Individuals, populations, communities and ecosystems
Definition of Species
A species is defined as a group of organisms that share common characteristics and can interbreed to produce fertile offspring. This concept is fundamental to understanding biodiversity and ecosystem dynamics.
Example: The grey wolf (Canis lupus) is a species of canine that can interbreed with other grey wolves to produce fertile offspring. However, while wolves can mate with domestic dogs (Canis lupus familiaris), producing fertile offspring, they are considered subspecies due to their distinct evolutionary histories and ecological roles.
NoteThe biological species concept, while widely used, has limitations. For instance, it doesn't apply well to organisms that reproduce asexually or to extinct species known only from fossils.
Identification of organisms
Taxonomists use a variety of tools to identify an organism. One such tool is the dichotomous key. It is a tool consisting of questions with two choices in each step and answering the questions leads the user to the right identification.
An example of a dichotomous key is below.
Population
A population is a group of organisms of the same species living in the same area at the same time, and which are capable of interbreeding.
NoteThe concept of a population is scale-dependent. For example, we could discuss the population of rabbits in a specific field, or the population of rabbits in an entire country.
Abiotic and Biotic Factors
Factors that determine the distribution of a population can be biotic or abiotic.
Abiotic Factors
Abiotic factors are the non-living, physical components of an ecosystem that influence organisms. These include:
- Temperature
- Sunlight
- pH
- Salinity
- Precipitation
- Wind
- Soil composition
- Altitude
In a desert ecosystem, key abiotic factors include high daytime temperatures, low precipitation, and intense sunlight. These factors shape the adaptations of desert organisms, such as the water-storing capabilities of cacti or the nocturnal behaviour of many desert animals.
Biotic Factors
Biotic factors involve the interactions between living organisms within an ecosystem. These include:
- Predation: Where one organism (predator) hunts and consumes another (prey).
- Herbivory: Consumption of plants by animals.
- Parasitism: A relationship where one organism (parasite) benefits at the expense of another (host).
- Mutualism: A relationship where both organisms benefit.
- Disease: Interactions between pathogens and their hosts.
- Competition: When organisms compete for limited resources.
In a coral reef ecosystem, mutualism is exemplified by the relationship between coral polyps and zooxanthellae algae. The algae provide the coral with nutrients through photosynthesis, while the coral provides shelter and compounds needed for photosynthesis to the algae.
