Front and center in the news today is the fact that climate change and various human activities are posing a hazard to the health of major ecosystems across our planet, threatening the survival of life on our planet as we know it.  But what makes a healthy ecosystem, and what does it mean for life when ecosystems undergo major changes, such as deforestation in rainforests caused by industry or a sudden decline of coral reefs due to the rise in ocean temperatures?  How far does the damage reach?  To understand these catastrophic events, we must take a step back and first consider ecosystems in more theoretical, less extreme terms.

Any ecosystem is healthiest and most stable when a diverse population of species lives there in specific proportions.  In general, an ecosystem has reached a healthy, biodiverse balance when it contains many species; no single species can dominate over the rest and monopolize access to resources like food, water, and shelter.  In such an ecosystem, competition for resources is in a sort of equilibrium, and all species can exist in relative harmony with one another because every species has access to enough the resources it needs to support a stable population of individuals.  

Healthy ecosystems are (somewhat) resistant to damage

A healthy, biodiverse ecosystem is generally well-equipped to weather unexpected changes because the species living in it can tolerate a diverse set of conditions.  But why does diversity make an ecosystem more stable, you ask?

Imagine, if you will, the following footwear situation:  currently the human race wears many different kinds of footwear, so if a factory closes down and one type of shoe disappears from store shelves, it’s not a big deal; anyone who preferred wearing that style of shoe just finds a similar brand and moves on with life.  In contrast, if everyone in the world only wore a single kind of shoe and the only factory that made those shoes closed down, everyone would suddenly find themselves barefooted and in a panic.

It’s an absurd example, to be sure, but the principle holds true in the natural world: in a biodiverse ecosystem, the distribution of needs (shoe preferences) are so varied that even if a species can’t get exactly what it needs through standard channels (their favorite shoe store), resources (different shoe styles) are equally varied and generally never exhausted, and so the ecosystem as a whole can usually still find a way to adapt and survive.  On the other hand, in an ecosystem with low biodiversity, most organisms depend heavily on a small number of resources to survive (a single style of shoe), and if one of those resources suddenly becomes unavailable, it will affect a larger proportion of the population, threatening the entire ecosystem.

Tipping the balance of a healthy ecosystem

Ultimately, however, no matter how biodiverse an ecosystem is, drastic changes, such as a fire, flooding, or the introduction of an invasive species with no natural predators, can still tip the balance and send the ecosystem into chaos.  No matter how healthy an ecosystem is, it can be upended when the demand for resources changes, or when a major consumer or producer in that ecosystem gets taken out of the equation. Consider a scenario close to home: imagine a healthy North American forest with many different kinds of plants and animals living in it.  Predators and prey depend on one another for food, and all the organisms in the forest make space for themselves to stay safe, grow, and prosper. In this forest, specifically, coyotes eat deer so that the deer population never gets too big. With fewer deer around, everyone’s happy because there’s plenty of vegetation in the forest for all of the deer and other animals to eat.  

coyote walking forest biodiversity ecosystemBut what if, for example, a parasite infects the coyote population?  What if a drought prevents coyotes from producing as many young, or, for some other reason, coyote numbers dwindle?  Without natural predators, the deer population will outgrow its resources and will consume virtually all of the vegetation in the forest.  At this point, the ecosystem is out of balance, because there isn’t enough food for such a large population of deer, let alone the rest of the animals in the forest.  

The deer, as well as the other plant-eating species, will begin to starve, and some species may even die out in that area (reducing local biodiversity).  Furthermore, if various plant-eaters disappear, their other predators lose a food source, and they start to die out, too. Other veggie-eaters start to flourish, and eventually, their populations become unsustainably large.  

At the same time, decaying organic material from the dead animals may attract bacteria and scavenger populations, which break down tissues to recycle the nutrients contained within them; but at the same time, this material may also attract disease.  

Every change in the ecosystem comes with specific costs and benefits, and every time one element of the ecosystem changes, it produces a ripple effect throughout the entire ecosystem, affecting seemingly unrelated components of the environment, just like dominoes.

Only if the deer population returns to a sustainable level, perhaps by the coyote population recovering to keep the deer population in check, can the ecosystem recover its balance.  But it is equally possible that the deer population will never return to normal, and some species that disappeared after the deer population exploded may never return to the area without help from humans.

Biodiversity in vulnerable ecosystems

Palmyra Atoll, NOAA photo by Erin Looney.

Palmyra Atoll, NOAA photo by Erin Looney.

In the end, seemingly small changes in an ecosystem can wreak large-scale havoc in ways so numerous that they almost seem incomprehensible.  A temperature change of a degree or two may kill a fundamental species of coral, and the logging of one tree species may leave animals without food or shelter.  Man-made waste generates overwhelming danger for all species, but also may also offer new sources of food and shelter. These specific changes may seem isolated enough until we consider that once these initial changes happen, the dominoes will continue to fall.  Who’s to say what new balance will be struck, and what that new ecological landscape will look like? Losses of a species or resource always leave an ecosystem less biodiverse and more fragile than it was before.

This principle is at the root of the devastation we see in our oceans and rainforests, which are some of the most established, biodiverse ecosystems on our planet.  Small changes have accumulated to trigger a cascade of increasing ecological imbalance, and it is unlikely, at this point, that any human intervention can help these ecosystems fully recover to regain the degree of biodiversity they had decades, even centuries ago. Although that doesn’t mean we shouldn’t still do everything we can to help!  

Loss of these ecosystems as we know them sounds terrible, but most of us don’t live in the oceans or the rainforests – these places have nothing to do with us and can’t affect us…right?  Not so! We are all connected – in the same way that a local increase in the deer population had a vast effect on the wellbeing of an entire theoretical forest, the rapid decrease in biodiversity that we’re seeing in oceans and rainforests, will eventually cause ecological changes that reach us as they start to affect the entire planet.  It is a bleak outlook, unfortunately, and one without any certain outcome. All we can do now is be conscientious of the effects our small actions have on larger ecosystems, try to restore what we can, and hope that in time Earth’s most precious ecosystems can recover from the damage that we have caused.

Every little bit helps and you CAN make a difference! Follow the links below for some suggestions on ways you can help restore Earth’s delicate ecological balance:  

WikiHow is always the first place I look when I need advice on how to do anything.  And as it turns out, they have a great article on simple ways that you can conserve energy and resources (in ways that will often help you save money, too!)

Learn about people who have gone zero waste and be inspired by them! Going zero waste is not nearly as impossible as it may seem, but even if you don’t want to go zero waste yourself, follow this link to learn more about how to be a conscientious consumer, recycle effectively, and reduce the waste you produce at the holidays, parties, and weddings. 

Kate Proudfoot is a post-doctoral scholar at the University of Chicago, where she received her Ph.D. in cell and molecular biology. Kate is also an organizer for Expanding Your Horizons Chicago, a one-day symposium aimed at engaging middle school girls in science.


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Total Solar Eclipse on April 8, 2024

Total Solar Eclipse on April 8, 2024

On April 8th, 2024, a total solar eclipse will sweep across North America, from Mexico to the Maine-Canadian border. For those who experienced the spectacular solar eclipse of 2017, this one will be similar, crossing the United States from west to east and passing through or near several major metropolitan areas. And while its path is quite different this time, Carbondale, Illinois, a reasonable destination for Chicago-area residents, will once again be on the line of totality.    

Just a little background on eclipses:  Lunar and solar eclipses are not uncommon – they each occur about twice a year when the moon is crossing the ecliptic, the path of the sun in the sky.

Two women representing the Illinois Science Council at an event.

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