Communities Flashcards
(25 cards)
Define community.
A community is a group of populations living together and interacting with each other within a given area.
Communities comprise all the populations in an area – including all plants, animals, fungi and bacteria. The members of a community will interact with the abiotic environment (habitat) to form a complex ecosystem.
Give an example of a community of organisms.
A pond community includes frogs, algae, water plants, fish, insects, and bacteria.
Outline interactions within a community.
Interactions between species are the foundation of community dynamics, influencing survival and reproduction. These interactions can be beneficial, harmful, or neutral, influencing survival, reproduction, and resource availability.
1. Herbivory: Herbivores feed on plants or algae.
2. Predation: One species (predator) hunts and eats another (prey).
3. Interspecific competition: occurs when different species compete for the same resources (‘inter’ = between)
4. Pathogenicity: infectious microorganisms living inside or on a host organism and causing disease
Define symbiotic relationships.
Symbiosis describes the close and persistent (long-term) interaction between two different species:
Mutualism – Both species benefit from the interaction (e.g. anemone protects clownfish, clownfish provides fecal matter for food)
Commensalism – One species benefits, the other is unaffected (barnacles are transported to plankton-rich waters by attaching to whales)
Parasitism – One species benefits to the detriment of the other species (ticks or fleas feed on the blood of their canine host)
Give examples for each category of interspecific relationship within communities.
Herbivory: cows grazing on grass
Predation: lions hunting gazelles
Interspecific competition: lions and hyenas competing for prey in the savanna.
Mutualism: bees pollinate flowers while collecting nectar.
Commensalism: barnacles are transported to plankton-rich waters by attaching to whales
Parasitism: ticks feeding on blood of other animals
Outline the mutualistic relationship within root nodules in Fabaceae (legume family).
Fabaceae are a family of legumes that form a mutualistic relationship with a nitrogen-fixing bacterium (Rhizobium)
The legumes gain nitrates that can be used to build essential molecules (like proteins and nucleic acids)
The bacteria gain carbohydrates which were produced by the plant via photosynthesis
Outline the mutualistic relationship within mycorrhizae in Orchidaceae (orchid family).
Orchidaceae are a family of flowering plants (orchids) that form a mutualistic relationship with a fungus
The fungus possesses long filaments (called hyphae) that connect to the plant roots forming an association called a micorrhizae
The hyphae greatly increase the surface area of the root system (more absorption), while the fungus gains carbohydrates from the plant
Outline the mutualistic relationship of zooxanthellae in hard corals.
Coral reefs consist of coral polyps which exist in a mutualistic relationship with photosynthetic algae (zooxanthellae)
The zooxanthellae carry out photosynthesis to provide carbohydrates for the coral polyp
The polyp secretes a calcium carbonate exoskeleton which provides shelter and protection for the algae
Define endemic and invasive species.
Endemic Species
* Naturally occurring in a specific region.
* Highly adapted to local environmental conditions.
* Often have specialized niches and rely on balanced ecosystem interactions.
Invasive Species
* Non-native species are introduced, often by human activity.
* Spread rapidly and can disrupt native ecosystems.
* Often lack natural predators in their new environment.
Explain the competitive exclusion principle.
The competitive exclusion principle states that two species cannot occupy the same ecological niche indefinitely.
If an invasive species has a competitive advantage, it can displace endemic species by:
Outcompeting for Resources: Taking over food, water, or breeding sites.
Occupying a Broader Niche: Exploiting more resources than native species.
Reproducing More Rapidly: Growing in population faster than endemic competitors.
Give an example of competative advantage over an endemic species.
Red Fox
The red fox was introduced to Australia following European colonisation and rapidly became an apex predator
The red fox shares a common diet with the native quoll (a carnivorous marsupial) and occupies a similar niche
Since the introduction of foxes, quoll populations have declined dramatically and certain species are now considered endangered
In certain areas, foxes are now being actively targeted for eradication in order to protect quoll populations
Why do invasive species thrive in new environments?
Invasive species thrive in new environments because they often:
Lack Natural Predators or Pathogens that would control their populations.
Have High Reproductive Rates, allowing for rapid expansion.
Possess Broad Ecological Niches, making them highly adaptable.
Show Resistance to Environmental Stresses, such as drought or pollution.
State strategies used to manage invasive species.
Biological Control: Introducing natural predators or pathogens to reduce invasive populations.
Chemical Control: Using pesticides or toxins, though this can harm non-target species.
Physical Removal: Manually capturing or eradicating invasive species.
Prevention: Implementing policies to prevent the introduction of new invasive species.
Explain association tests.
The type of relationship between two species can be assessed via a number of different research methods:
* Experiments can be conducted under controlled conditions, whereby chosen variables are manipulated
* Field manipulation may involve the removal of one species to determine the impact on another species
* Field observations can also occur, where sites are assessed for the presence or absence of each species
Explain comparative distribution of two species as an indicator of the type of their ralationship.
The comparative distribution of two species can be used as an indicator of the type of relationship between them
Interspecific competition is indicated (but not proven) if one species is more successful in the absence of another
In such circumstances, the two species do not tend to appear in the same environment (they have different realised niches)
Explain the use of chi-squared test.
If data has been collected via quadrat sampling, a chi-squared test can be performed to determine if there is a statistically significant association between the distribution of two species
If two species are typically found within the same habitat, they show a positive association (e.g. predator-prey dynamic)
If two species tend not to occur within the same habitat, they show a negative association (e.g. interspecific competition)
If two species do not interact, there will be no association between them and their distribution will be independent of one another
State the process of performing a chi-squared test.
- Collect data using quadrant sampling
- Create a contengency table
- Calculate expected values for each category
- Calculate a chi-squared value
- Determine statistical significance
Explain top-down control.
Top down factors are pressures applied by a higher trophic level to control the population dynamics of the ecosystem.
Predators reduce prey populations: Predators limit the abundance of prey by feeding on them, preventing overpopulation.
**Indirect Effects on Producers: **When predator populations increase, fewer herbivores graze on plants, allowing producers to thrive.
Explain bottom-up control.
Bottom up factors are pressures applied to lower trophic levels (e.g. producers) – such as the limited availability of resources.
Resource Availability: The abundance of producers (plants or algae) is influenced by resources like sunlight, water, and nutrients.
Cascading Effects: When resources are abundant, producer populations increase, which supports herbivores and predators.
When is the top-down control dominant?
Closed Systems: In environments like islands or reserves, predators play a crucial role in regulating prey populations.
Simple Food Chains: Ecosystems with few species see predators exert stronger control over lower trophic levels.
When is the bottom-up control dominant?
Nutrient-Limited Systems: Deserts, nutrient-poor lakes, or arid regions depend on limited resources like water or soil nutrients.
Complex Food Webs: Systems with many species rely more on resource availability than direct predation.
Define allelopathy.
Allelopathy is a biological interaction whereby an organism releases chemicals that influence the growth, survival or reproduction of another organism
Allelopathic interactions can be positive (beneficial effects) or negative (detrimental effects) and predominantly involve plants
Outline an example of allelopathy.
Black Walnut Trees (Juglans nigra) produce juglone, a chemical that inhibits the growth of nearby plants.
In areas where black walnuts grow, other plants often fail to thrive due to this chemical inhibition.
Define antibiotic secrition.
Antibiotic secretion is a strategy used by microorganisms, like fungi and bacteria, to inhibit the growth of competing microbes.
