Changes to Ecosystems

Have you ever gone on an extended holiday, only to come back and find your neighbourhood is not quite as you left it? It may have been something as small as some trimmed bushes, or perhaps some old neighbours moved out and some new neighbours moved in. In any case, something changed.

We might think of ecosystems as something constant – the Serengeti will always have lions, for example – but in reality, ecosystems are subject to change, just like everything else on this planet. Let's discuss the different changes to ecosystems, and the natural and human causes behind those changes.

Global changes in ecosystems

Ecosystems are communities of living organisms interacting with each other and their physical environment. Those interactions ensure that ecosystems are never static. Different animals and plants constantly compete against each other for access to resources like food and space.

This puts ecosystems in a perpetual state of fluctuation, ultimately leading to evolution by natural selection – that is, the process by which populations of living organisms change over time in order to better adapt to their environment. In other words, ecosystems globally are constantly changing!

Factors affecting ecosystems

Any ecosystem has two distinct factors or components. Abiotic components are non-living, including things like rocks, weather patterns, or bodies of water. Biotic components are living, including trees, mushrooms, and leopards. Living components must adapt to each other and the abiotic components in their environment; this is the fuel for change. Failure to do so spells extinction, meaning the species no longer exists.

But if ecosystems are already constantly changing, what do we mean by the term 'changes to ecosystems'? Well, we are mainly referring to events or processes that interrupt the way an ecosystem is already functioning. These are changes from without, not from within. In some cases, an outside event or activity may entirely destroy an ecosystem.

We can divide changes to ecosystems into two broad categories: natural causes and human causes. Together with evolution by natural selection, natural disasters and human-caused environmental degradation are the main ways any given ecosystem will experience change.

Natural causes of changes in ecosystems

If you've ever seen a fallen tree lying in the road the morning after a thunderstorm, you probably already have some idea of how natural events can cause changes in ecosystems.

But we're going a bit beyond small thunderstorms. A natural disaster is a weather-related event that causes widespread damage to an area. Natural disasters are not caused by humans (though, in some instances, human activity can make them more severe). Other natural causes like disease are not technically natural disasters but can cause similar levels of devastation.

Natural causes of changes in ecosystems include, but are not limited to:

• Wildfire/forest fire

• Flooding

• Drought

• Earthquake

• Volcanic eruption

• Tornado

• Tsunami

• Cyclone

• Disease

Some of these natural events may occur in conjunction with one another.

Natural disasters can fundamentally change an ecosystem. Entire forests can be burned down by a wildfire or uprooted by an earthquake, leading to deforestation. An area can be completely flooded, drowning all of the plants. A disease like rabies can spread through an area, killing large numbers of animals.

Many natural disasters only cause temporary changes to ecosystems. Once the event has passed, the area slowly recovers: trees grow back, animals return, and the original ecosystem is largely restored.

However, natural causes of changes to ecosystems can be permanent. This usually has to do with long-term changes to climate or physical geography. For example, if an area faces drought for too long, it may become more desert-like. Or, if an area remains permanently flooded after a hurricane or tsunami, it may become an aquatic ecosystem. In both cases, the original wildlife will likely never return, and the ecosystem will be forever altered.

Human causes of changes in ecosystems

Human causes of changes to ecosystems are almost always permanent because human activity often results in land-use change. This means that we humans will repurpose land that was once part of a wild ecosystem. We may cut down trees to make way for farmland; we may pave over part of a grassland to create a road. These activities change the way wildlife interact with each other and their environment, as it introduces new, artificial elements to a natural ecosystem. For example, animals that attempt to cross busy roads in search of more food will be at risk of being hit by a car.

If an area becomes urbanized enough, the original natural ecosystem may functionally cease to exist, and any animals and plants that remain in an area will be forced to adapt to human infrastructure. Some animals are quite good at this. In North America, it is not uncommon for squirrels, raccoons, and even coyotes to thrive in urban habitats.

Fig. 1 - A raccoon climbs a tree in an urban area

Besides land-use change, human management can play a role in ecosystems. You can think of human management of ecosystems as intentionally or unintentionally 'tinkering' with the natural function of an ecosystem. Human management includes:

• Pollution from agriculture or industry

• Manipulating pre-existing physical geography

• Hunting, fishing, or poaching

• Introducing new animals to an area (more on this below)

Dams and wind turbines, which we depend on for renewable, sustainable energy, can disrupt the natural swim patterns of fish or flight patterns of birds, respectively. Pesticides or fertilizers from agriculture can wind up in rivers and streams, altering the acidity of water, and in the most egregious cases, causing bizarre mutations or death.

Wildlife population changes in ecosystems

Groups of animals come and go in ecosystems depending on their material needs. This happens annually with many species of birds; they fly south during the winter, temporarily changing the biotic components of an ecosystem.

Fig. 2 - Many birds fly south for the winter, including the species shown on this map

Above, we mentioned introducing new animals to an area as a form of human management of ecosystems. This can be done for a number of reasons:

• Stocking an area for hunting or fishing

• Releasing pets into the wild

• Attempting to correct a pest problem

• Attempting to restore an ecosystem

The human introduction of wildlife to a new ecosystem is not always intentional. In North America, horses and pigs brought over by Europeans escaped into the wild.

We mentioned that, sometimes, humans introduce wildlife into an ecosystem in order to restore that ecosystem, which may have been previously disrupted by human activity or a natural disaster. For example, the United States government reintroduced wolves into Yellowstone National Park after they determined that their absence was having a negative effect on the health of other plants and animals.

In most other cases, this introduced wildlife is usually something we call an invasive species. An invasive species, introduced by humans, is not endemic to an area but adapts to it so well that it often displaces endemic species. Think of the cane toad in Australia or the Burmese python in the Florida Everglades.

Impact of climate change on ecosystems

There's an elephant in the room. No, not an actual elephant! Thus far, we haven't touched much on climate change.

When the Earth was at its warmest, ecosystems could support large dinosaurs like Tyrannosaurus rex. The most recent ice age, which ended 11,500 years ago, included animals like the woolly mammoth and the woolly rhinoceros. None of these animals survived climate change, and would not do very well in most of our modern ecosystems.

Fig. 3 - The woolly mammoth thrived at a time when the Earth was much colder

Our Earth's climate is largely regulated by gases in the atmosphere, including carbon dioxide, methane, and water vapour. Like the glass windows on a greenhouse, these gases capture and retain heat from the sun, warming our planet. This greenhouse effect is perfectly natural, and without it, it would be too cold for any of us to live here.

Today's changing climate is strongly correlated to human activity. Our industry, transportation, and agriculture emit a lot of greenhouse gases, amplifying the greenhouse effect. As a result, our Earth is heating up, an effect sometimes called global warming.

As the Earth continues to warm, we can expect an expansion of tropical and desert ecosystems at the expense of polar, tundra, and temperate ecosystems. Many plants and animals living in polar, tundra, or temperate ecosystems are likely to go extinct as a result of global warming, as they will be unable to adapt to new climactic conditions.

Additionally, natural disasters may become more common, putting virtually all ecosystems at risk. Rising temperatures will enable more droughts, cyclones, and wildfires.