3.Trophic cascade

 
Dear readers, 

Welcome back to the VOICEofप्रकृति !
                              (read : Voice of Prakriti)

Now that we have pondered significantly on trophic levels, allow me to introduce you to the next intriguing topic - Trophic cascades. Trophic cascades are powerful, indirect interactions that can control entire ecosystems. Confused ? Let's discuss how.

Firstly, let me introduce two variables that we’ll use from now on—'predator' and 'prey.' The predator is the one who hunts, and the prey is the one being hunted. Mostly, people sympathize with the prey. We often hoped the deer escapes being eaten in our favorite Jataka tales (animal stories often told in childhood), or we cheered for the defeat of the 'evil' tiger in The Jungle Book (humanized traits of tiger kept aside, predators are often portrayed as scary villains). Many would then believe life would be easier without predators right ? No killing, no harming other animals - everyone would live in perfect harmony. Sounds great, to be honest —except it only works in our imagination. In reality, nature doesn’t play by those rules. 

Do we truly understand the equal importance of predators?

What if I tell you that the presence of predators keeps the ecosystem alive ? 

The best demonstration seen in real life - How the return of wolves saved Yellowstone’s ecosystem.

For context, Yellowstone national park is widely regarded as the world's first national park. It is also the largest in US, home to hundreds of threatened and endangered species. In the 1920s, the US Government eradicated wolves as an effort to tame wilderness. They had eradicated wolves from national park area as well because humans feared that  IF (and, stress on the word if) they had remained, they would spread back to private lands. (Does this remind you of my last blog on human's underdog mentality ?)  

However, the absence of wolves caused the elk population to grow exponentially, leading to overgrazing and significant declines in Yellowstone’s vegetation. Elks are herbivores, feed on grass and greenery. In the absence of predation (in other words, when left unchecked), these elks lingered in one place, ate everything. When nothing remained, they moved on to the next location and continued to devour everything.
Eventually, overgrazing resulted in even bigger problems like riverbank erosion and loss of biodiversity resulting in a complete ecosystem imbalance. The government had to launch a restoration project called "Yellowstone Wolf Project" (grudgingly; it was no easy task — a seesaw battle raged on for 15 years, informally named as 'wolf wars'). 

Fig 1. Absence of wolves, elk population rise, overgrazing/ decline in vegetation, ecosystem imbalance.
(Created using Canva)

Nature's way of keeping checks and balances on the ecosystem is via predators. 

The 'controversial' comeback of wolves not only resulted in a check on elk population, but also altered their grazing patterns! Elks could not stay in one place for too long, preventing overgrazing and giving time for vegetation to fully recover between migrations. This meant that songbirds and other small animals like beavers could come back to make nests in their new habitat. Constantly running elks aerated the soil with their hooves, which improved water retention and allowed more grasses to grow. Increase in vegetation helped keep the air and water cooler, leading to a rise in fish populations. 

Fig 2. Wolves reintroduced, elk population in check, flora and fauna flourish, ecosystem regulated.
(Created using Canva)

This was a visual explanation of what 'trophic cascade' means.
"Cascade" refers to the ripple effect that occurs across multiple levels of a food chain when a significant change happens at one trophic level. Just like when you throw a tiny pebble into a lake, ripples spread across a large distance (illustrating a disproportionately large effect from something quite small). 
When a top predator (in this case, wolves) is added or removed from an ecosystem, it indirectly impacts every level below it, from herbivores to plants and even soil conditions. The changes "cascade" down, affecting the abundance, behavior, and interactions of species across multiple trophic levels. This demonstrates how predators can have far-reaching effects, ensuring the stability and health of the ecosystem. 

Each topic we've discussed so far has considerable depth, and while I could spend days discussing them with you, it’s important that we take one step at a time. I will look forward to seeing you next week with a new topic - Interdependence.