Organisms and their habitats form complex systems.
KEY CONCEPT 8.1
Ecologists identify a nesting organization of life from individuals to the biosphere, often focusing on the levels of population, community, and ecosystem to examine how species respond to and affect the natural world.
The field of ecology focuses on how species interact with other components in their environment. In other words, it is about relationships. These relationships can be examined at different levels. The term biosphere refers to the total area on Earth where living things are found—the sum total of all its ecosystems. An ecosystem includes all the organisms in a given area plus the nonliving components of the physical environment in which they interact. In the natural world, ecosystems assume a range of shapes and sizes—a single, simple tide pool qualifies as an ecosystem; so does the entire Mojave Desert.
species
A group of plants or animals that have a high degree of similarity and can generally only interbreed among themselves.
biosphere
The sum total of all of Earth’s ecosystems.
ecosystem
All of the organisms in a given area plus the physical environment in which, and with which, they interact.
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But having the entire biosphere (or even a large ecosystem) as the focus of study is usually too expansive to manage, so ecologists study how ecosystems function by focusing on species’ interactions with their physical surroundings (their habitat) and with other species in their community. They also study interactions between individuals of the same species within a population. These relationships define the unique ecological niche of each individual species. INFOGRAPHIC 8.1 and INFOGRAPHIC 8.2
habitat
The physical environment in which individuals of a particular species can be found.
community
All the populations (plants, animals, and other species) living and interacting in an area.
population
All the individuals of a species that live in the same geographic area and are able to interact and interbreed.
niche
The role a species plays in its community, including how it gets its energy and nutrients, what habitat requirements it has, and what other species and parts of the ecosystem it interacts with.
ORGANIZATION OF LIFE: FROM BIOSPHERE TO INDIVIDUAL
Ecologists recognize a nesting hierarchy of organization from the biosphere down to the individual organism. Each category is made up of the smaller ones. Ecologists often focus their study on populations, communities, and ecosystems and the interactions between organisms and their surroundings. In contrast, a zoologist or botanist might focus on individual animals or plants.
You are studying a pocket mouse that lives in an underground burrow where it stores seeds. Make a list of biotic and abiotic things that might be important to its survival.
Abiotic factors: heat, cold, rainfall, good soil for digging a burrow. Biotic factors: predators, competitors of the same and different species, types of plants & seeds, abundance of plants & seeds, organisms such as ants that might steal the seeds that were collected, or molds that would damage the seeds.
HABITAT AND NICHE
Species depend on suitable habitats in which to live. Species fill a specific niche in their community.
Why do ecologists usually study populations rather than entire species? When might they focus on an entire species?
It is difficult to study an entire species if it has populations that live in many areas. These different populations may themselves be different from each other and are not “interchangeable” in the way they interact with their environment or their needs. An ecologist might study an entire species if that species is limited in its distribution (perhaps it is endangered or highly specialized and only lives in one place) and accessible for study as an intact unit.
All ecosystems function through two fundamental processes that are collectively referred to as ecosystem processes: nutrient cycling and energy flow. Nutrient cycles are biogeochemical cycles that refer specifically to the movement of life’s essential chemicals or nutrients through an ecosystem. Energy, on the other hand, enters ecosystems as solar radiation and is passed along from organism to organism, some released as heat, until there is no more usable energy left. Therefore, we can say that matter cycles but energy flows in a one-way trip.
energy flow
The one-way passage of energy through an ecosystem.
nutrient cycles
Movement of life’s essential chemicals or nutrients through an ecosystem.
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KEY CONCEPT 8.2
All life on Earth depends on a constant input of new energy because once it is used, energy is degraded and no longer useful to organisms. New inputs of matter to Earth, however, are negligible, so life also depends on the constant cycling of matter resources.
Earth—or “Biosphere 1,” as the creators of Biosphere 2 liked to call it—is materially closed but energetically open. In other words, the plants and other organic material that make up an ecosystem, called biomass, cannot enter or leave the system, but energy can: Some energy leaves as heat or light, and new energy is absorbed from outside. In fact, plant biomass is produced with energy from the Sun through photosynthesis. INFOGRAPHIC 8.3
EARTH IS A CLOSED SYSTEM FOR MATTER BUT NOT FOR ENERGY
Energy can enter and leave Earth as light (solar radiation) and heat (terrestrial radiation), but matter stays in the biosphere, cycling in and out of organisms (biomass) and environmental components.
Why is it so important that species recycle matter and that they depend on a source of energy that is readily replenished (renewable)?
No new matter enters the biosphere (not in useful amounts anyway) so we must use and reuse what is here - we don't get new supplies. Energy, however, cannot be recycled - once used the remainder is dissipated as heat and no longer in a form that can be captured and used. Therefore, we always need new, fresh inputs of energy such as that supplied daily by the sun.
KEY CONCEPT 8.3
The biome that is present in a given area is influenced by the physical and climatic characteristics of its environment, particularly precipitation amount and temperature for terrestrial biomes.
Biomes are specific portions of the biosphere determined by climate and identified by the predominant vegetation and organisms adapted to live there. Biomes can be divided into three broad categories—terrestrial, marine, and freshwater. Within those three categories are several narrower groups, and within those are a variety of subgroups. An entire biome itself may be considered an ecosystem, as are the smaller groups and subgroups. For example, forests, deserts, and grasslands are the three main types of terrestrial biomes. Within the forest biome category are different types of forests, such as tropical, temperate, and boreal forests, and within each of those groups are subgroups (for example, dry tropical forest and tropical rain forest). INFOGRAPHIC 8.4
biome
One of many distinctive types of ecosystems determined by climate and identified by the predominant vegetation and organisms that have adapted to live there.
GLOBAL TERRESTRIAL BIOMES
What biome do you live in? Identify an area on another continent where you could travel and visit that same biome.
Answers will vary.
Which biome exists across the widest range of temperatures? Precipitation?
temp = desert; precip = temperate forest
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When ecologists study entire ecosystems, they are limited to making observations and trying to discern cause and effect from those observations. This is no small challenge; precise measurement of each and every relevant ecological factor is simply not possible, and even the simplest factor (for example, a change in rainfall, the loss of a single species, variations in solar radiation reaching the ground) can impact many of the other factors and affect the ecosystem as a whole. But this doesn’t mean we can’t gain insights from ecosystem-scale studies. Scientists measure important parameters of natural ecosystems to gather evidence to try to discern cause and effect; they often compare those that are affected by natural disasters or human impact to less disturbed ecosystems in a kind of “natural experiment.” From this, ecologists make their best estimations of how multiple factors affect each another (often via mathematical modeling). The more parameters that are properly measured and linked to one another, the better, but because all parameters and relationships cannot possibly be included, there may be a lot of room for interpretation when it comes to understanding what is happing at the ecosystem level.
Biosphere 2 offered ecologists an unprecedented research tool: a mini-planet where a variety of environmental variables—from temperature and water availability to the relative proportions of oxygen and carbon dioxide (CO2) at any given moment—could be tightly controlled and precisely measured. “Manipulating these variables and tracking the outcomes could greatly advance our understanding of natural ecosystems and all the minute, complex interactions that make them work,” says Kevin Griffin, a Columbia University plant ecologist who conducted research at the Biosphere 2 facility. “The plan was to use that knowledge to figure out how to repair degraded ecosystems in the real world, so that they continue to provide the services so essential to our survival.”
On top of all that, proving that humans could survive in a completely enclosed, manufactured system would take us one giant step closer to colonizing space.
But would it work?
The concept of enclosed ecosystems was not a new one. Since before they put a person on the Moon, astronauts and engineers had been tinkering with their own artificial ecosystems—systems they hoped could one day be used to colonize space. The earliest versions of this technology were developed in the 1960s and 1970s by Russian and American scientists who, in the spirit of their times, had pitted themselves against one another in a mad dash to the finish line. The ecosystems they designed ranged from small, crude structures in which a single person might last a single day, to larger, more sophisticated enterprises that could sustain a few people for a few months.
Biosphere 2 is by far the most elaborate. At just over 1 hectare (3 acres or about 2 football fields in diameter), it remains the largest enclosed ecosystem ever created and the only one to house several biomes under one roof. From a mountain under the dome’s 28-meter (91-foot) zenith, a stream rushes down through a tropical rain forest before snaking southward into a savanna. From there, the stream wends its way through a mangrove swamp into a million-gallon ocean, complete with a coral reef. On the other side of the ocean lies a desert. Biosphere 2 also includes a human habitat and an agricultural biome. INFOGRAPHIC 8.5
MAP OF BIOSPHERE 2
Biosphere 2 houses several biomes under one roof, each contributing to overall function. One of the challenges faced by designers was how to include a variety of biomes in the close quarters of the 3-acre Biosphere 2 structure. For example, in nature, a tropical rain forest would not be next to an arid desert. To deal with this, an ocean was placed between the desert and rain forest to serve as a temperature buffer.
Why was it important for the desert and rain forest biome sections of Biosphere 2 to be separated by another biome such as the ocean?
If they were side by side, the conditions at the edge of each would not be suitable for the species living in each. Separated by the ocean (which can help moderate temperature swings), each biome is more isolated and not likely to strongly influence the other.