Question

explain the concept of a food web and what happens if one species disappears; explain what factors contribute to changes in the size of populations; explain what biodiversity is and why it changes (either at the geologic time scale or human-caused changes); explain what potential changes will occur to the climate engine with increased greenhouse gases in the atmosphere;

Answer 1

> Food web is an important ecological concept. Basically, food web represents feeding relationships within a community. It also implies the transfer of food energy from its source in plants through herbivores to carnivores. Normally, food webs consist of a number of food chains meshed together. Each food chain is a descriptive diagram including a series of arrows, each pointing from one species to another, representing the flow of food energy from one feeding group of organisms to another. There are two types of food chains: the grazing food chain, beginning with autotrophs, and the detrital food chain, beginning with dead organic matter. In a grazing food chain, energy and nutrients move from plants to the herbivores consuming them, and to the carnivores or omnivores preying upon the herbivores. In a detrital food chain, dead organic matter of plants and animals is broken down by decomposers, e.g., bacteria and fungi, and moves to detritivores and then carnivores. Food web offers an important tool for investigating the ecological interactions that define energy flows and predator-prey relationship. Simplified food web in a desert ecosystem could be, grasshoppers feed on plants; scorpions prey on grasshoppers; kit foxes prey on scorpions. Applications of Food Webs are as follows:

• Food webs are constructed to describe species interactions (direct relationships): The fundamental purpose of food webs is to describe feeding relationship among species in a community. Food webs can be constructed to describe the species interactions. All species in the food webs can be distinguished into basal species (autotrophs, such as plants), intermediate species (herbivores and intermediate level carnivores, such as grasshopper and scorpion) or top predators (high level carnivores such as fox)
• Food webs can be used to illustrate indirect interactions among species: Indirect interaction occurs when two species do not interact with each other directly, but influenced by a third species.

• Food webs can be used to study bottom-up or top-down control of community structure: Food webs illustrate energy flow from primary producers to primary consumers (herbivores), and from primary consumers to secondary consumers (carnivores). The structure of food webs suggests that productivity and abundance of populations at any given trophic level are controlled by the productivity and abundance of populations in the trophic level below them. This phenomenon is call bottom-up control.

• Food webs can be used to reveal different patterns of energy transfer in terrestrial and aquatic ecosystems: Patterns of energy flow through different ecosystems may differ markedly in terrestrial and aquatic ecosystems. Food webs (i.e., energy flow webs) can be used to reveal these differences.

If one species in the food web ceases to exist, one or more members in the rest of the chain could cease to exist too. If one animal disappears, that's a loss of food for another animal. For example, if rabbits disappeared off of a food web, the predator, lets say it's a fox, would have a loss of food. So rabbits disappear, foxes lose food, if the foxes don't have food, they could die out, causing the foxes predator to die, etc.

> The human population is constantly changing. There are many factors that can influence the size of a population. Some factors result in an increase in the population, while others can cause a decrease in population size.

Factors that Increase Population Size There are two factors that result in an increase in the size of a population. First, there is natality, which is the number of individuals that are added to a population over a period of time due to reproduction. This term is often used to describe reproductive rates over a variety of time periods. The term most commonly used when describing natality in the human population is 'birth rate'. Birth rate is the number of individuals born per 1,000 individuals per year. An example of birth rate would be if a population of 5,000 people resulted in the birth of 50 children in a year, which would yield a birth rate of ten individuals per 1,000 per year. Birth rate is often reported as a percentage of the population. Birth rates can vary a great deal by region and can have drastic effects on the overall human population.

The second factor that can cause a rise in a population is immigration. Immigration is the migration of an individual into a place. When an individual immigrates to a new location, they increase the population within that area. Immigration is a factor that can influence the size of a specific population of humans, but does not influence the overall human population. For example, if an individual decides to move from London to New York, they would be immigrating to the United States and would therefore increase the population of the U.S. Their immigration would have no influence on the overall human population because no matter where they live, they are included in the size of the human population. The only way that immigration could influence the overall human population on Earth is if humans lived on a different planet and immigrated to Earth. In that scenario, the human population on Earth would increase.

Factors that Decrease Population Size The first factor that results in a decrease in the population size is mortality. Mortality is the number of individual deaths in a population over a period of time. In terms of the human population, mortality is often described as the death rate, which is the number of individuals that die per 1,000 individuals per year. Death rates are often used to describe how many individuals die in specific age groups. For example, the death rate of infants is often an important statistic to investigate when looking at changes in the population. Similar to birth rates, the death rate is also often described as a percentage of the population.

The second factor that decease the population size is emigration. Emigration can decrease a country's population size. For example, if you live in New York City and emigrate to Miami, you are decreasing the population of New York City but increasing the population of Miami, because you immigrated there. However, it's important to note that immigration and emigration don't change the earth's overall population, or the number of people alive at a given time. Immigration and emigration simply change the number of people in a given place.

Other factors that contribute to change in the size of population includes:

• Economic factors such as availability of jobs and wage levels which can affect migration to and from regions and countries. The attraction of higher wages has encouraged migration from many eastern European countries to the UK since 2004.
• Social factors such as education, migration, healthcare and lifestyle. In 1948 the NHS was set up in the UK which led to increased life expectancy due to freely available healthcare to the population. In the UK, education about the health effects of smoking and alcohol have helped increase life expectancy.

• Political factors such as government population policies and civil war. Population policies like China’s One-Child Policy has reduced the rate of natural increase in the country, however, it has also led to an ageing population and a greater number of males than females in the country. A civil war can lead to a decline in population, reduced population densities and can change the age-sex structure of a country with fewer males of fighting age due to deaths in the conflict.

> Biodiversity is the variability among living organisms from all sources, including terrestrial, marine, and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species, and of ecosystems. Biodiversity forms the foundation of the vast array of ecosystem services that critically contribute to human well-being. Biodiversity plays an important role in ecosystem functions that provide supporting, provisioning, regulating, and cultural services. Healthy ecosystems require a vast assortment of plant and animal life, from soil microbes to top level predators like bears and wolves. If one or more species is removed from this environment, no longer serving its niche, it can harm the ecosystem. Introducing foreign or invasive species into a habitat can have similar results, as the invasive species can out-compete the native species for food or territory. Dragonflies, ladybugs and beetles pollinate many of the crops we rely on for food, as well as plants in natural ecosystems. One type of pollinator cannot do it all, hence the importance of biodiversity. Loss of habitat—for example, when humans convert meadows into parking lots or backyards—is reducing pollinator populations. If pollinators were to disappear entirely, we would lose over one-third of all crop production. This would reduce or eliminate the availability of foods like honey, chocolate, berries, nuts and coffee. Biodiversity also provides ecosystem services or benefits to people. These benefits include: hurricane storm surge protection, carbon sequestration, water filtration, fossil fuel generation, oxygen production and recreational opportunities. Without a myriad of unique ecosystems and their respective diverse plant and animal life, our quality of life may become threatened.

There is no clear way of determining the total impact that humans are making on biodiversity; however, it is obvious that many actions by humans are causing a decrease in biodiversity. To determine the total impact that humans are making on a given environment, the area of productive land and water needed to produce the item that is being consumed and the need to account for the waste being generated by humanity must all be taken into account according to management and production practices in use during that time. Direct or indirect actions by humans have resulted in the decrease of biodiversity. The Convention of Biological Diversity states that there are both indirect and direct human drivers. Some of the indirect human drivers are demographic, economic, sociopolitical, scientific and technological, and cultural and religious factors. Some of the direct human drivers are changes in local land use and land cover, species introductions or removals, external inputs, harvesting, air and water pollution, and climate change. Human activity has substantially changed one-third to one-half of the world’s surface. In the next 50 years it is expected that humans will seriously impact 50-90 percent of land in developing countries. This is a result of growth in population and in over consumption of natural resources. The population of humans is, what many consider, the root of the biodiversity problem. The increase in human inhabitants causes a problem because with it comes a need to convert natural habitats to land for human consumption.

One way that the humans have been able to sustain their growth is by converting natural habitats to fields where foods can be produced. At least 23 percent of the earth’s land is being used for agriculture (31 percent of all land is unfarmable). Internationally, there is half a hectare of tropical forest disappearing to farmland every second. One of the potential dangers of decreasing the amount of natural habitats remaining is that species will no longer be present on earth. This directly affects agriculture because many of the species that are being destroyed for croplands may have been used for genetically enhancing crop products. In this manner, the increase in agricultural land actually harms our agricultural future.

Human actions have also played a role in climate change, which is also causing great danger for biodiversity. The change in climate is due to increased atmospheric concentrations of carbon dioxide, which causes increased land and ocean temperatures, and changes in precipitation and sea level rise. With the change in climate also comes a change in species. Climate affects the timing of reproduction and migration, the length of growing seasons, species distributions and population size, and the frequency of pest and disease outbreaks. It is also expected that the change in climate in the 21st century will have a much higher rate than the past 10,000 years and create an even bigger impact on biodiversity. It is expected that 80 percent of biologically rich regions will suffer great losses of plant and animal species because of global warming. The rate of change of habitats is expected to increase up to ten times due to global warming.

> Greenhouse gases are transparent to incoming (short-wave) radiation from the sun but block infrared (long-wave) radiation from leaving the earth's atmosphere. This greenhouse effect traps radiation from the sun and warms the planet's surface. As concentrations of these gases increase, more warming occurs than would happen naturally. The continued emissions of greenhouse gases will lead to climate changes. Future changes are expected to include a warmer atmosphere, a warmer and more acidic ocean, higher sea levels, and larger changes in precipitation patterns. The extent of future climate change depends on what we do now to reduce greenhouse gas emissions. The more we emit, the larger future changes will be. Many greenhouse gases stay in the atmosphere for long periods of time. As a result, even if emissions stopped increasing, atmospheric greenhouse gas concentrations would continue to increase and remain elevated for hundreds of years. Moreover, if we stabilized concentrations and the composition of today's atmosphere remained steady (which would require a dramatic reduction in current greenhouse gas emissions), surface air temperatures would continue to warm. This is because the oceans, which store heat, take many decades to fully respond to higher greenhouse gas concentrations. The ocean's response to higher greenhouse gas concentrations and higher temperatures will continue to impact climate over the next several decades to hundreds of years. Greenhouse gas concentrations in the atmosphere will continue to increase unless the billions of tons of our annual emissions decrease substantially. Increased concentrations are expected to:

• Increase Earth's average temperature
• Influence the patterns and amounts of precipitation
• Reduce ice and snow cover, as well as permafrost
• Raise sea level
• Increase the acidity of the oceans
• Increase the frequency, intensity, and/or duration of extreme events
• Shift ecosystem characteristics
• Increase threats to human health

These changes will impact our food supply, water resources, infrastructure, ecosystems, and even our own health.