Ecology

Ecology is the study of how living things, like plants, animals, and humans, interact with each other and with their surroundings. The word comes from an ancient Greek word for "house" and the study of things. Ecologists look at organisms as single individuals, groups, communities, ecosystems, and the whole living world, or biosphere.

This science overlaps with other areas like the study of where animals and plants live, how they change over time, their genes, their behavior, and the natural world in general. Ecology helps us understand how many animals and plants there are, how much they weigh, and where they live. It also looks at how they change to fit their environment, how they work together, and how energy and materials move through communities of living things.

Ecology began with a group of American plant scientists in the 1890s. It has practical uses in protecting nature, managing wet areas, taking care of natural resources, and understanding how humans fit into ecosystems. Ecosystems are systems where living things and their non-living surroundings constantly interact. They help control the Earth's climate, clean water, build soil, and protect against floods, among many other important functions.

Levels, scope, and scale of organization

Ecosystems can be very small or very large. A single tree might not seem important in a whole forest, but it is very important to the small plants and animals that live on or near it. Some tiny insects, called aphids, can live their whole lives on just one leaf, and each aphid can support many different kinds of bacteria.

Ecology looks at groups of living things in different ways. One way is by studying groups of the same kind of living thing, like a group of birds or a group of fish. Another way is by studying whole ecosystems, which are areas where living things and non-living things work together, like a forest or a lake.

Hierarchy

To study ecology, scientists organize living things into groups, like individuals, groups of the same kind of living thing, and even bigger groups that include many different kinds of living things working together. This helps scientists understand how small changes can affect the whole system.

Biodiversity

Biodiversity means the variety of life, from tiny genes to huge ecosystems. It includes the different kinds of plants, animals, and even tiny organisms that live together. Biodiversity helps keep our world healthy and provides things like clean air and water. Scientists study biodiversity to help protect it.

Habitat

A habitat is the place where a plant or animal lives, along with everything in that place that helps it survive.

Niche

An ecological niche is the role a plant or animal plays in its habitat, including what it eats and how it interacts with other living things.

Niche construction

Living things can change their habitats in many ways. For example, beavers build dams that create ponds, changing the environment for many other animals.

Biome

Biomes are large areas with similar climates and plant life, like forests, deserts, and tundras.

Biosphere

The biosphere is all the areas of Earth where life exists, from the top of the mountains to the deepest parts of the oceans.

Population ecology

Population ecology studies groups of the same kind of living thing and how they change over time. Scientists use math to understand how populations grow or shrink.

Metapopulations and migration

Metapopulations are groups of populations that can go extinct in one place and recolonize in another. Migration is when animals move from one place to another and return later.

Community ecology

Community ecology studies how different kinds of living things interact in the same area. Scientists look at how these interactions affect the numbers and types of species in that community.

Ecosystem ecology

Ecosystem ecology looks at how energy and materials move through ecosystems, like forests or lakes. Scientists study how plants, animals, and tiny organisms work together.

Food webs

A food web shows how energy moves from one living thing to another. Plants use sunlight to make food, and animals eat the plants or each other.

Trophic levels

Trophic levels are steps in a food web, showing who eats whom. Plants are at the bottom, and animals that eat other animals are at the top.

Keystone species

A keystone species is one that has a big effect on its ecosystem even if there aren’t many of them. For example, sea otters eat sea urchins, which helps keep kelp forests healthy. If sea otters were gone, the sea urchins could destroy the kelp forests.

Complexity

Main article: Complexity

Complexity means needing a lot of work to put many moving parts together. Nature's patterns, like where animals and plants live, are very complex. This happens because many natural actions work together across different sizes, from small areas to big landscapes. Small patterns don't always tell us about big ones, just like how putting puzzle pieces together can create a picture bigger than any single piece.

Ecology sees six kinds of complexity: space, time, structure, actions, behavior, and shape. Ecologists study how nature organizes itself in new ways at different sizes, from tiny molecules to the whole planet, and each size needs its own explanations.

Holism

Main article: Holism

Holism is very important in ecology. It talks about how life organizes itself into layers of whole systems. These systems work in ways that can't be guessed just by adding up their parts. For example, an entire ecosystem has its own special ways of working that aren't obvious by looking only at the plants, animals, and soil inside it alone. New qualities come from how everything interacts, not from changing the basic nature of each part.

Relation to evolution

Main article: Evolutionary ecology

Ecology and the study of how living things change over time are very connected. Both fields look at how animals and plants live, grow, and pass on traits to their young. They use similar tools to understand life, whether looking at family trees or classifying living things. There isn’t a clear line between ecology and evolution; they just focus on different parts of nature. Ecologists study how the world around us affects how species change, and these changes can happen very quickly — sometimes in just one generation.

Main article: Behavioural ecology

All living things, even plants, show different behaviours. Behavioural ecology looks at how animals and plants act in their world and how these actions help them survive and change over time. For example, we can watch how animals move, find mates, or work together. These behaviours can be passed down, just like hair colour, because they help the group live better and have more babies.

Main article: Social ecology (academic field)

Some animals, like ants, bees, and even some humans, work together in groups. Social ecology studies how these groups live and help each other. Animals in groups often share genes, so helping others can help their own family survive. This is why some animals might risk their own lives to help others — it helps their shared genes live on.

Main article: Coevolution

Animals and plants often help each other live. For example, some ants grow fungi for food, and some bugs live in our bodies and help us digest food. These partnerships help both sides survive. When two different kinds of living things live closely together, it’s called living together in a special way. Many plants live with tiny fungi in their roots, trading food for nutrients.

Main article: Biogeography

Biogeography studies where animals and plants live and how they change in different places. It looks at how moving around or being separated can change groups of animals and plants. For example, when new animals move to an island, they can grow quickly if there isn’t much competition. But as more animals arrive, they must fight for food and space, which changes how they live and grow.

Main article: r/K selection theory

r/K selection theory helps explain how animals change when they have lots of space or when they are crowded. When there’s plenty of space and food, animals can grow fast — this is called r-selection. But when space and food are limited, animals change to survive better in crowded places — this is called K-selection.

Main article: Molecular ecology

Molecular ecology looks at genes to understand how animals and plants change and live together. With new tools, scientists can study genes more easily, helping us learn about how life evolves and works in nature.

Human ecology

Main article: Human ecology

Ecology is a science that looks at how living things, including humans, interact with their world. Human ecology studies how people affect and are affected by their environment. It looks at humans as part of nature, working with plants and animals and changing the land in special ways.

Main article: Restoration ecology

People use ecology to help fix places that have been damaged. This is called restoration ecology. It involves working with nature to repair areas that have been disturbed, helping the land heal through careful planning and care.

Relation to the environment

Main article: Natural environment

The environment of ecosystems includes both physical and living parts. It is always changing and provides what organisms need to live at every stage of their lives. The word "environment" can mean many things, but it generally includes the world around us, both natural and made by humans.

The physical environment is everything outside the living things we study, such as temperature, light, and rocks. The living environment includes other plants, animals, and even tiny cells that share the same home.

Main article: Resilience (ecology)

Disturbances are events that change nature, like fires, floods, or droughts. These events can remove plants and animals from an area. Even though they seem harmful, disturbances are a natural part of ecosystems. Biodiversity, or the variety of life, can help protect ecosystems from these changes.

Main article: Early atmosphere

The Earth formed about 4.5 billion years ago. As it cooled, it developed a crust and oceans. Its early air was mostly hydrogen, but later it changed to methane and ammonia. Over time, living things changed the air to include carbon dioxide, nitrogen, and water vapor. These changes affected how sunlight reached Earth and helped trap heat. Simple life forms changed the air even more, leading to the air we breathe today.

The Earth's air and natural processes have always been balanced with life on Earth. This balance has gone through big changes and then long periods of stability. The earliest life forms helped turn hydrogen into methane. Later, some life forms began using sunlight, which changed the air even more. Over time, the air became filled with oxygen, a big change that happened about 2.4 to 2.3 billion years ago.

Radiation: heat, temperature and light

Life on Earth works best within certain temperature ranges. Heat is a type of energy that helps control temperature. It influences how fast plants and animals grow, how they behave, and how much food they can make. Temperature mostly depends on sunlight. The amount of sunlight and heat in different places affects where plants and animals can live. Heat and temperature are important for how living things use energy. Some animals, like reptiles, depend on the outside temperature to control their body heat. Others, like birds and mammals, can keep their body heat steady no matter the outside temperature. Light from the sun is the main source of energy for Earth’s ecosystems. Plants, algae, and some bacteria use light to make food through a process called photosynthesis. These plants use the energy from light to store energy in their bodies.

Physical environments

Water

Main article: Aquatic ecosystem

Wetlands, areas that are often wet or shallow, are important for many natural processes. They help cycle nutrients and elements around the world.

Diffusion of carbon dioxide and oxygen happens much slower in water than in air. When soil gets flooded, it loses oxygen quickly and can no longer support normal life. Water changes how light looks and behaves as it moves through. Some plants, like those in salty water, have special ways to handle salt and keep their balance.

Fish have special body systems that help them deal with salt levels in different kinds of water. Their gills help them either get rid of extra salt or take in more salt as needed.

Gravity

The shape of land and the way energy moves around is greatly affected by gravity. Gravity helps decide where plants grow and how animals move. It also affects the strength and size of living things. Trees grow branches in certain ways because of gravity, and animals have body systems that work despite gravity’s pull.

Pressure

Weather and water pressure put limits on what kinds of life can live in certain places, especially for animals that fly high or dive deep. These pressures affect how animals and plants can survive. For example, there is less oxygen at high altitudes, making it hard for some animals to live there. Plants also struggle to move water through their bodies when pressure changes. Deep ocean animals, like whales, dolphins, and seals, have special ways to handle the pressure of deep water.

Wind and turbulence

Wind and turbulence in air and water change ecosystems. On a large scale, wind patterns affect whole ecosystems. Wind can change temperature, nutrients, and chemicals in ecosystems. For example, wind over a lake mixes the water and creates layers that affect fish and algae.

Wind speed and turbulence affect how much water plants and animals lose and how they use energy. Wind changes as it moves over different lands and heights. For instance, winds hitting mountains can create dry areas on the other side, affecting which plants and animals can live there.

Fire

Main article: Fire ecology

Forest fires change the land by leaving behind different areas that recover in various ways. Some plants, like certain pine trees, need fire to open their seeds and grow.

Plants take in carbon dioxide and release oxygen. About 350 million years ago, there was enough oxygen in the air to allow fires to happen. Fire releases carbon dioxide and leaves behind ash. Fire is an important part of nature, and managing it is crucial for taking care of forests.

Soils

Main article: Soil ecology

Soil is the top layer of dirt that covers the Earth. It is very important for many parts of nature and farming. When plants and animals die, their remains break down in the soil, providing nutrients for new growth. Many small animals help break down leaves and other plant material, creating food for even smaller organisms. Together, these animals help form and change the soil. Soil contains tiny living things that feed on and are part of the food chain in ecosystems. As these organisms move through the soil, they help air circulate and support growth. Soil microorganisms are important for the balance of nature.

Biogeochemistry and climate

Main article: Biogeochemistry

Ecologists study how nutrients move and are used in nature. This research shows that ecosystems and Earth’s physical features are connected. Six key elements—hydrogen, carbon, nitrogen, oxygen, sulfur, and phosphorus—are the building blocks of all living things and are important for Earth’s natural processes. Even small actions by many living things can have big effects on Earth’s cycles.

History

Main article: History of ecology

Ecology has a rich and complex history. Ancient Greek thinkers like Hippocrates and Aristotle made early notes about nature, but they thought species did not change over time. Later, ideas about how living things interact with each other and their surroundings began to grow.

Important ideas in ecology, such as how food chains work and how populations change, started to form in the 1700s. The word "ecology" was first used in 1866 by Ernst Haeckel. Since then, ecology has become a major science, with many discoveries helping us understand how nature works and how to protect our planet.