1. What are the different types of species interactions? Give an example and explain why studying them is important.
Answer: In mutualism, like bats and flowers, both species benefit: the flower’s pollen is spread to other plants by the bat’s feeding patterns, and the bat gets pollen and nectar. Studying mutualistic relationships is important because it shows how species rely on each other and they form the basis of a lot of food and fiber production
In commensalism, like clownfish (nemo-fish) and anemones, one species benefits while the other is unaffected: the clownfish gets protection from predators without benefiting or harming the anemone. Studying commensalism is important because a detailed investigation can often uncover harms or benefits to the ‘unaffected’ organism.
In competition, like different birds competing for seeds, both species are negatively affected because requiring and using the same resource makes less available for both individuals. Studying competitive relationships is important because it forms the basis of Darwinian evolution and helps us to understand specialization and equilibrium in ecosystems.
In predation, like a fish eating small zooplankton, one species is benefited and the other is negatively affected. Studying predatory relationships is important because it can help us understand food webs and trophic cascades.
2. Competition: Definition questions
a. What are the two different types of species interactions within competition? Explain and give examples of each.
Answer: Intraspecific competition is competition between individuals of the same species, like birds of the same species in the same area which require the same resources. Interspecific competition is competition between individuals of different species, like various species of finches competing for the same resources.
b. What is the difference between exploitative competition and interference competition? Explain and give an example of each.
Answer: Exploitative competition (indirect competition) is when competing individuals or species indirectly impact each other negatively as they separately consume a resource. A couple examples are trees vying for the same nutrients and sunlight, with one eventually crowding out the other, and different types of fish competing for the same territory. Interference competition (direct competition) is when individuals aggressively defend their use of resources which causes harm to another individual. An example is the Salvia genus of sage which uses chemicals to inhibit the growth of other plants.
c. Give an example of exploitative and interference modes of competition for intraspecific and interspecific types of competition.
Answer: Exploitative/intraspecific – an organism overgrazing on land shared by multiple users. Interference/intraspecific – a territorial animal. Exploitative/interspecific – canopy plants taking available sunlight. Interference/interspecific – allelopathy (chemical competition).
3. Mutualism: Definition questions
a. What are the two broad types of mutualisms? Give an example of each.**
Answer: Facultative mutualisms are beneficial to each organism, but not essential to either’s survival. An example is the Boran-Honeyguide mutualism: Borans find honey more quickly by following the birds, and the birds get honey and larvae, but neither requires the other for survival. Obligate mutualisms are essential to the survival of one or both species. An example is the ant-Acacia mutualism: the ant needs the plant for shelter and food, and the Acacia needs the ant for protection against predators and clearing debris to prevent fires.
b. What are three sub-categories of mutualisms?
Answer: Trophic mutualism is a symbiotic interaction between two species where each species is the supplier of a limiting nutrient or energy source that the other can’t get by itself. An example is mycorrhizal relationships between plant roots and fungi. Defensive mutualism is an interaction where one species receives food or shelter in return for providing some type of defense against predator. An example is the ant-Acacia relationship. Dispersive mutualism is an interaction in which one species disperses pollen or seeds in exchange for some type of nourishment. An example is bees pollinating flowers.
4. Elephant seals along the coast of Alaska are highly territorial animals that are well adapted to the cold Arctic waters. They feed on squid, octopus, and a variety of fish, and depending on its size a male may maintain a harem of 30-100 females.
a.) Using this example, explain the three criteria for a resource.
Answer: A resource is: something that is consumed, which reduces its amount or availability; used by a consumer for its own maintenance and growth; affect biological processes in a way that reduces consumer population growth when its availability is reduced. For the elephant seals, food is a good example of a resource because it is eaten to help seals grow, but if it is overused the seal population growth will decline until it is in equilibrium with the resource.
b. Is temperature a resource? How about space? Why or why not?
Answer:Temperature is not a resource, because it's not consumed, even though it does affect the population. Space, on the other hand, is a resource, because a consumer can take it up and thus render others unable to use it, and if there is less of it, the populations will be impacted.
5. What does the Lotka-Volterra model demonstrate about the relationship between inter- and intraspecific competition for populations in equilibrium?
Answer: Intraspecific competition must be greater than interspecific competition for equilibrium to occur. The equilibrium point and time to equilibrium depend on r1 and r2 (growth rates for each population) and the competition coefficients and carrying capacities for each population. The net zero growth isocline shows where the rate of population growth of a species is zero by factoring in carrying capacity and the effect it has on the other species. Species limit their own growth before they reach densities at which they can exclude their competitors. Equilibrium occurs where the two isoclines cross.
Question 2: Describe Liebig's law of the minimum, and why under many conditions (explain which conditions), it does not hold strictly true.
* Populations are limited by single most scarce resource relative to demand. This is unique to each resource.
* The law only applies to resources which independently influence populations, but two or more may interact to determine consumer growth rate (synergistic).
Question 5: Explain the principle of competitive exclusion and how it relates to niche differentiation:
The Principle of Competitive Exclusion states that a single species will exist in a niche, and where competition arises, the dominant species will prevail. Niche differentiation involves the partitioning of certain resources among species so that one species does not out-compete the other. Therefore, differentiation of species' realized ecological niches enable the coexistence of two species in the same niche.
Question 6: What factors may be included in defining a niche?
Temporal (Life History, Seasonality, Nocturnal Nature, Breeding Period); Spatial (Geographic Range, Habitat, Lake Depth/Tree Height); Resource Availability (Food, Trophic Position)
Question 7: Explain the difference between fundamental niche and realized niche.
The fundamental niche is the broader of the two terms, describing the full range of environmental conditions under which an organism can exist. As a result of pressures and interactions from other organisms, species are usually forced to occupy a niche narrower in scope, known as the realized niche. The realized niche is a space in which a certain species is most highly adapted, thus representing where the species truly does exist.
Question 8: What is the difference between a parasitoid and a parasite?
Parasites consume part of the host but typically do not kill them. Parasitoids eventually kill the hosts they consume.
Question 9: What is negative association? Please provide an example.
A negative association between two species is when the benefit of one species can cause detriment to another, and can occur without direct competition for a shared resource. (i.e. algae and corals, the negative interaction is caused by a chain of events that is initiated by the algae emitting polysaccharides, which fed and led to the overabundance of microbes that typically live in coral at lower levels and both thrive. With the addition of the polysaccharides from the algae, the microbes increased to a point where they were consuming all of the surrounding oxygen and suffocating the coral.