4.1 Species, communities and ecosystems Flashcards
Essential idea:
The continued survival of living organisms including humans depends on sustainable communities.
Ecology
the study of relationships between living organisms and between organisms and their environment
Species
Species is a group of organisms that can interbreed to produce fertile offspring
If species are not closely related it is often impossible for individuals of the different species to breed.
If members of two closely related species do interbreed and produce offspring the hybrids will be sterile e.g. mules.
population
Population is a group of organisms of the same species that are living in the same area at the same time
Organisms of the same species separated geographically or temporally are unlikely to breed, though the ability to do so remains. The separated organisms are regarded as being members of different populations.
community
Community is a group of populations that are living and interacting together in the same area.
All organisms are dependent on interactions with members of other species for survival, e.g. a Lion depends on the availability prey species, such as Zebra and Antelope.
Communities also include plants and microbes and hence often involve thousands of species.
autotrophs
All autotrophs convert carbon dioxide (from the atmosphere or dissolved in water) into organic compounds.
Plant initially synthesis sugars (e.g. glucose) which are then converted into other organic compounds such as:
complex carbohydrates e.g. starch, cellulose
lipids
amino acids
Although most autotrophs fix carbon by photosynthesis. A few are Chemoautotrophs and fix carbon by utilzsing the energy in the bonds of inorganic compounds such as hydrogen sulfide.
The inorganic nutrient compounds, e.g. water, carbon dioxide, nitrates, phosphorous and oxygen are obtained from the abiotic environment, whether it be the soil, air or water.
organic molecules in relation to species
All organisms require organic molecules, such as amino acids, to carry out the functions of life, for example metabolism, growth, and reproduction.
Autotrophs synthesize their own organic molecules and are therefore known as producers
Heterotrophs however obtain their organic molecules from other organisms
mixotrophs
A few plants and algae use a combination of different modes of nutrition and are hence known as mixotrophs
Euglena sp. is a genus of Algae that will photosynthesize (autotroph) in sufficient light, feeding as an autotroph, but can also ingest particles of food by phagocytosis, which it then digests (heterotroph)
Venus flytrap (Dionaea muscipula) is found in subtropical wetlands and like most plants photosynthesize (autotroph), but also traps and digests both insects and spiders (heterotroph), to compensate for the nutrient poor soil of the wetlands.
Consumers definition and types
Heterotrophs that ingest other organisms obtain their organic molecules are known as Consumers
Consumers use a range of different food sources and feeding mechanisms. The combination of food source and feeding mechanism can be used to classify consumers.
Herbivores feed on producers (e.g. deer, zebra and aphids)
Omnivores feed on a combination of both producers and consumers (e.g. chimpanzee, mouse)
Carnivores feed on other consumers (e.g. lions, snake and ladybirds)
Scavengers are specialised carnivores that feed mostly on dead and decaying animals (e.g. hyenas, vultures crows)
detritivores
Detritivores are a type of heterotroph that obtain nutrients by consuming non-living organic sources, such as detritus and humus
Examples of detritivores include dung beetles, earthworms, woodlice and crabs
Humus is decaying leaf litter mixed with the soil
Detritus is dead, particulate organic matter. This includes decaying organic material and fecal matter
saprotrophs
Saprotrophs live on, or in, non-living organic matter. They secrete digestive enzymes on to the organic matter and absorb the products of digestion.
unlike most heterotrophs, saprotrophs are not consumers, as they do not ingest food: digestion is external as enzymes are secreted.
Because saprotrophs facilitate the breakdown of organic material, they are referred to as decomposers
Examples of saprotrophs include bacteria and fungi
ecosystem
Ecosystems consist of both the community and the environment. The abiotic environment has a fundamental impact on the community it supports. The community that can exists in a sand dune ecosystem is very different from the aquatic community in the adjacent sea.
Habitat
The environment in which a species normally lives
nutrient cycling
Elements required by an organism for growth and metabolism are regarded as nutrients, e.g. carbon, nitrogen and phosphorous.
The supply of nutrients is limited and therefore ecosystems constantly recycle the nutrients between organisms.
Autotrophs convert nutrients from inorganic form into organic molecules, e.g. carbon dioxide becomes glucose
Heterotrophs ingest other organisms to gain organic forms of nutrients
Saprotrophs breakdown organic nutrients to gain energy and in the process release nutrients back into inorganic molecules, e.g. fungi release nitrogen as ammonia into the soil. This ensures the continuing availability of nutrients to autotrophs.
Ecosystems are sustainable
Most flows of energy and nutrients in an ecosystem are between members of the biotic community. Relatively few flows of energy and nutrients enter or leave from surrounding ecosystems.
Therefore ecosystems are to a large extent self-contained and hence self-sustaining.
To remain sustainable an ecosystem requires:
Continuous energy availability, e.g. light from the sun
Nutrient cycling - saprotophs are crucial for continuous provision of nutrients to producers
Recycling of waste – certain by products of metabolism, e.g. ammonia from excretion, are toxic. Decomposing bacteria often fulfill this role by deriving energy as toxic molecules are broken down to, simpler, less toxic molecules.
