AP Biology Unit 10: Ecology Notes Pt. 1

1- Each female of a particular fish species produces millions of eggs per year. Draw and label the most likely survivorship curve for this species and explain your reasoning.

This species most likely has the survivorship curve 3. This is when there is a lot of offspring produced, but many die off young. Considering that the females of the particular fish species produce millions of eggs per year, the offspring don’t all survive until adulthood. Since many offspring die off young, there is no worry for overpopulation.

2- In 2009, the United States had a population of about 307 million people. If there were 14 births and 8 deaths per 1000 people, what was the country’s net population growth that year (ignoring immigration and emigration, which are substantial)? 

In this population, ignoring the immigration and emigration, the birth rate is 14/1000= 0.014 and the death rate is 8/1000=0.008. This means that there is a net population increase of 0.006 overall that year.  

3- Explain why a population that fits the logistic growth model increases more rapidly at intermediate size than at relatively small and large sizes.

A population that fits the logistic growth model increases more rapidly at intermediate size than at relatively small sizes because each individual has few resources, which causes the population to grow slowly. At relatively large sizes, each individual has more resources which causes the population to grow fast. The logistic growth model has an initial exponential growth, then it levels off at the carrying capacity, which is the k value. 

4- Suppose that of a cohort of 200 rats in a rat colony born in January, 160 are still alive at the start of March and 120 are still alive at the start of May.

a. What is the survivorship up to the start of March? Round to the nearest hundredth.

The survivorship up to the start of March is 160/200 or 0.80. 

b. What is the mortality rate from the beginning of March to the beginning of May? Round to the 

nearest hundredth.

    The mortality rate from the beginning of March to the beginning of May is 40/160 or 0.25. 

c. If the survivorship during May is 0.3, how many rats died during the month of May? Round to the nearest whole number.

    The population would be 0.3*120 so 36 rats survived. 120-36 is 84 so 84 rats died. 

5- You and your friends have monitored two populations of wild lupine for one entire reproductive cycle (June year 1 to June year 2). By carefully mapping, tagging, and taking a census of the plants throughout this period, you obtain the data listed in the chart

You cannot type in the table so write down the answers for population B here:  

B(birth rate during time interval)= 30

D(death rate during time interval)=100

b(per capita birth rate)=30/300=0.1

m(per capita death rate)=100/300=0.33

r(per capita rate of increase)=0.1-0.33=-0.23 or (30-100)/300=-0.23

1- A population of microscopic eukaryotic organisms growing in a large flask had the growth pattern shown.

In one paragraph, explain the biological factors that determine the shape of the growth pattern shown above in both period 1 and period 2.

The biological factor that determines the shape of the growth pattern is mainly the density dependent factors. Initially in period 1 when the population is small, the growth seen is exponential which is in a J shaped curve because there are enough resources to be able to support the speedy growth of the population. However in period 2, the growth of the population slows or plateaus. This is due to the density dependent limiting factors and the population reaching the carrying capacity. The carrying capacity is the maximum number of individuals in the population that the environment can support. This causes the entire graph to be a s shaped curve and is called the logistic model. Accumulation of toxic waste and increased death rate decreases the reproductive rate too. 

2- Directions: This is a short free-response question that requires about 6 minutes to answer. Read the question carefully and completely. Answers must be written out in paragraph form. Outlines, bulleted lists, or diagrams alone are not acceptable.

In an attempt to rescue a small isolated population of snakes from decline, a few male snakes from several larger populations of the same species were introduced into the population in 1992. The snakes reproduce sexually, and there are abundant resources in the environment.

The figure below shows the results of a study of the snake population both before and after the introduction of the outside males. In the study, the numbers of captured snakes indicate the overall population size.

Describe ONE characteristic of the original population that may have led to the population’s decline in size between 1989 and 1993.

One characteristic of the original population that may have led to the population’s decline in size between 1989 and 1993 was the decline of male snakes that were able to reproduce successfully with the females and produce offspring. One possible explanation for this could be an aged male population age, and they could not reproduce with the female population. 

3- Directions: Answers must be in essay form. Outline form is not acceptable. Labeled diagrams may be used to supplement discussion, but in no case will a diagram alone suffice. It is important that you read each question completely before you begin.

According to fossil records and recent published observations, two species of leaf-eating beetles (species A and B) have existed on an isolated island in the Pacific Ocean for over 100,000 years. In 1964 a third species of leaf-eating beetle (species C) was accidentally introduced on the island. The population size of each species has been regularly monitored as shown in the graph above.

(a) Propose an explanation for the pattern of population density observed in species C.

The pattern of the population density curve is a j shaped curve, which makes it an exponential growth curve. A possible explanation for the pattern of population density observed in species C could have been the low predation and lack of limiting factors. This means that the environment was suitable for the population, which allowed it to grow exponentially. They also may have a new evolutionary advantage brought to the island. This would have been a flight advantage that provides them with an advantage. 

(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 introduction of the beetle species C decreased the population density of species B. The introduction of the beetle species C did not impact the population density of species A. For species A there would have probably been no competition, since their population density was not impacted by the introduction of species C. For species B there would have been competition and a niche overlap considering how rapidly the population density of species B decreased upon the introduction of species C. This example proves that populations with the same niche can not both survive, and that there will be an increase in competition between species which lead to the demise of one of the species while allowing the other to thrive. The competitive exclusion principle states that no two species can occupy the same niche. 

College board video 8.5 Community Ecology

Structure of a community is based on species composition and diversity

• Community: a group of different species living together in the same location and interacting with each other (based on species diversity and species composition)

• Species diversity: variety of species and the quantity of individuals included in each species within a given community

• Species composition: identity of each species in the community

• Simpson’s diversity index measures the biodiversity of a habitat

• Higher index, more diverse community, based on random sample

Interactions among populations determine how energy and matter is accessed

• Communities change over time depending on population interactions, competition

• May result in a change in community structure, can occur within or between species, and competition is for food and habitat

• Positive interactions: mutualism (both benefit +/+), commensalism (one benefits, the other is unharmed +/0)

• Negative interactions: predator-prey (one uses another for food), parasitism (one benefits, the other is harmed +/-)

• Neutral interactions: no impact on the species involved

• Bracket or shelf fungi are tree parasites, absorb fruiting bodies from the bark and obtain energy, tree is weakened, reduced canopy so more free resources

Relationships among interacting populations can be modeled

• Predator-prey interactions: increase in predator occurs slightly after an increase in prey population, increase in predator population will eventually cause a decrease in prey

• Trophic cascade: negative effect the removal or decrease in a key species has on other trophic levels, populations can experience exponential growth or death with the removal of a key species, results in the interruption of the flow of energy through ecosystems

• Niche partitioning: decrease in competition over limited resources between two similar species because each species is accessing the resource in a different way

• Practice question: Intermittent streams only had a statistically lower macroscopic invertebrate species diversity than the seasonal streams, no error bar overlap

College board video 8.6 Biodiversity

Ecosystem diversity is related to the resilience to changes in environment

• Natural and artificial ecosystems with less components and less diversity are often less resilient to changes in the environment, may cause short and long term changes 

• Diversity of species in an ecosystem may influence the ecosystem organization

• Less vulnerable to drastic structural changes when the environment changes or when organisms are added or removed

Abiotic and biotic factors contribute to maintaining the ecosystem diversity

• Abiotic: climate, water and nutrients availability, light availability

• Biotic: Producers relied on for food and habitat and reduce erosion, dominant predators keep prey populations under controls with diverse diets

Keystone species effects are disproportionate relative to their abundance

• Keystone species: species the community structure depends on

• Smaller populations compared to other populations in the community

• When removed, the ecosystem often collapses, they control the size of multiple populations and overpopulation depletes resources

• Ex: African Elephant tusks dig up riverbeds and creates watering holes for many animals, dung provides habitats for insects, helps distribute seeds, feeding behaviors influence the landscape, removal of trees and shrubs provide paths for other animals 

• Practice question: If canopy trees were artificially planted immediately after the field was abandoned, the ground flora diversity will decrease. Since the ground flora increases and remains at the carrying capacity according to figure 2, if the canopy trees are planted, the ground flora will not have enough light to survive and thrive like it normally would. This would cause the ground flora diversity to remain low. 

Scientists analyzed data collected over a period of years in a game reserve in South Africa to test the hypothesis that competition with lions limits the abundance of leopards in the same community. The game reserve encompasses a variety of habitats, from open grassland to wooded areas around rivers and streams. It contains most of the indigenous mammal species and an adequate availability of their prey. For the most part, the leopards and lions show similar habitat preferences in the reserve.

The mass of the average lion is about three times that of the average leopard. The scientists analyzed several factors that might influence the abundance of each population, including the sizes of the animals preyed on by each species (Table 1).

Table 1. The dietary composition of leopards and lions according to the sizes of their prey animals

Because competition with lions might affect the population size of the leopards, the scientists also analyzed data on the lion and leopard population sizes in the game reserve (Figure 1). Figure 1. The total number of individuals in the leopard and lion populations over a six-year period.

(a)   Describe what scientists mean when they refer to an ecological community such as that shared by the leopards and lions.

 When referring to an ecological community such as that shared by the leopards and lions, it means that the two species feed on the same population of prey. They consume the same prey animals, so they show similar habitat preferences or in other words, share the niches. 

(b) Using the template, construct an appropriately labeled graph to represent the data in Table 1. Based on the data, determine the most common size of the leopards’ prey animals and the most common size of the lions’ prey animals.

Based on the data the most common size of the leopards’ prey animals are the medium prey. The most common size of the lions’ prey animals are the very large prey.  

(c) Based on the data in Figure 1, describe whether or how the size of the leopard population appears to have been affected by the lion population over the period for which data were analyzed. The scientists also estimated the consumed biomass of the prey animals of the leopards and lions. They estimated that the lions annually ate a total of approximately 175,000 kg of prey animals. This included approximately 110,000 kg of very large animals. Calculate, to the nearest whole number, the percent of the total biomass eaten by the lions that is composed of very large animals.

The size of the leopard population appears to not have been affected by the lion population over the period for which data was analyzed. The lions eat larger prey and the leopards eat smaller prey.  The percent of total biomass eaten by the lions that is composed of very large animals is 110000/175000 which is 0.6285. This makes the percent of total biomass eaten by the lions that is composed of very large animals is 63%. 

(d) Based on the data in Table 1 and the biomass of the very large animals eaten by the lions, predict the likely effect on both the lions and leopards if the availability of the very large animals becomes limiting in the reserve. After analyzing the data, the scientists claim that the leopards and lions coexist in the reserve through the use of niche partitioning. Use evidence from the data provided to support the scientists’ claim.

The effect on both lions and leopards if the availability of very large animals becomes limited in the reserve would severely harm the leopard population. Since the lions mainly consume larger prey, the lack of this resource would most likely cause them to have to resort to smaller prey. This would put the leopard population in danger since there would be an overlap in the prey which will be detrimental to the prey population as well as the predator population. They can coexist since the prey population that they rely on does not overlap in normal circumstances. 

2-Read each question carefully. Write your response in the space provided for each part of each question. Answers must be written out in paragraph form. Outlines, bulleted lists, or diagrams alone are not acceptable and will not be scored.

Glucose is the preferred carbon source for Escherichia coli bacteria. Researchers isolated E. coli-M, a strain of E. coli with a single mutation that inactivates a key enzyme in one of the three glycolytic pathways E. coli bacteria use to break down glucose. In an initial experiment to study the effect of the mutation on glucose utilization and  ATP  production by the bacteria, the researchers add  2×104  E. coli-M bacteria to 400  mL  of a growth medium that contains glucose. To measure the rate of bacterial growth, they monitor the optical density of the culture as a measure of the bacterial concentration over time.

(a)   Describe why monitoring the growth rate of the E. coli-M bacteria is a useful indicator of the effect of the glycolytic enzyme mutation on the bacteria.

Monitoring the rate of the e.coli bacteria is a useful indicator of the effect of the glycolytic enzyme mutation since if the mutation were to interfere with glucose breakdown, there would be less ATP produced and available for the cell to use. The ATP decrease in availability will consequently decrease the growth rate of the population, as well as the size of the population. 

(b)   Identify the most appropriate control the researchers should use when determining whether the mutation affects the growth rate of the E. coli-M bacteria.

The most appropriate control the researchers should use when determining whether or not the mutation affects the growth rate of the e coli would be to monitor the growth rate of the wilt type of the identical e coli that does not have the mutation. 

(c)   Predict the growth rate pattern of the E. coli-M bacteria when they are initially added to the growth medium if the mutation does not interfere with glucose utilization.

The e coli would most likely exponentially grow initially since the glucose can continue to be used as a source of energy. 

(d)   Provide reasoning to justify your prediction.

The growth medium should initially have nutrients and glucose that surpasses the requirement of the small necessity for bacteria. 

Darwin is considered the “father of evolutionary biology.” Four of his contributions to the field of evolutionary biology are listed below.

• The non-constancy of species

• Branching evolution, which implies the common descent of all species

• Occurrence of gradual changes in species

• Natural selection as the mechanism for evolution

Darwin’s ideas have been enhanced and modified as new knowledge and technologies have become available. Discuss how TWO of the following have modified biologists’ interpretation of Darwin’s original contributions.

• Hardy-Weinberg equilibrium

• Punctuated equilibrium

• Genetic engineering

Darwin’s idea of Hardy Weinberg equilibrium modified biologists’ interpretation of Darwin’s original contributions because it was able to prove that allele frequencies remain constant over time when there are no evolutionary changes to the organisms. Natural selection is a mechanism for evolution, but there are no allele frequency changes in populations with no genetic flow, no mutation, no natural selection, random mating, and a large population since it is not necessary for the well being of the population. It is a gradual change. The idea of punctuated equilibrium was supported by Darwin since he states that natural selection is a mechanism for evolution. Punctuated equilibrium is the idea that a gene pool may experience sudden change caused by a disaster if there was a long period of no change in the population. The populations with little to no diversity are unable to adapt to the specific environment, so natural selection causes the individuals who were able to survive to repopulate, essentially creating the bottleneck effect, and is able to cause evolution in populations. It is a gradual change.

College board video 8.3 Population Ecology

Population contains individuals from the same species that live in a particular area

• Complex interactions with one another and the environment

• Individuals interbreed with one another in the same population more than others

Adaptations are related to obtaining and using energy in environments

• Size of population relies on resource availability

• Less food, population shrinks, reproduction rate and offspring survivability decrease

• More food, population grows, reproduction rate and offspring survivability increases

• Different species have different adaptations to help survival such as storage of fat during winter, losing leaves and growing leaves based on day length, and migrations

Population growth dynamics rely on other factors

• Age at reproductive maturity, number of offspring produced, frequency of reproduction and survivorship of offspring to reproductive maturity can impact population growth

• dN/dt=B-D (change in population size/change in time=birth rate-death rate)

Reproduction without constraints and exponential growth (J shaped curve

• Exponential growth is a sharp increase in the growth of a population 

• Ideal conditions, resources are abundant, more individuals are reproducing

• dN/dt=rmaxN (change in population size/change in time=max per capita growth rate of population *population size)

• dN/dt=500-75/1=425 N=2500 rmax=415/2500=0.17

College board video 8.4 Effect of Density of Populations

Resource availability impacts population density(how close individuals in a population live)

• More food, population density increases, higher reproduction rate, limited space

• Less food, population density decreases, lower reproduction rate, spread out population

• Density dependent: factors that impact population size and rely on population density ex: competition for resources, territoriality, disease, predation

• Density independent: factors that impact population size and impact population size regardless of population density ex: natural disasters, floods, fires, volcanoes, pollution

Population can produce density that exceed the carrying capacity (S shaped curve)

• Logistic growth model: initially exponential growth, then stable maximum growth

• Max. number of individuals is called carrying capacity based on density dependent and density independent factors, limiting factors bring population back to carrying capacity

• dN/dt=rmaxN(K-N/K) change in population size/change in time=max per capita growth rate of population *population size *carrying capacity-population size/carrying capacity)

• dN/dt=rmaxN(K-N/K) 225-150=rmax*150(275-150/275), 75=rmax*68*2, rmax=1.10

• dN/dt=rmaxN(K-N/K) => 0.28*3652(4500-3652/4500)=193. 3652+193=3845 choice A.