Chapter 2 The Living World 第二章 生物系统

本章的生物概念相对重要，在理解了概念后，才能将其很好地应用。这些生物概念包括：

生物种群（biological populations）：在同一生活空间，相同物种 (same species)个体的集群。

群落（communities）：在同一生活空间，不同物种(different species)个体的集群。

生态位（ecological niches）：一个物种在所处环境中的生态作用(environmental function)。

物种间的相互作用（interactions among species）：物种之间的相互关系有很多种，例如寄生、腐生、竞争、共生等。

关键种（keystone species）：对保持生态群落的结构起着重要作用的物种。

物种多样性（species diversity）：在一定时间和区域内所有生物物种及其遗传变异和生态系统复杂性的总称。生物多样性包括了基因多样性、物种多样性、生态系统多样性等。

边际效应（edge effects）

主要陆生和水生生物群系（major terrestrial and aquatic biomes)

1 Ecosystem生态系统（图1—2—1）

1.1 Community Interactions群落间的相互作用

两个不同的物种常常会竞争同一个生态位，这种竞争关系抑制种群的增长，从而出现了以下5种物种间的相互作用。

It is not uncommon for the niches of two species to overlap. The overlap increases competition and can therefore limit population growth. This produces five main types of interactions among species.

1.1.1 Interspecific Competition种间斗争

种间斗争指两个或两个以上物种竞争相同的生存环境。

Interspecific competition refers to the competition between two or more species for the same limited resources in the environment such as food, nutrients, space, sunlight.

种间斗争导致的结果有三种：extinction, resources partitioning and character displacement.

In nature, there are two related outcomes, besides extinction, if two species inhabit the same niche and therefore compete for resources. One of the species will evolve through natural selection to exploit different resources. This is called resources partitioning. Another possibility is called character displacement, which occurred on the Galapagos Islands. Mammalian carnivores, Galapagos finches, Anolis lizards on island are examples of character displacement.

1.1.2 Predation 捕食

一个食肉动物以其他的生物为食。

A predator feeds on all or part of another organism known as its prey.

捕食又包括以下几种形式：

a. pursuit and ambush追求和伏击

b. mimicry模仿

c. camouflage伪装

d. chemical warfare化学战

植物通过本身的结构特点，比如刺毛，或者通过排放毒素来抵抗一些动物的捕获。

Plants have evolved spines and thorns and chemical poisons such as strychnine, mescaline, morphine, and nicotine to fend off attack by animals.

而有些动物采取隐藏等主动防御措施来抵抗其他动物的捕获。也有一些动物利用拟态、警戒色、保卫色等方式来保护自己。

Animals have evolved active defenses such as hiding, fleeing, or defending themselves. These, however, can be very costly in terms of energy. Animals have also evolved passive defenses such as cryptic coloration or camouflage that make the prey difficult to spot. Examples:

●警戒色Aposematic coloration is very bright, often red or orange, coloration of poisonous animals as a warning that possible predators should avoid them.

●警戒拟态（又叫贝氏拟态）Batesian mimicry is copycat coloration where one harmless animal mimics the coloration of one that is poisonous. One example is the viceroy butterfly which is harmless but looks very similar to the monarch butterfly, which stores poisons in its body from the milkweed plant.

●缪勒拟态In Mullerian mimicry, two or more poisonous species, such as the cuckoo bee and the yellow jacket, resemble each other and gain an advantage from their combined number. Predators learn more quickly to avoid and prey with that appearance.

1.1.3 Parasitism 寄生

一个生物寄生在另一个宿主生物中，从宿主生物中获取能量。

One organism (parasite) gains energy by living on or inside a host organism. A tapeworm in the human intestine is an example.

1.1.4 Mutualism 互利共生

两种生物相互作用，彼此有利。

Two organisms interact in a manner that is beneficial to both in some way. An example is the bacteria that live in the human intestine and produce vitamins.

互利共生又包括：

a. nutritional mutualism

b. gut inhabitant mutualism

1.1.5 Commensalism 共栖

两种生物中的相互作用仅有利于一方。

This interaction benefits one species but has little or no impact on the other. Barnacles that attach themselves to the underside of a whale benefit by gaining access to a variety of food sources as the whale swims into different areas. The whale is unaware of the barnacles.

1.2 Keystone species 关键种

在一个群落中与其他种相互影响，相互作用，并决定其他许多种生存的物种。

A species that plays such a vital role in sustaining the community's habitat and biodiversity that its disappearance has a disproportionately large impact on the community.

●Species diversity 物种多样性

Species diversity of any given area is a combination of species.

●Species richness 物种丰富度

The number of different species in one area at one time.

●Species evenness 物种均匀度

The relative abundance of individuals within each of those species.

1.3 Biomes生物群系

由植物、动物的各种生物群落组成，是生态学上气候条件相似并按照气候和地理划分的区域。生物群系包括：森林、草原、沙漠、灌木丛。

Biomes are large regions characterized by similar climate, soil, plants, and animals regardless of their global locations. Differences in average annual rainfall and temperature predict the type of biome.

1.3.1 Forests森林

森林是生产力最高的群落，包括热带雨林、温带落叶林和针叶林带。

Tropical rain forests, temperate deciduous forests, and taigas (boreal forests), are all dominated by trees. Forests, when compared to other biomes, are areas of high productivity and biodiversity.

下面是三种森林群落的比较总结（见表1—2—1）: AP Tips： 这里常作为AP考点

1.3.2 Grasslands 草原

草原生态系统受季节影响较大。

Tropical, temperate, and cold grassland shave too much moisture for deserts and too little moisture for forests. Grassland ecosystems are regulated by seasonal drought, occasional fires, and the grazing of herbivores.

下面是热带草原、温带草原和寒带草原的分布和特征对比（见表1—2—2）：

1.3.3 Deserts 沙漠

Low precipitation distributes unevenly throughout the year on the leeward side of large mountain ranges (rain shadow effect). There are intense heat and evaporation during the day and cooler nights.

沙漠也分热带、温带和寒带沙漠，AP考试有时也会要求考生做比较（见表1—2—3）。

1.3.4 Chaparrals (Temperate Shrublands) 灌木丛

Chaparrals are along the coastal areas of southern California, parts of the Mediterranean, and central Chile.

2 Energy Flow 能量流动

2.1 Energy Flow 能量流动

能量是沿着食物链不断转换、转化和流失的，如图1—2—2所示：

可以进入生态系统的太阳能是很少的，只有0.1%的太阳能可以被生产者（绿色植物）所利用。

A one-way flow of energy from the sun: Energy from the sun arrives at the earth in the form of solar radiation, which is required for life on earth. Only about 0.1% of all solar energy is captured by primary producers to start the food web. The rest of this energy helps to warm the earth's surface, which in turn generates wind circulation patterns, and also causes the evaporation of water. As solar radiation is utilized, low-quality heat is released into the environment (first and second laws of thermodynamics).

生产者占据第一营养级。营养级（trophic level）是指生物在食物链中所占据的位置。以相同的方式获取相同性质食物的生物体可以归为同一个营养级。大多数绿色植物和藻类（algae）都是生产者，利用叶绿素吸收光能，再通过光合作用将光能固定成可以利用的化学能。

2.2 Producers 生产者

Producers are at the first trophic level in the ecosystem and provide organisms who are consumers with a source of energy. Most producers acquire nutrients through the process of photosynthesis that converts solar energy into energy-rich carbohydrates for consumers. On land the dominant producers are green plants.

光合作用反应方程式：

Photosynthesis: Solar energy + 6H2O + 6CO2→ C6H12O6(glucose) + 6O2

然后还有一些细菌可以通过化能合成（chemosynthesis）作用将硫化物和二氧化碳固定成可以利用的有机物，这类化合自养细菌也是生产者。因此考生们注意，不是所有的生产者都是通过光合作用来生产有机物的。

化能合成反应方程式：

Chemosynthesis: Heat + 3H2S + 6CO2+ 6H2O → C6H12O6(glucose)+3H2SO4

2.3 Consumers消费者

消费者是指在生态系统中不能自己制造食物的生物体，又可以称为异养生物（heterotrophs）。大多数消费者通过有氧呼吸（aerobic respiration）来分解葡萄糖，从而获得能量。

Consumers cannot produce their own energy and therefore rely on the production from producers. Most consumers rely on the process of aerobic respiration to break down glucose consumed from other organisms. This process requires oxygen and releases the carbon dioxide that producers depend on.

有氧呼吸反应方程式：

Aerobic Respiration: C6H12O6(glucose) + 6O2→ 6CO2+ 6H2O + energy

2.3.1 Primary Consumers (Herbivores) 初级消费者

所有的食草动物都是初级消费者。

Primary consumers eat only primary producers.

2.3.2 Secondary Consumers (Carnivores and Omnivores)次级消费者

次级消费者包括食肉动物和杂食动物。

Secondary consumers feed on other consumers for energy. Some rely only on feeding exclusively on other consumers and are referred to as carnivores, or meat eaters. Some feed on both consumers and plants and are referred to as omnivores.

2.3.3 Tertiary Consumers 三级消费者

三级消费者大多数是食肉动物。

Tertiary consumers are predators at the top of the food chain and are typically carnivores. These apex predators usually have very few natural predators in the ecosystem.

2.3.4 Detritivores 食腐质者

食腐质者是以动物的尸体等腐质为食的动物。

Detritivores feed on detritus (parts of dead organisms and fragments of waste of living organisms). Examples include earthworms, mites, and some beetles. Larger organisms that feed on carrion (rotting carcasses) are known as scavengers and would include organisms like vultures.

2.3.5 Decomposers 分解者

细菌和真菌等可以分解动、植物残体，使之成为无机营养物质，以维持生态平衡。分解者通过无氧呼吸或发酵将有机物转化成无机物。比如酵母菌（yeast）通过酒精发酵将葡萄糖转化成为酒精和二氧化碳。

微生物在生态系统中除了承担分解者的重要职责外，还为大气层制造了氧气。人体中也存在着数以百万的微生物，没有微生物，人类的消化系统、免疫系统都不能有效地起作用。

Decomposers are bacteria and fungi that recycle organic material from dead organisms into inorganic nutrients that support the growth and development of primary producers.

酒精发酵反应方程式：

Ethanol Fermentation: C6H12O6(glucose) → 2C2H5OH(ethanol) + 2CO2

2.4 Food Chains and Food Webs 食物链和食物网

2.4.1 Food Chains 食物链

The most obvious interaction between different organisms in an ecosystem is feeding. During feeding, one organism is obtaining food—energy and raw materials—from another one.Usually one organism eats another, but then may itself be food for a third species. The feeding relationships of the different organisms in the ecosystem can be shown in a food chain.

2.4.2 Food Webs 食物网

Since so little energy is transferred from the base to the top of a food chain, a top carnivore must eat many herbivores. These herbivores are probably not all of the same species. In turn, each herbivore is likely to feed on many different plant species. All these different feeding relationships can be shown in a food web.

The more complicated a food web, the more stable the community is. For example, in the woodland food web shown opposite, if the number of squirrels fell, the owls could eat more worms, mice and rabbits. The mice and rabbits would have less competition for food from squirrels, and so might reproduce more successfully.

2.5 Gross Primary Productivity and Net Primary Productivity总生产力和净生产力

能量是沿着生态系统中的食物链和食物网不断流动的。在食物链（food chain）中，能量简单地从一个营养级(trophic level)传递到下一个营养级。而在食物网(food web)中，能量的流动较为复杂。能量在传递的过程中也是不断流失的。因此就产生了总生产力(gross primary productivity)和净生产力(net primary productivity)两个概念。

2.5.1 Concepts概念

Gross primary productivity is defined as the rate at which primary producers converts solar energy into chemical energy through photosynthesis. However, since some of the available chemical energy available to an organism is lost through respiration, a better measure to determine the available energy for higher trophic levels in the ecosystem is to measure the net primary productivity that accounts for this loss.

2.5.2 Conversion Formula公式

net primary productivity=gross primary productivity (photosynthesis) -aerobic respiration (by plant)

3 Ecosystem Diversity 生态系统多样性

3.1 Biodiversity 生物多样性

生物的基因、物种以及它们的生存环境的多样性，称为生物多样性。通常我们衡量生物多样性主要看指定区域中物种的数量和物种的丰富性。物种数量越多，种类越多，我们说该地区生态环境越稳定。

Biodiversity is the variety of species, the genes they contain, and the ecosystems they live in. In general, biodiversity is the highest around the equator and decreases moving toward the poles. Ecosystems that are highly diverse are typically more stable and able to withstand environmental change.

3.2 Natural Selection 自然选择

3.2.1 Natural Selection 自然选择

自然选择主要包括：过度繁殖、生存斗争、遗传变异、物种多样和适者生存。自然选择是生物进化的重要机制。

Natural selection is a biological mechanism for evolution. Some organisms have particular traits, or genes, that give them an increased chance for survival in their environment. Therefore, they will most likely reproduce more often than other organisms lacking these genes and will increase the percent of the population who express this successful trait.

●Over-production 过度繁殖

All organisms produce more offspring than can possibly survive, and yet populations remain relatively stable. For example: a female peppered moth may lay 500 eggs, but the moth population does not increase by the same proportion.

●Struggle for existence 生存斗争

Organisms experience environmental resistance. They compete for the limited resources within the environment. For example: several moths may try to feed on the same nectar-producing flower.

●Variation 物种多样

Within the population there may be some characteristics that make the organisms that have them more suited for this severe competition. For example: some moths might be stronger fliers, have better feeding mouthparts, be better camouflaged while resting or be less affected by rain.

●Survival for the fittest 适者生存

Individuals are most successful in the struggle for existence (that are the best suited/adapted to their environment) are more likely to survive than those without these advantages. For example: peppered moths: dark-coloured moths resting on soot-covered tree trunks will be less likely to be captured by predators than light-coloured moths.

●Advantageous characteristics are passed on to offspring遗传变异

The well-adapted individuals are more likely to breed than those that are less well-adapted. They pass on their genes to the next generation.

3.2.2 Environmental and Natural Selection 环境与自然选择

生物体的区别和特征都是相对而言的，造成生物体多样性的根本原因在于环境的改变。那么环境又是如何影响自然选择的呢？环境的改变主要包括地理变化和气候变化。

●How can geologic and climatic events impact natural selection?

a. Geologic Events 地理变化

板块和陆地的活动

Tectonic activity and movement of continents have either brought populations into new areas or have separated populations from one another and they must adapt to their new conditions.

地震和火山的喷发

Earthquakes and volcanoes happen along plate boundaries and separate populations or eradicate populations as their habitats are destroyed.

b. Climatic Events 气候变化

Periods of warming and cooling have shaped earth's ecosystems as long-term climatic events have historically changed sea levels, caused glaciers to form or recede, and shifted locations of biomes. Organisms unable to adapt to changing conditions have become extinct and replaced with organisms better suited for the new environment.

●How do new species arrive from these types of environmental changes?

a. Geographic Isolation 地理隔离

地理隔离指某些地理原因如板块运动、气候变化等使两个种群彼此隔开，阻碍了种群间个体的自由交换，从而使基因交流受到影响。地理隔离会导致生殖隔离，从而产生新物种。

Geographic isolation occurs when members of a population are physically seperated for long periods of time due to geologic and climatic events.

b. Reproductive Isolation生殖隔离

Reproductive isolation occurs as a species can not breed successfully with related species due to geographical, behavioural, physiological or genetic barriers.

3.2.3 Types of Selection 选择类型（表1—2—4）

Natural selection can change the frequency of inherited traits in a population by five different ways.

3.3 Adaptation 适应性

适应性指通过长期自然选择，生物体与环境相适应的能力。

Adaptation refers to a genetically inheritable trait that makes an organism more likely to survive and reproduce.

3.4 Evolution (Biological Evolution) 进化（生物进化）

Evolution is the change in the genetic make-up of a population over time. The evolution of different species is classified into five patterns: divergent evolution, convergent evolution, parallel evolution, coevolution and adaptation radiation.

●Divergent evolution 分裂演进（图1—2—3）

When a population becomes isolated from the rest of the species, it becomes exposed to new selective pressures, and evolves into a new species.

●Convergent evolution 趋同进化（图1—2—4）

When unrelated species occupy the same environment, they are subjected to similar selective pressures and show similar adaptations.

●Parallel evolution 平行进化（图1—2—5）

Parallel evolution occurs when two related species that make similar evolutionary adaptations after their divergence from a common ancestor.

●Coevolution 共同进化（图1—2—6）

Coevolution refers to the reciprocal evolutionary set of adaptations of two interacting species.

●Adaptive radiation 辐射进化（图1—2—7）

Adaptive radiation refers to the emergence of numerous species from a common ancestor introduced into an environment. Each newly emerging form specializes to fill an ecological niche.

3.5 Speciation 物种形成

Speciation refers to changes in the genetic make-up of a population over time. That leads to an entirely new species.

环境变化影响物种进化的方式：

地理隔离（geographic isolation）——自然选择（natural selection）不同——进化方向（evolutional direction）不同——产生差异（differences）——生殖隔离（reproductive isolation）——新物种（new species）

3.6 Ecosystem Services 生态系统服务 (又称生态系统公益)

人类直接或间接从生态环境中受益。

Ecosystem Services are economically valuable services provided by nature. The value of all the ecosystem services provided to humanity by nature is estimated to be as high as $30 trillion.

Ecosystem services include: pollination, water purification and storage, climate regulation, flood control, protection from ultraviolet (UV) radiation, protection from storms, pest control, lumber production, pharmaceutical production, food production, soil formation, nitrogen fixation and recreational opportunities.

4 Natural Ecosystem Change 自然生态系统变化

4.1 Climate Shifts 气候变化

From tree rings, fossilized plants, insect and pollen samples, gas bubbles trapped in glaciers,deep ice core samples, lake sediments, stalactites and stalagmites, marine fossils, sediments, dust analysis, many evidences, we found that climate has significantly changed.

There are various factors influence the climate.

●Albedo 反照率

Snow and ice has the highest albedo; ocean water has low albedo.

●Greenhouse effect 温室效应

Without water, carbon dioxide and methane, the earth will be cold.

●Carbon cycle 碳循环

The emission of carbon dioxide results in warming.

●Landmass distribution 大陆分布

Ocean water is much more absorbent than landmasses so that continents reflect a lot more solar energy back into space than the ocean. Earth with landmasses clustered at low latitudes than near the poles.

●Precession 旋进

The wobble of Earth on its axis changes the amount of energy received by the sun. Changes in the orientation of Earth in space also have an effect on climate.

●Volcanoes and plate tectonics 火山和板块运动

Volcanoes produce carbon dioxide. Plate tectonics affect atmospheric carbon dioxide.

4.2 Ecological Succession 生态演替

生态演替指随着时间的推移，一种类型的生态系统被另一种类型的生态系统所替代的过程，包括初级演替和次级演替。

Ecological succession refers to the gradual change in species abundance and diversity after a disturbance. There are two types of ecological succession that take place after environmental disturbances.

●Primary succession 原生演替

Primary succession is the establishment of a biotic community from a previously life-less terrain (uncommon).

●Secondary succession 次生演替

Secondary succession follows a disturbance in an ecosystem that has damaged or removed part of the established community but leaves in place soil or sediments.

另外还有一些其他的演替方式，比如：

●Allogenic succession 异发演替

Allogenic succession occurs as changes in the environmental conditions create conditions beneficial to new plant communities.

●Progressive succession进展演替

Progressive succession occurs as communities become more complex over time by having a higher species diversity and greater biomass.

●Retrogressive succession 倒退演替

Retrogressive succession occurs as the environment deteriorates and results in less biodiversity and less biomass.

5 Natural Biogeochemical Cycles 自然生物地球化学循环

C、H、O、N、P、S是生物界最主要的六大元素。这些元素以分子和化合物的形式，通过空气、水、土壤在生态系统中不断循环。

5.1 Carbon Cycle 碳循环（图1—2—8）

5.1.1 What is Carbon Cycle什么是碳循环

Plants and some bacteria, manufacture compounds from carbon dioxide during the process of photosynthesis. Animals obtain them in a ready-made form by feeding on other living organisms and decomposers obtain them as they break down the dead bodies or wastes of other living organisms. The processes of feeding, respiration, photosynthesis and decomposition recycle the carbon over and over again. Theoretically, the amount of carbon dioxide fixed by photosynthesis should equal the amount released by respiration. As a result, the most accessible form of carbon in the non-living environment, that is carbon dioxide, remains at about the same concentration year after year. Other processes may affect this regular cycling of carbon. The way in which these different processes contribute to the cycling of carbon is illustrated opposite.

5.1.2 The Significance of Carbon Cycle 碳循环的重要性

Critical for: Nucleic acids, carbohydrates, proteins, lipids.

Largest reservoir: Oceanic sediments.

Atmosphere: Carbon dioxide gas makes up only a small portion of the troposphere (0.038%). This greenhouse gas acts as a natural thermostat for earth's surface temperature.

5.1.3 Human Impacts on Carbon Cycle 人类对于碳循环的影响

人类对于碳循环的主要影响在于增加空气中二氧化碳的含量，从而引起全球变暖。

Human impacts include: increasing the carbon dioxide concentration in the atmosphere, causing global warming.

The two major ways that increase concentration of carbon dioxide are:

燃料燃烧Burning of fossil fuels

树木砍伐Clear-cutting

5.2 Nitrogen Cycle 氮循环（图1—2—9）

5.2.1 What is Nitrogen Cycle什么是氮循环

Once nitrate has been formed by either nitrogen fixation or nitrification, it can be absorbed by plants through their roots. Eventually the plant dies, and its body is added to the animal wastes and remains in the soil. Decomposers break down the nitrogen compounds in these wastes and remains and the formation of nitrate can begin again.

氮循环是生态系统中最重要的营养物质的循环，它是初级生产力的限制因子（limiting factor）。氮循环包括氮的固定（nitrogen fixation）、氨化作用（ammonification）、硝化作用（nitrification）、反硝化作用（denitrification）。

●Nitrogen fixation 氮的固定

Nitrogen fixation is the conversion by bacteria in the soil and cyano bacteria in aquatic systems of nitrogen gas in the atmosphere into ammonia and ammonium.

●Ammonification 氨化作用

Decomposers convert organic remains of organisms into detritus and eventually into inorganic ammonia and ammonium ions.

●Nitrification 硝化作用

Bacteria convert ammonia or ammonium ions in the soil into nitrate ions for plants to uptake.

●Denitrification反硝化作用

Bacteria primarily in the sediments of aquatic zones such as lakes, ocean, swamps, estuaries, and bogs, convert ammonia and ammonium ions into nitrogen gas and nitrous oxide, a greenhouse gas.

5.2.2 The Significance of Nitrogen Cycle 氮循环的重要性

●Critical for: Proteins and nucleic acids. Often a limiting factor for primary productivity.

●Largest reservoir: The atmosphere. Nitrogen gas (N2) makes up 78% of the troposphere.

5.2.3 Human Impacts on Nitrogen Cycle人类对于氮循环的影响

Human impacts include: Eutrophication. Nitric oxide (NO), a raw material for photochemical smog and acid rain. Increased denitrification by anaerobic bacteria releases the greenhouse gas nitrous oxide (N2O).

具体表现为以下三方面：

●Excess nitrates过量的硝酸盐

Nitrates from animal feedlot waste and municipal sewage discharge runs off into nearby waterways. These extra nutrients create anoxic, low dissolved oxygen, conditions in waterways which deplete the aquatic diversity.

●Burning of fossil fuels 燃料的燃烧

●Using inorganic fertilizers使用无机肥料

5.3 Phosphorus Cycle 磷循环

●Critical for: DNA, ATP, and the bones and teeth of vertebrates. Often a limiting factor for primary productivity.

●Largest reservoir: Oceanic sediments and terrestrial rock layers. No atmospheric reservoir.

●Human impact: Eutrophication（富营养化）.

Excess phosphate runs off into nearby waterways from sewage, mining waste, and fertilizers, like nitrates, these excess phosphates can promote algal growth in aquatic systems, which eventually leads to low levels of oxygen and therefore depletes aquatic diversity.

5.4 Sulfur Cycle 硫循环

●Critical for: Proteins, vitamins.

●Largest reservoir: Oceanic sediments.

●Human impacts include: An impurity in coal and petroleum, when burned, sulfur dioxide (SO2) is released into the atmosphere. Once in the atmosphere, sulfur dioxide can form sulfuric acid (H2SO4) that contributes to acid deposition.

5.5 Hydrologic/Water Cycle水循环（图1—2—10）

●Critical for: Life. The movement of water across the earth's surface helps shape the topography of the Earth.

●Largest reservoir: Surface water (oceans, lakes, rivers).

●Human impacts include: Unsustainable withdrawal of large amounts of water for societal and industrial uses. Removal of large areas of wetlands and creating new non-porous tracts of land (parking lots, roads, buildings) decrease the earth's natural absorptive abilities and increase erosion and the chance for flooding. Clearing large amounts of vegetation (deforestation) for urban growth, agriculture, mining, etc., decreases transpiration rates, which can decrease precipitation as well as reduce infiltration of water into soils.