1
What is the hierarchy of organization recognized by ecologists, and why might it be useful to recognize such distinctions?
INFOGRAPHICS 8.1 AND 8.2
Which of the following is the correct hierarchy of life?
Individual, community, biome, ecosystem, population, biosphere
Individual, population, community, ecosystem, biome, biosphere
Biosphere, community, biome, ecosystem, population, individual
Biome, biosphere, population, ecosystem, community, individual
B
The word niche refers to an organism’s ________, while its habitat refers to its ________.
role and relationships in its community; environmental surroundings
life cycle; role and relationships in its community
environmental surroundings; tolerance limits
“address”; “job description”
A
Why do ecologists focus mainly on the study of populations, communities, and ecosystems?
Ecology focuses on the interactions of a species with the biotic and abiotic components of its environment. These are the levels of organization manageable enough to allow the ecologist to study interactions between and within these levels as they investigate the habitat requirements for and niche of a given species. This adds to our understanding of how a natural ecosystem functions. While biomes (or the entire ecosphere) could be studied from this same perspective (interactions), the large scale of a biome, not to mention the ecosphere, generally requires study at the ecosystem level with extrapolations made to the larger level.
2
Why do ecosystems need a constant input of energy? How do they deal with the fact that Earth does not receive appreciable new inputs of matter?
INFOGRAPHIC 8.3
What does it mean for the Earth to be energetically open but a closed system with regard to matter?
Energy can be used again and again, but matter can be used only once.
Organisms can create new energy but not matter.
Earth receives new energy inputs but not significant new matter inputs.
Energy inputs exceed matter outputs.
C
Why is it essential that sustainable ecosystems rely on an energy source that is readily replenished, like sunlight, rather than nonrenewable sources, such as fossil fuels?
Once energy is used by an organism, it is converted to a form that is no longer useful (heat) and is therefore not considered a viable energy source for life. Any organism or ecosystem that relied on an energy source that is not readily replenished, like fossil fuels, would eventually run out.
3
What are biomes, and how do environmental factors affect their distribution and makeup?
INFOGRAPHICS 8.4 AND 8.5
Which biome description is correct?
Grasslands receive less rainfall than forests but more than deserts.
Forests have freezing temperatures regularly.
Grasslands are much warmer annually than forests.
Deserts are hot year round—much hotter than forests.
A
Look at the location of temperate deciduous forests on Earth in the biome climograph in Infographic 8.4. What can you surmise about the climatic conditions in North America and Europe/Asia where these forests are found?
These regions must receive similar amounts of precipitation and experience similar seasonal temperatures throughout the year.
4
What is a population’s range of tolerance, and how does it affect the distribution of a population within its ecosystem or its ability to adapt to changing conditions?
INFOGRAPHIC 8.6
Which of these is an example of a population’s range of tolerance?
The season with the most rainfall
The number of competing species in the area
The hottest and coldest temperatures it can survive
The quality of nesting sites in the area
C
The population that would have the best chance of surviving an environmental change would be the one with:
the narrowest range of tolerance for temperature.
the greatest genetic diversity.
the largest population size.
the least variation among individuals.
B
Using the example of spring wildflowers and the critical factor of rainfall, explain the term environmental gradient (for rainfall) and the term range of tolerance (in terms of the distribution of wildflowers within their range).
Rainfall amounts vary from place to place and may increase or decrease incrementally over space — such as up a mountain or away from a coastal region (an environmental gradient). A given population of a wildflower species will grow best and population will be larger in an area of optimal rainfall; nearby areas that receive slightly more or less rain, will still support the flowers but fewer individuals would be found in these less optimal habitats. Above and below certain rainfall amounts, the species will not be found — this represents the upper and lower ranges of tolerance for this species and this environmental parameter (rain).
5
How do carbon, nitrogen, and phosphorus cycle through ecosystems? How are these cycles being disrupted, and what problems can this disruption cause?
INFOGRAPHICS 8.7, 8.8, 8.9, AND 8.10
True or False: Plants and other producers are the only types of species that perform photosynthesis, whereas all species perform cellular respiration.
TRUE
Of the three matter cycles discussed here, the only one that does not have an atmospheric component is the __________ cycle.
Phosphorus
What is the purpose of photosynthesis?
It produces a form of chemical energy that the plant can use as needed.
It allows plants to remove excess CO2 from the atmosphere.
Plants do it to produce oxygen so animals (and humans) can breathe.
It is a way for producers and consumers to release the energy stored in sugar molecules.
A
List the steps involved in the nitrogen cycle. What would happen if a wildfire burned so hot that it sterilized the soil, killing all the microbes?
Atmospheric nitrogen (N2) is converted to nitrate (NO3) by lightning or through biological processes (by soil bacteria or those living symbiotically in the roots of some plants) to ammonia (NH3) — a process known as nitrogen fixation. Alternatively, nitrogen in organic matter (dead leaves, animals, etc.) is broken down by bacteria or fungi in the process of decomposition to form ammonium (NH4). The NH4 is converted to NO3 by different bacteria in a process called nitrification. Plants can take up NO3 and use it in day-to-day functioning (i.e. to make proteins or DNA) or the NO3 can be broken down by denitrifying bacteria (denitrification) which releases N2 back into the atmosphere, completing the cycle.
If soil lost its microbes (soil bacteria and fungi) to fire then decomposition and nitrification would not occur and much of the ecosystem’s nitrogen would be tied up in dead matter rather than being passed onto plants to be used. Denitrification would also not occur, reducing the nitrogen returned to the atmosphere (which would not have a big impact since N2 is so abundant). Plant growth would be thus be limited to species with symbiotic nitrogen fixing bacteria in their roots or on the rate of NO3 production from lightning (a small amount). This would impact all the other species in the ecosystem since plants support the food chain in terrestrial ecosystems.
Consider the ways in which human impact is affecting the carbon, nitrogen, and phosphorus cycles. What do these various human actions all have in common? Why might this be a concern?
All have resulted in the release of more carbon, nitrogen, and phosphorus into the environment in forms that can be taken up by living things. Extra nutrients can upset the natural matter cycles as they may accelerate the growth of some organisms beyond what would be seen naturally. This is especially true in areas where these nutrients might be naturally limited in supply such as aquatic ecosystems that receive extra nitrogen or phosphorus. [In the case of extra CO2, it might spur extra photosynthesis but this effect appears to be limited — the biggest impact is from the fact that CO2 is a greenhouse gas and extra amounts are contributing to climate change.]
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