The video explores Botswana's substantial elephant population, emphasizing the species' ecological significance as a keystone player in maintaining biodiversity within their habitat. It delves into the sudden mystery of elephant deaths between 2020 and 2021, drawing concern from ecologists and conservationists due to the unknown causes.

The video demonstrates the role of ecology in understanding environmental interactions, separating ecology from conservation, while explaining the position of elephants in the food chain and ruling out factors like predation or starvation for the mass die-off. It concludes that the elephants were poisoned by neurotoxins produced by cyanobacteria in contaminated watering holes, a phenomenon exacerbated by climate change.

Main takeaways from the video:

Please remember to turn on the CC button to view the subtitles.

Key Vocabularies and Common Phrases:

1. keystone species [ˈkiːstoʊn ˈspiːʃiːz] - (noun) - A species on which other species in an ecosystem largely depend, such that if it were removed the ecosystem would change drastically. - Synonyms: (foundation species, crucial species, pivotal species)

Just ask any of the dung beetles snacking on elephant poop or the giraffe drinking from a watering hole dug by an elephant. Elephants are the life of the party here. Not because of their great dance moves, but because of their importance in the lives of so many other species, qualifying them as what's known as a keystone species.

2. abiotic factors [eɪˌbaɪˈɒtɪk ˈfæktərz] - (noun) - Non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. - Synonyms: (non-living elements, environmental processes, inorganic factors)

And though we don't always stop to think about them, non living elements or abiotic factors play a huge role in influencing our environment as well.

3. biogeochemical cycles [ˌbaɪoʊˌdʒioʊˈkemɪkəl ˈsaɪkəlz] - (noun) - Cycles that involve the movement of chemicals in and between ecosystems, incorporating both biotic and abiotic elements. - Synonyms: (nutrient cycles, ecological cycles, biochemical cycles)

The ecosystem is where we can observe and study the circulation of the chemical elements that make up both the biotic factors, like elephants, and the abiotic factors like rocks or soil. These are called biogeochemical cycles.

4. ecosystem services [ˈiːkoʊˌsɪstəm ˈsɜːrvɪsɪz] - (noun) - The benefits provided by ecosystems to humans, which include food production, water purification, and maintenance of biodiversity. - Synonyms: (natural services, environmental benefits, ecological goods)

Well functioning ecosystems also provide ecosystem services that can directly benefit humans.

5. trophic levels [ˈtroʊfɪk ˈlevəlz] - (noun) - The hierarchical levels in an ecosystem, comprising different species that are organized according to their feeding relationships. - Synonyms: (food chain levels, energy levels, ecological rankings)

Those links in the chain organize species into trophic levels, which are the groups of species in a food chain that share the same relationship to the flow of energy through the ecosystem.

6. apex predator [ˈeɪpɛks ˈprɛdətər] - (noun) - A predator at the top of a food chain, with no natural predators. - Synonyms: (top predator, alpha predator, dominant predator)

The Fox that eats the beaver is a secondary consumer and the eagle that eats the fox is a tertiary, the top of the food chain........it's what's called an apex predator.

7. photosynthesis [ˌfoʊtoʊˈsɪnθəsɪs] - (noun) - The process by which green plants, algae, and some bacteria use sunlight to synthesize foods with the aid of chlorophyll. - Synonyms: (chlorophyll absorption, solar energy conversion, plant food production)

Through the process of photosynthesis, plants use the energy from the sun to assemble raw chemical ingredients, carbon dioxide and water, into energetically charged sugars.

8. hydrosphere [ˈhaɪdrəsfɪr] - (noun) - The part of the earth composed of water; includes oceans, rivers, lakes, and other bodies of water. - Synonyms: (water body, aqueous zone, water domain)

On this scale, abiotic factors include where the air is, where the water is, and where the land is. We call these the atmosphere, the hydrosphere, and the geosphere.

9. neurotoxins [ˈnʊroʊˌtɒksɪnz] - (noun) - Toxins that are poisonous or destructive to nerve tissue. - Synonyms: (nerve poisons, neural toxins, toxic substances)

And cyanobacteria can produce poisonous neurotoxins. So this led scientists to the conclusion that these toxins poisoned the elephants, causing the massive die offs.

10. cyanobacteria [ˌsaɪ.ə.noʊ.bækˈtɪə.ri.ə] - (noun) - A group of bacteria that can photosynthesize and may form harmful algal blooms. - Synonyms: (blue-green algae, phototrophic bacteria, cyanophytes)

The elephants bodies were often found close to watering holes. And when scientists tested the water, they found high levels of cyanobacteria, a bacterium capable of photosynthesis.

Intro to Ecology - Why Did All These Elephants Die? - Crash Course Biology #5

Home to more than 130,000 elephants, Botswana Africa has the world's largest elephant population. And in Botswana, elephants are kind of a big deal. Just ask any of the dung beetles snacking on elephant poop or the giraffe drinking from a watering hole dug by an elephant. Elephants are the life of the party here. Not because of their great dance moves, but because of their importance in the lives of so many other species, qualifying them as what's known as a keystone species. Even some of the elephants behaviors that seem destructive are actually helping sustain other living things, like when they're knocking down trees. This can help smaller plants grow and thrive. And you won't hear the zebra quite the foodie when it comes to these small plants complaining about a few fallen trees.

So in 2020 and 2021, when hundreds of elephants in Botswana died suddenly, ecologists and conservationists became really concerned, especially because the causes were a mystery. So today we'll be ecological detectives on the case.

Hi, I'm Dr. Sammy, your friendly neighborhood entomologist and this is Crash Course Biology. But let's back up. In order to be ecological detectives, we need to set the scene. And the scene is a bit more complicated than in the library with a candlestick. For ecologists, the scene is kind of everywhere. But more importantly, it's the connections between everyone and everything everywhere.

Ecology is the study of how living things interact with each other and their environment. And when ecologists talk about the environment, they're referring to all of the living and or non living stuff that makes up the world around us. So your dog is a part of your environment and he's a biotic factor because he's living. And so are the fleas on your dog. Even if a ol spike isn't a fan, they're a part of your dog's environment. And though we don't always stop to think about them, non living elements or abiotic factors play a huge role in influencing our environment as well.

Climate and water are two examples of abiotic factors. The climate of a frozen tundra is super different from a rainforest. And so different organisms live in each of those ecosystems. And a watering hole serves as a place of interaction between lots of different species. So we're not only connected to other life, we are deeply connected to our environment too. And just like life, we can study ecology on so many scales, from the tiny to the tremendous.

Let's start big. The biosphere is the part of our planet, from several kilometers above the ground to the deepest depths of the ocean, that all earthbound Life calls home. Everywhere that stuff lives counts as part of the biosphere. On this scale, abiotic factors include where the air is, where the water is, and where the land is. We call these the atmosphere, the hydrosphere, and the geosphere.

Okay, let's zoom in a little. Within the biosphere, there are many different ecosystems. Ecosystems are all of the organisms and non living things that interact with each other in a specific area. And there's typically no empty space between ecosystems. They just bump right up against each other. Like how the shoreline is home to different types of critters than the ocean. And the ocean itself is home to different types of marine life at different ocean depths.

The ecosystem is where we can observe and study the circulation of the chemical elements that make up both the biotic factors, like elephants, and the abiotic factors like rocks or soil. These are called biogeochemical cycles. So, for example, a plant can absorb phosphorus minerals from the soil. Then the phosphorus in the plant can end up becoming part of a grazing cow. And eventually that same phosphorus returns to the soil again when the cow poops. biogeochemical cycles are integral to a functioning biosphere. They're responsible for everything from making it rain through the water cycle to producing the air we breathe through the carbon cycle. And ecologists study this remarkably diverse set of interactions.

So it's no wonder that people conflate ecology and environmental conservation. While ecology may lead to strategies to preserve and protect the environment, an ecologist focuses on relationships between organisms and their surroundings. So an ecologist might examine which plants thrive in elephant trampled areas and compare that to similar areas where elephants haven't stomped their size 18ft. And a conservationist's goal is to protect or restore the environment. For example, poaching elephants for the ivory in their tusks is a major issue in Botswana, and conservationists there work to prevent it. And that brings us back to our mystery.

You might be thinking that poachers killed the elephants. And that's not an unreasonable guess, because poachers are responsible for the deaths of 20 to 30,000 African elephants every year. But the elephants in Botswana were found with their tusks intact. So if it wasn't poachers, what was it? To look for more clues, we need to consider the situation from a few different vantage points.

One of the coolest things about ecosystems is that there's only one size limitation it needs to fit in the biosphere. An ecosystem can be as enormous as the savannah in Botswana, or as tiny as a puddle inside a muddy elephant footprint. And the different types of ecologists study the interactions of living things with their environment from a more or less zoomed in perspective. Of course, we won't be able to cover all of the specializations within the field of ecology, but we'll highlight five main fields.

Landscape ecology has the biggest playground. Geographically speaking, it's focused on multiple connected ecosystems and the interactions between them. One step smaller is ecosystem ecology, which is the study of interactions and dynamics of all of the organisms, plus all of the non living things in a specific area. Even more zoomed in, there's community ecology, which looks at interactions of two or more species within a specific location. And relatedly, population ecology focuses on the dynamics surrounding just one species, a population in a specific area. Finally, like a parent watching their little kiddo navigating a new playground, behavioral ecology focuses on the way an organism acts in response to its environment. So let's use our knowledge of the fields of ecology to investigate the elephant deaths in Botswana.

One place we might want to start is with ecosystem ecology. By studying where species sit on the food chain, we can find clues to what might have caused their deaths. When we're talking about the food chain, we have to remember that the laws of physics apply. Energy is conserved, and so is mass. In fact, one of the goals of ecosystem ecology is to track how mass and energy move through an ecosystem. To see how this breaks down in one particular example, I'll introduce you to my favorite water dwelling buck tooth rodent, the beaver.

Let's go to the thought bubble. Beavers love to munch on lilies, grasses and clover. So plants really. Through the process of photosynthesis, plants use the energy from the sun to assemble raw chemical ingredients, carbon dioxide and water, into energetically charged sugars. They pretty much make a sweet biochemical solar cell. This photosynthetic organism is the very first link on our food chain, what ecologists call a producer. And the producer doesn't always have to be a plant. It could also include algae or bacteria that are capable of photosynthesis or chemosynthesis.

The rest of our chain is made up of consumers who take advantage of the energy stored in the sugars that the plant makes. The same way that you take advantage of your friend's power bank. When your phone is on 4%, those links in the chain organize species into trophic levels, which are the groups of species in a food chain that share the same relationship to the flow of energy through the ecosystem. The beaver is the second rung in our food chain, a primary consumer of the clover. The Fox that eats the beaver is a secondary consumer and the eagle that eats the fox is a tertiary, the top of the food chain. Now, the eagle doesn't really have any natural predators, so it's what's called an apex predator.

We've also got some action going on at the edge of the food chain. Decomposers like fungi and detritivores break down decaying organic matter. Fungi use chemical reactions to do the trick. And our friend, the dung beetle is one of those detritivores and he eats dung. Dung beetle. Lets not do lunch, but thank you for all that you do. And thank you thought bubble.

So if we think like an ecologist and look at where elephants sit on the food chain, maybe we can see where the system breaks down. Elephants are voracious plant eaters, primary consumers that eat things like grass, shrubs, bark and fruit. To look closer, we can visualize data about how energy flows through the trophic system. This type of visualization is important in helping ecologists recognize patterns in biology.

And an ecological pyramid lets us represent that energy flow graphically. Energy transfer through a food chain is a pretty inefficient process, with the plant getting only about 1% of the possible energy from sunlight and each trophic level harvesting only about 10% of the energy from the level below it. This inefficient energy transfer limits a food chain to four or five levels max. By the time we reach a third or fourth level consumer, the ecosystem can support relatively few apex predators.

As for predators, elephants are so large that they don't really have any. Sure, maybe a baby gets snagged by a lion here and there, but very rarely do the adults. So we can rule out predation as the cause of the deaths. So maybe it was starvation. Let's look at the other end of the chain. Primary producers determine the energy budget for all other organisms in the food chain.

The total available energy from all of the producers is called the gross production of an ecosystem. But plants also need energy to fuel their own biological processes. The net production of the ecosystem is the remaining energy that is actually left over for the rest of the ecosystem to use. Another way to represent the flow through the ecosystem is using mass. A biomass pyramid plots the total mass at each trophic level at any given time. So it's more like a quick snapshot of the available energy.

In Botswana, the elephants were all relatively healthy and well fed, and there didn't appear to be a food shortage. So it was clear that something else was causing their deaths. The elephants bodies were often found close to watering holes. And when scientists tested the water, they found high levels of cyanobacteria, a bacterium capable of photosynthesis. cyanobacteria thrive in warm, stagnant water, and increased global temperatures due to climate change have made them more prevalent. And cyanobacteria can produce poisonous neurotoxins. So this led scientists to the conclusion that these toxins poisoned the elephants, causing the massive die offs.

Solving this mystery, as often happens in science, leads us to more questions, and ecology gives us the tools we need to answer these questions about life and the environment. But don't forget, we are not just passive bystanders watching the journey. Well functioning ecosystems also provide ecosystem services that can directly benefit humans. Food production is one of the major services that ecosystems provide us humans. And thinking back to the burrito that I had for lunch, I'm going to recognize the primary producers and consumers that harvested the energy that I just took advantage of to record this video. And ecosystems also help to purify the drinking water that I use to wash down that burrito.

And there's so much more. Tall trees in a forest buffer strong winds that might damage the places we live. And even the decomposers and detritivores perform an important service by not letting all that dead stuff and waste lie around for too long. In fact, the nutrients that they return to the soil might just end up as an atom inside of you one day. Life, all of it, is interconnected, and ecology helps us visualize these connections.

Plus, ecology lets us see and study our connection to our environment. Understanding these relationships can help us build the tools to address global issues that affect humankind and really, almost all life on Earth. Whether you'll use this knowledge to do biological research or better understand the world around you, or to elect leaders that support science policies that you value, learning about ecology benefits all of us. In the coming episodes, we'll look at the interactions in communities and populations and then zoom back out to see how ecology can help us understand climate change and guide conservation efforts.

And maybe with the knowledge that we're building about ecology, we can be better citizens of this amazing biosphere that we all call home.

Ecology, Conservation, Biology, Science, Global, Climate Change, Crashcourse