What's the Most "Animal" Animal? Crash Course Zoology #2

Summary

In this episode of Crash Course Zoology, host Rae Wynn-Grant explores the diversity of the animal kingdom, aiming to identify the 'most animal' animal. With an estimated 1.5 million known species and more to be discovered, the video discusses various zoological techniques to estimate global species richness. It highlights the significance of the phylum Arthropoda, particularly beetles within the order Coleoptera, as the most common type of animal. The script also touches on the potential for future discoveries to redefine our understanding of the 'mode animal'.

Takeaways

• 🌐 There are approximately 1.5 million known animal species, but many more remain undiscovered.
• 🧐 Zoologists study animal diversity to understand the life of most animals and the variations among them.
• 📊 The 'mean' animal concept is impractical due to the impossibility of averaging physical features across species.
• 🔍 The 'median' animal is challenging to identify due to uncertainties in the divergence timeline of animal groups.
• 🐛 The 'mode' animal, or the most common type, is a more feasible approach to represent the average animal.
• 🌿 Terry Erwin's study in 1982 estimated 30 million species of tropical arthropods using the diversity ratio technique.
• 🌱 The global species richness is estimated to be between 8 to 10 million species, based on various scientific methods.
• 🦋 Arthropods, particularly insects, are the most diverse and numerous animal group, making them strong candidates for the 'mode' animal.
• 🌎 Macroecological patterns and the species-area relationship help zoologists estimate global species richness.
• 🧬 DNA barcoding is a modern technique used to identify species and contribute to the understanding of global species richness.
• 🐞 Beetles, as part of the phylum Arthropoda, are considered the 'mode' animal due to their vast number of species and diverse habitats.

Q & A

What is the significance of finding the 'most animal' animal in zoology?

Finding the 'most animal' animal helps zoologists understand the common traits and behaviors of most animals. By identifying a species that best represents the majority of metazoans, researchers can make sense of the vast diversity in the animal kingdom and gain insights into how most animals live.

Why wouldn't calculating the average number of legs or eyes help in identifying the 'most animal' animal?

Averaging out features like the number of legs or eyes would result in unrealistic animals, like those with three legs. This method doesn't accurately represent how real animals live or function, making it unhelpful for understanding common animal traits.

What is the mode animal, and why is it important?

The mode animal represents the most common type of animal in terms of species numbers and characteristics. Studying the mode animal is important because it offers insights into the life and traits of the most prevalent animals, helping zoologists understand the majority of animal species.

How did Terry Erwin estimate the number of arthropod species in the tropics?

Terry Erwin used a diversity ratio technique by counting beetle species in a hectare of tropical forest. He calculated how many were host-specific and then extrapolated these numbers to estimate the total number of arthropods in the tropics, concluding there were 30 million species.

Why has Erwin's estimate of 30 million tropical arthropod species been recalculated over time?

Erwin's estimate has been recalculated because not all forests have the same number of tree species, and not all trees host the same number of unique beetle species. Improvements in methodologies, such as DNA barcoding and macroecological patterns, have refined these numbers over time.

How does DNA barcoding help zoologists estimate species richness?

DNA barcoding allows zoologists to compare genetic material across species, which can help identify unknown species or reveal that what was thought to be one species is actually two or more. This method provides a more precise way to estimate global species richness.

What is the phylum Arthropoda, and why is it considered highly successful?

Phylum Arthropoda includes over 1.1 million species, making it one of the most diverse and successful groups in the animal kingdom. Its members, such as insects, crustaceans, and spiders, have adapted to various habitats, allowing them to thrive across different environments.

What characteristics define beetles as the 'most animal' animal?

Beetles, as part of the largest group of arthropods, have six legs, three body segments, compound eyes, antennae, and a hard exoskeleton. They are highly adaptable, found in various habitats, and have evolved to fill many ecological niches, making them representative of the 'most animal' animal.

Why are chordates not considered the 'most animal' animal despite their popularity?

Chordates, which include fishes, mammals, and birds, are popular and well-known, but they only make up about 0.03% of all animals. In contrast, arthropods, particularly insects, are far more numerous and diverse, making them a better representation of the majority of animals.

Why might beetles not always remain the 'most animal' animal?

As zoologists continue discovering more species and exploring groups like nematodes and parasitic wasps, beetles may eventually be unseated as the 'most animal' animal. The discovery of more species could change our understanding of the most common traits in the animal kingdom.

Outlines

00:00

🌍 Introduction to Zoology and Animal Diversity

The introduction sets the stage by emphasizing the incredible variety of animal species that have evolved over millions of years. Rae Wynn-Grant introduces the concept of diversity in animals, from how they move, reproduce, and feed, to their overall interactions with the environment. We currently know of about 1.5 million animal species, but many more are yet to be discovered. The script then transitions to defining the 'most common' or 'mode' animal in the animal kingdom and what it means for zoologists to explore this diversity.

05:02

🔍 Estimating Animal Species Richness

This section delves into the techniques used by zoologists to estimate species diversity on Earth. It discusses Terry Erwin’s 1982 study, where he calculated the diversity of tropical arthropods, particularly beetles. By using a diversity ratio technique, Erwin estimated that there were around 30 million arthropod species in the tropics alone, with beetles making up a large portion. The script explains how zoologists can make these complex calculations by studying small samples and extrapolating them to estimate global species numbers.

10:07

📊 Improvements in Species Estimates

Following Erwin’s initial calculations, zoologists have refined these estimates using macroecological patterns and DNA barcoding. They have determined that not all forests or species groups are the same, and diversity varies across habitats. As of 2021, scientists have identified 1.5 million species and estimate a global species richness of 8 to 10 million animals. New technologies and discoveries will continue to change these estimates. The script also begins exploring the idea of the 'mode' animal and the common traits that define the average animal in the Metazoa group.

🐞 The Mode Animal: Introducing Arthropods and Beetles

This section identifies arthropods as the most successful and diverse phylum in the animal kingdom, with over 1.1 million species. The focus narrows down to insects, specifically beetles, which represent a quarter of all known animals. These insects share traits like six legs, compound eyes, and a hard exoskeleton. The Coleoptera order (beetles) is highlighted for its immense diversity, with beetles thriving in nearly every habitat on Earth. This part emphasizes the importance of understanding common traits to identify the ‘mode’ animal.

🌱 Beetles: Thriving in Every Habitat

The last section celebrates beetles as the quintessential 'mode' animal, thriving in diverse habitats and filling numerous ecological roles. From eating various local foods to adapting to different environments, beetles have evolved to fill countless niches. The conclusion notes that while beetles are currently the dominant 'mode' animal, this could change as zoologists study other species, such as nematodes and parasitic wasps. The script ends by mentioning how future discoveries could shift our understanding of which animal best represents the diversity of life.

🎓 Closing Thoughts and Sponsor Information

In the conclusion, the script transitions to a sponsorship message for Great Courses Plus, encouraging viewers to explore educational content beyond zoology, such as a recommended botany course. It promotes The Great Courses Plus as a resource for expanding knowledge on a variety of topics and highlights its subscription model. The episode credits follow, thanking the production team and inviting viewers to support Crash Course through Patreon.

Keywords

💡Metazoa

Metazoa refers to the subkingdom of multicellular animals in the kingdom Animalia. In the video, Rae Wynn-Grant discusses Metazoa as the animal kingdom, emphasizing the diversity of species that have evolved from the first animal ancestor. The term is used to illustrate the vast array of life forms that exist within the animal kingdom, from simple organisms to complex mammals.

💡Species Richness

Species richness is a measure of the number of different species present in a particular ecosystem or area. The script mentions that zoologists estimate global species richness to be between 8 to 10 million species, highlighting the immense biodiversity on Earth. This concept is crucial to understanding the scale of animal life and the challenge of cataloging and studying it.

💡Diversity Ratio

A diversity ratio is a method used by zoologists to estimate the number of species in a particular group relative to another. The script uses the example of Terry Erwin's study, where he calculated the number of beetle species compared to tree species to estimate the total number of tropical arthropod species. This technique helps to understand the abundance and distribution of different species.

💡Macroecological Patterns

Macroecological patterns refer to large-scale ecological patterns that describe the distribution and abundance of species across the globe. The video mentions that more species live in the tropics than at the poles, which is an example of a macroecological pattern. Understanding these patterns helps scientists predict where new species might be found and how biodiversity is distributed.

💡Phylum

A phylum is a level of classification in the biological taxonomy, ranking below the kingdom and above the class. The script discusses phyla as large groups of animals that share key characteristics and evolutionary history. Phyla are important for understanding the evolutionary relationships and diversity within the animal kingdom, such as Arthropoda, which includes insects, crustaceans, and spiders.

💡Chordates

Chordates are a phylum of animals that includes mammals, birds, reptiles, amphibians, and fish. They are characterized by having a notochord at some stage of their life cycle. The script points out that there are 65,000 species of chordates, making them a significant but relatively small part of the overall animal kingdom. This term is used to illustrate the prevalence of non-chordate species.

💡Arthropoda

Arthropoda is the largest phylum in the animal kingdom, including insects, arachnids, crustaceans, and others. The script highlights that arthropods are the most diverse and numerous group of animals, with over 1.1 million species. This phylum is considered the 'rockstars' of evolution, showcasing the adaptability and success of arthropods in various environments.

💡Coleoptera

Coleoptera is an order within the class Insecta, commonly known as beetles. The script identifies beetles as the largest order within the insect class, with over 386,000 species. The discussion of Coleoptera in the video emphasizes the diversity and ubiquity of beetles, making them a strong candidate for the 'most animal' animal.

💡DNA Barcoding

DNA barcoding is a molecular technique used to identify species by comparing a short segment of DNA. The script mentions that zoologists use DNA barcoding to estimate species richness and to differentiate between species that might have been previously classified as a single species. This method is a modern approach to understanding biodiversity and species identification.

💡Ecological Niche

An ecological niche is the specific role or position that a species occupies in its environment, including its habitat, food sources, and behavior. The script discusses how beetles have evolved to fill a variety of specialized niches in different habitats. Understanding ecological niches is essential for grasping how species coexist and interact within ecosystems.

Highlights

Introduction to Crash Course Zoology by Rae Wynn-Grant, exploring animal diversity and evolution.

In 2021, there are about 1.5 million known animal species, but there are many more left to discover.

Zoologists use various statistical methods like mean, median, and mode to identify the most common traits in animals.

One method to estimate global species richness is calculating diversity ratios, such as comparing the number of beetle species to tree species.

In 1982, entomologist Terry Erwin estimated there were 30 million species of tropical arthropods, primarily based on beetle species.

Erwin’s estimation method involved analyzing host-specific beetles on trees in the Panamanian forest, leading to over 12,000 species of beetles in a single hectare of forest.

Zoologists today also use techniques like DNA barcoding to estimate species richness and identify unknown species.

The current estimate of global animal species richness ranges between 8 to 10 million species.

Beetles, belonging to the phylum Arthropoda, are the most common group of animals, with over 386,000 species.

The most common animal in the world today is likely a beetle, specifically from the Coleoptera order.

Arthropods dominate the animal kingdom with over 1.1 million species, making them the most successful evolutionary group.

Arthropods have key features like jointed limbs and hard exoskeletons, allowing them to thrive in diverse environments.

Zoologists classify animals using binomial nomenclature and phyla, grouping animals based on evolutionary history and body plans.

While beetles are currently the most common, nematodes or parasitic wasps could become more prominent as we discover more species.

The video promotes The Great Courses Plus, offering a library of lectures from top university professors, including a course on Plant Science.

Transcripts

Thanks to Great Courses Plus for Supporting PBS.

There are animals who can swim, walk, burrow, or fly.

There are plant-eaters and animal-eaters, and...everything-eaters!

Animals that spawn eggs, win their mates in fierce contests, or partner for life.

From that first animal ancestor evolved a staggering variety of species over hundreds

of millions of years.

Today in 2021 we know of about 1.5 million different animals out there, but there are

still so many to discover. 

Before we dive into the wild diversity of how animals function, behave, and interact

with each other and their environment, let's start with understanding just one.

The animal that best represents all of Metazoa, the animal kingdom. 

I’m Rae Wynn-Grant, and this is Crash Course Zoology.

INTRO

Zoologists want to know what’s an average animal and what’s a rare animal because

it helps us understand what the life of most animals is like and make sense of all the

wild variations out there.

Now before we pick the “most animal” animal, we have to decide how we’re going to judge.

In statistics we talk about the mean, median, and mode as ways to decide on the average

of something, and...I think we can try something similar with animals. 

Maybe to find the “mean” animal we try to average out the features of all the animals.

Like add up the number of legs and eyes and divide by the number of animals we included.

But then we’d end up with something that doesn't match reality at all, like an animal

with a body plan for 3 legs.

And that wouldn’t tell us anything about how real animals live. 

Or, we could try to find the median animal by ordering them from the first to diverge

from other animals to latest.

Then, we could pick one that diverged in the middle.

But that’s also hard to do because we don’t know exactly when every animal group diverged.

So the easiest move that will still give us insight into how most metazoans live seems

to be figuring out the “mode” or most common type of animal. 

First, we need to figure out how many different species, or different types of animals, there

are.

In fact, generations of zoologists have tried to calculate the total number of species on

Earth, or the global species richness.

One technique calculates a diversity ratio, or how abundant one group of species is compared

to another.

Like how many beetles there are compared to types of trees. 

Counting all the species in an area would be exhausting and probably would take forever.

So instead zoologists make really accurate counts of a group of species that they know

well, and assume that information is representative of all the animals in the area. 

In 1982, an entomologist, or a zoologist who focuses on insects, named Terry Erwin from

what’s now the Smithsonian National Museum of Natural History used the diversity ratio

technique to estimate that there were 30 million species…of just tropical arthropods.

So 30 million species of insects, crustaceans, arachnids...but mostly beetles.

Let’s go to the Thought Bubble.

Trudging through the Panamanian forest, Erwin smoked out his quarry from the canopy with

the aid of a backpack insecticide cannon.

Which doesn’t sound great for the beetles, but the reality of studying animals is that,

sometimes, you also study dead animals and it’s often up to the zoologist to decide

what she’s ok with, though there are some regulations.

After meticulously examining each arthropod back in his US lab, Erwin estimated over 1,200

beetle species lived in each tree that he sampled from.

Then he did the math. 

Erwin estimated 13.5% of beetles would be host-specific.

This meant about 162 of the original 1,200 species of beetle would only live on the type

of tree he sampled. 

A hectare of tropical forest can have 40 to 100 species of tree, so Erwin decided his

hypothetical hectare would have 70 species on average. 

That would mean there would be 11,410 host-specific beetles, plus the remaining 1,038 beetle species

that are willing to live in any old tree.

Altogether that’s over 12,448 species of beetles in a single hectare of forest! 

Since 40% of arthropods are beetles, Erwin then estimated there would be 31,120 species

of arthropods per hectare.

He bumped that up by a third to account for species on the forest floor that avoided his

pesticide fog to get 41,389 total arthropods. 

This was just one hectare of one forest, but Erwin then extrapolated his formula to include

other tropical forests.

Which is how Erwin concluded there were 30 million species of arthropods in the tropics

alone!

Whoo.

Thanks, Thought Bubble.

And since the 1980s, Erwin’s estimate has been recalculated to make various improvements.

Like not all forest communities are the same -- not all trees host 162 unique species,

and not all forests have 70 types of tree. 

Aside from diversity ratios, zoologists also use global trends in where species tend to

live called macroecological patterns to estimate global species richness.

Like that more species live in the tropics than at the poles. 

We can also explore the species-area relationship to calculate the global species richness.

Like larger areas have more species because there are more unique ecological roles to

fill. 

And geographical features like mountains, rivers, or oceans can also affect species

numbers by isolating populations from each other.

More recently, zoologists are turning to a new technique called DNA barcoding to make

their estimates of species richness.

Comparing bits of DNA can identify unknown animals or even check if what zoologists think

is one species isn’t actually two or three.

So using all our different methods from diversity ratios and macroecological patterns to DNA

barcoding, in 2021 we’ve counted 1.5 million animal species, and estimate that the global

species richness is 8 to 10 million.

And those numbers will change with new information and techniques. 

Next, to decide on the “most animal” animal, we have to look across all these millions

and millions of animals and figure out which traits are rare and which are common.

Like being able to fly sounds so cool, but flight is actually pretty common. 

To keep track of all the different traits, remember we use binomial nomenclature and

break animals up into a similarity hierarchy starting by grouping animals of the same type

together as a species. 

At the very top of the hierarchy is the entire animal kingdom, but just below that zoologists

collect species in large groups, called phyla or phylum if we’re just talking about one

group, based on their evolutionary history and their body plan. 

A phylum is like a genre of animals -- they share some key characteristics, but each lineage

within a phylum is a little bit different. 

Our mode animal probably belongs to the most successful phylum -- which for us means the

phylum that’s made it all the way to the top of the Billboard Top 40(-ish) of Evolution

and has lots of different species with a wide variety of traits.

Diverse phyla are like the mainstream hits: they’re unlikely to go extinct because they

have so many species spread across different habitats and niches.

And phyla with just a few species are the hidden indie gems -- much less successful,

and much more vulnerable to getting wiped out. 

The Top phyla aren’t who you’d think! 

Like so far we know there are 65,000 species of Chordates, or animals with a flexible rod

to support their body called a notochord, which includes fishes, amphibians, mammals,

reptiles, and birds.  

That sounds like a lot, but remember the global species richness is between 8 and 10 million.

So they’re the pop music of the animal kingdom -- super famous and popular, but only about 

0.03% of all animals. 

And there are 35-ish different phyla, so despite what we might see and hear, most other animals

are… well… non-chordates! 

Phylum Arthropoda includes over 1.1 million different species, making them the true rockstars

of evolution.

Named for their jointed limbs, arthropods have a segmented body covered in a hard exoskeleton

and include insects along with crustaceans, milli- and centi-pedes, horseshoe crabs, spiders,

scorpions, and other chelicerates. 

So to narrow it down and get into what our mode animal looks like, eats, and where it

lives, let’s live a day in the life of the “most animal” animal! 

Allow me to introduce you to the humble, uh, "mode animal." 

As insects are the biggest group of arthropods, our mode animal moves through life on six

legs with three body segments, compound eyes, antennae, and a hard exoskeleton.

That still just paints a vague insect-shaped picture, 

so the biggest Order within Class Insecta is Coleoptera, the beetles.

Beetles diverged a very long time ago, with the earliest fossils being 300 million years

old, so they’ve had a lot of time to split off into over 386,000 estimated species, representing

about one fourth of all known animals.

But all these beetle cousins share a few key body parts, so our mode animal definitely

has front wings that form a protective shell. 

To find our average friend, one need only lift up the nearest rock or sift through the

sand as beetles can live almost anywhere.

With every new habitat comes a slew of specialized niches that beetles have evolved to fill. 


And with so many different habitats, beetles have grown to eat all sorts of things- 

so there’s lots of local delicacies out there to help lots of young larvae store up

energy.

Our mode animal will be an average joe in a wildly diverse family photo, like a carpet

beetle squeezed in between a weighty Titan beetle and a cheery ladybug.

But today, our friend is special because it's so average.

Have a great day little beetle!

But just because beetles are popular now doesn't mean they always will be!

As zoologists pay more attention to things like nematodes and parasitic wasps, maybe

one of them will unseat the beetle as the mode animal as we discover more and more species

and revise our estimates.  

Next time we’ll continue exploring what it means to be an animal and how they’ve

evolved into so many different shapes and sizes. 

Thanks to Great Courses Plus for Supporting PBS. 

The Great Courses Plus is a subscription on-demand video learning service with lectures and courses

from professors from top universities and institutions.

Through your subscription, you get access to a library of lectures about anything that

interests you...science, math, history, literature, or even how to cook, play chess, or become

a better photographer. 

One new course I recommend to help round out your knowledge of the biosphere is Plant Science:

An introduction to Botany hosted by Dr. Catherine Kleier.

In this course you’ll learn how plants are different (but sometimes still surprisingly

similar) to animals, you’ll learn about what came first - pollen or the pollinator

- and the story of how animals and flowers coevolved, and you’ll even explore a day

(and year) in the lives of plants! 

To learn more, click on the link in the description below to start your trial today.

Thanks for watching this episode of Crash Course Zoology which was produced by Complexly

in partnership with PBS and NATURE.

It is shot on the Team Sandoval Pierce stage at Porchlight Studios in Santa Barbara, California

and made with the help of all these nice people.

If you’d like to help keep Crash Course free for everyone, forever, you can join our

community on Patreon.