Ecosystems complex, magical webs


We are often reminded of damage we inflict on various ecosystems. Just what are ecosystems?

For a start, "system" implies there are a number of parts that interact. "Eco" specifies living organisms and their environment play a central role.

All living things have unique requirements to thrive and reproduce. This leads to incredible diversity of plants and wildlife. Thankfully, this generates the stunning beauty and fascinating animal behaviors that stir our sense of awe of the living world.

There is a large variety of ecosystems and they come in all sizes. Generally, one is referring to a physical space occupied by organisms of many different kinds. Importantly, the relationships between those organism and the physical resources within that space are relatively stable.

Not to be confused with ecosystem is the concept of a biome. It has broader implications, and focuses primarily on climatic and geographic conditions. Major factors delineating a biome include geographic latitude (arctic, boreal, temperate, sub-tropical and tropical), humidity (humid, semi-humid, semi-arid and arid) and elevation.

The physical environment, including the atmosphere, soil, water and sunlight, plays no small role in an ecosystem. Many aquatic and terrestrial ecosystems have been identified within biomes. Some of the most prominent are deserts, coral reefs, temperate forests, prairies, savannahs, tundra, taiga and a number in costal and deep oceanic waters.

Tropical rainforest ecosystems serve as an example. Though a Brazilian rainforest has different animals and vegetation than a rainforest in Asia, they have many commonalities. These include plants and animals that have very similar roles in their respective forest.

Within their physical space are four characteristic layers: emergent, canopy, understory and forest floor (the soil and low-lying vegetation).

The emergent layer is defined by a sparse distribution of species of very large trees towering above the canopy. These trees are not sheltered from high winds or intense heat from direct sunlight. One finds eagles, bats, butterflies and some monkeys living in these heights.

The canopy is made up of dense tree cover and associated vegetation. Canopies provide homes for the most diverse collection of creatures on Earth, including birds, monkeys and sloths. Some estimate a quarter of the world's insects live here.

Between the canopy and forest floor is the understory. It is home to many birds, snakes, lizards and mammals such as monkeys, jaguars, leopards and deer. Insects are also abundant. Since only about 5 percent of sunlight reaches these depths, seedlings struggle for light and plants have large leaves.

Finally, with roughly 2 percent of sunlight penetrating to the forest floor, vegetation is sparse and must be adapted to low light conditions. Here, under hot, humid conditions, fungi thrive. They contribute to decay of plant and animal matter.

Within each layer, organisms are adapted to the conditions of that layer for their nutritional, shelter and reproductive needs. The space a population of organisms occupies or roams to meet those needs is called its habitat. This can include excursions into and exploitation of resources arising in other layers.

It is the interdependence of the organisms within the entire ecosystem that accounts for many of its distinctive characteristics. Essential are the multiple food webs that circulate both energy and nutrients throughout the system.

Understanding these circulations gives valuable insight into interactions and vulnerabilities of the ecosystem. Every animal and plant depends on other animals and plants for their existence. The web can be so intricate that the loss of one species can disrupt the entire web.

Generally, at the bottom of the food web are plants that generate organic material from photosynthesis. This is the ultimate energy source for most living things. Insects then eat plants and each other.

Additionally, there are organisms that live off the processing of decaying organic matter. This returns vital nutrients to the soil.

Making a living off these organisms are small animals such as fish, birds, frogs, possum, squirrels, chipmunks, voles and bats.

Moving up the web are larger animals such as snakes, owls, monkeys, deer and parrots. Large carnivores such as tigers, jaguars, leopards, crocodiles, alligators, boa constrictors, anacondas, pythons and eagles round out the top of the food web.

Often critical needs include things other than food. Examples include small organisms that live in water pooled in the petals of flowers or leaves. Some fruit-bearing plants require fertilization by birds possessing uniquely shaped bills and tongues.

Should those birds be decimated, the fruit upon which monkeys and bats depend will not be available. Monkeys and bats are food for larger carnivores, and their droppings and remains contribute nutrients to soil for vegetation.

Each organism functions as a node in a vast web. An organism may have more than one source to fill a given need. Consequently, some disruptions of the web are more crucial than others. But, each disruption degrades the overall health of the forest.

Deliberate ecosystem destruction isn't pretty. Rarely do the supposed gains outweigh the losses. Nutrients in rainforest floors must be continuously renewed. Once they are stripped of vegetation they quickly lose their ability to support life.

Areas deforested for agricultural expansions quickly become depleted, erosion-prone wastelands. It is estimated we destroy an acre-and-a-half of rainforest every second. At this rate we will soon learn of our dependence on some of the more extensive global webs of life.

Steve Luckstead is a medical physicist in the radiation oncology department at St. Mary Medical Center. He can be reached at


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