The Geography of Ecosystems There are many different ecosystems: rain forests and tundra, coral reefs and ponds, grasslands and deserts.
Climate differences from place to place largely determine the types of ecosystems we see. How terrestrial ecosystems appear to us is influenced mainly by the dominant vegetation. The word "biome" is used to describe a major vegetation type such as tropical rain forest, grassland, tundra, etc. It is never used for aquatic systems, such as ponds or coral reefs. It always refers to a vegetation category that is dominant over a very large geographic scale, and thus is somewhat broader geographically than an ecosystem.
Figure 3 : The distribution of biomes. We can draw upon previous lectures to remember that temperature and rainfall patterns for a region are distinctive. Every place on Earth gets the same total number of hours of sunlight each year, but not the same amount of heat.
The sun's rays strike low latitudes directly but high latitudes obliquely. This uneven distribution of heat sets up not just temperature differences, but global wind and ocean currents that in turn have a great deal to do with where rainfall occurs.
Add in the cooling effects of elevation and the effects of land masses on temperature and rainfall, and we get a complicated global pattern of climate. A schematic view of the earth shows that, complicated though climate may be, many aspects are predictable Figure 4. High solar energy striking near the equator ensures nearly constant high temperatures and high rates of evaporation and plant transpiration.
Warm air rises, cools, and sheds its moisture, creating just the conditions for a tropical rain forest. Contrast the stable temperature but varying rainfall of a site in Panama with the relatively constant precipitation but seasonally changing temperature of a site in New York State. Every location has a rainfall- temperature graph that is typical of a broader region. Figure 4.
Climate patterns affect biome distributions. We can draw upon plant physiology to know that certain plants are distinctive of certain climates, creating the vegetation appearance that we call biomes. Note how well the distribution of biomes plots on the distribution of climates Figure 5. Note also that some climates are impossible, at least on our planet.
High precipitation is not possible at low temperatures -- there is not enough solar energy to power the water cycle, and most water is frozen and thus biologically unavailable throughout the year. The high tundra is as much a desert as is the Sahara.
Figure 5. The distribution of biomes related to temperature and precipitation. Summary Ecosystems are made up of abiotic non-living, environmental and biotic components, and these basic components are important to nearly all types of ecosystems.
Ecosystem Ecology looks at energy transformations and biogeochemical cycling within ecosystems. Energy is continually input into an ecosystem in the form of light energy, and some energy is lost with each transfer to a higher trophic level. Nutrients, on the other hand, are recycled within an ecosystem, and their supply normally limits biological activity.
So, "energy flows, elements cycle". Energy is moved through an ecosystem via a food web, which is made up of interlocking food chains. Energy is first captured by photosynthesis primary production. The amount of primary production determines the amount of energy available to higher trophic levels. The study of how chemical elements cycle through an ecosystem is termed biogeochemistry.
A biogeochemical cycle can be expressed as a set of stores pools and transfers, and can be studied using the concepts of "stoichiometry", "mass balance", and "residence time". Ecosystem function is controlled mainly by two processes, "top-down" and "bottom-up" controls. A biome is a major vegetation type extending over a large area. Biome distributions are determined largely by temperature and precipitation patterns on the Earth's surface. Review and Self Test Review of main terms and concepts in this lecture.
In this way, its biotic components are organisms and their species, predators, parasites, and competitors. On the contrary, the concentration of nutrients, the temperature, sunlight, turbulence, salinity and density are its abiotic components. Show how useful this article has been. Gig Economy — What Is It?
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The biosphere benefits from this food web. The remains of dead plants and animals release nutrient s into the soil and ocean. These nutrients are re- absorb ed by growing plants.
This exchange of food and energy makes the biosphere a self-supporting and self-regulating system. The biosphere is sometimes thought of as one large ecosystem —a complex community of living and nonliving things function ing as a single unit. More often, however, the biosphere is described as having many ecosystems. Biosphere Reserves People play an important part in maintaining the flow of energy in the biosphere.
Sometimes, however, people disrupt the flow. For example, in the atmosphere, oxygen levels decrease and carbon dioxide levels increase when people clear forest s or burn fossil fuel s such as coal and oil. Oil spill s and industrial wastes threaten life in the hydrosphere. The future of the biosphere will depend on how people interact with other living things within the zone of life.
A network of biosphere reserves exists to establish a working, balanced relationship between people and the natural world. Currently, there are biosphere reserve s all over the world. The first biosphere reserve was established in Yangambi, Democratic Republic of Congo. Yangambi, in the fertile Congo River Basin, has 32, species of trees and such endemic species as forest elephants and red river hogs.
The biosphere reserve at Yangambi supports activities such as sustainable agriculture , hunting, and mining. One of the newest biosphere reserves is in Yayu, Ethiopia. The area is developed for agriculture. Crop s such as honey, timber, and fruit are regularly cultivate d. This shrub is the source of coffee. Yayu has the largest source of wild Coffea arabica in the world.
Biosphere 2 In , a team of eight scientists moved into a huge, self-contained research facility called Biosphere 2 in Oracle, Arizona. Inside an enormous, greenhouse-like structure, Biosphere 2 created five distinct biomes and a working agricultural facility.
Scientists planned to live in Biosphere 2 with little contact with the outside world. The experiments carried out in Biosphere 2 were designed to study the relationship between living things and their environmentand to see whether humans might be able to live in space one day.
The mission was supposed to last years, with two teams of scientists spending 50 years each in the facility. It is now accepted that most of these purported cases of succession in the fossil record were really replacement sequences consisting of the remains of different local or regional ecosystems, paced by environmental fluctuations often caused by large-scale climatic and geologic processes Miller It is an odd fact that ecology and evolutionary biology developed as essentially separate fields during most of the twentieth century.
Other than the notion of adaptation a term used in many ways, both as verb and noun—process and product , evolutionary theorists had little of substance to say about the connections between the economic ecologic and genealogic evolutionary realms of life. The most important property of life was the reproduction of fertile offspring, as well as the perfection and spread of such reproductive systems. Ecology was seen as mostly the backdrop to these most essential processes. Although a reunion of evolutionary biology and neoecology has been heralded in recent articles and books reviewed in Johnson and Stinchcombe , the most dramatic breakthroughs seem to be coming from reevaluation of the fossil record from a hierarchical perspective.
The difference in perspective between neo- and paleoecology needs to be worked out, both here and with respect to other observations and conceptual issues.
What we seem to be seeing in the fossil record, however, is a pattern of stability not associated with communities or local ecosystems but, rather, involving large, inclusive regional ecosystems.
At this higher level of organization, we must look for novel processes that maintain composition and organization over times spans in the order of hundreds-of-thousands to millions of years Miller —opening nothing less than a new frontier for ecologic theory. Elisabeth Vrba , , was the first to draw attention to these events, referring to them as turnover pulses. Eldredge , has built on this theme with his sloshing bucket model of evolution. In his broad view of evolutionary theory, the larger the environmental jolt, the bigger the evolutionary reaction, an inherently hierarchical approach.
Small disturbances produce little in the way of phenotypic evolution, and global-scale mass extinctions are very rare—albeit associated with some of the grandest evolutionary transformations in the history of life on Earth. In his thinking, nothing much happens in terms of adaptive evolution until the regional systems get into trouble—a connection between ecologic and evolutionary systems I call macroevolutionary consonance Miller In other words, most of the species-level evolution during the Phanerozoic Eon i.
This is an extremely interesting idea that needs more empirical work, but it would never have been conceived in the first place without the kind of hierarchical perspective I have described. I think these developments clearly demonstrate that evolution does not simply take place on an ecologic stage; evolutionary and ecologic processes are interconnected and interwoven at varied scales, often take place concurrently and in coordination, and simultaneously propel and constrain one another in ways we have barely imagined when it comes to turnovers, extinctions, and appearance of new species Miller Species-lineage extinctions and speciation events during a turnover pulse; invasions and abandonments would also occur.
The varied patterns include: A extinction of an abundant, ecologically dominant species; B extinction of a moderately abundant species; C rare species originating from an abundant ancestor; D an abundant species that undergoes a reduction in abundance, but subsequently recovers; E formerly abundant species reduced to rarity; F a rare species that persists through the turnover pulse; G a rare species that becomes abundant and ecologically dominant in the subsequent regime; H an abundant species derived from a rare ancestral species; I a rare species that vanishes early in the turnover pulse; and J a rare species yielding many descendant species based on Miller , Fig.
The sloshing bucket model of evolution. A represents the frequency of disturbances of different intensities and geographic scope through time, N ; B represents the accumulation of adaptive speciation during the Phanerozoic, S.
The ecologic structure of turnover pulses. What actually produces hierarchical organization in the first place? Nested dynamic systems are a real feature of life on Earth, but what produces this ubiquitous pattern of nestedness?
The genealogic hierarchy can be viewed as the simple by-product of living systems making more of themselves and spreading to different geographic localities. The ecologic hierarchy arises from interacting aggregates of organisms occurring in more than one setting having at least slightly different resources, opportunities, and hazards.
Fundamentally, hierarchies of living organisms and organism aggregates seem to be essentially about packing the maximum amount of complexity into the same container or package. There are principles of thermodynamics involving large, complex systems at work here that need elucidating. Salthe , reviewed some of these issues. But hierarchies actually deal with complexity by teasing it apart; it is as if hierarchies are more honest in their simple recognition that a system is complex than is an approach that seeks unity in characterizing the system in simple terms—such as in description of evolution provided by later versions of the synthesis.
The alert reader will have detected a vein of scientific realism running through all this Blackburn : not only does owning up to hierarchical organization of biologic systems enrich and extend my ability to generalize about how life works, I can also take that fateful stroll across a flood plain as I pretended to do earlier in this essay and personally encounter patent examples of these nested systems and experience at least some of their basic properties.
We know what the possibilities are: the question becomes, how can we use this more inclusive view of life to expand and improve ecologic and evolutionary theory, to make instruction in evolutionary biology more comprehensive and realistic, and to forge new and mutually enriching connections to related disciplines?
Hierarchy theory: a vision, vocabulary, and epistemology. New York: Columbia University Press; Google Scholar. Toward a unified ecology. Hierarchy: perspectives for ecological complexity. Chicago: University of Chicago Press; Blackburn S.
Truth: a guide. Oxford: Oxford University Press; Brown JH. Darwin C. On the origin of species. Facsimile of 1st ed. Harvard: Harvard University Press; Quaternary ecology: a paleoecological perspective.
London: Chapman and Hall; Eldredge N. Unfinished synthesis: biological hierarchies and modern evolutionary thought.
New York: Oxford University Press; Macroevolutionary dynamics: species, niches, and adaptive peaks. New York: McGraw-Hill; Hierarchy and macroevolution. Palaeobiology: a synthesis.
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