27.1: What is an Ecosystem?
An ecosystem is the interaction between all abiotic and biotic factors in an environment and can be classified as terrestrial or aquatic. Terrestrial ecosystems are categorized based on the climate, including annual temperature, rainfall, and seasonality. Aquatic ecosystems are separated further into freshwater and marine, and then by depth, which influences water temperature and the amount of sunlight that penetrates the water.
Terrestrial ecosystems are classified into biomes, characterized by both the climate of the environment and the types of organisms that live there. Areas near the Earth’s equator that exhibit high, aseasonal temperatures and high quantities of annual rainfall are rainforests and house some of the most diverse habitats in the world. Ecosystems with high temperatures but deficient annual rainfall are deserts. Although desert ecosystems share these characteristics, their biodiversity can vary vastly.
On the other side of the spectrum, the ecosystem with very low annual temperatures and low annual rainfall is the arctic biome. This ecosystem has the lowest biodiversity. Between these three major biomes are the seasonal tundra, temperate grassland and savanna ecosystems. These ecosystems exhibit oscillatory annual changes in both temperature and rainfall and harbor animals and plants specifically adapted to those seasonal changes.
Aquatic ecosystems are further divided into two categories: freshwater and marine environments. Freshwater ecosystems—the rarest of the ecosystems composing around 2% of the Earth’s surface—include lakes, rivers, streams, and wetlands. The major factors that influence the biodiversity within these ecosystems are the water flow, temperature, and depth.
The shallow area near the edges of ponds and lakes is called the littoral zone. The littoral zone is the warmest area of the water body and includes many aquatic producers, consumers, and animals that have both terrestrial and aquatic lifestyles. The limnetic zone, or the deep-water surface, is well lit and is dominated by plankton. The profundal zone, or deep water, mostly consists of organisms that eat dead organisms and do not photosynthesize since little light penetrates the depth.
In streams and rivers, water flows quickly, recycling oxygen and also keeping the water relatively cool. Species diversity is related to the width and depth of the river, with larger sections of the river being more diverse than the narrower sections. Finally, wetlands are areas of shallow standing water like marshes, swamps, and bogs, and are characterized by often hot and moist environments. These ecosystems have the highest biodiversity of all of the freshwater ecosystems including a variety of plant, animal, fungi and bacterial life.
Marine ecosystems—the most common composing almost 75% of the Earth’s surface—are different from freshwater ecosystems due to the high salinity of the water. They are also separated based on water depth: shallow ocean, deep ocean water, and deep ocean surface. The most diverse of these ecosystems is shallow water, which hosts most of the world’s coral reefs and associated marine life. In addition to shallow-ocean, the deep ocean surface also hosts a variety of marine life—due to the amount of sunlight that penetrates—including plankton, which performs around 40% of all the photosynthesis on Earth.
Due to the minimal amounts of light that penetrates the depths of the water, the deep ocean ecosystem contains a less diverse but often unusual set of organisms adapted to the darkness and high pressures. This ecosystem is also the least known of all of the ecosystems due to the vast amount of space it covers. However, scientists are now able to explore this frontier due to new technologies such as the human occupied vehicle Alvin. Currently, this vehicle has allowed researchers to access 2/3 of the ocean floor up to 4,500 m deep.
Regardless of the characteristics of the specific ecosystem, all share the same dynamic processes of energy and matter transformation through photosynthesis and feeding relationships among organisms. Ecosystems are powered by a constant influx of solar energy that flows through the ecosystem while the matter is recycled.