Ecology

Interdependency in Ghanaian Ecosystems

Ghana has many different ecosystems, from coastal mangroves to northern savannas. These ecosystems are shaped by the relationships between biotic, living things (like plants and animals) and abiotic, non-living things (like climate, soil, and water). These interactions affect the variety of life and how well the ecosystems work.

Energy Flow

Energy flow describes the one-way movement of energy through an ecosystem. It begins with producers (such as green plants) that capture sunlight through photosynthesis, and continues through various levels of consumers (herbivores, carnivores, and decomposers).

a. Energy moves in a single direction, from the sun to producers, then to consumers.

b. At each level, some energy is lost as heat, making the flow non-cyclic.

Nutrient Cycling

Unlike energy, nutrients cycle within ecosystems through biogeochemical processes.

Nutrient cycling involves the movement and exchange of organic and inorganic matter, which is reused in the production of new biomass.

The Carbon Cycle

The carbon cycle is a key biogeochemical cycle that involves the exchange of carbon among the biosphere, pedosphere (soil), geosphere (land), hydrosphere (water), and atmosphere.

The carbon is driven through when,

a. trees absorb carbon dioxide from the atmosphere during photosynthesis.

b. trees die or are burned (e.g., through slash-and-burn agriculture), and carbon is released back into the atmosphere.

Other sources of atmospheric carbon include

i. respiration by animals and plants

ii. decay of organic matter

iii. emissions from burning fossil fuels

Figure 3.11: Carbon cycle Nitrogen Cycle The nitrogen cycle is a biogeochemical process through which nitrogen changes between different chemical forms as it moves through the atmosphere, land and aquatic ecosystems.

In Ghanaian agriculture, leguminous crops such as groundnuts and cowpeas play a key role in this cycle. These plants form symbiotic relationships with nitrogen-fixing bacteria found in their root nodules. The bacteria convert atmospheric nitrogen into forms usable by plants, thereby naturally enhancing soil fertility.

The cycle begins with nitrogen fixation, where atmospheric nitrogen gas is converted into ammonia by nitrogen-fixing bacteria or lightning. Through nitrification, soil bacteria change ammonia into nitrites and then nitrates, which plants absorb through their roots.

Animals obtain nitrogen by feeding on plants or other animals. When plants and animals die or produce waste, decomposers such as bacteria and fungi break down the organic matter through ammonification, releasing ammonia back into the soil. Finally, during denitrification, certain bacteria convert nitrates back into nitrogen gas, which returns to the atmosphere and completes the cycle.

Figure 3.12: Nitrogen cycle The Water Cycle The water cycle is the continuous movement of water between the Earth’s surface and the atmosphere. This cycle involves key processes.

1. Evaporation: During this process, heat from the sun changes liquid water from rivers, lakes, oceans, soil, and other surfaces into water vapour, which rises into the atmosphere. Together with transpiration from plants, this adds moisture to the air.

2. Condensation: In the cold atmospheric air, water vapour cools back to water and gathers to form clouds.

3. Precipitation: Here, the condensed water falls back to earth as rain, snow or hail (depending on how cold the air is).

4. Runoff is the water flowing over land into bodies of water like lakes and the sea.

Quick Investigation Exercise: Do you know why lakes are freshwater and the sea is salty?

In Ghana, seasonal rainfall patterns play a crucial role in determining how much water is available across ecosystems. These fluctuations affect both terrestrial (land) and aquatic (water) communities, influence biodiversity, plant growth and animal behaviour.

Figure 3.13: Water cycle Food Chains, Food Webs and Decomposition Food Chains A food chain is a linear series of organisms through which energy and nutrients flow as one organism consumes another. It shows a single pathway of energy transfer within an ecosystem. Here are examples of food chains from various ecosystems in Ghana.

1. Forest Ecosystem (Kakum National Park): Dead leaves → Termites → Agama lizard → African harrier hawk

2. Savanna Ecosystem (Northern Ghana): Grass → Grasshopper → Guinea fowl → Serval cat

3. Coastal/Marine Ecosystem (Gulf of Guinea): Phytoplankton → Anchovy → Sea bream → African Fish eagle

4. Freshwater Ecosystem (Lake Volta): Algae → Water insects → Tilapia → Nile perch → Kingfisher

5. Wetland Ecosystem (Amanzuri Wetlands): Water plants → Tadpoles → Mudfish → African fish eagle Each link in a food chain represents a trophic level, which is the position an organism occupies in a food chain or ecological pyramid based on its feeding behaviour. The main trophic levels include:

a. Producers – First trophic level

b. Primary consumers – Second trophic level

c. Secondary consumers – Third trophic level

d. Tertiary consumers – Fourth trophic level At each stage of energy transfer, approximately 90% of the energy is lost, mostly as heat, and through waste such as undigested food, uneaten parts, death, and decomposition. This significant energy loss explains why food chains typically consist of only 4 to 5 trophic levels.

Figure 3.14: A terrestrial food chain Food Webs A food web is a system of interlocking and interdependent food chains, illustrating the complex feeding relationships within an ecosystem. In real ecosystems, energy transfer is more complex than in simple food chains. For example, in Ghana’s forest ecosystems, one type of tree can support many herbivores (plant-eating animals). These herbivores, in turn, are hunted by different predators. This creates a rich and dynamic web of interactions among different species.

Food webs highlight

a. multiple feeding relationships among organisms

b. alternative energy pathways, allowing flexibility in energy flow

c. ecosystem’s strength due to redundancy in species roles. This means that an ecosystem is stronger and more resilient when multiple species can perform similar roles.

Keystone Species and Ecosystem Stability

The removal of a keystone species (one that has an extremely large impact on its environment relative to its abundance) can lead to powerful shifts in ecosystem structure.

For example, in Mole National Park, a decline in large predators like lions and leopards could result in a surge in herbivores like the duiker and hartebeest populations, ultimately causing significant vegetation changes and altering the balance of the ecosystem.

Figure 3.15: An example of a terrestrial food web Decomposition Decomposition is the process by which organic substances are broken down into simpler forms of matter, releasing nutrients back into the ecosystem.

Importance of Decomposition in Ecosystems

Decomposition plays a vital role in how an ecosystem functions by:

1. recycling nutrients in dead organic matter into forms usable by plants

2. preventing the accumulation of dead material in ecosystems

3. contributing to soil formation and enhancing soil fertility

4. completing biogeochemical cycles, such as the carbon and nitrogen cycles Decomposers in Ghanaian ecosystems In Ghana, decomposers include:

1. Fungi like mushroom species and mycorrhizal fungi are especially abundant in humid forest regions.

2. Bacteria are microscopic organisms that break down organic matter.

3. Invertebrates, such as termites, earthworms, and dung beetles.

Factors Affecting Decomposition

Several environmental factors influence the rate of decomposition.

1. Temperature: Decomposition occurs faster in warmer regions

2. Moisture: Seasonal changes affect decomposer activity

3. Oxygen availability: Aerobic conditions speed up decomposition

4. pH levels: Optimal pH supports microbial activity In Ghana’s cocoa-growing regions, effective management of organic matter decomposition is important for maintaining soil fertility and reducing reliance on chemical fertilisers.

Biological/Symbiotic Associations (Symbiosis)

Biological association refers to the relationship between different species living together in the same ecosystem. These relationships involve varying degrees of physical association and interdependence, which may be:

a. beneficial

b. harmful

c. neutral Mutualism Mutualism is a type of biological relationship in which both species benefit from the association. Common examples include the points mentioned below.

1. Mycorrhizal Symbiosis: A relationship between fungi and forest trees.

a. Fungi provide minerals and enhance water absorption for the tree

b. The tree supplies carbohydrates (food) to the fungus

2. Pollination

a. Bees collect nectar from plants as food

b. In return, they transfer pollen grains, aiding plant reproduction

3. Nitrogen-Fixing Bacteria in Legumes

a. Bacteria in root nodules fix nitrogen for plant use

b. The plant provides nutrients and shelter to the bacteria

4. Gut Microbiota in Ruminants

a. Microorganisms in the digestive systems of animals like cattle and goats digest cellulose

b. The microbes receive food and protection from the host animal

Figure 3.16: Honeybee on a coneflower Mutualism is ecologically important because it:

a. creates interdependencies that promote ecosystem stability

b. allows organisms to access resources or habitats that would otherwise be unavailable

c. drives co-evolutionary processes, leading to increased biodiversity. This means that certain interactions between species can encourage them to evolve together over time. As they adapt to each other, new species may emerge, leading to greater biodiversity.

d. supports essential ecosystem functions, such as pollination and nutrient acquisition These relationships are often highly specific and have evolved over long periods. Disruption of mutualistic interactions can lead to serious ecological consequences, including:

a. reduced agricultural productivity

b. decline in the ability of a forest to regenerate.

Such impacts are particularly relevant in Ghana’s diverse ecosystems, where mutualism plays a key role in maintaining ecological balance.

Commensalism Commensalism is a biological relationship between two different species in which one organism benefits, while the other is neither helped nor harmed.

1. The benefiting organism is called the commensal

2. The unaffected organism is referred to as the host Some common examples observed in Ghanaian ecosystems include the following.

a. Cattle egrets feeding on insects stirred up by grazing livestock.

b. Epiphytic ferns growing on tree trunks in forested areas.

c. Small fish sheltering among mangrove roots along the coast.

d. Birds nesting in tree cavities.

e. Remora fish attach to sharks for access to food scraps, transport, and protection.

Figure 3.17: Egret feeding on insects stirred up by a grazing cow Commensalism offers several ecological benefits, including:

a. making habitats more complex, which helps to support more types of plants and animals.

b. providing alternative survival strategies so that some organisms can adapt and find new ways to live and thrive.

c. encouraging new partnerships between species over time: As species interact, they can form helpful connections with each other.

In Ghana’s farms, commensalism often supports beneficial organisms that aid in natural pest control, e.g. Spiders build webs near cocoa trees to capture pest insects without harming the trees. This helps farmers to reduce the use of chemical pesticides, saving money and protecting the environment.

Parasitism Parasitism is a biological relationship in which one organism (the parasite) lives on or inside another organism (the host), causing harm to the host while benefiting from the interaction. In severe cases, the parasite may eventually lead to the host’s death.

Quick Question: Why do parasites rarely kill their host?

Common Examples in Ghana

1. Plasmodium (a malaria parasite transmitted by Anopheles mosquitoes) in humans(host).

2. Mistletoe growing on shea and mango trees (hosts).

3. Intestinal worms affecting humans and livestock (hosts).

4. Parasitic fungi attacking cocoa and other crops (hosts).

Figure 3.18: Mistletoe on a tree Figure 3.19: Dodder on a green-leafed plant Ecological Importance of Studying Parasites Understanding parasites in a habitat is crucial because:

a. they can sometimes help regulate host populations.

b. they drive the development of the host’s defences.

c. they contribute to disease exposure in organisms.

d. scientists use parasite presence to assess ecosystem health.

In Ghanaian farms, controlling parasites like cocoa black pod disease or stomach worms in goats is essential. Without proper management, crops may fail, and animals may become ill, leading to financial losses for farmers.

However, in forests and grasslands, parasites can play a regulatory role, preventing any single species from dominating. This promotes species diversity and strengthens ecosystem resilience.

Saprophytism Saprophytism is a mode of nutrition in which organisms obtain nutrients from dead and decaying organic matter. These organisms are known as saprophytes.

Examples of Saprophytic Relationships

1. Fungi decomposing fallen logs in forest ecosystems.

2. Bacteria breaking down leaf litter.

3. Termites consuming dead wood.

4. Mushrooms emerging after the rainy season.

Figure 3.20: Bracket fungi on a tree trunk Ecological Importance Saprophytism contributes to ecosystem health by:

a. driving nutrient cycling, essential for productivity.

b. improving soil formation and fertility.

c. preventing buildup of dead organic material.

d. supporting food webs based on detrital energy pathways (energy from dead plants and animals) In Ghana, traditional farming practices often include fallow periods, i.e. resting intervals between planting seasons. These allow decomposition to replenish soil nutrients. Without saprophytes, nutrients would remain locked in dead matter, leading to infertile soils and reduced food production.

Note

Detrital: Relating to dead and decaying organic matter that serves as a source of food for decomposers and detritivores.

Example in Ghana

A fallen cocoa leaf decomposing on the forest floor is detritus. Earthworms and termites feed on it, making it part of a detrital food chain.

Example of a Detrital Food Chain

Dead leaves → Earthworm → Bird → Hawk Epiphytism Epiphytism is a biological relationship where one plant (the epiphyte) grows non- parasitically on another plant (the host), using it solely for physical support, not for nutrients.

Examples in Ghana’s ecosystems

1. Orchids growing on trees in tropical forests

2. Mosses and lichens on tree trunks

3. Ferns nestled in tree crevices

4. Algae growing on aquatic plants

Figure 3.21: Bromeliad, an epiphyte growing on a tree trunk Ecological Importance of Epiphytism Epiphytism plays a vital role in maintaining ecosystem health and complexity. Its ecological benefits include the following.

1. Increasing structural complexity within forest ecosystems.

2. Creating microhabitats that support other organisms, such as insects and amphibians.

3. Enhancing canopy biodiversity, especially in tropical rainforests.

4. Participating in nutrient cycling, particularly by capturing nutrients from rainfall and air.

In Ghana’s relic rainforests, epiphytes are especially diverse. They contribute to ecosystem complexity by forming habitats for other species and by capturing water and nutrients that might otherwise be lost, thereby supporting overall biodiversity and ecological balance.

Ecological Importance of Interdependency

Interdependency among living organisms is essential for the stability and sustainability of ecosystems. Its importance includes:

a. ensuring a stable ecosystem through mutual dependence among species.

b. providing critical services such as food, clean water, and fertile soil necessary for survival.

c. supporting ecosystem conservation, which depends on the interconnected relationships among all living things and not just individual species.

Healthy ecosystems thrive when species work together, forming networks of support that maintain balance, productivity, and resilience.

Activity 3.4 “Ecosystem Explorers: Discovering Symbiotic Relationships” Objective: Identify, describe and classify examples of mutualism, commensalism, parasitism, saprophytism and epiphytism in the school compound or local environment and compile your findings into a collaborative field guide.

Instructions

1. Field exploration

a. Work in pairs or small groups.

b. Go around the school compound or the nearby area.

c. Look for examples of these relationships in plants, animals, insects or fungi.

d. For each type of biological association, write down one example you find.

e. Describe what is happening in that relationship, i.e. who benefits, who does not but is not harmed, who is harmed and how.

f. Draw or take a picture of each example if you can.

2. After your exploration, create a field guide that includes:

a. A title and your group’s name.

b. A section for each relationship with your example, description and an illustration.

c. Any interesting facts or local names of the species you found

3. Present your field guide to the class. Make sure your notes are clear and complete.

Caution: Be respectful of nature. Don’t harm any organism.

Activity 3.5 Decomposition uncovered Objective: Observe and compare how different plant materials decompose.

Materials

• Various plant materials (e.g., grass, leaves, fruit peels)

• Soil or compost

• Clear plastic containers/bags

• Water

• Notebook for observations

• Rulers (for measuring size changes) Instructions

1. Choose three different plant materials.

2. Collect equal volumes of each material (e.g., a cup or handful).

3. Place the materials in separate clear containers/bags filled with equal amounts of soil/compost.

4. Lightly water the materials to keep them moist.

5. Check the containers/bags once a week for 3-4 weeks.

6. Measure and record any changes in size (using a ruler) and appearance (colour, texture).

7. At the end of the observation period, create a chart to show the changes observed for each material over time.

8. Discuss which materials decomposed the fastest and potential reasons for the differences.

a. What factors influenced the decomposition rates?

b. Why is decomposition important for soil health and ecosystems?

Plant Density Sampling Techniques

Plant density is the number of individual plants per unit area in a habitat. Plant density gives us a better understanding of vegetation composition, ecosystem stability, and biodiversity.

Instruments used for estimating plant populations and densities include quadrats and line transects. The plant density within a habitat is determined by the formula, Plant Density = Plant density = = or Where N = number of individual species counted, A = total area sampled.

Steps for collecting data for calculating Plant Density

1. Define a clear study area and choose an appropriate sampling method (quadrat, transect, etc.).

2. Place the sampling instrument randomly or systematically within the area.

3. Count all individuals of the target plant species in each sampling unit.

4. Calculate the total number of plants and the total area sampled.

5. Divide the total number of plants by the total area to determine density (plants/m²).

Figure 3.22: A frame quadrat in a school field For example, if five different 1m² quadrats are randomly placed in a school field to estimate the density of Tridax procumbens (plant with white flowers in the figure), and the number of Tridax in each quadrat is counted to be 12, 8, 14, 10, 6.

Figure 3.23: Using a quadrat to sample Then the density of Tridax in this habitat is determined as follows:

Total number of Tridax = 12 + 8 + 14 + 10 + 6 = 50 plants Total area sampled = 5 quadrats × 1m² = 5m² Plant density = = 10 plants/m² The density of Tridax procumbens is therefore 10 plants per square metre in the school field.Top of Form Precautions in estimating plant density in a habitat

1. Ensure truly random placement of sampling instruments to avoid bias.

2. Use an appropriate quadrat size (smaller for dense vegetation, larger for sparse).

3. Maintain a constant identification criterion for the target species.

4. Collect sufficient samples to ensure reliability (minimum 5-10 quadrats).

5. Consider seasonal variations in plant growth and flowering.

Relationships between plants in the environment and human health

1. The presence of green plants in the environment helps to reduce stress and boost the mood of an individual.

2. Plants clean the air by using up carbon dioxide and producing oxygen. This activity of plants helps to replenish oxygen levels and protect humans from respiratory illnesses.

3. Crops are grown in farms and gardens to provide food (nutrients) for growth and good health.

4. Many plants have medicinal properties and are used in traditional and modern medicine to treat various ailments.

5. Parks and gardens serve aesthetic purposes to improve human health in humans.

Activity 3.6 Plant Sampling and Density Calculation

Objective: Conduct plant sampling and calculate mean density.

Materials

• Quadrat frames (or tape measures)

• Data recording sheets Instructions

1. Select a specific habitat area to sample.

2. Identify a specific plant species you want to sample

3. Place quadrats randomly within your area and count the number of plants identified in each quadrat.

4. Calculate the mean density of plants per unit area.

5. Repeat instructions 2 to 4 for different areas and determine variations in the density of the plant.

6. Research various factors that influence the plant’s distribution.

7. Select a specific factor to focus on and gather data from your sampled areas to support your ideas.

8. Analyse how your chosen factor affects plant distribution within the sampled areas.

9. Share your results with the class

Estimating and Analysing Body Mass Index (BMI) of

a Person Body mass index (BMI) is a simple measure used to classify individuals as underweight, normal weight, overweight, or obese and is a common health indicator of weight-related health risks. The BMI value is calculated by dividing the mass or weight (Kg) of a person by the height squared (m²).

The formula is BMI = Remember, BMI doesn’t distinguish between muscle and fat mass.

Figure 3.24: The BMI scale for adults The table below provides the category for BMI.

Table 3.1: Categorisation of BMI

BMI Range/kg/m²Category

Below 18.5 Underweight

18.5 - 24.9 Normal weight 25.0 - 29.9 Overweight 30.0 – 39.9 Obese 40.0 and more Morbidly obese Top of FormSteps for Calculating BMI

1. Measure body mass (weight) in kilograms.

2. Measure height in metres.

3. Find the square of the height measured

4. Divide the weight by the squared height value.

Quick Exercise

For example, the following data were collected from five mechanics in a shop in Kasoa. Calculate the BMI Mass and height of five mechanics in a shop at Kasoa.

Mechanic Mass/kg Height/m Height²/m²Kofi 65 1.70

Musa 55 1. 65 Kwame 80 1.85

Akosua 50 1. 65 Yaw 85 1.75

Interpret the BMI values in the table below as a summary of the results of the five mechanics.

Mechanics BMI Category

Kofi Musa

Kwame Akosua

Yaw Common precautions to take when estimating BMI

1. Use calibrated scales and measure height with the person standing straight against a wall.

2. Take measurements without shoes and in light clothing only.

3. Do not calculate BMI for pregnant women or very muscular individuals.

4. Use age-specific BMI charts for children and adolescents.Top of Form Limitations of using the interpretations of BMI

1. The method does not distinguish between muscle and fat.

2. It may not be appropriate for athletes, pregnant women and the elderly.

3. Ethnic variations exist in body composition.

4. Children and adolescents require a different interpretation using age-specific charts.

Activity 3.7 Investigating Body Mass Index

Objective: Calculate and analyse BMI data and errors.

Materials BMI calculation worksheets, graph paper or digital tools for creating tables, a weighing scale and a tape measure (to be provided by the teacher or visit any health post for measurement to be taken) Sample worksheet Body mass compares your mass to your height using the following equation: BMI= Your task

1. Collect data on age, weight and height from volunteers to fill the rows in the tables.

2. Calculate the BMI of each volunteer.

Age Weight/Kg

Height/m BMI

category Age Weight/Kg Height/m BMI category Age Weight/Kg Height/m BMI category Instructions

1. Measure your height and weight

2. Share your values with as many classmates as possible while you collect their values as well (minimum of 10)

3. Calculate your BMI and that of the others, using the formula:

BMI =

4. Create a frequency table categorising BMI into underweight, normal weight, overweight, and obese.

5. Draw a bar graph to represent the number of classmates in each category.

6. Analyse findings for possible errors and suggest solutions to minimise these errors.

7. Present findings focusing on strategies for accurate measurements.