4.1 species, communities and ecosystems

Define species according to the biological species concept.

The biological species concept defines a species as organisms that can (actually or potentially) interbreed with each other to produce fertile offspring and cannot breed with others. In other words, the organisms of the species are reproductively isolated.

Describe limitations of the biological species concept.

1. Cannot test the reproductive isolation of fossils which must be classified into species based on morphology.

2. Even for living species, it is hard to determine if populations are reproductively isolated especially if they are geographically isolated.

3. Many species, especially prokaryotes, reproduce asexually and must be classified based on morphology and/or biochemical characteristics.

Define autotroph and heterotroph.

An autotroph is an organism capable of making energy-containing organic molecules from inorganic sources via photosynthesis (involving light energy) or chemosynthesis (involving chemical energy). Autotrophs are the producers in a food chain, such as plants or algae.

A heterotroph is an organism that is unable to synthesise its own organic compounds from inorganic sources, and as a result must feed on organic matter produced by, or available in, other organisms.

Describe the feeding behaviours of consumers.

Consumers are organisms that need to eat food to obtain their energy. All heterotrophs are consumers.

Describe the feeding behaviours of detritivores.

Detritivores are heterotrophs that obtain nutrients by consuming detritus. Detritus is particulate organic material such as the bodies or fragments of dead organisms and/or faecal material.

Describe the feeding behaviours of saprotrophs.

Saprotrophs live on dead organic matter and feed by a process in which dead or decaying organic material is extracellularly digested (outside of the cell) by a variety of enzymes that are excreted by the organism. After digestion, the nutrients are then absorbed into the organism.

Define population and community.

A population is organisms of the same species that live in a particular geographic area at the same time.

A community is all the populations of various species living and interacting in a common location.

Define abiotic and ecosystem.

Abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors such as climate and geology can determine which species of organisms will survive in a given environment.

An ecosystem is the interaction of the community of living organisms with the abiotic components of their environment. The biotic and abiotic components are of an ecosystem are linked together through nutrient cycles and energy flows.

Define nutrient.

Nutrients are molecules required by an organism for growth, repair, and normal metabolism.

Outline how nutrients enter living systems.

Through a nutrient cycle a nutrient is able to move from inorganic matter back into a living system. In this example, the process is initiated by an autotroph which synthesises organic molecules which then move through food web pathways. Eventually the nutrient convert back into inorganic nutrients through metabolism or decomposition.

Outline the generalized flow of nutrients between the abiotic and biotic components of an ecosystem.

Elements such as carbon, nitrogen, oxygen, and hydrogen are moved through biotic components of an ecosystem through food chains and recycled through abiotic environments including the atmosphere, water, and soil.

Define sustainability.​

Sustainability is the capacity of ecosystems to maintain their essential functions and processes, over time.

Give an example of an unsustainable practice.

Unsustainable practices are not able to be maintained at the current rate or level.
Examples include:
Pollution and contamination of air, land, and water.
Deforestation.
Soil degradation and erosion.
Wasteful consumption of water.

Outline three requirements of a sustainable ecosystem.

Sustainable ecosystems require nutrient availability , an ability to detoxify waste products and a supply of energy.

Define mesocosm.

A controlled experimental system that simulates natural environments on a smaller scale, allowing researchers to study ecological processes in a more manageable setting.

Evaluate the use of a mesocosm to understand habitats and environments

Supporting arguments:

• (They make it possible to) investigate interactions between species, e.g. competition / impact of changing abiotic factors, while other variables are controlled

• Variables other than the variable being tested will not influence the results

• Mesocosms can be designed to mimic a natural environment as closely as possible

Negative arguments:

• In natural environments there are other abiotic factors/biotic factors that cannot be controlled OR (closed) mesocosms are unrealistic representations of a natural environment

• The results gained from studying a closed system/mesocosm cannot be directly applied to a natural environment

State that chemical elements can be recycled but energy cannot

Chemical nutrients and energy tend to flow in the same direction for most of an ecosystem (from autotrophs to heterotrophs). The big difference is that the chemical nutrients can be recycled in the ecosystem while the energy is ultimately lost from the ecosystem to the universe at large.

Explain the concept of ecosystem sustainability

The concept of ecosystem sustainability states that. . .

• When organisms die, the inorganic nutrients in their tissues are broken down by detritivores/saprotrophs/decomposition

• (During decomposition) inorganic nutrients are released into the soil (more than can be absorbed by the saprotrophs themselves) where they can be taken up/absorbed by producers/plants

• Producers/plants use inorganic nutrients (from the soil) to build their tissues (e.g. nitrates are needed to build proteins and nucleic acids)

• Inorganic nutrients pass to consumers when producers are eaten/consumed

• Provided that decomposition occurs, inorganic nutrients will continue to be released into the soil and re-enter the food chain / ecosystems will not run out of inorganic nutrients