Introduction

Natural selection is an evolutionary mechanism. A common ancestor for all living things, according to Darwin's definition of evolution (Caporale et al., 2013), is a "descent with modification”. Adapted organisms have a better chance of surviving and passing on their genes to future generations. As a result of this process, species evolve and become more distinct throughout time. Individuals' survival-enhancing genetic variations are transmitted down through generations in a process known as natural selection. There are more creatures that can live and reproduce as a consequence of this. In addition to being known as the hippo, other popular names for the hippopotamus include the common hippopotamus, and river hippopotamus. Ancient Greek slang meaning "river horse" inspired the name of this species. The Pygmy Hippo as well as the Common Hippo is now the only Hippo species left. Hippo species are believed to have gone extinct in at least three separate ways, according to Pluhá?ek et al. (2015). Hippos have gone extinct in a few places throughout the years. The Malagasy Hippo is the most recent addition.

Hippos and whales, despite their disparate appearances, have a common progenitor that lived around 55 million years ago, making them near living cousins. Flacke et al. (2015) mentioned that about 16 million years did the first known hippos appear (the modern-day hippos only appeared 7.5 million years ago). Even though the crown group's hippos aren't as old as the other hippos, they do stretch the record back a little farther. Despite its smaller size and lighter weight, the Common Hippopotamus towers above its Pygmy counterpart. Despite the fact that the two species have many similar characteristics, such as a wide snout, huge mouth, a short barrel-shaped belly, as well as short legs, there are notable morphological distinctions between the two. Hippos are well suited to water existence. Additionally, habitat loss and degradation pose a risk to hippos. Dependant on natural waters, hippos is endangered by droughts, agricultural as well as other water diversion, and the loss of pastureland. The hippopotamus previously roamed from the Cape to the Nile Delta, but is now mostly limited to protected regions as a result of human influence.

Hippo Timelines, Relative Species, Lifespan and Likelihood of Survival

The hippopotamus life cycle includes a number of distinct phases. An eight-month examination of endocrine systems indicated that female hippos may enter puberty as early as 4 years old during their 8 month gestation period (Guo et al., 2022). Hippos are often reproductively mature between the ages of 5 and 7 years.

A study of the breeding behaviour of hippopotamus by Chen et al. (2010) revealed that peak conception occurred at the conclusion of the summer season and peak birth occurred at the start of the late winter season. This is due to the orientation of the female; as with the spermatozoa of other big mammals, hippopotamus male’s spermatozoa remain active throughout the year.

Hippopotamus are really whales' closest "relatives," and they're more closely linked to each other than one may imagine. Scientists have discovered a family resemblance between whales & land-dwelling animals that lived 52 million years ago, derived from fossil evidence. Cetaceans (whale, dolphin, porpoise, and other sea mammals) are the closest extant cousins of the Hippopotami, despite their anatomical similarity to other even-toed ungulates on land. At 25 years of age, hippos may continue to develop until they reach their full size. They may live for 40 on average in the wild, which means they've had almost half of their life to grow. The hippopotamus life cycle includes a number of distinct phases. More over one-third of all captive hippos reach the age of fifty as mentioned by Weston, (2003). Having access to food, medical treatment, and protection from poachers and predators all contribute to their longer life expectancy.

As a result of human-wildlife conflict as well as encroachment on their natural habitat, dozens of hippos are slaughtered each year. Under the pretence of protecting them, hippopotamuses are regularly slaughtered for their flesh & their ivory canine teeth, which are both precious. As environmentalists' relentless efforts continue to garner support for restrictions on elephant ivory, purchasers are on the lookout for alternatives. Because hippopotamus canines may be carved, hippo tooth exports have increased by about 530 percent every year. The hippo population has also been affected by continuing civil upheaval and is caught in snares in zones of relative calm. The number of hippopotamuses in the Democratic Republic of Congo (DRC) has plummeted by 95 percent (Tsahar et al., 2009). To keep their unique skins wet, these aquatic animals need constant access to water. Additionally, floods and other hazards to the aquatic ecology will lessen their odds of survival.

Hippos, according to palaeontologists, migrated from Africa to Eurasia approximately six million years ago & then were extinct by the conclusion of the Pleistocene, when the global temperature dropped. Hippo ancestry has yet to be fully established, despite this tiniest expansion of hippopotamuses back in time. Anthracotheres termed bothriodontines are the most probable ancestors of hippos; however it is unclear whether they evolved in Asia or Africa. By the conclusion of the Pleistocene Epoch, mankind had wiped off all species outside of Africa due to climate change & overhunting. It is possible that the extinction of 3 species in Madagascar occurred around the time when humans arrived there roughly 1,000 years ago (Maust et al., 2018).

Ecosystem and Relationships

Africa's slow moving lakes and rivers are home to hippos, which are undoubtedly suited to aquatic existence. Hippos are found throughout sub-Saharan Africa. The majority of their time is spent immersed in water to keep the skin cool and wet. National Geographic reports that, as amphibians, hippo spends up to 16 hours every day in the water. Hippos are often found in lakes, rivers & mangrove swamps. Each territorial bull oversees a body of water as well as a herd of 5 to 30 cows and calves. Both reproduction and birth take place in water. Hippos keep cool throughout the day by remaining submerged in water, emerging at twilight to feed on grasses. Near water, hippos often eat on areas of short grass. Nonetheless, they must sometimes go many kilometres to get sustenance. Their sense of hearing enables them to detect the noise of falling fruits, while their smell enables them to locate food. They prefer short, shrubby grass as well as little green shoots and stolons. If they consume other plants, they prefer to avoid tough grasses, which are more hard to process and do not adhere to the soil for burying roots or fruits. Hippos consume an average of 80 pounds of food every night (Chen et al., 2020), or 1 to 1.5 percent of their overall weight.

The backs and heads of hippopotamuses are popular resting spots for a wide variety of animals, including Egyptian geese, cormorant, and cattle egrets (which feed on ticks and other insects).  The backs of hippopotamuses are a favourite feeding ground for Common Sandpipers, who eat water creatures. Both ox pecker species feast on the injured tissue on the skin of the hippo. The parasites & insects that the Oxpecker bird feeds on come from the hippopotamus' back. Hippopotamus sickness is prevented, and the bird gets a meal. The barbel fish and hippos share a unique mutualistic interaction. This indicates that both animals benefit from these encounters. Using its tongue to scrape the hippopotamus's skin and the hippo's mouth, the fish gets its meal (Subalusky et al., 2019).

For the ecology of Africa's lakes and rivers, the hippo is a crucial animal. African aquatic ecosystems are aided by their dung, which is solid waste. The concern is that hippo numbers are declining, according to biologists. Ecologists fear this might have negative effects. If hippos become extinct, lakes may run out of fish to feed their inhabitants because an essential part of the African river ecology is hippos' waste. This habitat is under jeopardy due to a decline in the number of hippopotamuses. For instance, food shortages near Lake Victoria might result in the long term which would impact the survival rate of Hippos. Aside from poaching for their unique canine teeth and flesh, hippopotamuses have a bleak future owing to habitat degradation brought on by human settlement, deforestation, as well as pollution. Water & vegetation distribution changes have a significant impact on hippos, especially in areas where there are large populations (Masese et al., 2020). Low rainfall/flow seasons may cause population decreases or crashes, resulting in increased mortality and sluggish reproduction due to a lack of available viable water bodies and inadequate grazing.

From land to water, Hippos excrete vast amounts of silicon, a vital ingredient for ecosystems. Grass-eating animals defecate in sources of water, which feeds fish and bolsters the population of lakes and rivers. They transfer nutrient from land to water by feeding on land and excreting waste in water. An essential part of the African lake & river ecology is hippos' waste. As the number of hippopotamuses decreases, this ecosystem is under crucial risks of extinction.

Evolution, Adaptation and Extinction of Hippos

The earliest known hippo ancestral fossil is from roughly 20 million years old, whereas the oldest recorded cetacean fossil dates from 53 million years ago. Naturalists used molar characteristics to classify hippos and pigs until 1909. Studies from proteins in the blood, molecular systematics, DNA as well as the fossil record show that their closest relatives are cetaceans (Whale, dolphin, and porpoises) as mentioned by Shurin et al. (2020). Cetaceans and hippos split around 50 million years ago, but research reveals that the two species may be more closely linked than previously thought. During the Miocene Epoch (20 million years ago), a fossil matching today's pygmy hippopotamus was discovered. 

The most current hypothesis about the origin of Hippopotamidae proposes that hippos & whales had a semiaquatic ancestor that diverged from other artiodactyls about 60 million years ago. Approximately 52 million years ago, this proposed ancestral group likely separated into two divisions again. The Protowhale Pakicetus as well as other early whale predecessors are generally known as Archaeoceti. They may have evolved into cetaceans about 50 million years ago according to Inman et al. (2021). This group finally experienced total aquatic adaption to become cetaceans. The second branch evolved into the Anthracotheres, a huge family of four-legged animals, the oldest of which resembled thin hippos with relatively tiny and narrow skulls during the late Eocene. Except for the lineage that developed into Hippopotamidae, all Anthracotheres lineages fell extinct throughout the Pliocene before leaving progeny.

Hippos are mainly found in or near water. Although they favour shallow waters, hippopotamuses ought to be able to submerge entirely if the water is deep enough. Over half of Africa's continent, from the eastern to the western coast, and all along the Nile River, was formerly home to river hippopotamuses. Despite the fact that they still occupy 30 of Africa's southern nations, their population is fragmented and no longer spreads over the whole continent. Among the most frequent river hippos, Zambia & Tanzania are home to the biggest numbers (Chen et al., 2020). The home range of pygmy hippos is much less than that of typical river hippos. Liberia's forests are their primary habitat, although there are also tiny populations in neighbouring nations.

According to Chichorro et al. (2019) extinction is often the result of a shift in the environment. Some species have the adaptability to different environments, whilst others do not. Occasionally, if a change occurs slowly enough, the essential adaptations may be developed over many species by the organisms. Hippos are endangered by droughts, agricultural as well as other water diversion, and the loss of grazing grounds because of their need on freshwater systems. Human-induced global warming is expected to generate more severe droughts in Africa that will harm hippos, decreasing their reproductive capacity and increasing death rates.

External Factors Affecting Survival of Hippos, Threats to their Survival and Conservation Efforts

Considering the external factors climate change is putting hippopotamuses at risk because of habitat loss and devastation. Because of their reliance on freshwater systems, hippos are particularly vulnerable to threats like as droughts. It is anticipated that global warming will be harmful to hippos, resulting in a decrease in their reproductive potential and an increase in mortality as discussed in previous section. Hippos are becoming more and more isolated, with fewer places to find food and refuge. Both hippo species are threatened by habitat loss & deforestation, but human-wildlife conflict is also on the rise because to the lack of natural habitat, which leads to the deaths and captures of these animals. As a consequence of habitat loss and fragmentation, the number of patches increases, the size of the patches decreases, and the isolation of patches also increases. Hippos face a number of dangers, the most serious of which being habitat destruction and the illicit ivory trade. A 200-year decline in the number of hippos isn't yet considered an endangered species, but their habitat is shrinking (Kanga et al., 2012).

Conflicts between people and hippopotamuses are becoming more prevalent as humans advance into hippo habitat. The violent behaviour of hippos, particularly dominant males, is well-documented. Human boats that approach hippo area without warning are at danger of being aggressively reacted to. Hippos may also eat crops grown on human territory, such as farms. The hippopotamus may be killed as a result. As hippo & human regions increasingly overlap, these clashes are becoming more frequent. Dams & water diversion for agriculture are only two examples of human-made waterway projects that might harm hippos and their natural environment (Roberts et al., 2020).

Hippo populations suffer as a result of the illicit ivory trade. They are constructed of ivory, which is the same substance as elephant tusks. To carve, hippo's teeth are softer than elephant's, which makes them simpler to work with. Immediately after the 1989 prohibition on elephant ivory, desire for hippo ivory soared. Because of this, hippo populations are fast diminishing. Young hippos, on the other hand, are vulnerable to natural predators, but adults have few enemies. Among the predators that might pose a hazard to juvenile hippos are crocodile, lion, hyenas, and leopards. Hippos are now primarily restricted to protected regions, and their numbers have dropped by 7-20% in the last decade as per Baker et al. (2020). The common hippopotamus as well as the pygmy hippopotamus are both classed as Vulnerable & Endangered, respectively. The number of hippopotamuses in the Democratic Republic of Congo (DRC) has plummeted by 95 percent. To keep their unique skins wet, these aquatic animals need constant access to water. A large grazer like a hippopotamus would have a significant influence on the ecosystem if it were to vanish from its natural environment. Because hippopotamus canines may be carved, hippo tooth exports have increased by about 530 percent every year. The species might be extinct within a century if present trends continue.

Because hippopotamuses like water, protecting their waterways and natural grasslands is a top priority. The IUCN Red List considers hippos to be Vulnerable. Even while hippopotamuses aren't in danger of extinction just yet, their natural habitat has shrunk dramatically in the previous two centuries. One way to conserve these species is to ban the illegal trade of their teeth and protect their grasslands.  Even while there are groups dedicated to saving several of Africa's most "at-risk" creatures such as elephants & cheetahs, there is none specifically dedicated to saving the hippopotamus (Djagoun et al., 2013). The greatest way to conserve hippopotamuses is to keep big tracts of land protected. In national parks, poachers have the least level of protection against them. The Ugandan Waterway Project has been successful in decreasing and discouraging poaching owing to the work of Global Conservation as well as the Ugandan Conservation Association (UWA, 2022). The Uganda Wildlife Association (UWA) was able to deploy patrols from marine ranger posts created as part of this project on Lake Edward & Lake George. Poachers are pursued and apprehended by these rangers, who then arrest them and seize their illicit wares. Through the support of this grant, the hippopotamus population at the UWA may be monitored and changes in the population can be studied. African Wildlife Organization also assists communities in erecting enclosures, fencing, and ditches to keep grazing hippo away from farms & reduce human-wildlife conflict. 

Conclusion

This study aimed to describe the ecosystem of Hippopotamus and how it changed due to evolution. The study bridges the gap between old researches and new to locate their ancestors from evolution era. The hippopotamuses have been around for a long time. They may have roamed the Earth over 55 million years ago, based on evidence. Whales & porpoises are the closest living relatives of the hippopotamus, but a new research reveals that the hippo's closest modern-day cousins are the cetaceans. Furthermore, it reveals that hippo was one of the first big animals to arrive on the African continent around 35 million years before, long before giraffe or bovine arrived. Fossils that date back 16 million years have been discovered in Africa. However, the origins of the Hippo race's existence are still a matter of conjecture. It is possible to come up with a number of intriguing theories. Believed to have lived in the dense woodland places where sunshine would not harm their delicate skin.

However, several hypotheses concerning the origins of the Hippopotamus indicate that the animals migrated to freshwater when something on Earth removed the forest regions. They couldn't go into the ocean since they were too exposed on land and in their hands. Hippos are said to have grown in size throughout this time period. They had a good chance of surviving whatever Earth-shaking event happened. The evolution of hippopotamuses is thought to have had a little role in their survival. For instance, because of their enormous size, many other creatures in the wild will avoid them completely. There is a need for their survival; otherwise it will take only a century for their extinction from Earth.

References

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