ecosystems

• An ecosystem includes all the organisms living in a particular area known as the community as well as all the non-living elements of that particular environment
• The distribution and abundance of organisms in a habitat is controlled by both biotic (living) factors e.g. predators and pathogens and abiotic (non-living factors) such as light levels and temperature
• Each species has a particular role in its habitat called its niche which consists of its biotic and abiotic interactions with the environment
• Succession is the change of one community of organisms into the other
• Primary succession occurs when an area previously devoid of life is colonised by communities of organisms, for instance after the eruption of a volcano
• Pioneer species such as lichens are the first to colonise such areas and are adapted to survive in harsh conditions
• As organisms die, they are decomposed by microorganisms, adding humus and leading to the formation of soil, making the environment more suitable for more complex organisms
• Over time, the soil becomes richer in minerals, enabling larger plants such as shrubs to survive, eventually establishing a climax community, which is a self-sustaining and stable community of organisms
• Secondary succession occurs in a previously colonised area where an existing community has been cleared, such as after forest fires
• In any ecosystem, plants synthesise organic compounds from atmospheric or aquatic carbon dioxide
• Most sugars synthesized by plants are used for plant respiration, while the remaining sugars are used for the synthesis of biological molecules forming plant biomass
• Biomass can be measured in terms of mass of carbon or dry mass of tissue per given area per given time
• Net primary productivity (NPP) is the rate at which energy is transferred into the organic molecules that make up new plant biomass, after accounting for respiratory losses
• Gross primary productivity (GPP) is the rate at which energy is incorporated into organic molecules in plants in photosynthesis, in a given area or volume, in a given time
• Net production of consumers (N) such as animals can be calculated by: N= I – (F+R), where I represents the chemical energy store in ingested food, F represents the chemical energy lost to the environment in faeces and urine, and R represents the respiratory losses to the environment
• Nitrogen is an essential component of metabolism required for the synthesis of proteins and nucleic acids
• Nitrogen needs to be fixed in the form of ammonium ions or nitrates to be useful to plants
• Nitrogen fixation occurs through processes involving bacteria such as Rhizobium in root nodules of leguminous plants
• Ammonium ions are released by bacteria in the putrefaction of proteins from dead organic matter
• Plants absorb nitrates from the soil for nucleotide synthesis
• Denitrifying bacteria convert nitrates back to nitrogen gas in anaerobic conditions
• Carbon is a component of all organic molecules and is recycled through the environment by processes such as photosynthesis, feeding, respiration, and decomposition
• Abundance of organisms can be measured using methods such as line transects, quadrats, and belt transects
• Limiting factors that determine the carrying capacity of an environment include food, water, light, oxygen, nesting sites, shelter, parasites, and predators
• Competition between organisms occurs when a particular resource is in limited supply
• Predator-prey relationships lead to fluctuating population sizes of predators and prey
• There are two types of competition between organisms: interspecific competition between individuals of different species and intraspecific competition between individuals of the same species
• Conservation aims to maintain or increase biodiversity within a habitat by allowing sustainable use of resources, while preservation aims to maintain biodiversity levels and the habitat intact by minimizing the effects of human activities
• Management of an ecosystem can provide resources in a sustainable way through practices such as coppicing, selective felling, pollarding, efficient production, and controlling human activities that impact animal and plant populations
• Conservation projects aim to minimize the negative effects of human activities on ecosystems, such as overfishing and introduction of non-native species
• Ecosystem management strategies include controlling the number of tourists/visitors, involving local communities, educating local communities, actively managing vegetation, and controlling the introduction of species