Directions: Paraphrase answers below that correspond with the questioned asked make sure it is not the same.
This assignment is based on your reading for the last two modules. From the books section 44.2 Demographics of Populations, 44.3 Population Growth Models, 44.4 Regulation of Population Size, 44.5 Life History Patterns, and 44.6 Human Population Growth answer the following:
1. Describe the difference among type I, II, and III survivorship curves.
- Type I allows most individuals to survive well past the midpoint of the lifespan and death doesn’t happen until near the end of the lifespan, like large mammals and humans living in developed countries. Type II is when survivorship decreases at a constant rate throughout the lifespan, and death is often unrelated to age. In Type III, most individuals die very young, like in many invertebrates, plants, and fish.
2. Explain why a bell-shaped age pyramid indicates a growing population.
.This is because as the size of the reproductive group equals the size of the reproductive group, a bell shape forms.
3. Describe ecological factors that might result in iteroparity rather than semelparity.
.Some factors would include environmental changes, such as a increase in natural resources and food that provides for a greater population. This would allow for iteroparity to produce more offspring since there would be more reproductive events within a single lifetime. The food, shelter, and habitat need to be increased for more reproductive events to be conducive to the population’s sustainability.
4. Explain how carrying capacity (K) limits exponential growth.
.This is the maximum numbers of individuals of a given species a community can support, and since the population cannot grow unchecked, it will eventually result in them depleting all the resources necessary to sustain them. More predation, competition, and lowering resources will cause a decline in birth rate and increase in death rate.
5. Describe the effect that population density can have on competition and predation.
.With a greater population within a single area (greater population density), there is more competition for the same resources. Predation also grows as the prey population becomes denser, since this makes prey easier to find.
6. Provide examples that show how a density-independent factor can act as a selective agent.
.One example would be a flood, which does not necessarily destroy greater populations of a dense population versus a less dense one. However, the larger the population, the more impacted by the flood, and this could become a selective agent.
7. Compare and contrast the general characteristics of a K-strategist and an r-strategist.
.In the r-strategist, population is low compared to K and the r-strategists are often small individuals maturing early with short lifespans. They spend most energy in producing small offspring and little energy parenting. The more offspring, the more they are likely to survive to reproduce themselves. In the K-strategists, species use energy to their own growth and survival, as well as offspring. They spend more time parenting and producer fewer offspring that are larger.
8. Explain why a population may vary between K and r strategies.
.A population may vary between the two strategies in order to maintain alternation of generation life cycles, and also adult size is not always determining factors for life history patterns. To check the population and maintain sustainability, a population may vary between K and r strategies.
9. Compare the population growth of the LDC’s with that of the MDC’s.
.LDC’s grow at a rapidly expanding rate compared to that of MDC’s, since there may be less access to contraceptives, lower health care, increased need to have offspring for economic purposes of working, or cultural norms.
10. Describe why replacement reproduction still leads to continued population growth.
.Most nations continue growing because of age structure of populations and lifespan, and if more young women enter reproductive years than older women leaving them, the replacement reproduction leads to population growth.
11. Explain how an increase in the consumption of resources by LDC’s would affect the consumption by MDC’s.
.Increased consumption of resources by LDC’s can impact consumption by MDC’s because it can cause more waste or deplete resources, which make it more difficult to obtain for MDC’s. Greater environmental impact could seriously alter consumption habits of MDC’s by the behaviors of LDC’s.
Next, based on your reading of sections 45.1 Ecology of Communities, 45.2 Community Development, and 45.3 Dynamics of an Ecosystem, answer the following:
1. Describe the two factors that can cause predator and prey populations to cycle in a predictable manner
a.The population density of the predator can be affected by the prevalence of the prey. Furthermore, predation and parasitism can increase the abundance of the predator and parasite, but there is a cost to the prey or host population. An increase in population size of predators depends on prey population size, and vice versa. One explanation is that the biotic potential of the predator is too large and prey is overconsumed, adversely impacting both populations. Alternatively, the biotic potential of predators may be unable to keep up with the prey and the the prey population crashes by going over the carrying capacity, adversely impacting predator populations.
2. Give examples of mutualism and explain how each species benefits.
.Mutualism occurs when both members of the symbiotic relationship benefit. For example, the bacteria in the human intestinal tract gets food from us, but it also synthesizes vitamins that humans need. Both human and bacteria benefit. Sea anemones live on the backs of crabs, which gives them more access to food, while the crab utilizes the stinging tentacles of the anemone to get food and protection.
3. Compare and contrast the various models used to explain succession.
.Primary succession occurs when soil is formed from exposed rock because of wind, water, or abiotic factors. This happens when there is no base soil, like in volcanic eruptions or glacial retreats. Secondary succession occurs when there is a disturbance which changes grasses to shrubs to a mixture of shrubs and trees progressively. This requires soil to already be present. Facilitation model of succession occurs when each group of the species gets ready for the next, developing the area in an ideal way that is sequential. The inhibition model is the opposite, as the colonists or plants in that area stay there and hinder other plant growth until the colonists are dead or damaged. Finally, the tolerance model indicates that both can develop together, simultaneously.
5. Compare the flow of energy to the flow of chemicals through an ecosystem.
.As energy flows from one organism to another in the ecosystem, only a fraction of the original amount of energy is transferred. Over time, the more the energy flows, the more it dissipates into the environment as heat and other forms of energy. This means there must be a constant source of solar energy being put into the environment so the energy can be replenished.
6. Provide examples of how human activities can alter biogeochemical cycles.
.The four biogeochemical cycles, including water, carbon, phosphorus, and nitrogen, can be altered by human activities because chemicals can be removed from reservoirs and exchange pools, making them available to biotic communities. Pollution can alter the necessary balance of nutrients producers need in the environment. Groundwater mining, release of CO2 from greenhouse gases and N2O from fertilizers and CH4 from methane can alter the carbon cycle, mining phosphate ores and runoff from fertilizer and livestock waste and sewage treatment plants causes eutrophication of waterways, while fertilizer from N2 run off and alter the nitrogen cycle.
7. Describe the various biogeochemical cycles: water, carbon, phosphorus, nitrogen.
.The water cycle is also called the hydrological cycle and freshwater is distilled through saltwater from evaporation. Then, the salts are left behind, then condensation occurs. This forms a cloud, which allows the water to then cool and fall as rain over the ocean and land. The plants go through transpiration when water evaporates from them and gravity will return all freshwater to the sea. The precipitation allows water to go to the ground and maintain a saturation zone called the water table, and wells and springs accumulate water. In the carbon cycles, CO2 is exchanged between ecosystems and the atmosphere. Plants take CO2 through photosynthesis, then incorporate themselves into nutrients which are consumed, and respiration by organisms returns the CO2 to the atmosphere. In the water, CO2 combines with water to make bicarbonate ions, the main source of carbon for algae, and respiration by aquatic organisms allow the CO2 to become bicarbonate ions. The phosphorus cycle occurs when phosphorus from ocean sediments move to land because of geologic uplifts, and the weathering of rocks puts those ions in the soil. Plants can access some of that, passing it to animals that eat the plans, that he decay of dead organisms results in phosphate ions for producers again. The phosphate levels of the environment impact the population sizes of an ecosystem, and runoff allows for marine sediments to accumulate, recycling when a geological upheaval exposes sedimentary rocks. The nitrogen cycle includes the use of nitrogen fixation when nitrogen gas is turned to ammonium, and plants can use it. This allows for organic compounds with nitrogen to be available to plants, which make proteins and nucleic acids. Nitrification and assimilation and denitrification are also components of the nitrogen cycle, allowing for a natural form of counterbalancing nitrogen fixation (though this is interrupted by human activities).