(Gateway): Community Level Systems

The Cycling of Materials on Earth

• Atoms exist as part of different compounds and cycle between them through an ecosystem

• The materials cycle between the biotic and abiotic components of an ecosystem

• The biotic components means the living parts, for example plants, while the abiotic components are the non-living parts, for example soil

• This cycling is observed in the elements carbon and nitrogen, and in the compound water

The Nitrogen Cycle

• Humans can eat protein in the form of meat from other animals

• We break down this protein into what is called, amino acids

• Amino acids build to make proteins in our bodies, for example, in order to repair the damaged tissues

• Once humans die, our proteins are broken down into amino acid building blocks which returns to the soil to be used by other living organisms, such as plants

The Importance of Microorganisms

• The decomposing bacteria and fungi are known as microorganisms which play a vital role in breaking down dead organisms

• Microorganisms are important because they help return minerals and nutrients back to the environment so materials can then be used by other organisms

• When these microorganisms decompose dead matter, they carry out the process of respiration and as a result, they release carbon dioxide to the environment and this is a contributing factor to the carbon cycle

The Carbon Cycle

Carbon is a crucial element in our everyday lives. Carbon is present in every living organism, inside fats and proteins in our cells. The carbon cycle describes the process of how carbon moves between living organisms and the environment.

Processes in the carbon cycle:

• Photosynthesis - carbon starts in the form of carbon dioxide and ends as glucose

• Respiration - carbon starts in the form of glucose and ends as carbon dioxide

• combustion (burning) - carbon starts in the form of fuel and ends as carbon dioxide

1. Carbon enters the atmosphere in the form of carbon dioxide, produced from respiration and combustion.

2. Carbon dioxide is absorbed by producers to synthesize carbohydrates, such as glucose, in photosynthesis.

3. When animals feed on plants, the carbon compounds are moved down along the food chain. Most of the carbon that is consumed ends up being exhaled as carbon dioxide during respiration

4. These animals and plants eventually die and are ingested by decomposers and the carbon in their bodies returns to the atmosphere once again as carbon dioxide

The Water Cycle

Water is an essential compound for life on Earth. It is important for:

• Maintaining habitats

• Allowing nutrients to flow between organisms and the environment

• Survival of organisms

Processes in the water cycle:

1. Evaporation: water changes from liquid to gas, such as evaporation of water from ponds, lakes, rivers, and oceans by using energy from the Sun

2. Condensation: after evaporation, water can cool down and turn from a gas to a liquid and this can be seen as often forming clouds

3. Transport: water inside clouds can be drifted very far away by strong winds and therefore transported to other areas

4. Precipitation: a process that occurs during rain, snow, hail, and sleet.

5. Surface run-off: after precipitation, water will be absorbed into the ground, however, if large quantities of water falls or the ground is already wet then this results in some water running along the surface of the ground

6. Infiltration: when water fallen from precipitation is absorbed into the ground and this can be stored within aquifers which are underground rocks

7. Transpiration: it is necessary for plants to maintain a constant supply of water to their leaves for photosynthesis, support and transport of minerals. They allow some water to evaporate as water vapor from their leaves so there is a continuous cycle of water supply to their leaves from the soil.

Effects of Temperature, Water and Oxygen on the Rate of Decomposition

Decomposition is the breakdown of dead matter, also known as rotting. The microorganisms, bacteria and fungi help in the process of decomposition. Decomposition plays a crucial role in the cycling of elements, such as carbon, from one living organism to the next.

Rate of decomposition - speed at which dead matter is broken down by decomposers.

Rate can be estimated by measuring changes in:

• pH

• Mass, or

• Temperature

Factors Affecting Rate of Decomposition

1. Temperature: high temperatures prevent decomposition while low temperatures slow down the rate of decomposition. This is because high temperatures destroy enzymes and proteins which also means killing the microorganisms that carry out decomposition. At low temperatures, the activity of enzymes is reduced, leading to a slowdown in the rate of decomposition, and inhibiting the growth and reproduction of microorganisms.

2. Oxygen availability: lack of oxygen will reduce or inhibit most decomposition. Microorganisms require oxygen for aerobic respiration, however, some bacteria don’t need oxygen to survive as they use anaerobic respiration.

3. Water content: lack of water reduces or inhibits decay. Water is essential for the transportation of materials and to facilitate reactions within microorganisms. Decomposers rely on water to break down their food. If there is no water, the microorganisms will not survive.

Marking Compost

Gardeners and farmers enhance the soil's quality by incorporating organic compost. Compost, which is derived from deceased plants, undergoes decomposition by bacteria, fungi, and other organisms like worms when applied to the soil. This breakdown process ensures the recycling of minerals, allowing them to be absorbed by new plants for growth. Additionally, the presence of compost enhances soil quality by improving aeration and water retention.

The Most Favorable Conditions for Composting:

Decomposition is the process that leads to the formation of compost. Hence, the variables that influence the pace of decomposition also impact the speed at which compost is produced.

Many gardeners usually create compost in a designated heap or bin. To accelerate decomposition, specific conditions are maintained inside the compost area:

1. Warmth - compost bins are typically designed in black to absorb heat, while heaps are often covered with old carpets to provide insulation.

2. Moisture - water is regularly added to maintain a suitable level of moisture.

3. Aeration - the compost is regularly turned using a garden fork to mix the contents, prevent compaction, and introduce oxygen.

Investigating the Best Conditions for Composting

A study can be conducted to investigate the factors influencing the decomposition rate.

• A practical approach would involve placing cut grass in black bin bags and inserting a thermometer into the opening of each bag before sealing it shut.

• Different conditions can be applied to each bag. For instance, one bag could contain dry grass while another contains moist grass. The bags are then placed in identical environments, and the temperature is noted regularly. As the grass decomposes, the temperature within the bags will increase. The bag with the most significant temperature rise indicates the highest level of decomposition.

Organization in Ecosystems

Effect of Abiotic Factors on Organisms

Abiotic factors affecting the abundance and distribution of organisms:

The abundance refers to the quantity of organisms within an ecosystem. A community encompasses all the living organisms residing in a specific habitat. The dynamics of communities are influenced by abiotic factors, which are non-living elements.

This includes:

• Light intensity

• Temperature

• Moisture levels

• pH of soil

Light Intensity

Certain plants have adapted to thrive in bright sunlight, such as cacti, which originate from deserts. Conversely, other plants, like orchids found in rainforests, have evolved to flourish in darker environments. If an orchid were placed in a sunny spot and a cactus in a dimly lit area, both plants would struggle to thrive.

Temperature

Plants and animals are adapted to thrive in specific temperature ranges. For instance, attempting to grow a cactus or orchid outside in cold weather would result in their death. Likewise, animals like the polar bear, which are specialized to live in the extreme cold of the North Pole, would struggle to survive in warmer climates.

Moisture Levels

Houseplants can be killed by people overwatering them rather than underwatering. Plants usually cannot survive in waterlogged soils because this provides them with little oxygen, as a result the cells in their roots struggle to be able to respire so the roots end up rotting and the plant dies. However, plants such as pitcher plants, thrive best in bags providing high moisture levels. To measure how wet an is, a Soil moisture meter can be used accurately determine this.

pH of Soil

The pH level of soil greatly impacts the variety of plants that can thrive. For instance, azaleas thrive in acidic soil and struggle in alkaline environments, while clematis prefers alkaline soil. Hydrangeas are unique as they can grow in both acidic and alkaline soils, with their flower color changing accordingly. Much like universal indicator paper, hydrangea flowers turn pink in acidic soils and blue in alkaline soils.

The pH of water also influences the types of aquatic organisms that can survive there. Different species have adapted to survive in specific pH levels present in water. pH meters are a reliable tool for determining the pH levels of both soil and water.

Biotic Factors Affecting Organisms in Ecosystems

Organism communities can be affected by biotic factors, which include:

• Availability of food

• Presence of new predators

• Competition between organisms

Availability of Food

Food is necessary for all animals to survive. The availability of food is a major contributing factor in the number of animals living in an ecosystem. Areas of rich food supply like the rainforests would have more living species compared to other areas like deserts and the Polar region where food is scarce.

New Predators

The introduction of new predators to an ecosystem can have a significant impact. In a well-balanced ecosystem, predators and their prey have evolved together, allowing predators to catch enough prey to survive without depleting the entire population.

However, the introduction of a new predator can disrupt this balance. For instance, the introduction of red foxes to Australia has raised concerns about their impact on native birds and small mammals. The arrival of new predators can lead to a rapid decrease in prey numbers, subsequently reducing the food supply for existing predators.

Out-Competition

When a new species is introduced to an ecosystem, it can out-compete native species. For example, several hundred years ago, wealthy individuals brought grey squirrels from North America to England and released them into the wild. The smaller native red squirrels were unable to compete with the larger grey squirrels. Due to their larger size, grey squirrels could store more fat and survive harsh winters, leading to a dramatic reduction in the number of red squirrels and their habitats.

Abiotic Factors

Abiotic factors are non-living. The community of living organisms in an ecosystem can also be affected by abiotic factors which include:

• Light intensity

• Temperature

• Moisture levels

The Effect of Abiotic Factors on Organisms

A shingle beach features small stones instead of fine sand. Seeds of plants can become lodged between the small stones and begin to grow, especially at the upper part of the shore, away from the waves. Two students established a line across a shingle beach. They commenced at the highest point of the beach and progressed toward the sea. At every five meters, they positioned a square frame on the beach and recorded the height of all the plants discovered within the frame. Subsequently, they computed the average of this information. Their findings are displayed in the graph below.

• The relationship between distance from the top of the single shore and the average height of plants

Competition in a Community

Many communities of diverse organisms exist within an ecosystem. Each of these organisms is trying to survive in the ecosystem.

Animals require access to:

• Food

• Water

• Space (territory)

Plants must get access to:

• Sunlight for photosynthesis

• Water

• Mineral salts

• Space

The various organisms within an ecosystem engage in competition for essential resources necessary for their survival. The resources available within an ecosystem are limited.

If an organism is unable to obtain the necessary resources for survival, it will perish. While animals can attempt to relocate to a different habitat in search of more resources, plants are unable to relocate to a new location.

Fluctuations in the population of organisms may result from changes in abiotic elements such as water and sunlight, or biotic factors such as the introduction of a new predator or pathogen.

Interdependence within a Community

Interdependence is the relationship between organisms in an ecosystem relying on each other for survival. When organisms interact with one another it affects their survival. This can be observed clearly in predator-prey cycles, mutualistic relationships and parasitism

Predator-Prey Cycles

Predator-prey cycles:

1. There are always more prey than predators

2. As the number of prey increases, the predator population also increases due to the availability of more food.

3. With the increase in predators, the prey population decreases as more of them are consumed.

4. As the prey population decreases, the predator population also decreases due to the scarcity of food.

There is interdependence between the predator and the prey, and any change in the population of one directly impacts the other. In a healthy, balanced ecosystem, the populations of predators and prey generally remain relatively stable.

Mutualism

Certain organisms depend on other species for their survival. For instance, oxpecker birds feed on ticks and larvae that infest the skin of large animals such as buffalo. As a result, oxpeckers are referred to as a cleaning species. This is a clear example of mutualism, where both species benefit from the relationship.

Other instances of mutualism include:

Lichens - formed by algae and fungi coexisting. Algae can photosynthesize and produce food, which is then shared with the fungus. In return, the fungus provides shelter for the algae in harsh conditions.

Leguminous plants - such as peas, beans, and clover, host colonies of nitrogen-fixing bacteria in nodules attached to their roots. The plants receive nitrogen-containing compounds from the bacteria, while the bacteria obtain sugars from the plants.

Parasitism

Parasites are organisms that inhabit the body of a host organism. While the parasite benefits from this relationship, the host suffers negative consequences. Parasites typically do not kill the host because it would result in the loss of their source of nourishment.

Examples:

• Fleas reside on the skin of other animals and consume their blood, nourishing the flea while weakening the host.

• Tapeworms live within other animals by attaching themselves to the host's intestines and absorbing its nutrients. This causes the host to lose nourishment and may lead to weight loss, diarrhea, and vomiting.

• Head lice feed on the blood of other animals by biting them.

• Mistletoe roots integrate into the veins of the host tree to extract nutrients and minerals.

Trophic Levels

A simple food chain can look like this:

algae → mosquito larvae → dragonfly larvae → perch

The combination of all food chains within an ecosystem forms a food web. Each level within a food chain or web is known as a trophic level. In every food chain, the lowest level consists of producers, which are typically plants or algae capable of photosynthesis, converting carbon dioxide and water into glucose and serving as the primary source of biomass for the food chain.

• In the food chain mentioned, algae act as the producers.

• Subsequent trophic levels consist of consumers, which are unable to produce their own food.

• The second trophic level in all food chains comprises herbivores or omnivores, known as primary consumers. In the previously mentioned food chain, mosquito larvae function as the primary consumers.

• The third trophic level is occupied by carnivores or omnivores that consume the primary consumers, known as the secondary consumers. In the above food chain, dragonfly larvae serve as the secondary consumers.

There may be additional levels of carnivorous consumers, referred to as tertiary and quaternary consumers. The highest level is occupied by a carnivore, often referred to as the top or apex predator - such as the perch in this example. Organisms at the top of a food chain have no natural predators.

Decomposers such as bacteria and fungi are responsible for breaking down deceased plant and animal material. They release enzymes onto the surface of the deceased organisms to facilitate the breakdown process and subsequently absorb the digested smaller food molecules.

Pyramids of Biomass

Biomass

Biomass refers to the organic material derived from living organisms. Your body mass is an example of biomass as it is composed of living tissues. Similarly, wood is categorized as biomass since it was previously part of a living plant. However, fossil fuels do not fall under the category of biomass, as they are the remnants of organisms that perished millions of years ago and have undergone significant chemical alterations from their original living tissue.

Pyramids of Biomass

The quantity of biomass present at various trophic levels within a food chain can be quantified. The collective biomass at each trophic level is commonly depicted using a modified bar chart known as a biomass pyramid. In a food chain within a thriving ecosystem, the biomass at each trophic level typically decreases.

An example of a food chain is:

clover → snail → thrush → sparrowhawks

In an ecosystem, clovers have a higher biomass than snails, and snails have a higher biomass than thrushes, and so on. The pyramids of biomass in a healthy ecosystem should take the shape of a perfect pyramid. When they do not, it may indicate that the ecosystem is unhealthy and at risk.

Drawing pyramids of biomass:

1. Bars equally spaced around the midpoint

2. bars touching

3. bar for the producer at the bottom

4. length of each bar proportional to the amount of biomass available at each trophic level

Transfer of Biomass

The arrow in a food chain represents the transfer of biomass from one organism to another.

Here is an example:

maize → locust → lizard → snake

The energy from the Sun is harnessed by maize during the process of photosynthesis. When locusts consume the plant, they in turn receive some of this energy. As a result, biomass is passed from the maize to the locusts. When lizards consume the locusts, they obtain some of the biomass from the locusts, and the cycle continues.

Loss of Biomass

The transfer of biomass from maize plants to locusts is not fully efficient. Approximately ten percent of the biomass moves from one trophic level to the next. The remaining ninety percent is utilized by the organisms in that trophic level to fulfill their life processes.

Biomass may be lost between stages due to:

• Excretion: Water and urea are excreted in urine.

• Respiration: Carbon dioxide and water are byproducts of aerobic respiration, which is carried out by organisms to maintain body temperature and provide energy.

• Egestion: Undigested food moves through the organisms and is expelled as solid feces.

Due to the fact that only about ten percent of the biomass at each trophic level is transferred to the next, the total biomass transferred becomes significantly reduced after just a few trophic levels.

As a result, food chains are seldom longer than six trophic levels.In reality, only approximately one percent of the energy from the Sun that reaches the plant’s leaves is utilized by the plant in the process of photosynthesis. While this may seem insignificant, it still provides adequate power for nearly all food chains on our planet.

Calculating Efficiency of Biomass Transfers

The efficiency of biomass transfer measures the amount of biomass transferred from one trophic level to another. Typically, about 10% of biomass is transferred between trophic levels in a robust ecosystem, with the remaining 90% being utilized by organisms for life processes.

Calculating Efficiency

Here is an example:

phytoplankton → zooplankton → herring → sea lion

What is the efficiency of this transfer?

To complete this calculation, we divide the amount from the higher trophic level (the zooplankton) by the amount from the lower trophic level (the phytoplankton) and multiply by one hundred. That is, we divide the smaller number by the bigger one (and multiply by one hundred).