Ecology FRQs
(b) Based on the data on the graph, estimate the percent of the total energy that the plant has allocated to the growth of leaves on the first day of July.
Based on the data from the graph, we can see that 50% of the plants total energy has been allocated to leave development. Roughly 30% was allocated to root development, about 15% to the stems, and 5% to vegetative buds.
(b) Using the information presented in the graph, describe the relationship between antagonism and genetic relatedness in the communities of Vibrio bacteria sampled for the study.
Based on the graph, antagonism and genetic relatedness are inversely related. In other words, two bacterial strains that have a more distant genetic relationship are more likely to have an antagonistic relationship.
(a) Endosymbiosis has been proposed as a model for the evolution of eukaryotic cell structure. Identify and explain TWO pieces of evidence that support the endosymbiotic theory.
First, chloroplasts and mitochondria have their own circular DNA/plasmids. This is significant because prokaryotes also carry DNA in circular, plasmid form. They are also the only organelles other than the nucleus to carry DNA. Second, both the mitochondria and chloroplast reproduce in the same way a prokaryotic cell such as bacteria does: they pinch in half, dividing the cell into two.
(c) Interdependence of organisms exists at all levels of ecosystems. Identify the trophic levels of each of the organisms in the following food web. Predict the effect on the ecosystem if the rabbits were removed and explain your prediction.
Grass is the primary producer, rabbits and mice are the primary consumers, owls and coyotes are the secondary consumers, and fungi is a decomposer, which is the final trophic level. If rabbits were removed, the food chain and flow of energy would be disturbed. Grass will increase in population size, since on of its main consumers is no longer a threat, however the owl population will decrease in size as they now depend entirely upon mice for food.
(b) In an effort to control the number of midges, an area within the ecosystem was sprayed with the fungus Metarhizium anisopliae, which significantly decreased the midge population. Based on the data in the table, predict whether the spraying of the fungus will have the greatest short-term impact on the population of the stoneflies, the caddisflies, or the hellgrammites. Justify your prediction.
I predict that the spraying of the fungus will have the largest impact on the stonefly population. This is because the fungus is intended to reduce the midges population, and stoneflies have the highest dietary dependency on midges of all the species on the food chain. Specifically, 90% of the stonefly diet is midges, while midges only make up 30% and 10% of the cladissflies and helgramite populations respectively.
(d) Predict TWO factors that will most likely limit the population growth of species A in treatment group I
One factor that will likely limit the population growth of species A in treatment group I is an excess of metabolic waste. Metabolic waste diffuses out of the unicellular organisms via a process called excretion. More protists means more excretion is occurring. This is harmful because excreted waste is toxic, and the more waste that builds up in the jar, the more protists will die. Another limiting factor is competition for food. Like any species, intraspecific competition occurs when a species is at or near carrying capacity without unlimited resources. Protists need nutrients to survive and asexually reproduce. If there are too many cells for each to get enough nutrients, the population will inevitably decline.
(a) Describe a cause of logistic growth of the ragweed population.
One likely cause of logistic growth in the ragweed population is limited resources, a density-dependent factor. As the population approaches carrying capacity (or increases in density), the growing population will not have enough nutrients within its ecological niche to properly feed every member of the population. As a result of malnourishment, many individuals will not reach reproductive years and produce offspring, causing an inevitable stabilization in population size.
(c) The student claims that species A and B compete for the same food source. Provide TWO pieces of evidence from the data that support the student's claim.
One piece of evidence suggesting that species A and species B share the same resources is that the growth rate for species A is slower in group II. This is significant because, in group II, there is cohabitation between the two species. If species A grows slower in the presence of species B, that indicates there is some limiting factor, such as competition for resources, acting on them, and preventing them from growing at the same rate they would without the presence of species B (group I). Another piece of evidence is that the growth rate for species B in group II is also slower. This again implies competition for resources.
(a) Describe ONE type of molecular evidence that can be used to determine the genetic relatedness of bacterial strains isolated from naturally occurring populations.
One type of molecular evidence that can be used to determine the genetic relatedness of bacterial strains is by examining differences in nucleotide sequneces for specific gene regions. Mutations occur on a "molecular clock," meaning that every X years a mutation will occur. Therefore, the more mutations a species has from an original sequence, the more distant their relationship is.
(b) Based on the representation in Figure 1, explain why the scientists claim that plot B would be more resilient than plot A in response to a sudden environmental change.
Plot B would be much more resilient in the case of a disturbance as it has much greater species diversity. Species diversity is crucial to the stability of a community because if there are only a couple of species inhabiting an ecosystem and one or both of those species are particularly susceptible to certain types of natural disasters, they will likely not be able to recover after such a disaster occurs (or the community would regrow at a much slower rate). However, if there are many species within a community, some will likely be able to withstand certain disturbances and will aid the regrowth of the community/ new growth of new species via secondary succession.
(b) For TWO of the following, describe the type of interaction that occurs between the organisms, and explain the role of each organism in this relationship. Rhizobium bacteria and legumes Clown fish and anemones Tapeworms and pigs Honeybees and flowering plants
Rhizobium bacteria and legumes have a symbiotic/mutualistic relationship. The plant benefits because the bacteria fix nitrogen and produce a plant hormone known as IAA in the legumes nodules, and the bacteria benefits because they are provided shelter/a stable habitat. Tapeworms and pigs have a parasitic relationship, with tapeworms being the parasite and pigs being the host. Parasitism implies that the parasite benefits by feeding off of and slowly killing the host. In this case, the tapeworms reside in the pig's intestine (but can spread to blood and muscles) and take up nutrients while damaging tissues and causing localized growths within the pigs.
(a) Propose an explanation for the pattern of population density observed in species C.
Species C has a J-shaped curve, which represents exponential growth. Exponential growth occurs when the species' birth rate surpasses the death rate. In order for there to be more births than deaths, there must be a higher percentage of individuals living into their reproductive years and reproducing, than those dying before having offspring. For the majority of individuals to survive and reproduce, there must be a lack of limiting factors, which is any aspect of an ecosystem that places constraints on population growth rate and size. Limiting factors include intraspecific competition resulting from limited resources, lack of available mates, high levels of predation, and harsh environmental conditions.
(b) Describe the effect that the introduction of beetle species C has had on the population density of species A and species B. Propose an explanation for the patterns of population density observed in species A and in species B.
The addition of species C had little to no effect on species A but decreased the size of population B. Species A likely experienced no change in population size because there was no competition between species A and C. Specifically, they likely inhabit different ecological niches, meaning both species utilize different resources and require different environments within the same community, therefore, limiting exploitative or interference competition. On the other hand, species B's decrease can be attributed to both species A and B requiring the same specific resources or environmental factors within the ecosystem, leading to high levels of competition between them. When two species inhabit the same community and have identical resource requirements, one will inherently be eliminated or suffer a decline in population size.
(a) Describe why the amount of light available to the Chlorella culture might affect the growth dynamics of the alga.
The amount of light available to the chlorella culture affects the growth dynamics of the algae because the light is the driving force for photosynthesis. Photosynthesis involves the fixation of carbon into glucose, and that glucose provides the energy needed for the plant to grow and develop. Therefore, more light means more photosynthesis and growth, whereas less light means less photosynthesis is occurring and there is less energy available to the plant for maturation.
(c) Based on the data, describe the time period during which Chlorella approximates exponential growth. Based on the data and assuming logistic growth, describe the time period during which the Chlorella population has reached the carrying capacity of the culture. Based on the data, calculate the growth rate per day for the 5-day period with the greatest growth rate.
The chlorella approximates exponential growth between days 0 through 15. On days 20 through 30, the chlorella reached its carrying capacity. We know this because that is the point at which the growth rate begins to slow, which can be attributed to resources becoming scarce. The growth rate is greatest between days 10 and 15, and the growth rate per day for this period is roughly .27 10^6 per mL/day because the difference between days 10 and 15 is roughly 1.35 divided by 5 (to find the average rate per day).
(c) For each of the following disturbances, discuss the immediate and long-term effects on ecosystem succession. (i) A volcano erupts, covering a 10-square-kilometer portion of a mature forest with lava. (ii) A 10- square-kilometer portion of a mature forest is clear-cut.
This would be an example of primary succession, meaning that the disturbance left the region with no soil. After the disturbance, lava is degraded by microbes which causes the establishment of reproductive bodies not requiring soil (such as fungi and lichen). They layer the ground and conduct processes such as nitrogen fixation, which leads to the formation of soil. Because there are no annual plants or shrubs, there is no shade and light is prevalent. Consequently, as the soil is laid down, photophilic organisms are able to grow and thrive. This is a very slow process as soil formation is time-intensive. This would be secondary succession meaning that some soil and seed banks are left intact. However, the loss of trees increases erosion rates and lessens the quantity of soil in the region. Also as a result of tree loss (and loss of other shade-providing plants), there is an influx of direct sunlight in the region, benefiting smaller photophilic plants. As photophilic plants grow and proliferate, the growth of shade-tolerant plants is encouraged, and species richness increases.
(a) Based on the food sources indicated in the data table, construct a food web in the template below. Write the organism names on the appropriate lines AND draw the arrows necessary to indicate the energy flow between organisms in the ecosystem.
algae ---> caldissflies ----> stoneflies ---> helgramites (extra arrow from c to h)
(a) Circle ONE arrow that represents transcription on the template pathway. Identify the molecule that would be absent if enzyme YUC is nonfunctional.
circle around either of the top two arrows. If YUC is non-functional, enzyme IAA would be absent.
(b) Using the template, construct an appropriately labeled graph to represent the data in Table 1. Based on the data, determine whether the concentration of Chlorella on day 20 is statistically different from the concentration on day 15 and from the concentration on day 25.
statistical difference between days 15 and 20, no difference between 20 and 25
(b) Predict how the deletion of one base pair in the fourth codon of the coding region of gene Trp−T would most likely affect the production of IAA Justify your prediction.
A deletion of one base pair in the fourth codon of gene Trp-T would result in decreased or no production of IAA. This is because the mutation would cause a phase shift, meaning that the entire gene region will be altered so that each codon contains a different sequence of nucleotide bases than a non-mutated Trp-T gene would. As a result, (depending on the specific bases that have shifted into each codon), it is likely that the wrong amino acids will be coded for, leading to a fault or non-existent enzyme. This inadequate Trp-T enzyme offsets the rest of the pathway, and so there will also be diminished or no I3PA, YUC, and IAA.
(a) Describe ONE characteristic of the original population that may have led to the population's decline in size between 1989 and 1993.
A lack of genetic diversity among the original snake population may have caused a decline between 1989 and 1993. Natural selection may have favored certain alleles to the point at which the majority of the population carries that specific set of alleles (or a very similar combination of alleles). Because of this, the population will be much more susceptible to environmental changes such as temperature increases/decreases, natural disasters, the introduction of new predators, etc., as certain genotypes that would have been selected for during a given environmental change, do not exist. So, if any environmental change occurred between those years, a lack of diversity would likely have caused their declining population size.
(c) Describe how the data support the statement that there are abundant resources in the environment.
An abundance of resources is required for population growth. If there were not enough resources to support more individuals within the population then it would be impossible for population growth to occur, as malnourished snakes would not reach reproductive years and the birth rate would not be able to surpass the population's death rate. However, it is evident that the population saw rapid growth between 1995 and 1999, so there must be enough resources to support the continuously increasing population.
(a) Discuss the expected changes in biodiversity as the stages of succession progress as shown in the diagram above.
As the stages of succession progress, biodiversity increases. This increase occurs because the annual plants act as a pioneer species and alter the habitat in a way that makes it more suitable for other species to live and proliferate. For example, the annual plants provide shade for shade-tolerant plants to emerge. And as diversity among primary producers increases, there is also an influx in diversity among consumers. This is because there will be less competition among those consumers for specific producers, and less competition inherently brings population size closer to carrying capacity.
(b) As shown in the table, the student established treatment group II with 5 individuals of each species. Provide reasoning for the reduced initial population sizes.
Because treatment group II consists of individuals from both species A and B being grown together, and treatment group I has the two species being grown separately, they must half the number of individuals per species in group I so the initial number of individuals per container is the same for both groups. Additionally, the reduction can serve as a control for population density.
(e) A researcher removed a plant nodule and identified several "cheater" rhizobacteria that do not produce IAA or fix nitrogen. Describe the evolutionary advantage of being a bacterial cheater in a population composed predominantly of non-cheater bacteria. Plants can adjust the amount of carbon-containing molecules released into nodules in response to the amount of nitrogen fixed in the nodule. Predict the change in the bacterial population that would cause the plant to reduce the amount of carbon-containing molecules provided to the nodule.
Cheater bacteria that do not produce IAA or fix nitrogen have an evolutionary advantage because they have more available energy for reproduction and are therefore better suited to reproduce more frequently. If the noncheater bacteria population were to increase, less nitrogen would be fixed. Because plants adjust the amount of carbon-containing molecules released into nodules based on the amount of nitrogen fixation occurring, this decrease in nitrogen would also cause a reduction in the carbon-containung molecules.
(c) Provide reasoning to show how the results of the study support the claim that cooperation among Vibrio bacteria can increase the fitness of some individual bacteria living in a natural environment.
Cooperation among Vibrio bacteria promotes the growth of bacterial strains that are closely related to those producting the antimicrobial secretions. We know this because close ancestral relationships decreases the likelihood of being impacted by the secretions. Therefore, individuals who are more distantly related to the bacteria face selective pressure by the secretions, while those who are closely related gain a selevctive advantage as their growth will more likely not be hindered.
(e) Many protists contain an organelle called a contractile vacuole that pumps water out of the cell. The student repeated the experiment using a growth medium with a lower solute concentration. Predict how the activity of the contractile vacuole will change under the new experimental conditions. Justify your prediction.
In a growth medium with a lower solute concentration, the contractile vacuole will become more active. This is because the contractile vacuole's role is to pump water out of the cell, and in this case, the cell is hypertonic with respect to the environment, meaning that diffusion cannot passively occur out of the cell because the water would be moving against its concentration gradient. Therefore, the vacuole is needed to actively (using ATP) push the water against the gradient.
(d) Explain why invasive species are often successful in colonizing new habitats.
Invasive species are often successful in colonizing new habitats because they are losing a limiting factor that existed in their previous environment. For example, when a specific predator or disease that kept the species below its carrying capacity is eliminated as a threat, population size will inherently grow because more individuals will live into their reproductive years and reproduce. Additionally, specific traits or adaptations to the population's previous environment often act as a novel evolutionary advantage. For example, a special enzyme utilized by the population to digest certain foods from their past ecological niche may enable them to consume certain resources in their new habitat that other species cannot, giving them an advantage.
(d) Explain how an invasive species such as ragweed affects ecosystem biodiversity, as illustrated in Figure 1.
Invasive species such as ragweeds are able to outcompete surrounding species for resources or space. Because ragweeds begin germinating earlier, they are able to uptake resources before other native plants would first require them, so they are essentially beating the native species to obtain resources. As a result, the death rate of many native species increases as a result of inadequate resources, while the ragweed population grows throughout the community. As a result, the community's species richness and evenness sharply declines (as ragweeds dominate the region), so biodiversity also decreases.
(a) Based on an analysis of the data, describe the effect of karrikins on seed germination in the autotrophic host plants and the obligate parasitic weed plants.
Karrikins have a great effect on the germination of autotrophic plants because they are able to mimic strigolactone, a signaling hormone that stimulates seed germination and plant development. In contrast, the obligate parasitic weeds were not heavily effected by the karrakins, likely because their germination is dependent upon close proximity to their host and those hosts utilize strigolactone, rather than karrakins to stimulate root development.
(c) In a third group of plots, the researchers removed all seedlings of all plants that germinated before June 1. All plants that germinated after June were left untouched. Using the template in the space provided for your response and the symbols shown in Figure 1, represent the expected plant species that would be found in this third group of plots three months later. Draw no more than 12 symbols. Assume all other environmental conditions are the same as for the initial study described.
More a trifada than other species (maybe 7-8) The other 5 would be a mixture of the other species
(a) Identify the direct source of the energy used for plant growth during the first week of May, and identify the part of the plant that grew the most during the same period.
The direct source of energy for plant growth during the first week of May is the nutrients stored in the seed. Seeds contain all of the materials plants need to develop into complex plants (fiber, fats, vitamins/minerals, antioxidants), and therefore are the direct source of initial plant growth. The part of the plant that grew the same amount during the given time frame is the roots. This is because the root is the first to emerge from the seed, and the absorption of water by the root is needed for the rest of the plant (the shoot) to emerge.
inherently brings population size closer to carrying capacity. (b) Describe and explain THREE changes in abiotic conditions over time that lead to the succession, as shown in the diagram above.
The first change in abiotic conditions that caused the succession is an increase in soil quantity. As annual plants undergo fragmentation and decompose, they produce detritus (decaying organic matter). The decomposition of that detritus creates humus, which means more soil as humus is a key component of soil. This humus improves the survival of plants by giving them better anchoring within the soil, and also encourages the growth of new plants. Another factor that caused the succession (also relating to the soil) is the soil's quality. With the increase in humus, the soil gains vital nutrients such as nitrogen and carbon, which support plant survival and progeny. This increased plant growth and health improves the suitability of the environment for other species by providing benefits such as shade and energy, therefore, contributing to the succession. Finally, the last factor is an increase in transpiration. Plants lose about 90% of their water via transpiration, and the process increases the humidity of the region. Increased humidity causes a shift from xerophytic plants (require very little water), to more mesophytic plants (not requiring a very wet nor very dry environment).
(c) Compared with perennials (plants that live more than two years), annual plants often allocate a much greater percentage of their total energy to growth of their reproductive parts in any given year. Propose ONE evolutionary advantage of the energy allocation strategy in annual plants compared with that in perennial plants.
The increased allocation of energy to reproductive parts compared with that of perennials is beneficial to the annual plants because it increases likelihood that their lineage will persist. Annual plants live for less than one year, and if the reproductive parts of these plants were not fully and efficiently developed before their death of an annual plant, they would not be able to or be far less likely to reproduce. So, by allocating more energy to the development to their reproductive parts, they increase their likelihood of producing offspring and therefore also help ensure they do not face endangerment/extinction from lack of offspring.
(b) Propose ONE reason that the introduction of the outside males rescued the snake population from decline.
The introduction of the male snakes likely rescued the original population from decline by adding genetic diversity. If the population was initially declining because it was unable to adapt to some environmental change occurring within its ecological niche, the addition of new alleles via these male snakes may have enabled certain traits to be selected for, so the population could adjust and thrive within a changing environment.
(d) Rhizobacteria are a group of bacteria that live in nodules on plant roots. Rhizobacteria can produce IAA and convert atmospheric nitrogen into forms that can be used by plants. Plants release carbon-containing molecules into the nodules. Based on this information, identify the most likely ecological relationship between plants and rhizobacteria. Describe ONE advantage to the bacteria of producing IAA.
The most likely ecological relationship between rhizobacteria and plants is mutualism. Mutualism implies that both species involved benefit from the interaction, and in this specific case, the bacteria receive increased carbon and carbon-based molecules as well as habitation in the nodules, in exchange for converting the nitrogen for plants to use. The bacteria's production of IAA is also beneficial to the plants as it is an auxin, meaning it is a hormone that acts on target cells by causing them to divide, elongate, or differentiate-- all processes which are crucial to plant development.
(c) Predict the population density of species C in 2014. Provide a biological explanation for your prediction.
The population species of species C will continue to increase in 2014. This is because there is a lack of competition between species A and C, and species C has a competitive advantage over species B and is forcing species B out via competitive exclusion. Therefore, they will not face competitive or limiting factors, enabling the species to continue growing in size.
(c) Explain one feedback mechanism by which a cell could prevent production of too much IAA without limiting I3PA production.
The production of IAA could be managed by a negative feedback mechanism in which increasing levels of IAA inhibit the pathway. IAA could act as an allosteric inhibitor of the YUC enzyme, meaning that the active site of YUC will be altered so it cannot properly bind to I3PA and catalyze its conversion to IAA. Because I3PA production is dependent upon the enzyme Trp-T, not YUC, the allosteric inhibition of YUC would enable the cell to regulate IAA without impacting I3PA production.
(b) A researcher proposes that the obligate parasitic weed requires exposure to a signal from the host plant before it can germinate. Using the data as evidence, provide support for the researcher's claim and give ONE reason the response would be an advantage for the weed plants.
The signal required by parasitic weeds for development is strigolactones. A host plant gives off these strigolactones, which stimulates seed germination and root development in the parasitic weeds. This is represented in the graph "Obligate Parasitic Weed," as the percent germination increases from 0 to 60 as the strigolactone concentration goes from 0 to 10^-9, showing that the strigolactones are needed for germination to occur. This can be beneficial for the plant as they, unlike non-parasitic plants, do not need to produce their own strigolactones which saves them energy.