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1. What is a cohort life table, and what data is required to construct one? You will be asked to fill in the blanks of a life table. (Bring a calculator)
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Definition
a.A cohort life table or dynamic life table is used to track the fate of a group of individuals born at a given time and are followed from birth to death. The data you need is individuals that are born over several time periods.
cohort chart values
Nx= the number of individuals from the original cohorts that are alive at the specified age (x)
lx- the probability at birth of surviving to any given age (x)
Dx= how many individuals that have died between age classes
Qx= the number of individuals that have died in a given time divided by the number alive during the age interval
Lx= the average number of individuals alive during the age interval x to x+1
Tx= the total of years lived into the future by individuals of age class in the population.
Ex= the average number of years that an individual of a given age (Nx) is expected to live into the future.
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2. What is a population projection table, and what information can you get from constructing this table? You will be asked to fill in the blanks of a life table. (Bring a calculator) |
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a.A population projection table is the chart of growth of a population developed by calculating the births and mortality of each age group over time. In order to construct one population projection table,
we need:
lx = the probability at birth of surviving to any given age (x).
qx = age – specific mortality rate = the number of individuals that died in a given time interval (dx) divided by the number alive at the beginning of that interval (nx).
sx = age – specific survival = 1 – qx
bx = mean number of females born to a female in each age group.
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3. What is definition of the net reproductive rate (R0)? How can the value of R0 for a population be used to assess whether a population is increasing or decreasing?
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Definition
The net reproductive rate (R0) is the average number of females that will be produced during a lifetime by a newborn female. It provides a method to evaluate both the individual (fitness) and population consequences of specific life history characteristics.
In most cases, the females are the one who affect the population rate by reproducing offspring. Thus the number of females in the population plays a crucial role to determine whether that population is increasing or decreasing.
R0 = 1: on average, females will replace themselves in the population → stable population
R0 < 1: females are not replacing themselves in the population → decreasing population
R0 > 1: females are more than replacing themselves in the population → increasing population
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4. Compare and contrast a Type I, Type II, and Type III survivorship curve. Give an example of an organism from each type.
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Definition
Type I- Population in which individuals have long life spans, survival rate is high throughout life span, with heavy mortality rate at the end.
ex.: humans, other mammals, and some plants.
Type II- Population in which individuals survival rates do not very with age.
ex. adult birds, rodents, reptiles, and perennial plants
Type III- Population of individuals whose mortality rates are extremely high in the early parts of life.
ex. fish, many invertebrates, and plants |
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5. What is the difference between geometric and exponential growth? What factors limit exponential growth (carrying capacity) resulting in logistic growth?
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In geometric population growth a constant number of individuals is added at each time interval, population growth is finite, and the number of individuals added to the population is not proportional to population size.
For exponential growth the reproductive rate is constant per individual, the number of individuals reproducing is proportional to the population size, essential resources such as food and space are unlimited, and the environment is constant so no seasonal/ annual variations can affect birth rates or death rates.
The factors that limit exponential growth resulting in logistic growth are that resources are limited and birth and death rates change. Resources like food, space and nutrients availability.
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6. Explain the relationship between N and K (i.e. if N is less than K, then…; if N = K, then…; if N is greater than K, then…). Explain why the population growth rate is fastest at K/2.
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Definition
N and K are two factors used in calculating population growth.
N refers to population size and K refers to carrying capacity(the number of individuals of a species that can be supported in a habitat.
When N is low relative to K population growth follows the exponential growth model pattern.
As N approaches K population growth slows down.
When N=K the population has reached carrying capacity and population growth is 0.
If N surpasses K then population growth will become negative and declines below K and will struggle to stay around K.
The population growth rate is fastest at N=K/2 because before reaching this point, the population still grows exponentially, and after this point, the population growth rate becomes logistic. In addition, the exponential growth rate leads the population size to expand incredibly large and fast while the logistic growth rate makes the population grow smaller and slower. It starts off as a potential J shaped curve (exponential curve), but initially turns into S shaped curve (logistic curve).
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7. Describe the difference between scramble and contest intraspecific competition and how the outcome differs between these two types of competition.
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Scramble competition occurs when growth and reproduction are depressed equally across individuals as competition intensity increases.
Contest competition takes place when some individuals claim enough resources while denying others a share.
In its extreme, scramble competition can lead to all individuals receiving insufficient resources for survival and reproduction, resulting in local extinction. In contest competition, only a fraction of the population suffers – the unsuccessful individuals. Therefore, scramble completion might easier lead to local species extinction.
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8. What is self-thinning in terms of competition? How does this benefit the population?
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Definition
In terms of competition, self-thinning is an inverse relationship between the average mass of the individuals and the density of the surviving individuals.
This means that the mortality of some individuals increases resource availability for the remaining individuals and therefore increasing growth of those individuals.
This benefits the population because there are more resources to be used by fewer individuals, and those fewer individuals have a higher chance of surviving.
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| 9. What conditions must be established before a researcher can definitively state that two species are competing for a resource? Is establishing that two species overlap in their use of a resource a sufficient condition to determine that interspecific competition is occurring? Explain your answer. |
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Definition
The two species must reside in the same realized niche.
If the two species are competing for the same resources then the species may be indirectly interacting with each other by exploiting resources which would affect the availability of the desired/needed resource.
The two species may also interfere with each others opportunity or physical ability to get the needed resources by preventing the other species from accessing the resources.
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10. What is the competitive exclusion principle? What is the difference between a species fundamental niche and its realized niche? How is it possible for 2 species to occupy the same niche successfully? Give 3 different situations to support your answer.
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Definition
The competitive exclusion principle states that two competitors that require the same resources who reside the same niche cannot coexist.
The fundamental niche is the set of conditions and resources under which a species can survive, thrive,and reproduce.
The realized niche is the area within the fundamental niche, where the species really takes up.
The only way for two species to live within the same niche is if they both occupy the same fundamental niche, but only “interact or come into contact” through the realized niche area.
The two species might occupy different sections of the fundamental niche and only compete within the realized niche section when needing to exploit resources.
The two species might live in separate sections of the fundamental niche and they may share the realized niche, by adjusting behavior.
Perhaps the two species live in separate parts of the fundamental niche, but only take up just enough of the realized niche to survive comfortably.
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| 11. Environmental factors such as temperature and salinity are not consumable resources, but species that occupy the same habitat often differ in their response to these factors (adaptations and/or ability to acclimate). How might these types of environmental factors influence the outcome of competition between two species occupying the same habitat? |
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Environmental factors like temperature and salinity are examples of non-consumable resources that influence the outcome of competition between two species through the idea that these factors directly affect plant growth and plant reproduction.
These factors are important because the factors of temperature, salinity and other factors may decide whether a species may or may not have an advantage or disadvantage in defeating its competitive neighboring species.
These factors may not be consumable, but they are direct and reflect on the two species abilities to out compete one another within the same habitat.
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12. Why would predator population growth lag behind prey population growth? If the predator population is removed and the prey population growth continues on the same boom and bust cycle, how would you explain this?
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The predator's population growth lags behind the prey population's growth because the predator's population size is very crucially dependent on the prey's population size. If the predator population is removed then the prey's population growth will continue normally and on the boom and bust cycle because the prey's population does not depend on the predator's population. The prey's population depends on resource factors like food, water, nutrients, space, and other factors like diseases in overpopulated groups. |
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13. In Hindu mythology, Brahma created a large and monstrous creature that grew so rapidly that it devoured everything in its path. In reality, predators are much more selective about what they eat. What factors appear to be important in determining what a predator selects to eat among the possible array of potential prey?
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Definition
In real situations, predators are selective about what they eat because it is important to know whether or not the prey is worth the time and energy spent looking for, handling, and digesting the prey.
Another factor could be whether or not the prey is out-hunted by competing predators.
The energy eventually going to be gained from the prey must be greater than the energy spent searching, catching, and eating the prey. |
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| 14. How can predator populations function as agents of natural selection in prey populations? How can prey populations function as agents of natural selection in predator populations? |
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Predator populations function as agents of natural selection in prey populations by pressuring individuals in prey population to either have the characteristics and behaviors that can help the prey avoid from becoming consumed by the predators, or not being able to outrun, outsmart, or out-skill the predators.
The prey populations function as agents of natural selection in predator populations by determining which of the top competing predators has the skills, characteristics, and strategy of catching the prey populations that have the opposite struggle of trying to avoid from becoming prey. |
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| 15. In both predation and parasitism, one organism derives its energy and nutrients from the consumption of another organism. How do these two processes differ? What is the difference between an ectoparasite and an endoparasite and how does this difference affect their “relationship” with the organism they parasitize? |
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In predation, the consumption of the prey gives the predator energy and nutrients. In parasitism, the organism being parasitized is the host. The parasite depends on the host for resources like food or nutrients, and has no intentions of completely killing off the host because that would also cause the death of the parasite or force the parasite to find a new host.
A ectoparasite is a parasite which lives outside of its host, usually on the skin, within the fur, or lining of the hairs. An endoparasite is a parasite which lives inside its host, usually burrowing beneath the host's skin, within one of the host's organs, in the host's bloodstream, or within one of the host's body cavities.
The ectoparasite must make sure of its ability to latch onto the outside of the host's skin to leech, while the endoparasite must face the problem of making sure it can fight off the host's immune system and avoid being destroyed or killed by the host's body. |
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16. A parasite trematode begins its life cycle in a snail where it hatches. The snail nourishes the trematode into a swimming larva and leaves the snail and enters the California killifish. By traveling to the killifish’s brain the behavior of the killifish is altered, moving jerkily near the water’s surface. This behavior attracts the attention of the killifish’s predator, the great blue heron. The trematode will then reproduce in the gut of the heron completing its life cycle. Trematode eggs are deposited with heron feces in the water where they will be picked up by snails. How might such a complex life cycle have evolved? |
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Definition
This complex cycle of having several intermediate hosts, and one definitive host probably evolved due to its effectiveness of survival.
The parasite trematode best uses its form of indirect transmission because it gives itself the most potential and greatest opportunity at life.
Instead being able to thrive in one single host, its lifestyle was best molded into different stages depending on different hosts before reaching its maturity in its final/definite host.
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17. What is mutualism? What is the difference between facultative and obligate mutualism? Provide 3 different examples and explain the relationship between the organisms, also indicate whether the example is facultative or obligate. |
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Mutualism is a relationship between two organisms, in which both organisms benefit from. Facultative mutualism is having a mutual relationship between two organisms, but without having any direct relationships. Obligate mutualism is a having a mutual relationship between two organisms in which both organisms are very much dependent on each other; if one organism declines and dies then the other organism will be affected in the same way.
For example:
The relationship between the Yucca Lord’s candle and the Yucca moth are obligated because the Yucca moth is the only pollinator of the Yucca Lord’s Candle, and in return the Yucca moth only lays eggs in the Yucca Lord’s Candle.
The relationship between fungus and alga are obligated because they create lichen. The alga cells get oxygen and creates sugars for the fungus while the fungus provides shelter and protection for the alga cells.
The relationship between a specific type of chorella/green algae and a certain type of hydra would be due to the fact that they share with each other. The hydra shares nitrogen with the chorella, while the chorella shares some of its product of photosynthesis with the hydra.
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18. Distinguish between a keystone species and a dominant species. Be sure to include what would happen if either of these was removed from the community.
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A keystones species does not have to be the dominant species; it plays an very important role and has a huge impact on the community relating to its abundance.
If the keystone species is removed then the community would be very negatively affected, in species diversity and the community’s overall ability to thrive.
A dominant species is the species that has the most abundance in an environment and carries the most biomass of all the species. Removing the dominant species is not as harmful as removing the keystone species.
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19. Distinguish between a food web and a food chain. When/why would ecologists choose to use each model? |
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A food web displays the connection of energy flow between different organisms.
A food chain on the other hand, is very organized and it starts with the sun, then goes straight to the producers, then to the primary consumers, then to the secondary consumers, and then to the tertiary consumers. |
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20. Distinguish between primary and secondary succession. Explain the process of each.
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Primary succession occurs on site previously unoccupied by a community. In other words, this is truly a brand new exposed surface. For instance, a habitat which has never been occupied by life now starts to become a new place for many new lives, starting with different types of grass. As time goes by, grass become shrub and shrub become tall trees. It might take many many years for a “virgin” land to become a forest.
Secondary succession occurs on previously occupied sites after disturbance. In this case, there might have some plants which were able to survive the disturbance now start to grow, to reproduce again. After a while, these plants and some new vegetation will make a forest.
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| 21. A neighborhood planner wants to develop in coastal sage habitat and it’s your job to find the best option for managing the habitat patches that will remain. The diagram below shows a series of options for habitat patch management. Each row A-F gets progressively worse in terms of maintaining a healthy habitat. Your job is to explain why the column on the left is better than the column on the right for each row A-F. |
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A. The first area is better than the second area because the habitat patch is larger than the second one.
B. The first area is better than the second area’s four different patches because instead of having four separated areas without connected pathways, area one is one whole combined area.
C. The first area is better than the second area because it is clumped and located in a closer proximity than the second area.
D. Area one is a better habitat because area one’s habitat patches are closer to each other compared to area two’s patches which aren’t as within the same access distance as area one’s.
E. Area one has paths which connect its three habitat patches while area two’s habitat patches are unconnected and therefore less convenient/efficient as an area.
F. Area one is better compared to area two because area two is so stretched out and completely made up of border/edge while area one is made up of both core area and edge area.
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22. The Theory of Island Biogeography envisions the species richness of island communities as a balance. What factors are involved in this balance? How does this theory apply to fragmented habitat on mainlands?
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Definition
The factors that are involved and apply to the Theory of Island Biogeography's balance of species richness of island communities are an island's size, immigration rate, emigration rate, how close the island might be from land, the number of species on the island, and how much extinction may be occurring on the island.
These factors can be used to be applied on fragmented habitats on mainlands, but instead of worrying about patch size factors like resources and whether or not these fragmented habitats are neighboring other broken off habitats. |
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23. Describe the effects of temperature, moisture, length of photosynthetic period, and nutrient availability on net primary productivity in terrestrial ecosystems. Which of the two main food chains is more dominant in terrestrial ecosystems and why?
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Definition
Net primary productivity (NPP) increases with increasing mean annual temperature and rainfall. A higher mean annual temperature means a higher annual intercepted solar radiation. Thus the length of the growing season will also be stretched. Therefore, sites with a higher mean annual temperature typically support higher rates of photosynthesis and are associated with a longer time period over which photosynthesis can occur. In addition, it is the combination of warm temperatures and an adequate water supply for transpiration that gives the highest primary productivity. Moreover, the availability of essential nutrients required for plant growth directly affects ecosystem productivity.
Within any ecosystem there are two major food chains: the grazing food chain and the detrital food chain. The detrital is more dominant because in the detritus food chain, the consumer trophic levels are continuously recycled, while the grazing food chain is only unidirectional.
The grazing food chain is unidirectional in the sense that it isn't recycled and is going in only one direction.
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| 24. Explain the difference between primary production and secondary production. How is secondary production affected by primary production? Explain why energy is lost as it is transferred from one trophic level to another. What are the effects of energy loss on the biomass of different trophic levels? |
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Definition
Primary production is the community of organisms which make up the a whole amount of biomass. Most of this biomass is created by plants; since these plants are the primary producers through the process of photosynthesis, they fixate carbon. The source of energy these primary producers use for primary production is solar energy from the sun.
Secondary production is the total of biomass which includes all of the consumer organisms’ biomass. The secondary production is solely dependent on the primary production for energy so primary limits secondary.
Energy is lost as it is transferred from one trophic level to another because as energy is transferred from one level to the next, some energy is lost depending how efficient the energy transfer is.
As energy is lost through each trophic level change, biomass is also lost.
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25. Describe how atmospheric carbon dioxide levels fluctuate daily, seasonally, and geographically. Explain why such fluctuation occurs. Why is the carbon cycle tied to energy flow charts? |
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Atmospheric carbon dioxide levels fluctuate daily due to factors like consistency, different stages of photosynthesis during the day, and less carbon dioxide gathered during sunlight gathering.
Atmospheric carbon dioxide levels fluctuate seasonally and geographically due to factors like temperatures, solar radiation, and amounts of water which then directly affect the lay of the land.
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26. Why is Earth considered both an open and closed ecosystem? Describe three ways that nutrients can be lost from a particular ecosystem.
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Earth is considered to be both an open and closed ecosystem.
It is an open system because energy is able to leave Earth. It is a closed system because the nutrients are enclosed in Earth.
One way nutrients that can be loss from an ecosystem is by soil erosion, nutrients from the soil being taken away by wind or water.
Another way nutrients are lost is through water leaching the nutrients downward into the soil.
Nutrients are also lost by environmental conditions that export nutrients in the form of gases. |
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27. Explain the difference between the two basic types of biogeochemical cycles, using nitrogen and phosphorus as examples of each. Describe a pathway of nitrogen from the atmosphere into the body tissue of an herbivore. |
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In gaseous bio-geochemical cycles the main pools of nutrients are the atmosphere and the oceans, some nutrients that are in this cycle are nitrogen, carbon dioxide, and oxygen. In sedimentary bio-geochemical cycles the main pool of nutrients is the soil, rocks, and minerals, a nutrient in this cycle is phosphorus.
For molecular nitrogen (N2) to be used by organisms it must be fixed in a process called fixation this is done by high energy fixation in which factors such as lightening provide the high energy needed to combine nitrogen with the oxygen and hydrogen of water, the second method of fixation is biological fixation which is accomplished by different kinds of micro organisms such as bacteria. Nitrogen is also freed up for use by other organisms by the breakdown of dead organic material in a process called mineralization. In terrestrial ecosystems nitrogen is taken up (assimilation) by plants in the form of ammonia and nitrates, the plants then convert them into amino acids. Herbivores then eat these plants, which convert the obtained nitrogen into different types of amino acids.
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