Category Predators and Prey

What are the species in the wild that change their appearance to escape predators?

There are many species in the wild that change their appearance to escape predators. This is camouflage. But did you know that some species can even change their gender? Let's read up on them.

CLOWNFISH

Clownfishes live in social groups and consist of a dominant female (the largest in size) surrounded by a male and other immature juveniles. Their social hierarchy is based on size and determines the breeding. In a group, the fishes age and grow larger together, without any change in the hierarchy. But this changes when a dominant female dies. When this happens, others will try to use the opportunity to climb up in rank. The male will rapidly change sex to fill in the vacated position. And another fish will turn into a mature male and complete the breeding pair.

HAWKFISH

The hawkfish which is found on coral reefs from Australia to Japan lives in harems (one male with several females). These reef dwellers basically start life as females. Things change when there is a shift in the number of females in the harem. If a male takes on more females into the harem, then, one of the females changes its sex and becomes a male. It then breaks away from the harem and in the process takes half of the harem along with it. It has also been observed by researchers that when a new male gets challenged by another male, it reverses its sex back to a female. This bi-directional sex change is seen in certain reef fishes.

BLACK SEA BASS

Black sea bass is a commercially important species. These are capable of switching their gender from female to male. They are born as females in the wild. They turn into males when they are two to five years old. Research on sea bass reveals that sex change occurs when there is a dip in the male population. If the female sea bass senses a decrease in the male population, they switch their sex.

BANANA SLUG

Banana slugs are wormlike mollusks and they grow up to 10 inches. These animals are hermaphrodites, that is they have both male and female organs. So they don't change their sex back and forth but are unique as they can use both their male and female reproductive organs at the same time. This they do to self-fertilise when necessary. Even when they are capable of self-fertilisation, the majority of banana slugs will take a partner.

GREEN FROG

Researchers have found that frogs spontaneously change sex in the lab and the same has been seen in the wild. In fact, among the green frog population, this sex change is quite common. Earlier research established that sex reversal in frogs may be related to pollution introduced by humans. When exposed to some pollutants (synthetic estrogens and herbicides) in the lab, it has led to genetically male frogs developing outwardly as females. Further studies have proved that this change could be a natural occurrence in amphibians, even in pollution-free settings.

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What does the brightly colored skin of some frogs signal to their predators?

Have you ever wondered about the vibrant colours of some frogs? Did you know that their colouring is a warning to predators that they are foul-tasting and poisonous? Read on to know more fascinating facts about these amphibians.

It is small enough to fit into the palm of one’s hand, but it packs a powerful punch. A single golden poison dart frog, measuring just 6 on long, contains sufficient poison to kill 10 grown humans! The frog species derives its name from the centuries-old practice of the Emberá and Chocó, indigenous peoples of Colombia and Panama, who tipped their blowgun darts with its poison while hunting.

The poison is called a batrachotoxin (some beetles and birds also have it). The word batrachos is Greek for frog’. Even minute amounts lead to paralysis and death.

Poisonous species

There are only four species of frogs that are so poisonous that even a tiny drop is enough to kill small mammals (monkeys, for example) and birds. Most of them produce poison only potent enough to kill insects-flies, crickets, ants, termites. and beetles which are their main prey.

The frogs average around 2.5 cm in length. They are found in the wild only in the tropical rainforests of South and Central America.

The frogs sport gaudy colours and patterns, usually in combination with black-orange, red, blue, yellow, purple, pink, green, and even silver! Their colouring is a warning to predators that they are foul-tasting and poisonous. Once a predator has tried eating one and survived, it avoids similar-looking frogs.

The fire-bellied snake of the Amazon forests is resistant to golden poison frog toxin and is its only predator.

The little frogs usually live in the leaf litter on the forest floor, near streams and ponds, but a few species also live high up in the canopy and may never come down. Unlike most frog species that are nocturnal, poison frogs are active during the day when their colours can be best seen.

Caring for the young

Females lay from one to 30 eggs at a time in a dark, moist place such as the base of a big leaf, the hollow of a tree trunk or crook of a branch. Both parents are involved in the care of the eggs. When the eggs hatch, the parents carry the tadpoles on their backs and deposit them in water. Blue poison frog tadpoles eat their own siblings, so the parents must find a different water body for each individual hatchling!

The female feeds the tadpoles with unfertilized eggs that contain small amounts of poison, so that even the tadpoles are protected from predation.

Researchers are studying poison frogs to see if their toxins can be used in medicines, mainly painkillers. The poison from the phantasmal poison frog has been found to be 200 times more effective than morphine and without its side-effects!

Fact File

  • Wild poison frogs ingest the poison from the different bugs they eat and store it in their skin. Frogs bred in captivity lose their toxicity.
  • In the past decade, hundreds of frogs have died of a fungus that grows on their skin, preventing them from absorbing oxygen and water.
  • The population of the more brilliantly coloured poison frogs has plummeted because they are popular as pets.

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Why are whale sharks different?

Whale sharks are the largest fish to be identified and can grow up to 10 metres in length. They consume a wide variety of sea animals and planktons in a rather interesting manner. They just keep their mouths wide open and scoop the tiny plants and fishes as they move close to the surface of water.

The whale shark belongs to the category of filter feeders, just like the world’s second largest fish, the basking shark. This means that their huge jaws filter everything it comes across, to find its food. This mechanism is similar to that of the baleen whales, where too, a cross-flow filtration is observed. These giants prefer warm waters and are found in all tropical seas. They also migrate to the continental shelf of the central west coast of Australia during the spring season. During this time, the coral spawning of the Ningaloo Reef of this region provides the whale shark with plenty of plankton to feed on.

Although whale sharks are massive, they are very docile. They even allow swimmers to hitch a ride at times! Currently listed as a vulnerable species, these animals face the threat of hunting, as in some parts of Asia, people continue to hunt them.

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How do we know that humpback whales communicate through songs, or about the sounds that pervade the ocean depths?

How do scientists know that humpback whales communicate through songs? That’s because they have ears placed on the bottom of the ocean at strategic points! These ‘ears’ are part of a network of underwater microphones or hydrophones placed by various scientific research organisations that eavesdrop on the sounds that pervade the inky depths-from the squeaky whistles and moans of whales and the rumbling of earthquakes, to the drone of ships passing overhead.

The sounds provide a lot of information about the world beneath the waves. The information can reveal how man-made noise affects the creatures of the deep as well as predict if the movement of tectonic plates is going to cause an earthquake.

Sound travels much further than any other form of energy in the ocean, with low-frequency sound reaching thousands of kilometres deep. Data collected from hydrophones shows that shipping activity cripples communication between whales and other marine mammals that use sound and echolocation to find their mates, fellows, and prey. The noise from ships is so loud that these animals are forced to ‘shout to be heard! According to a diver, the disturbance caused by a ship passing above is like being hit in the chest with a heavy golf club.

Data collected from hydrophones shows that shipping activity cripples communication between whales and other marine mammals that use sound and echolocation to find their mates, fellows, and prey.

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Shark attacks: what’s going on?

When one says conservation efforts to save a species have paid off, it usually means one thing a steady increase in the species population. And that’s good news. Recently though conservation efforts paying off had a slightly unexpected result. What is it? Come, let’s find out.

In summer, great white sharks move up the Atlantic coast of the U.S., towards New England. Their numbers normally hit the peak between August and October. But a few weeks ago, an unusual increase in human-shark encounters was evident along the U.S. East Coast, The reason? Experts believe it could ironically be due to the “conservation wins for vulnerable species”. There has been an increase in great white shark numbers, which experts think is the result of continued protection. And this likely led to increased human-shark encounters too.

An important factor in the shark number increase is the fact that the number of its main prey -the seal-has seen an uptick too due to protection. Scientists also believe that the increasing encounters could be “linked to the sharks bait fish-menhaden, also known as porgies or bunkers, recovering”. But they also warn that “it’s tricky to figure out how much of it is increasing populations moving around as a result of changing ocean conditions from climate change.”

Though there have been instances of sharks being portrayed in pop culture as blood-thirsty, that’s far from the truth. Studies have shown that sharks can mistake surfers or swimmers for their usual prey meaning many attacks could be the result of mistaken identity. Researchers say that if the number of beach-goers is anything to go by, there should be tens of thousands of shark attacks every year whereas the truth is that annual global deaths due to shark attack is five. When more sharks come close to land for feeding and more people go swimming, the encounters are likely to increase.

And with climate change experts expect “that the increase in ocean temperatures will gradually lengthen the season during which sharks are present in the northern United States”. This could mean increased chances of encounters in the future. Increased vigilance and self-awareness will go a long way in minimising the risk of attacks, feel experts.

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