Edge effects facts for kids
In ecology, edge effects are changes that happen where two different habitats meet. Think of it like the border between a forest and a field. At this border, the conditions are different from deep inside either the forest or the field. These changes can affect the types of plants and animals that live there.
When habitats are broken up into smaller pieces (this is called habitat fragmentation), there are more edges. This means edge effects become much stronger and can spread throughout the entire area. While some areas with more edges might have a greater variety of species (more biodiversity), it's not always a good thing.
Today, cities are growing, and human activities are constantly breaking up natural landscapes. This increases edge effects. Some species, especially invasive ones that can adapt easily, benefit from these changes. But other species, especially those that need very specific habitats, suffer. For example, in the Lacandon Jungle in Mexico, the number of birds that can't handle edge effects is going down as more edges appear.
Contents
What Are Edge Effects?
Edge effects describe the unique conditions found at the boundaries of different habitats. These boundaries can be natural, like where a forest meets a grassland, or they can be created by humans, like where a farm field meets a forest.
Types of Edges
Edges can be described in different ways:
- Natural Edges: These are stable borders created by natural features, like a coastline where land meets the ocean.
- Changing Edges: These borders are created by natural events like fires or floods, or by human activities. They can change over time.
- Sharp Edges: One habitat ends suddenly and another begins, like a forest stopping abruptly at a farm field.
- Wide Edges (Ecotones): This is a large transition area between two distinct habitats. It's like a blended zone where conditions slowly change from one habitat to the next.
- Wiggly Edges: The border isn't a straight line; it's curvy or uneven.
- Holed Edges: The border has gaps or holes where other small habitats exist within it.
Even differences in height, like a cliff face, can create an edge between different areas.
How Edges Affect Life
The conditions at habitat borders allow certain plants and animals to live there.
Plants at the Edge
Plants that grow at forest edges often need a lot of sunlight. They also tend to be good at handling dry conditions. Examples include shrubs and vines.
Animals at the Edge
Many animals that live at edges need more than one type of habitat to survive. For example, white-tailed deer, elk, cottontail rabbits, and robins often use both the forest and open areas. Some animals travel between habitats, while others are found only at the edges.
Larger habitat areas usually have more native species than smaller ones. The width of the edge also matters. A wider, more gradual edge can create different zones of edge effects, leading to more variety.
When animals create paths along borders, more sunlight can reach the plants there. This helps more plants grow, which means more food for plant-eating insects. This can then lead to more birds nesting, and so on, up the trophic levels (the food chain).
Sometimes, if borders are very wide or overgrown, some species might get stuck on one side, even if they could live on the other. Edge effects can also sometimes harm the original ecosystem by changing natural conditions.
Negative Impacts of Edges
Edge effects can also cause problems. For example, fertilizer from a farm field might wash into a nearby forest, polluting the habitat.
The main ways edges affect an area are:
- Environmental Changes: Conditions like temperature, light, and moisture change near an edge.
- Direct Changes to Species: The number and location of species change because of the new physical conditions at the edge.
- Indirect Changes to Species: How species interact changes. This can include more predation (animals hunting each other), brood parasitism (like birds laying eggs in other birds' nests), competition for resources, and changes in how plants are pollinated or how seeds are spread.
Human Impact on Edges
Human activities like building cities and farming create many new edges. Often, these changes are bad for both the size of habitats and the species living there.
Some problems caused by human-made edges include:
- New invasive species or non-native plants and animals being introduced.
- More frequent and severe fires.
- Pets acting as predators or competing with wild animals.
- Trails and roads cutting through habitats.
- Pollution and erosion.
- Loss of places for animals to find food.
- Breaking up habitats into smaller pieces (Habitat fragmentation).
- Deforestation (cutting down forests) and changing how land is used.
Examples of Edge Effects
When a natural area borders a disturbed or unnatural area, the natural ecosystem can be seriously affected far into its interior.
In 1971, a scientist named Odum noted that there are often more songbirds in places like estates or college campuses than in large, uniform forests. This is because these places have many edges where different habitats meet.
Amazon Rainforest
One study found that the area of the Amazon Basin affected by edge effects was actually larger than the area that had been completely cleared. In the Amazon, changes in micro-climate (small-scale weather) were seen up to 100 meters (330 feet) into the forest from an edge.
Smaller forest pieces are more likely to catch fire from nearby farm fields. Forest fires are more common near edges because more light gets in, which dries out the plants. This dry plant material acts as fuel, allowing fires to spread into the forest. More fires since the 1990s are slowly changing the Amazon forests. The changes in temperature, humidity, and light also help non-forest species, including invasive ones, move in. All these changes mean that forest fragments tend to lose their native biodiversity, depending on their size, shape, and how isolated they are.
North America
There are far more forest edges in the United States now than when Europeans first settled North America. Some species have actually benefited from this. For example, the brown-headed cowbird is a brood parasite. It lays its eggs in the nests of songbirds that live near forest edges. Poison ivy is another plant that thrives in edge habitats.
On the other hand, dragonflies eat mosquitoes, but they have more trouble surviving near human settlements than mosquitoes do. So, trails and hiking areas near towns often have more mosquitoes than deep forest habitats. Plants like grasses, huckleberries, flowering currants, and trees like the Douglas-fir (which need a lot of light) all do well in edge habitats.
When developed land is next to wild land, problems with invasive exotic species often occur. Plants like kudzu, Japanese honeysuckle, and multiflora rose have harmed natural ecosystems. However, the open spots and edges also provide places for species that like more light and low-growing plants. Deer and elk especially benefit from edges because their main diet is grass and shrubs, which are common in these areas.
Edges and How Habitats Change
Edge effects also play a role in ecological succession. This is the process where plant communities change over time. Different species are suited to either the edges or the central parts of a habitat, leading to a varied distribution. Edges also vary depending on which way they face. For example, an edge facing north or south will get different amounts of sun, leading to different plant patterns.
Images for kids
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Edges are where two or more habitat types meet, like this area in Pennsylvania, United States.
See also
- Ecotone
- Habitat fragmentation
- Landscape ecology
- Ruderal species
- Spatial ecology
- Woodland edge
