Ecology Exam 2 Chapters 16,17,18

Question 1

If the mountain tree shrew and summit rat of Borneo were to go extinct, what would likely happen to the pitcher plant that currently lives in a mutualism with these two mammals?

Answer 1

Since the pitcher plants live in the mountains of Borneo where insects are not abundant, they depend on feces of tree shrew and rats to obtain nitrogen that they need to grow and reproduce. If both animals go extinct, then nitrogen and phosphorus uptake by the plants would significantly decrease, making it much more difficult for them to survive without either of these and lack of insects. If shrews and rats go extinct, it would be very difficult for pitcher plant to survive as there would be deficiencies of Nitrogen and Phosphorus availability.

Question 2

If facultative mutualists do not require another species to help them, why do they engage in mutualism?

Answer 2

Facultative mutualists provide fitness benefits to each other, but their interaction is not critical to the persistence of either species. For example, a group of tiny insects known as aphids suck the sap from plants and produce a droplet rich in carbohydrates that is consumed by several species of ants. The ants gain a source of food, and in exchange, they protect the aphids from predators. Since both benefit, engaging with each other improves both of their overall fitness without being solely dependent on the other for survival.

Question 3

If garlic mustard were to reduce arbuscular mycorrhizal fungi in an apple orchard, what effect would this have on apple crops?

Answer 3

BLOT: Arbuscules help the fungus provide nutrients to the plant. reducing arbuscular fungi will have a negative effect on the trees and the fruit yield will be less nutritive and less healthy.

The amount of apple crops would decrease because soils from tree roots of those trees with mycorrhizal fungi would have little or no colonization by mycorrhiza fungi. Since tree growth is directly related to amount of mycorrhizal fungi more fungal species, more biomass of roots and shoots and more uptake of phosphorus) , the garlic mustard would have the largest negative effect on those apple orchards that greatly depend on presence of the fungi. If there will be reduced or no number of fungi, the fruit yield will be less nutritive and less healthy.

Question 4

How would you respond to someone who states that a mutualism is favored by natural selection because each species is trying to increase the other species’ fitness?

Answer 4

The species in a mutualistic relationship do get benefitted but their benefit is no responsibility or job of either of the organism. There is also selfish association as both organisms care more about improving their own fitness, and become mutualists if their own fitness improves. Also, a mutualistic relationship can change into a relationship in which one species receives a benefit but does not provide one in return, where natural selection favors mechanisms that enable organisms to defend themselves. For example, with plants and mycorhizzal fungi, if a fungus reduces the benefit it provides to a plant, the plant should respond by providing a smaller benefit to the fungus. This shows that sometimes, natural selection favours cheaters, where one tries to receive the benefit of being in the mutualistic relationship while minimising the costs, eventually leading to reduced fitness for both.

Question 5

What is the evidence that plants can detect non beneficial species of mycorrhizal fungi and respond to them appropriately?

Answer 5

The plants can detect the non beneficial species by the phosphorus content present in the soil. Limited phosphorus would indicate that the fungal species was not providing a benefit for the plant’s photosynthesis. Upon detection, the plants are able to allocate more of its photosynthetic products to the more beneficial fungus.

Question 6

For a tree that uses a facultative mutualist animal to disperse its seeds, what would be the impact of the animal going extinct?

Answer 6

If the tree is completely dependent on animal dispersion and the animal goes extinct, then the seeds won’t be able to spread out and germinate. If the seeds have a hard coat that resists digestion, they pass through the animal’s digestive system and are still able to germinate. However, the seeds cannot germinate in the soil unless they have passed through like an elephant’s digestive system. The tree needs the elephant to consume and disperse its seeds, but as elephant populations decline, the tree is losing its only seed disperser. Although it won’t affect the survival rate of the tree, it will reduce its reproductive rate and cause the tree to reproduce closer to itself rather than expanding at far distances that the elephant helped with.

Question 7

Why should wild strawberries, which have animal- dispersed seeds, not make their fruit very colorful and sweet until the seeds are fully developed?

Answer 7

The seeds need to stay inedible or hidden until they are fully developed. As a result, many fruits are green and relatively camouflaged while the seeds are developing. At this stage, the fruit is typically quite unpalatable. However, once the seeds have fully developed, the fruit becomes ripe, the tissues of the fruit become palatable, and it commonly changes color to be highly visible to animal dispersers. Thus, the strawberries delay ripening, colourful and tasty so that the undeveloped seeds aren’t eaten prematurely.

Question 8

In a desert biome, how could you determine if the distribution of plant species indicates whether the community is independent or interdependent?

Answer 8

Independent communities are those in which the species do not depend on each other to exist. They have species that live in the same place because they have similar adaptations and habitat requirements. Interdependent communities are those in which species depend on each other to exist. You can determine if a community is interdependent if it can be determined by line transect studies or by monitoring the results of removing one or more plant species from the community. If species rely on each other to persist to overcome the lack of water in the area, then removing a species from a community should cause other species in the community to decline. If they don’t need each other to persist, then removing a species should leave other species in the community unaffected or even improve their fitness if they happen to compete with the species that is removed.

Question 9

Given that the distributions of many animals are determined by the species composition of the plant community, what might you predict about the diversity of animals in an ecotone compared to each adjacent habitat?

Answer 9

Blot: Diversity in an ecotone will be higher compared to each adjacent habitat due to the constant movement of species between habitats. There should be greater diversity of animals in an ecotone because it’s expected that ecotones support a large amount of plant species, including those from each of the adjoining habitats and species adapted to the ecotone’s special conditions. ecotones may also be speciation hotspots where new forms evolve.

Sharp changes in environmental conditions over a relatively short distance, accompanied by a major change in the composition of species, create a boundary known as an ecotone. Although some species move between the adjacent communities that come together to form the ecotone, most species live in one of the communities and spread into the ecotone. There should be greater diversity of animals in an ecotone because it’s expected that ecotones support a large amount of plant species, including those from each of the adjoining habitats and species adapted to the ecotone’s special conditions.

Question 10

If you observe zones of different plant species as you move uphill from the edge of a pond, what ecological processes would you hypothesize might underlie these plant distributions?

Answer 10

I would say that there were multiple ecotones forming with competition for space and need to resist desiccation that lead to different plant species living in certain intertidal zones. The distribution of species in the different zones of the coastline likely reflects a combination of tolerance to changing abiotic conditions and the outcome of species interactions that include competition, predation, and herbivory. For example, stellate barnacles live in the upper intertidal zone, whereas the rock barnacles live in the lower intertidal zone.

Question 11

Why do ecologists consider both species richness and species evenness when they quantify species diversity?

Answer 11

Richness: number of species in a community (does not tell us about abundance)
Eveness: tells us about relative abundance of each species
We look at this because both are needed to calculate the weighted average of species in relation to their abundance in a given community.

Species richness refers to the number of species in a community, but doesn’t tell how abundant a species is. Species evenness is a comparison of the relative abundance of each species in a community. The greatest evenness occurs when all species in a community have equal abundances, and the least evenness occurs when one species is abundant and the remaining species are rare. Both are needed to calculate the weighted average of species in relation to their abundance in a given community.

Question 12

Compare and contrast log-normal abundance distributions and rank-abundance curves

Answer 12

Log-normal distributions are found by plotting the abundance categories of each species on log2 scale and plotting # of species with each abundance category. Rank-abundance curves show the relative abundance of each species in a community in rank order from the most abundant to the least abundant.

Question 13

Why might an increase in total resources or number of added resources lead to declines in species diversity in a lake?

Answer 13

BLOT: the added nutrients can cause some species to dominate, which leads to the decline of other species. this reduces richness.

Adding soil nutrients like nitrogen or phosphorus causes added fertility which causes a decline in the species richness of producers such as plants and algae. Typically, the total biomass of producers increases when a fertilizer is added. However, this added fertilizer causes a few species to dominate the community, while rare species—which are often competitively inferior—begin to decline until they eventually disappear from the community.

Question 14

Rabbits in Australia were once overabundant and decimated the vegetation. Why are the rabbits in Australia not an example of a keystone species?

Answer 14

Blot: not keystone because without them the community will still survive and wont collapse. there will not be much change without them. Unlike rabbits, beavers are needed to build dams which help other species thrive. we can go without rabbits theyre just food

Keystone species greatly affect the structure of communities even when there aren’t many individuals of that species. They aren’t a keystone species, becuase without them, the community would not collapse, and would not change which competing plants dominate the community (superior competitors) and which are inferior. Also, unlike beavers, rabbits are not ecosystem engineers that cause structure habitat to change, like large ponds that develop new non flowing pond areas for new animals to colonise.

Question 15

Compare and contrast density- and trait-mediated indirect effects.

Answer 15

When two species interact in a way that involves one or more intermediate species, it is called an indirect effect. Indirect effects that are caused by changes in the density of an intermediate species are called density-mediated indirect effects. For example, increased densities of sea stars in intertidal communities cause a decline in mussels, which allows other species such as snails to occupy the limited open space on the rocks. The positive indirect effect of sea stars on snails occurs because the sea stars reduce the density of mussels. Trait-mediated indirect effects are indirect effects that are caused by changes in the traits of an intermediate species. This commonly happens when a predator causes its prey to change its feeding behavior, which in turn alters the amount of food consumed by the prey. For example, the loss of large predators in a national park, due to poaching, can lead to forest-dwelling antelopes coming out to feed in the open grasslands.

Question 16

What evidence would convince you that a grassland was experiencing top-down control versus bottom-up control?

Answer 16

Blot: When a community is controlled from the top down, a trophic cascade occurs. The trophic level just below the top predator decreased in abundance and the next trophic level increases in abundance.

For example, we if the abundance of zebras in a grassland declines and the abundance of shrubs increases, we can hypothesize that lions (top predators that feed on zebras) control the community (top-down).

When the abundances of trophic groups in a community are determined by the amount of energy available from the producers in that community, it is referred to as bottom-up control. When communities are controlled from the bottom up, an increase in the abundance of producers results in an increase in the abundance of higher trophic levels. When the abundance of trophic groups is determined by the existence of predators at the top of the food web, it is called top-down control. When communities are controlled from the top down, a trophic cascade occurs from the top down: The trophic level just below the top predator decreases in abundance, and the next lower trophic level increases in abundance. For example, four trophic groups that consist of large fish, small fish, zooplankton, and phytoplankton: If an increase in phytoplankton causes an increase in the zooplankton, small fish, and large fish, the abundance of the trophic groups experiences bottom-up control. If an increase in the abundance of large fish causes a decrease in the small fish, an increase in the zooplankton upon which the small fish feed, and a decrease in phytoplankton, the abundance of the trophic groups experiences top-down control.

Question 17

In a pond that experiences succession, what relationship would you expect regarding changes in species richness over time?

Answer 17

I would expect the succession to cause rapid increase in species richness that slows over time and eventually plateaus. This is because we would begin with few or no species and then species richness would increase rapidly before the pond can’t control more marine species, and then declines

Question 18

Why should we not expect a single climax community on recovering coal mines?

Answer 18

blot: ongoing environmental changes and differences in abiotic conditions affect climax plant growth on each coal mine. the species composition of a climax community can exhibit variation over space and time within a given biome. Moreover, a climax community can be short-lived if a disturbance should wipe it out, so climax communities can change with different species.

Coal mining is responsible for a host of environmental impacts, including air pollution, water pollution, land degradation, and acid rain. The burning of coal is also responsible for releasing large amounts of carbon dioxide into the atmosphere, which is a major contributor to climate change. The species composition of a climax community can exhibit variation over space and time within a given biome. Moreover, a climax community can be short-lived if a disturbance should wipe it out, so climax communities can change with different species. With coal mines, if there are environmental changes like increased nitrogen in the soil that increase amount of organic matter, species richness increases with pioneer wind-dispersed species combined with colonization of later succession species, like woody plants.

Question 19

Compare and contrast the concepts of facilitation, inhibition, and tolerance in the context of ecological succession.

Answer 19

Facilitation is a mechanism of succession in which the presence of one species increases the probability that a second species can become established. Early-succession species do this by altering the environmental conditions of the site in a manner that makes it more suitable for other species to establish and less suitable for themselves. Inhibition is a mechanism of succession in which one species decreases the probability that a second species will become established. Common causes of inhibition include competition, predation, and parasitism. That is, individuals of one species can inhibit those of other species by outcompeting them for resources, eating them, or attacking them with noxious chemicals or antagonistic behavior. Early in succession, inhibition can prevent movement toward a climax community, while late in succession, inhibition can prevent the pioneer species from colonizing and surviving. Tolerance is a mechanism of succession in which the probability that a species can become established depends on its dispersal ability and its ability to persist under the physical conditions of the environment. For example, species that can tolerate the stressful environmental conditions of early succession—such as low moisture or more extreme temperature fluctuations—can become established quickly and dominate early stages of succession.

Question 20

If two plant species have similar dispersal and competitive abilities, what factor might help determine which species occupies an early seral stage?

Answer 20

Blot: factor is the priority effect. this helps us determine which species occupies the early seral stage. the arrival of one species at a site that affects the subsequent colonization of other species is known as a priority effect.

The priority effect can determine which species occupies the early seral stage. The arrival of one species at a site that affects the subsequent colonization of other species is known as a priority effect. For example, if bryozoans (invertebrates that live in colonies attached to rocks and that feed by filtering the water) become established first, they can prevent the establishment of tunicates and sponges—two other groups of filter-feeding animals that attach themselves to rocks. They can prevent colonization by tunicates and sponges, which compete for space on the rocks.

Question 21

Compare and contrast the classic and modern explanations for the succession of ponds and lakes.

Answer 21

Blot: Succession in the modern model is attributed to periods of extended drought.
Succession in classical describes gradual and steady accumulation.

The classical explanation for succession in lakes and ponds describes a gradual and steady accumulation of organic matter that eventually fills in the basin and converts it to a terrestrial habitat. Contrary to the classic model of slow and continuous succession over long period of time, ponds and lakes can experience long periods of several hundred years in which little succession occurs, followed by brief episodes of rapid change. Modern studies have shown that succession can occur in occasional large bursts when multiyear droughts allow vegetation to extend along the dry part of the basin. When water becomes abundant again, the extended vegetation floats on the water’s surface and grows in thickness. Multiple drought events allow the vegetation to expand; eventually it covers the water’s surface and fills in the basin.

Question 22

If two locations in the northeastern United States follow different paths of succession but end up at the same climax community, how will Jaccard’s coefficient of similarity change over time?

Answer 22

Jaccard’s coefficient value of zero indicates that two communities have no species in common, whereas a value of one indicates that two communities have an identical composition of species. It will start at 0, but get closer to 1 over time.

Question 23

Why do early- and late-succession species tend to possess different adaptations?

Answer 23

Blot: they face inherent trade offs. think seed size, size of maturation, growth rate, shade.
The traits of early-succession and late-succession plants are different because they face inherent trade-offs. Early succession plants produce many small seeds, have long seed viability, low root:shoot ratio, fast growth rate, small size at maturation and low shade tolerance. However, late succession plants produce few large seeds, have short seed viability, high root:shoot ratio, slow growth rate, large size at maturation and high shade tolerance. For example, pioneer species of terrestrial plants are typically better at dispersing seeds to newly created or disturbed sites. They produce many small seeds that are easily dispersed by wind or that stick to passing animals. However, they are not tolerant of the high-shade conditions of late-succession plant communities.

Question 24

If one species provides a habitat as part of a mutualistic relationship, what is the probable effect on the abundance and distribution of the other species?

Answer 24

Blot: other species will be heavily reliant on the one that gave the habitat. without help of habitat species 2nd species abundance and distribution will decrease. For example, ants and Acacia trees: trees provide habitat for ants to get nectar and thorns and a place to make nests from in exchange for being defended from herbivores. If large herbivores are limited, then its not as productive energy wise for the trees to produce so much nectar (big cost trade-off). This would decrease # of trees occupied by ants, since there would be less available nectar, requiring ants to adapt and find other sources of nectar.

The other species evolves to become heavily dependent on the species that provided the habitat, to the extent that if at any point the 2nd species doesn’t provide as much of a benefit to the 1st species, then the 2nd species would not be able to survive outside the range of 1st species. The abundance and distribution of the 2nd species declines as the 1st species is less likely to entice the 2nd species. For example, ants and Acacia trees: trees provide habitat for ants to get nectar and thorns and a place to make nests from in exchange for being defended from herbivores. If large herbivores are limited, then its not as productive energy wise for the trees to produce so much nectar (big cost trade-off). This would decrease # of trees occupied by ants, since there would be less available nectar, requiring ants to adapt and find other sources of nectar.