Answers and tips
Questions to explore
"Away from the grass on the plains, one year old and one withered away." Wildfires burn endlessly, spring winds blow and grow again", "In the wilderness in the north of our country, the population density of various herbaceous plants is getting higher and higher in spring and summer, and the opposite is true in autumn and winter.
discuss
1. What are the main environmental factors that contribute to seasonal changes in the populations of these plants?
Answer: Non-biological factors such as sunlight, temperature, water, etc.
2. What are the effects of changes in the number of these plant populations on the fertility and mortality rates of local animal populations?
Answer: In spring and summer, the grass is lush, the food of plant-eating animals is abundant, the birth rate is increased, and the mortality rate is reduced; in autumn and winter, the opposite is true. Changes in the number of plant-eating animal populations can affect the birth and mortality rates of carnivores.
Reflection • Discussion 1
1. What are the inorganic factors that affect the population density of herbaceous plants in the area?
Answer: Sunshine.
2. Under the influence of the same abiotic factors, the population density change of Spiny herb is quite different from that of the annual poncho and the Canadian yellow flower, why is this?
Answer: The adaptability of different plants to light conditions varies.
3. In addition to the above factors, what are the non-biological factors affecting changes in population sizes? Try to illustrate each by example.
Answer: In addition to light conditions, changes in population size are affected by non-biological factors such as temperature, water, wind, and fire.
Sidebar Reflection Question 1
After reading this text, can you ask any questions?
Tip: This is a very open-ended topic. Students are encouraged to ask a variety of real-world questions that can be explored. For example, what factors affect the population of understory plants, in addition to being mainly limited by sunlight?
Reflection • Discussion 2
1. How to interpret the experimental results in Data 1?
Answer: There is a competitive relationship between the double-core grasshopper and the large grasshopper, and the number of weakly competitive insects will continue to decline.
2. How to explain the synchronous periodicity of changes in the populations of lynx and snow rabbits?
Answer: There is a predatory relationship between lynx and snow rabbit. When the number of snow rabbits as prey rises, the lynx increases because of the abundance of food, the birth rate of its population rises, the mortality rate decreases, and the number will increase; conversely, when the number of snow rabbits as prey declines, because of the lack of food, the birth rate of its population declines, the mortality rate rises, and the number will decrease.
3. Which is the cause and which is the effect of the change in the number of lynx and snow rabbit populations?
Answer: The increase in the population of lynx increases the predation pressure on the snow rabbit, resulting in an increase in the mortality rate of the snow rabbit and a decline in the number of populations; when the number of snow-free populations declines, the lack of food for the lynx is reduced, the birth rate of the lynx population declines, the mortality rate rises, and the population also declines; the decline in the population of lynx reduces the predation pressure on the snow rabbit and allows the number of snow rabbits to recover; the number of snow rabbits rises, the food for the benefit causes is sufficient, the birth rate rises, the mortality rate decreases, and the population increases. In this cycle, the population number of the two is mutually influencing, which is a circular causal relationship.
4. In addition to lynx, are there any other factors that affect the change in the number of snow rabbit populations?
Answer: Yes. There are other predators, competition from other plant-eating animals, plants as food, and abiotic factors.
Sidebar Reflection Question 2
Fishing nets should not be too small, otherwise it will affect fish production in the coming year. Why? Please explain from the perspective of population characteristics.
Answer: If the nets are too small, many juveniles will also be caught, affecting the age structure of the fish population, which in turn affects the birth rate of the fish population and reduces fish production in the coming year.
Thinking training
In biology, the causal relationship of many physiological or ecological processes is cyclical, that is, a certain event as the cause of change, the result of which becomes a new condition, imposed on the event that was originally the cause, causing it to produce new results, and so on. Please analyze the circularity of causality in the following biological processes and answer questions.
1. Regulation of thyroid hormone secretion.
Answer: The hypothalamus secretes thyroid-stimulating hormone-releasing hormone (TRH), which acts on the pituitary gland and prompts the pituitary gland to secrete thyroid-stimulating hormone (TSH); TSH reaches the thyroid gland with blood circulation, prompting the thyroid gland to increase the synthesis and secretion of thyroid hormones. When the amount of thyroid hormones in the blood increases to a certain extent, it inhibits the secretion of hormones related to the hypothalamus and pituitary gland, which in turn reduces the secretion of thyroid hormones. In this process, the increase in TRH and TSH content is due to the increase in thyroid hormone content is the result; the increase in thyroid hormone content becomes a new "cause", and after feedback regulation, a new "fruit" that inhibits the secretion of TRH and TSH is produced, and so on, so that the thyroid hormone content in the blood is maintained at a relatively stable level.
2. Correlation of population changes in prey and predator populations.
Tip: See the answers to question 3 in this section, "Other Biological Factors Affecting Population Sizes," in this section.
3. Can similar examples be found in human activities?
Tip: This is a highly open-ended question, and students should be encouraged to make associations and look for similar examples of human activity.
Practice and application
First, the concept of testing
1. Population changes are influenced by environmental factors. Based on this, the following statements are correct.
(1) Weak understory light will reduce the population of all understory plants. (×)
(2) Only environmental factors that affect fertility and mortality in populations can affect population sizes. (×)
2. In nature, some predator populations and prey populations fluctuate periodically, as shown in the model below. Please analyze the relationship and influencing factors of the quantitative changes shown in the two figures.
(1) A reasonable explanation or generalization of this phenomenon is (D)
A. It has nothing to do with intraspecific competition
B. The two always trade between the two
C. Independent of plant population
D. The two are mutually restrictive and mutually causal
(2) Changes in the number of predator populations and prey populations do not all fit this model, and the unreasonable explanation for this is (C)
A. The predator population has a variety of prey
B. The prey population has a variety of predators
C. The ability of prey to evade predators is significantly improved
D. Predator populations are too small to constrain prey population growth
Second, expand the application
1. An ecology monograph reads: "Ecology becomes a predictive science when the future can be predicted; ecology becomes a management science when the future is determined." "Combined with the knowledge learned in this chapter, talk about your understanding of this sentence, if you are interested, you can also read more information to understand the research progress of ecology and its application in practice."
Tip: Judging from the content of this chapter, this sentence makes a lot of sense. For example, according to the population change model, the trend of population change can be predicted, and according to the law of population change and its influencing factors, corresponding countermeasures can be formulated in species protection, fishery management, pest control and other aspects.
2. At the beginning of the 20th century, moose were introduced to an isolated island. The population changes in abundance between 1915 and 1960 are shown in the table below.
(1) The decline of the population from 1915 to 1943 is expressed by a graph.
Tip: Take the year as the abscissa and the population number as the ordinate, and draw a curve chart based on the numbers in the table.
(2) From 1915 to 1930, the population increased, what are the possible reasons?
Answer: Plenty of food, no predators, suitable climate, etc.
(3) The population of this population later fell sharply, what are the possible reasons?
Answer: Plants that are used as food are eaten in large quantities, resulting in food insufficiency; natural disasters, etc.
Review and improve
1. Multiple choice questions
1. The following description is consistent with the concept of population density (C)
A. Annual yield of one hectare of rice
B. Number of weeds per square meter of grass
C. The number of crucian carp per square meter of water surface in a lake
D. The number of new individuals per year for gray hamsters in a given area
2. Due to premature cooling in autumn in an area, many locusts die before laying their eggs. The following year, the population density of locusts in the area decreased significantly. A reasonable explanation for the decline in locust population density is (A)
A. Decline in the birth rate B. Mortality rate rises
C. The influx rate decreases D. The emigration rate rises
3. According to the age structure of the population, the trend of birth rate and mortality rate can be speculated. The following statement is correct (B)
A. The age structure is stable, and the birth rate is greater than the mortality rate
B. The age structure is growth-oriented, with birth rates greater than mortality rates
C. The age structure is declining, with a birth rate greater than the mortality rate
The age structure is stable, with a birth rate smaller than the mortality rate
4. Regarding population growth, the following statement is correct (C)
A. Populations introduced into new environments can grow in a "J" shape for a certain period of time
B. In the case of changing environmental conditions, the population fluctuates around the K value
C. Population growth has a stable trend around K-values under constant environmental conditions
D. Natural populations grow to a certain extent and remain stable at K values, so they all grow in an "S" shape
5. The main stages of brewing with yeast are: feeding→ inoculation→ ventilation culture→ sealed fermentation. From post-inoculation to pre-seal period, the plot for yeast population population change is (C)
2. Non-multiple-choice questions
1. Rhododendron macrophyllum is a tall tree concentrated in the mountainous area of Gaoligong Mountain, Yunnan, China. Its distribution range is very small, it is difficult to introduce to other places, and it is an endangered species. The large tree rhododendron has thick litter under the forest, and the seeds are difficult to disperse to the soil matrix layer, so the germination rate is very low in the natural environment; the seedlings grow slowly and take a long time to flower; the plants have weak hardiness and will die in the -2 °C environment, and the mortality rate of young trees is high. Please answer the following questions.
(1) What environmental factors affect the population of Rhododendron macrophylla?
Answer: dead leaves, sunlight, temperature.
(2) It has been suggested that artificial removal of litter under the forest should increase the seed germination rate of rhododendrons and promote population growth. What do you think of this advice?
Tip: This question needs to be avoided from a linear causal perspective. This suggestion makes sense only from the point of view of increasing the germination rate of large trees; however, the decomposition of litter increases the nutrients in the soil, which, if removed artificially, may cause soil depletion.
(3) Because the rhododendron plant is tall, the flowers are large and gorgeous, and it is of great ornamental value, there is a risk of vandalism. What advice do you have for protecting the rhododendron of the big tree?
Tip: This question has a certain openness. Suggestions that can be referred to include strengthening publicity and education, prohibiting trade, and establishing nature reserves within the distribution range of the big tree Du Peng.
2. Przewalski's gazelle is an endangered animal endemic to China and is now only distributed in the grasslands around Qinghai Lake in China. In 1994, the number of Przewalski's gazelles in China was less than 300. In recent years, przewalski's populations have continued to rise as a result of a series of protective measures. In 2018, the number reportedly reached 2 793, but the threat they faced remained. The bones of Przewalski's gazelles can often be seen near the ranch fence, either the remains of wolves after predation, and some were killed by thorns on the fence. Due to road and pasture fences, Przewalski's gazelle is segregated in 13 distribution areas.
(1) From the perspective of genetics and evolution, the Przewalski's gazelle population in different distribution areas is in isolation, what is the adverse effect on the continuation of this species?
Answer: Przewalski's gazelle in different distributions is in isolation, which is not conducive to the reproduction and gene exchange of the population, which may reduce the genetic diversity of the population; it may also cause inbreeding, and there are more genetically defective offspring, which is not conducive to the reproduction of the population and the evolution of the species.
(2) Some people suggest that predators such as wolves be hunted in large quantities to protect Przewalski's gazelle, do you agree with this suggestion? Tell us your reasons.
Answer: Both Przewalski's gazelle and wolf are products of biological evolution and are organic components of nature. From a co-evolutionary perspective, the presence of wolves is conducive to the evolution of Przewalski's gazelle.
(3) Many herders responded to the government's call to take the initiative to dismantle the pasture fence, but then there were cases of livestock being bitten by wolves and foxes; strict grazing can make room for Przewalski's hartebeest, but will reduce the income of herders. How should the relationship between protecting przewalski's gazelle and safeguarding the interests of pastoralists be reconciled?
Tip: This question has a certain openness. Students can be encouraged to think positively and cultivate a sense of social participation. For example, it is proposed that the government should implement the policy of protecting the Przewalski's gazelle and introduce measures to protect the interests of local herders, such as subsidies and the development of other industries.