Living things interact with each other and with nonliving factors in
ecosystems. Abiotic factors are the nonliving parts of an ecosystem. The
Sun influences climate, another abiotic factor. Climate is the pattern
of weather that occurs in an area over many years.
Most life on Earth depends on energy from the Sun, an important abiotic factor. Green plants use energy from the Sun to make food. Other animals eat those green plants. Still other animals eat those animals. The Sun’s energy also controls many other abiotic factors in the environment. Temperature is one of the abiotic factors that affects plant growth. Plants grow best in regions that are moderate, not too cold and not too hot. Plants also grow well when the temperature does not change greatly. This means that daily and seasonal temperatures are consistent. Because there are more plants, regions with constant warm temperatures support the greatest numbers of living things. Water is another important abiotic factor to almost all life on Earth. Water helps organisms absorb nutrients and is important in ridding organisms of wastes. More organisms can survive in places with plenty of water.
Soil contain different minerals, such as limestone or quartz. These minerals affect the chemistry of the soil, such as the acidity or alkalinity. Plants do not grow well if the soil is too acidic or too alkaline. Farmers and gardeners also measure the concentrations of important plant nutrients, including nitrogen, phosphorus, and potassium.
Like the Sun, air is also an important abiotic factor. Humans and many other organisms can only survive in places where the air contains enough oxygen. Many organisms use oxygen to help their cells release energy. Most organisms that use oxygen can only survive for five minutes without it before cells begin to die. At higher elevations, the mountain air contains less oxygen. Mountain climbers carry oxygen tanks to help them breathe. Some organisms can use less oxygen than can others. The air in a particular ecosystem determines the organisms that will live there.
Biotic factors are the living parts of an ecosystem. Every organism in an ecosystem depends on other organisms. Plants and animals in an ecosystem compete with others for food or living space. Some benefit each other by providing food, a place to live, or a way to hide from enemies. Each species plays a different role. Together they are the biotic factors of the ecosystem.
In ecosystems, the population of an organism refers to all the individuals of that species that live in a given location. For example, a scientist might study the population of condors in California or great white sharks in the Pacific Ocean. In a smaller ecosystem, a scientist could study the population of frogs in a pond. A community is all the populations of species that occupy an area. In nature, populations expand until the biotic or abiotic factors become limiting. A limiting factor is an environmental factor that limits how large a population can grow. If populations get too large, competition for resources, such as food and water, will cause some individuals to die.
Limiting factors can change over time. For example, in ecosystems that normally have plenty of rain, water can become a limiting factor during a drought. Different factors limit different species. Sun-loving plants do not grow well in the shade or in dense forests. But mushrooms and forest wildflowers will grow well in the shade.
Hawks, snakes, and many other organisms make up California’s coastal scrub community. These communities have many shrubs and few trees. They are accustomed to hot, dry summers and mild, wet winters. During summer, many shrubs lose their leaves to conserve water. Animals living in this community must adjust to great differences between summer and winter water supplies. All living things need water, but some need more water than others. Organisms that live in sandy deserts are adapted to a life that has little water during much of the year.
An adaptation is any physical or behavioral characteristic that allows an organism to be better suited to the environment. Cactus have waxy coverings to prevent water loss from evaporation. Another way organisms survive in deserts is by staying inactive during the hot, dry summers. During the brief wet periods, wildflowers bloom, and animals gather food before the dry weather forces them to become inactive again. Some animals have the ability to cool themselves. Animals living in harsh climates use shelter to protect themselves from abiotic factors. In deserts and polar regions, for example, frogs dig burrows to avoid the heat or cold.
All organisms need space in which to live and grow. In a garden or a forest, plants will grow best if they do not have to compete with other plants. Animals also need space. Some animals defend their territories in order to protect enough land to meet their needs for food, water, and shelter.
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