Ecology and Conservation of Natural Resources Notes
10.1 Definitions
Organism's environment consists of all external factors acting upon it, divided into:
Physical environment
Biotic environment
Ecology studies the relationships between organisms and their environments. It examines biological organization beyond the organismic level, including populations, communities, and ecosystems. The interactions between living things and the physical world (rocks, soil, rivers) constitute the ecology of the world.
An ecosystem includes all biotic (living) and abiotic (non-living) components in a habitat and their interactions, fundamentally a life-supporting environment. Ecosystem size varies from a drop of water to a continent. Examples: forests, grasslands, deserts, lakes, and ponds. An ecosystem serves as the home or habitat for its living organisms.
Physical/Abiotic Components
Abiotic means non-living. Major components include climate, edaphic (soil-related), and physiographic factors (related to landforms). These encompass:
Sunlight
Rainfall - These factors dictate which living organisms can survive.
Temperature - An important factor affecting survival of animals and plants.
Soil Type & Rocks
Soil Drainage
pH (acidity)
Water
Dissolved Oxygen Levels
Currents
Winds - These also affect organism survival.
Biological/Biotic Components
Living components affecting an organism's ability to survive. Examples:
Predator populations (lions affecting prey numbers)
Herbivore populations (caterpillars affecting plant survival)
Food Availability - Particularly affects animals.
Parasites
Diseases
Natural resources are naturally occurring useful elements.
Habitats are either:
Terrestrial (land-based)
Aquatic (water-based), which can be further divided into:
Marine (salt water)
Freshwater (lakes, ponds, rivers, streams)
10.2 Cycling Matter Through Ecosystems
Recycling in nature involves continuous exchange between living and non-living components. Nutrients are taken in and materials are lost through breathing and excretion. Organisms are interdependent and interact with their physical environment. Materials are moved through feeding, excretion, respiration, and decomposition. Without recycling, continuous life is impossible. Decomposers (bacteria and fungi) return nutrients to the ecosystem. They use saprobiotic nutrition, secreting enzymes onto dead matter, digesting complex molecules into simpler ones, and absorbing these products. This extracellular digestion occurs in the soil or wherever dead matter is located.
Ammonification, performed by bacteria and fungi, releases the amino group from amino acids and converts it to ammonia as a byproduct, which is vital to the nitrogen cycle. This is typical of many chemical reactions in nutrient cycles.
Carbon Cycle
The two basic life processes in carbon cycle are respiration and photosynthesis. The main processes involved in cycling carbon through ecosystems are:
Photosynthesis: Fixes inorganic carbon (carbon dioxide) into organic compounds (e.g., glucose).
Feeding and Assimilation: Transfers carbon atoms in complex molecules to the next trophic level where they become a part of the organism.
Respiration: Releases inorganic carbon dioxide from organic compounds.
Fossilization: Formation of fossil fuels (e.g., coal, oil, peat) from und decayed organisms.
Combustion: Burning fossil fuels, releasing carbon dioxide into the atmosphere.
Nitrogen Cycle
The primary nitrogen source is the atmosphere. Nitrogen is found in proteins, amino acids, DNA, RNA, ATP, and ADP. Nitrogen allows organisms to synthesize:
Genetic Material (DNA)
Structural Materials (Proteins)
Energy Transfer Molecules (ATP)
Main processes:
Plants absorb nitrates from the soil.
Nitrates are used to form amino acids, which synthesize proteins.
Animals eat plants, digest proteins, and assimilate amino acids into animal proteins.
Plants and animals die, creating detritus containing fixed nitrogen in organic molecules; excretory products like urea also contain nitrogen.
Decomposers decay excretory products and detritus, releasing ammonium ions (NH_4^+). This is ammonification.
Nitrifying bacteria oxidize ammonium ions to nitrates (NO3^-), used by plants. This is nitrification, and involves an intermediate product called nitrite (NO2^-).
Denitrification and nitrogen fixation alter the amount of nitrogen in circulation.
Denitrifying bacteria reduce nitrate to nitrogen gas, decreasing available nitrogen.
Nitrogen-fixing bacteria convert nitrogen gas into ammonium ions.
Free-living bacteria (Azotobacter, Klebsiella) reduce nitrogen gas to ammonium ions, which are oxidized to nitrates by nitrifying bacteria.
Bacteria in legume nodules (Rhizobium) convert nitrogen gas to ammonium ions, used by the legumes to synthesize amino acids. This nitrogen becomes available to other organisms upon decomposition of the legumes.
Phosphorus Cycle
The core cycle is similar to the nitrogen cycle. Phosphorus is present as phosphates.
Phosphate is absorbed from soil/water by plants.
Passed along food chains to herbivores and carnivores.
On death, bodies decompose, releasing phosphate ions from phospholipids, ATP, DNA, and RNA.
Phosphates enter soil/water via rock weathering and fertilizers.
Over millions of years, phosphate ions can leach into seas and become part of sedimentary rock.
Sulphur Cycle
The core cycle involves the soil, plants, animals, and decomposers. Long-term rock formation/weathering and fossil fuel combustion are also components.
Sulphate ions in the soil are taken up by plants and incorporated in plant tissue (methionine and cysteine amino acids).
Passed to animals via feeding/digestion.
On death, sulphate-reducing bacteria (Desulphovibrio) release sulphur as hydrogen sulphide (smell of bad eggs) under anaerobic conditions.
In aquatic environments, hydrogen sulphide is oxidized to sulphur by photosynthetic sulphur bacteria—equivalent to photolysis of water in plant photosynthesis.
Sulphur bacteria (Thiobacillus) oxidize hydrogen sulphide (or sulphur) to sulphate (SO4^{2-}), with sulphite (SO3^{2-}) as an intermediate step—an oxygen-requiring process under aerobic conditions, making sulphate ions available to plants again.
Sulphur can be incorporated in rocks, including fossil fuels.
Combustion of fossil fuels oxidizes sulphur to sulphur dioxide (SO_2), a pollutant and contributor to acid rain. In the atmosphere, sulphur dioxide oxidizes to sulphite/sulphate, which dissolve in rainwater to form sulphurous and sulphuric acid.
Water Cycle
Rain is absorbed by plants, and water evaporates via transpiration. Animals drink water and exhale it. Rain falls into water bodies, runs off the land, or flows underground.
Water is essential:
Composing 70% of cells.
Requirement of photosynthesis.
Basis of all transport systems in organisms.
Means of removing excretory products.
Crucial for cleaning, manufacturing and generating electricity.
Usable for hydroponics (growing plants in soil-free medium).
10.3 Ecological Succession
Community composition changes over time, with orderly replacement of communities until a stable one is established. This gradual change is succession. Lichens alter abiotic conditions, causing rock to crumble. Decomposers act on lichen remains, releasing mineral ions into the crumbled rock, forming a primitive soil. This environment supports mosses given sufficient water.
Succession involves:
Organisms colonizing an area.
Changing abiotic conditions.
Altered abiotic conditions allowing new species to colonize.
New competitor species becoming dominant.
Continuing alteration of abiotic conditions, allowing more species to enter.
Succession stages are called seres. As producers colonize, they create niches for other organisms. The first invaders are colonizers. Succession increases the complexity of food webs. The climax community is the final, most complex state.
Trends in succession:
Total biomass increases.
Species diversity increases.
Number of ecological niches increases.
Food webs become more complex.
Community becomes more stable.
Xerosere: Succession from rock.
Hydrosere: Succession starting from water.
Climax communities vary by:
Climate
Grazing animals
Temperature
Precipitation (rainfall)
Soil type
Soil depth
Primary succession occurs on bare land or after volcanic eruptions. The pioneer community is the first to occupy bare land.
Secondary succession occurs when the original community is destroyed by fire, earthquakes, or human clearing. It is quicker than primary succession because:
It does not start from bare rock/open water.
There is a seed bank of climax plant types.
Soil is already present.
10.4 Biomes
Biosphere: Worldwide sum of ecosystems. Can be grouped into biomes: large regions with characteristic climate and organisms. A biome features:
Typical flora (plants).
Typical fauna (animals) adapted to specific climate and soil.
Temperature and precipitation are key climatic factors. Biomes include:
Terrestrial
Defined by temperature, rainfall, soil, flora, and fauna
Desert (hot)
Less than 250 mm rain/year or no rain
Hot temperature
Poor soil quality
Desert (cold)
Cold temperature
Poor soil quality
Thorn Forest (scrub)
Hot summer, cold winter
Poor soil quality
Less than 70 cm rainfall
Trees with long roots and small, thick leaves
Tundra
Low rainfall (less than 250mm) and frozen water
Boreal Forest (Taiga)
Coniferous forests of northern cold winter climates.
Slightly warmer temperate and low rain fall (100 to 350 mm)
Dominated by evergreen trees
Temperate Deciduous Forest
Relatively warm summers and cold winters.
Annual rainfall ranges from 750 to 2500 mm.
Tropical Montane Forest
Hilly areas with high altitude.
Wet temperate forests between 1000-2000 meters.
Alpine vegetation above 3000 meters.
Tropical Rainforest
Near the equator.
Rainfall between 2000 to 4500 mm.
Aquatic
Marine biomes
Freshwater biomes
10.5 Conservation and Biodiversity
Biodiversity: Variety of life forms and interdependence of living things. It refers to the number of species in an ecosystem. Species diversity considers the success of each species. A diversity index indicates ecosystem health. A low value suggests dominance by few species. Simpson’s index of diversity:
d = {{{N(N-1)}}} {{\sum{n(n-1)}}}
Where:
d = index of diversity,
N = total number of organisms,
n = total number of organisms per species.
A higher index suggests more successful species and a more stable ecosystem.
Biodiversity also includes:
Ecological diversity: Number of ecological niches colonized.
Genetic diversity: Variability within and between populations of a species.
Biodiversity is the overall variability of life, including:
Species richness and diversity.
Ecological variability.
Genetic variability.
Loss of biodiversity is a major concern, leading to disappearing renewable resources on a global scale. Biodiversity measures the species weath in a given place; includes everything from the smallest microbe to the largest animal.
Importance of biodiversity:
Ecosystems are linked globally, so reduced biodiversity in one area affects others.
Purifies air and water.
Decomposes and removes waste.
Photosynthesis stabilizes the atmosphere and climate.
Plant roots hold soil together to reduce flooding and maintain soil fertility.
Pollination, seed dispersal, soil fertility, and the nitrogen cycle depend on biodiversity.
Provides genetic diversity for crop development.
Threats to biodiversity:
Direct effects:
Deforestation: Conversion to agriculture and other land uses.
Fuelwood collection and illegal logging
Overgrazing: Reduces forage.
Introduction of improved crop varieties: Reduces crop genetic diversity.
Overhunting (poaching): Reduces species numbers.
Invasive species: Outcompete native species.
Indirect effects:
High population growth
Undervaluation of biodiversity resources
Unsustainable exploitation promoted by legal/institutional systems
Disregard of traditional land management systems
Deforestation occurs to clear land for human activities or to obtain timber.
Agriculture reduces biodiversity because:
Areas are dominated by a single species.
Organisms are regarded as pests.
Hedgerows are removed, reducing niches.
Biodiversity loss contributes to:
Worsening health
Food insecurity
Increased vulnerability
Lower material wealth
Worsening social relations
Less freedom of choice
Conservation means protecting a living environment.
Methods to conserve biodiversity:
Protect individual species (illegal to capture/kill).
Reduce pollution (carbon dioxide levels).
Reduce habitat loss (stop deforestation, replant forests).
Protect large habitat areas.
10.6 Vegetation and Wildlife
Vegetation: A plant community grown naturally without human aid & left undisturbed. Cultivated crops and orchards are not part of natural vegetation.
Plants are used for:
Food.
Drinks.
Building materials.
Economy.
Endemic species: Organisms found only in a particular area. Ethiopia has 7000 higher plant species, with 800 endemics.
Examples: Teff (Eragrostis teff), Euphorbia spps, noug or niger seed (Guizotia abyssinica), enset (Ensete ventricosum), Ficus vasta Forssk, zigba, juniper (tid), kererro and sembo trees.
Vegetation: A sustainable resource.
Wildlife: Living organisms (flora and fauna) in natural habitats. Wildlife includes animals, bees, butterfly, crustacean, fish and moth and aquatic or land vegetation, which form part of any habitat.
Ethiopia's wildlife: A genetic bank for domestic animals and source of tourism income.
Endemic species: 28 endemic mammals (Gelada Baboon, Walia ibex, Menelik’s Bushbuck, Mountain Nyala, Swayne’s Hartebeest, Ethiopian wolf), and also endemic bird species (heavy-headed, thick-billed raven, the wattled ibis, the black winged lovebird, the white-collared pigeon and the Prince Ruspolis Turaco. We also have six endemic reptiles and around 33 endemic amphibians). These animals are found only within Ethiopia.
10.7 Global Warming and Air Pollution
Pollution: Contamination of the natural environment by harmful substances, locally (litter) or globally (acid rain, global warming, ozone hole).
Pollutant: Something that contaminates air, soil, and water.
Air pollution: Smoke from burning fuel (fossil fuels: coal, oil, gas), releases unburnt hydrocarbons (black carbon) into the air. Exhaust from burning fuels in cars, homes, and industries, and wood fires releases soot.
Smoke pollution causes global dimming.
Carbon dioxide is produced by respiration, used in photosynthesis, and released by burning wood and fossil fuels.
Increased carbon dioxide (and methane) traps heat close to the Earth's surface, raising temperatures and affecting climate, and possibly increasing hurricane activity.
Carbon monoxide, produced by burning fossil fuels, combines irreversibly with hemoglobin, reducing oxygen carrying capacity.
Acid rain results from air pollution. Burning fossil fuels releases carbon dioxide, sulphur dioxide, and nitrogen oxides.
Sulphur dioxide and nitrogen oxides pollute air, causing breathing problems and smog. They dissolve in rain and react with oxygen to form dilute sulphuric acid and nitric acid: acid rain.
Effects of acid rain:
Harmful to aquatic life, increased acidity in water and affect eggs hatching.
Harmful to vegetation, increased acidity, leeched nutrients and toxins in soil, brown spots appear on leaves.
Solution to reduce acid rain:
Use cleaner fuels.
Remove oxides of sulphur and oxides of nitrogen before releasing. (Flue gas desulphurization).
Use renewable energy.
Limit the number of vehicles on the roads and increase public transport.