Positive and Negative Interactions Flashcards
What type of interaction is predation/parasitism and why?
Positive / Negative - Organisms get their nutrition by eating others, consumer benefits whilst consumed loses.
What type of interaction is competition and why?
Negative / Negative - Members of the same species using the same resource. Gause’s principle of competitive exclusion states ‘no two species can occupy the same niche indefinitely when resources are limiting’. One species will outcompete the other or will occupy the same area through niche differentiation.
What type of interaction is commensalism and why?
Positive / Neutral - One species benefits whilst the other is unaffected, e.g brown headed cowbirds follow grazing cattle and bison and forage on insects flushed from the vegetation.
Summarise the commensalism or mutualism arguement
Sometimes there is no clear divide between commensalism and mutualism. An example of this is the interaction between clownfish and anemones. Clownfish benefit from food particles in the anemone and the waving of fins oxygenate the anemone at night.
What type of interaction is amensalism and why?
Negative / Neutral - One organism is harmed whilst the other is unaffected and tends to be accidental. E.g a herd of elephants crushing plants and insects whilst moving through a forest.
Describe amensalism in blue-footed boobies
Blue footed boobies nest at coastal sites if nazca boobies are absent.
If they are present, they nest further inland.
Nazca boobies nest at coastal sites whether the blue-footed boobies are present or not.
Nestling segregation is caused by attacks of non-breeding adult nazca boobies on blue-footed boobie nestlings.
No discernible cost or benefit for nazca boobies.
What type of interaction is mutualism and why?
Positive / Positive - Both species benefit.
What is obligate mutualism?
Interaction is necessary for the survival and reproduction of both partners.
Give an example of obligate mutualism
Acacia trees need ants to grow and reproduce, the ants are only found on acacia trees.
The ants prevent herbivores from feeding on the plant by killing/chasing them off and remove other plants growing nearby which lowers competition.
The tree provides the ants with a safe home, where they live in the large thorns and provide two food sources, extrafloral nectaries and beltian bodies.
What is facultative mutualism?
Each participating species can survive/grow/reproduce without each other but do much better if the partner is present.
Give an example of facultative mutualism
In many coral reefs cleaning stations occur where several species of fish and shrimp remove dead skin and parasites from larger fish.
Cleaners enter the mouth of larger fish.
Fish get parasites removed and have better health, cleaners get a food source and protection as larger fish guard cleaners from predators.
What is community structure?
The diversity of organisms, their abundance and how they interact with each other.
What forces underpin community structure?
Competition - most dominant (Gause’s principle).
Niche differentiation avoids competition.
Biases community assembly towards ecologically divergent species.
What is the sigificance of positive interactions?
Benefit one participant and cause no harm to the other. Recent work has suggested that such interactions could outweigh competition - the positive benefits of mutualism counterbalance the negative forces of competition. Allows diverse communities to evolve that do not partition resources if positive interactions are strong enough.
