of the atmosphere, chilling the planet.

Graptolite 2-3 cm length

Graptolites, like most Ordovician life, were sea creatures. They were filter-feeding animals and colony builders.

2.  Late Devonian, 375 million years ago, 75% of species lost

Read at http://craterexplorer.ca/late-devonian-extinction/ 

The likely culprit for this extinction was the newly evolved land plants that emerged and covered the planet during the Devonian period. Their deep roots stirred up the earth, releasing nutrients that washed into the ocean. This might have triggered algal blooms, which drew oxygen out of the water, suffocating bottom-dwellers like the trilobites.

— Trilobite, 5 cm length

Trilobites were the most diverse and abundant of the animals that appeared in the Cambrian explosion 550 million years ago. Their great success was helped by their spiky armour and multifaceted eyes. They survived the first great extinction, but were nearly wiped out in the second. 

3. End Permian, 251 million years ago, 96% of species lost

(Ref: The five extinction events https://cosmosmagazine.com/palaeontology/big-five-extinctions)

Known as “the great dying”, this was by far the worst extinction event ever seen; it nearly ended life on Earth. 

What caused it? A perfect storm of natural catastrophes. A cataclysmic eruption near Siberia blasted CO2 into the atmosphere. Methane-producing bacteria responded by belching out methane, a potent greenhouse gas. Global temperatures surged, while oceans acidified and stagnated, producing vast quantities of poisonous hydrogen sulfide. It set life back 300 million years. 

- Tabulate coral, 5 cm

The tabulate corals were lost in this period – today’s corals are an entirely different group.  Rocks after this period record no coral reefs or coal deposits. 

4. End Triassic, 200 million years ago, 80% of species lost

Of all the great extinctions, the one that ended the Triassic is the most enigmatic. No clear cause has been found.

- Conodont teeth 1 mm

Palaeontologists were at first baffled about the origin of these toothy fragments, mistaking them for bits of clams or sponges.  They were one of the first structures built from hydroxyapatite, a calcium-rich mineral that remains  a key component of our own bones and teeth today.  

6. End Cretaceous, 66 million years ago, 76% of all species lost

Volcanic activity and climate change had already placed life on earth under stress. The asteroid impact provided the final blow and ended the dinosaurs’ reign . 

- Ammonite 15 cm length

The delicate leafy sutures decorating this shell represent some advanced engineering, providing the fortification the squid-like ammonite required to withstand the pressure of deep dives in pursuit of its prey. Dinosaurs may have ruled the land during the Cretaceous period but the oceans belonged to the ammonites. 

Only a few dwindling species of ammonites survived. Today, the ammonites’ oldest surviving relative is the nautilus.