C. Ecology Exam 2

What happens to populations at different points along the logistic growth curve?

• At bottom on logistic growth curve, low population

• Lots of resources

• Less competition

• Probability of dying/starving is low

• As population increases/reaches carrying capacity

• Birth rate decreases

• Running out of resources

• More competitions

What is per capita growth?

Percentage of a population that will be born or will die with each time step

How are population sizes determined by density compensation?

• Determined by environment and the number of species competing

Example of density compensation

birds on the island vs mainland (pieces of the pie)

How do predators control prey species?

• Predators are more likely to control prey when the prey is invasive

• Can see behavioral and morphological changes when predators are present

Why do terrestrial ecosystem appear mostly “green” to us?  Why are there so many plants?  How does this change with predator abundance?

• Competition is always on the highest level of the tropic system

• If a secondary predator is added to the tropic level then producers are now limited by predation leading to less biomass

What type of conditions make keystone predators particularly powerful shapers of the community?

• Where competitively superior prey exist and where they can disproportionately impact the environment because of it

Examples of keystone predators and their prey

• Otters in kelp forests (sea urchins and snails)

• Starfish on shorelines (barnacles and bivalves)

How are the nonconsumptive effects of predation tested for?

• Behavior: where they are during the day and how they avoid predation

• Life history and development: How fast they develop in nymph stages to avoid predation (how big can we get before getting eaten)

• Morphology: Inducible defenses such as armor in daphnia; only present when predation stress

Define and explain the types of competition.

• Direct: Interference competition; direct denial of resources

o Territories, aggression, chemicals

• Indirect: Exploitative competition; indirect denial of resources

o More efficient in using or taking a resource (food, space, light)

o Ex. Eating faster than a competitor

What type of species would you expect to compete more strongly with another? Why?

• Species that have a niche overlap and that are within close proximity of each other

• The opposite could be argued because the existence of no overlap could be the result of competition

How are zero net growth isoclines used to determine when species can coexist?

• The middle of the two vectors is where the species can coexist

• To the left of the vector that species wins, the the right of the other that one wins

How does apparent competition affect predator abundance?

• It increases the amount of predators that are preying on the two species

• When populations of one prey are reduced the other one is increased sort of like density dependance

How does facilitation differ from mutualism?

• Facilitation is a subset of mutualism. It is an interaction in which at least one thing is benefiting. One thing has enhanced ability to grow, survive, or reproduction in an interaction. (Foundation species and ecosystem engineers)

How is altruism different from reciprocal exploitation?

• Altruism is the remembrance of helpful acts that are reciprocated in the future that enhance fitness.

• It is a form of mutualism that you scratch my back I scratch yours; apple being eaten by you and you spreading its seeds. Fish eating parasites and fish getting rid of those parasites

Which types of mutualisms would be expected from different species?

• Energetic, nutritional: fruits, allege, plants and mycorrhizal fungi

• Protective: ants protecting trees, trees protecting other trees, clownfish

• Transport: moving species with species unable to move, usually moving alleles in return of something like pollen

Define and explain the different types of mutualisms

• Specialist: are totally reliant on that one species for that return (star orchid and hawk moth)

• Generalist: Can have many things reciprocate the return (bees and flowers)

When should you expect mutualism evolution?

• When something is very hard to do but very easy for someone else to do. Why not trade these easy resources to each other. Its mutually beneficial

Example of mutualism evolution evidence

Mycorrhizal fungi and trees trading sugar and water

How does cheating affect mutualistic interactions?

• Species that cheat are maintained at a low level and don’t give reward so tit for tat won’t work.

• Natural selection can select for defenses against cheating