Humans and the Environment

Earth is objectively speaking, the best planet.

We’ve got oceans filled with things that look like this, and this, and also this, towering

forests full of things that literally eat light and air, clouds, rainbows, clouds that

look like rainbows, adorable sloths, funky look

ing caterpillars, and a universe of invisible

tiny things that can do everyt

hing from make food to power the cycle of nitrogen on this

here hunk of rock.

This beautiful, weird, corner of the universe has everything a person could need - and that’s

because of the environment.

What is the environment?

Well, it’s everything.

And we humans depend on it for our literal existence.

So don’t you think you should learn a little more about it?

In this series of lessons on environmental science Miriam and I are going to explore

all the ways humans interact with and rely on the environment.

Welcome to the Essentials of Environmental Science!

Environmental science is an interdisciplinary scientific approach to studying the Earth’s

natural systems, human impacts on those systems, and potential solutions to environmental problems.

People who work in the field of environmental science draw on aspects of biology, chemistry,

economics, politics, human geography, urban planning, the list goes on, in their study

of the natural world.

The scope of environmental science has steadily broadened over the last 100 years: starting

from anthopocentrism - a human-centered worldview which has its roots in the European societies

from which most modern scientific practices descend.

Then into biocentrism - which ascribes value to human and non-human life, and finally into

ecocentrism - which values the well-being of entire ecosystems including all the living

and nonliving elements.

These three terms: anthropocentrism, biocentrism, and ecocentrism, describe standards of environmental

ethics.

Depending on a culture’s - or a scientist’s - worldview, the environmental ethic will

influence what questions are asked and what value we put on the answers.

Today’s environmental problems, from water pollution to endangered species to climate

change, require us to look for answers through the broadest lens: the ecocentric ethic.

Humans have had a huge impact on our natural world, especially since the Industrial Revolution.

One 2011 article put it this way: “for better or for worse, the earth system now functions

in ways unpredictable without understanding how human systems function and how they interact

with and control earth system processes.”

To truly understand environmental systems and human impact, it is important to not simply

study an organism, like an endangered species, or a pollution source, like an oil spill,

in isolation.

Instead, we should try to understand natural or human-caused disruptions to the environment

from an ecocentric approach–looking at the bigger systems at play.

If you learn one thing from watching our series on environmental science, make it this: We

humans benefit from the environment, but we are also part of it.

That means our actions can and do affect Earth systems, so a lot of environmental science

focuses on how to protect, preserve, and restore the systems human activity degrades.

One way scientists do this is by constructing models to represent natural systems and all

of their interconnected factors.

Models are powerful scientific tools with the ability to both explain and predict.

A model could be code on a computer that recreates the physical processes of the earth’s climate,

but it can also be a chart or graphic that represents the carbon cycle.

Here’s a model of the planet’s hydrologic cycle.

Environmental science helps us to understand how all the living and nonliving components

are interrelated.

Rain falls, runs into surface waters or down into the groundwater.

Or, the water can be taken up by plants for photosynthesis.

This model represents all these actions with squiggly lines and rain drops.

However, like any scientific model, it’s not perfect.

It cannot possibly represent everything going on at any one time.

The only thing that can do that is the earth itself.

But even though we can’t run global-scale experiments, a model does allow us to predict

what would happen if something in the system changed.

For example, if humans clear-cut a forest, this model would predict that there will be

less evapotranspiration from the trees into the atmosphere.

We could then expect to measure less water vapor in the atmosphere around that location.

So, models help us to understand, one, a system, two, how natural and human disturbances occur,

and three how, where, or when to measure those changes.

It is through this process that environmental science can analyze and address environmental

problems.

Now - I know I just said that you don’t want to look at a single organism exclusively,

but it is probably easier to start thinking about how biotic, or living, and abiotic,

or non-living, components fit into a system, by beginning with one example.

Let’s use a single white-tailed deer, a member of the species Odocoileus virginianus

to define some terms and look at how an ecosystem works.

Biologists define species in a number of ways, but one common definition of species is a

group of organisms that can successfully reproduce with each other.

A group of individuals of that species of deer living in a particular area is called

a population.

But this population of deer isn’t alone in an empty void.

They’re hanging out, at the same time and the same place, with lots of other populations

– like pine trees, fungi, squirrels, or bats.

Together, an ecological community is a group of populations living in one area at a particular

time, interacting with one another.

If you add in all the abiotic components, like the air, rocks, water, and even something

like the temperature, then you’ve got an ecosystem.

When studying a single species, like a white-tailed deer or an African elephant, nothing works

in isolation; therefore, we can’t study anything in isolation, so researchers need

to consider all the abiotic and biotic components of that species and its ecosystem together.

Think about it: Organisms in a tropical rainforest have adapted to different conditions than

those in a savannah, or a tundra, a desert, or in temperate grasslands.

We call these different broad regions of the planet, defined by their patterns of rainfall

and temperature, biomes.

Latitude - the distance north or south from the equator - can be a useful tool in determining

where certain biomes exist.

It is no surprise that the hot, humid conditions all along the equator created tropical rainforest

biomes around the world.

At higher latitudes, the cooler parts of the world, you’re more likely to find biomes

like tundra or the boreal forest.

This graph, created by ecologist Robert Whittaker, represents the different major terrestrial

biomes.

The y-axis is average precipitation and the x-axis is average temperature.

Whittaker’s graph works because terrestrial biomes are mainly defined by their temperature

and precipitation patterns, however, this doesn’t tell us much about the wide variety

of aquatic ecosystems that exist in oceans, rivers, lakes, swamps, coral reefs, and marshes.

Aquatic ecosystems are defined by things like salinity, water flow, and depth.

This all kind of feels like a bunch of definitions, but they are important to understand, because

everything from prehistoric to modern life as we know it was constructed in and around

these natural systems.

We humans benefit immensely from all aspects of the natural world.

We depend on earth’s systems for clean air to breathe, clean water to drink, and fertile

soil in which to grow crops.

We also place aesthetic and cultural value onto our natural resources through poetry,

songs, and paintings dedicated to and inspired by nature.

All together, this practically endless list of benefits that the natural world provides

are called ecosystem services.

Here’s an example to get your head around ecosystem services: the oceans are full of

fish, which is a huge benefit for millions of people around the world.

But, that isn’t the only service the ocean provides, it absorbs lots of carbon dioxide

from the atmosphere, helping to regulate the entire planet’s climate.

And a huge portion of the oxygen we breathe comes from photosynthetic marine plankton.

The ocean also serves as a highway system for transporting goods from country to country

on cargo ships, and we even harness the energy of waves and tides to generate electricity.

Biodiversity, in all its forms, is an area that especially demands protection.

There are three main types of biodiversity: 1) genetic diversity

within a population, 2) species richness - species diversity within an ecosystem, and 3) ecosystem

diversity in an area.

A population with large genetic diversity has greater potential to adapt to environmental

changes.

High species richness makes an ecosystem more stable, and better able to recover from disturbances.

And an area with a rich diversity of habitats and ecosystems can support a more robust and

stable community of organisms.

So biodiversity overall helps an ecosystem be more resistant and resilient in the face

of environmental changes, whether they’re natural hazards or human impacts.

An ecosystem with high biodiversity is like a giant, well-spun spider’s web: lots and

lots of interconnected points.

If the web has a little rip in one area, it can probably still function, because it is

supported and held together by hundreds of other strands woven together.

But if the web is only made of two or three strands, then the same small rip could collapse

the entire web.

Within that ecosystem web, species constantly interact with each other and those relationships

have shaped those species evolution.

And some of the most important evolutionary relationships are predator/prey relationships:

Who’s eating who.

Food webs and trophic pyramids are both scientific models which represent how predators and their

prey interact within an ecosystem, but they emphasize different things.

The arrows in a food web map the flow of energy and nutrients within the system, which in

general goes from plants, to primary consumers, to secondary consumers.

On the other hand, the pyramid helps to quantify how energy moves between different trophic

levels – from producers all the way up to apex predators – and emphasizes why there

are proportionally fewer species as you move up the pyramid.

In other words, why there’s always more mice than eagles, and why it takes so much

grass to make a cow.

Another important ecosystem relationship is competition.

Limited resources, like food or nesting sites, can cause competition.

This can be within species - intraspecific competition - or between different species

- interspecific competition.

Elephants and giraffes may experience interspecific competition for water in an arid climate.

Two trees of the same species can experience intraspecific competition for sunlight needed

for photosynthesis.

These competitive pressures for limited resources are strong driving forces for natural selection,

and individuals with the adaptations to get more resources tend to survive better.

A final major way in which different species interact is symbiosis.

Generally symbiosis is broken into three categories: one, parasitism in which one species benefits

and the other is harmed, like a tapeworm in a dog’s intestine.

Two, mutualism.

In a mutualistic relationship both species benefit, like bees pollinating flowers.

And three, commensalism, where one species benefits and the other isn’t necessarily

affected.

Whales don’t really care about the barnacles on their skin, but the barnacles rely on the

whales for a lot.

All these types of interactions–predator/prey, competition, symbiosis–influence how a population

grows.

Here’s a model representing the growth of a population of squirrels in a city park.

If we look at how that population changes over time, we see that it experiences lots

of growth early on, when a pair of squirrels first discover this amazing new park, but

then eventually the population reaches its carrying capacity.

Carrying capacity, which is normally written as an uppercase K, is the maximum number of

organisms (of one species) that an area can sustain.

In our city park here, the carrying capacity is about 65 squirrels, but if we head underground,

the carrying capacity for earthworms is probably in the millions.

Food, space, and the threat of predation help to define a population’s carrying capacity.

And because squirrels and earthworms require different resources - that’s why they have

such different carrying capacities.

On the flipside from population growth or upper limits, when the numbers of a particular

species are low enough that it might become extinct, we consider that species endangered.

Some qualities make certain species more at risk than others of becoming endangered or

extinct.

Like size: large organisms with big home ranges and habitat needs like elephants or grizzly

bears are at greater risk; or specialization: super specialized organisms with specific

dietary needs or habitat requirements like pandas and koalas are also at greater risk.

And reproduction rates: organisms who reproduce slowly and require many years of parental

care, like blue whales or a mountain gorilla, they’re at greater risk too.

Contrast those species with something like a… cockroach, which reproduces early and

prolifically and are more generalists than specialists when it comes to diet and habitat.

Being able to quickly reproduce is an evolutionary advantage that maximizes the chance that a

random genetic mutation will help an individual survive a disturbance.

An African Elephant, with its much slower reproduction rate and specialized habitat,

does not have that evolutionary capacity for change on a rapid scale.

So some species need more protection than others - how do we do that?

In the United States, we have the Endangered Species Act, which protects not only the species,

but also its habitat.

This is crucial because without its habitat, that species cannot exist in nature.

Hopefully, by now I’ve done my job and showed why it is so important to protect species,

habitats, and biodiversity.

But - what are we protecting biodiversity from?

[beat] Us.

The main anthropogenic, or human, threats to biodiversity can be summarized by the acronym

HIPPCO: Habitat Destruction, Invasive Species, Population Growth, Pollution, Climate Change,

and Overexploitation.

Starting with Habitat loss: Simply put, if an organism loses its habitat, it cannot survive.

Related to habitat loss is the concept of habitat fragmentation.

Let’s say that this snake requires this much area for its habitat.

But then people show up and build a road here, a few houses there, a mall over here.

There’s still some patches of our snake friend’s natural habitat, but they’re

separated from each other.

This separation reduces the ability of individual organisms to reach each other and will reduce

the genetic diversity of the population.

When considering habitat loss and fragmentation, we also need to think about scale.

Human land use affects different organisms in different ways.

Consider the differences in home ranges between a small anole lizard - maybe no more

than 100 square meters - and a grizzly bear, which requires up to 1600 square kilometers

of territory.

Next: Invasive species - species that are not native to an area but end up there nonetheless

-often because of people - are another huge threat to biodiversity.

Burmese Pythons in the Everglades, lionfish in coral reefs (both of which are a result

of humans releasing their pets), or even kudzu vines in the southeastern US, an imported

plant “pet” that escaped gardens, are all invasive species.

Because they usually don’t have natural predators in their new environments, populations

of invasive species can explode and outcompete native species.

The presence of lionfish can reduce the number of smaller fish on a coral reef by almost

80%.

On to Pollution, which is both a visible and invisible threat to biodiversity.

You can see an oil spill actively harming wildlife and damaging habitats.

But a lot of pollution isn’t quite as obvious: like, sulfur or lead in the air or pharmaceuticals

or other toxins in the water.

One of the greatest sources of pollution right now is the use of fossil fuels; when burned,

oil, gas, and coal release tons of air pollutants AND dangerous greenhouse gases that lead to

climate change.

Climate change is the focus of this entire channel - and it’ll get its own episode

in this series.

But, I want to point out right now that global warming and climate change are affecting more

than human lives.

Rising temperatures, more acidic oceans, and the many other impacts of climate are also

affecting wildlife biodiversity in a big way.

Coral reefs are bleaching at an increasing rate as warmer ocean temperatures cause tiny

coral animals to expel the symbiotic algae that provide them with a majority of their

food.

And after a bleaching event - if the algae don’t come back, the coral will die.

Finally, using living natural resources at a faster rate than they can reproduce is overexploitation.

Catching fish quicker than they can make baby fish collapses fisheries - and the related

fishing industry that relies on them.

Killing elephants for their ivory will decimate a population quicker than it can repopulate.

When environmental science can identify overexploitation, laws, policies, and international treaties

can come in to help regulate our consumption of these resources and protect biodiversity.

So as you can see environmental science is a large and diverse field of study that encompasses

many different scientific disciplines at various scales from the microscopic to the macroscopic.

Which is pretty fitting, because the environment itself is this thing that is everywhere.

And while one of the main lessons you should take from these videos is that humans are

not separate from these natural systems, we are in a unique position to study them for

two main reasons: one, we rely on ecosystems and the numerous types of services they provide

in order to support our own populations and civilizations.

And two, as the species with the most influence, and as far as we know the most intelligence

on Earth, we are also in a unique position to study and preserve these ecosystems for

the benefit of all species.

The rest of this playlist will be a tour through various ecosystems, looking at the services

they provide, and how human and other living populations interact with all of this.

Thanks for watching, and we’ll see you in the next one.