"Biodiversity is more in tropics.” Discuss.
Answers
Answer:
Biodiversity is the variety and variability of life on Earth. Biodiversity is typically a measure of variation at the genetic, species, and ecosystem level.[1] Terrestrial biodiversity is usually greater near the equator,[2] which is the result of the warm climate and high primary productivity.[3] Biodiversity is not distributed evenly on Earth, and is richest in the tropics.[4] These tropical forest ecosystems cover less than 10 percent of earth's surface, and contain about 90 percent of the world's species.[5] Marine biodiversity is usually highest along coasts in the Western Pacific, where sea surface temperature is highest, and in the mid-latitudinal band in all oceans. There are latitudinal gradients in species diversity.[6] Biodiversity generally tends to cluster in hotspots,[7] and has been increasing through time,[8][9] but will be likely to slow in the future.[10]
Rapid environmental changes typically cause mass extinctions.[11][12][13] More than 99.9 percent of all species that ever lived on Earth, amounting to over five billion species,[14] are estimated to be extinct.[15][16] Estimates on the number of Earth's current species range from 10 million to 14 million,[17] of which about 1.2 million have been documented and over 86 percent have not yet been described.[18] More recently, in May 2016, scientists reported that 1 trillion species are estimated to be on Earth currently with only one-thousandth of one percent described.[19] The total amount of related DNA base pairs on Earth is estimated at 5.0 x 1037 and weighs 50 billion tonnes.[20] In comparison, the total mass of the biosphere has been estimated to be as much as 4 TtC (trillion tons of carbon).[21] In July 2016, scientists reported identifying a set of 355 genes from the Last Universal Common Ancestor (LUCA) of all organisms living on Earth.[22]
The age of the Earth is about 4.54 billion years.[23][24][25] The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago,[26][27][28] during the Eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. There are microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia.[29][30][31] Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old meta-sedimentary rocks discovered in Western Greenland.[32] More recently, in 2015, "remains of biotic life" were found in 4.1 billion-year-old rocks in Western Australia.[33][34] According to one of the researchers, "If life arose relatively quickly on Earth .. then it could be common in the universe."[33]
Since life began on Earth, five major mass extinctions and several minor events have led to large and sudden drops in biodiversity. The Phanerozoic eon (the last 540 million years) marked a rapid growth in biodiversity via the Cambrian explosion—a period during which the majority of multicellular phyla first appeared.[35] The next 400 million years included repeated, massive biodiversity losses classified as mass extinction events. In the Carboniferous, rainforest collapse led to a great loss of plant and animal life.[36] The Permian–Triassic extinction event, 251 million years ago, was the worst; vertebrate recovery took 30 million years.[37] The most recent, the Cretaceous–Paleogene extinction event, occurred 65 million years ago and has often attracted more attention than others because it resulted in the extinction of the non-avian dinosaurs.[38]
The period since the emergence of humans has displayed an ongoing biodiversity reduction and an accompanying loss of genetic diversity. Named the Holocene extinction, the reduction is caused primarily by human impacts, particularly habitat destruction.[39] Conversely, biodiversity positively impacts human health in a number of ways, although a few negative effects are studied.[40]
The United Nations designated 2011–2020 as the United Nations Decade on Biodiversity.[41] and 2021–2030 as the United Nations Decade on Ecosystem Restoration[42] According to a 2019 Global Assessment Report on Biodiversity and Ecosystem Services by IPBES, 25% of plant and animal species are threatened with extinction as the result of human activity.
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Explanation:
The increase in biological diversity of some groups from the poles toward the equator is one of the most fundamental patterns of life on earth. This gradient pattern, often referred to as the latitudinal gradient in species diversity, was initially documented by Alexander von Humboldt in 1807, when he stated: ‘‘The nearer we approach the tropics, the greater the increase in the variety of structure, grace of form, and mixture
of colors, as also in perpetual youth and vigor of organic life’’. Ever since the first hypothesis, the number of explanatory hypotheses for why this gradient exists, has
increased, and currently more than 30 different mechanisms and factors have been proposed and debated to explain it. Although known for about two centuries, this pattern still lacks a general consensus, which makes it probably as one of the great modern challenges of macroecology. In general the pattern predicts that when moving from high to low latitudes the average species richness increases, this pattern has been well documented for a wide spectrum of taxonomic groups (e.g., mammals, fishes, insects, and plants). However, there are notable exceptions to this general pattern of high biodiversity in the tropics. For example, neither wasps (Ichneumonidae: Hymenoptera), aquatic plants, ectoparasites in fish, birds, nor mammals seem to exhibit species richness in relation to decreasing latitudinal gradients. Thusly, the latitudinal gradient in species richness might be more complex than initially observed by Humboldt and others. Consequently, all hypotheses which attempt to explain this
phenomena should be based on biotic, abiotic, historical, geographical, and biogeographic factors, environmental stability, habitat heterogeneity, productivity,
stochastic forces, ecological and evolutionary time, species ranges, environmental gradients, interspecific interactions and many others mechanisms. Many of the current hypotheses, found in the literature, are not mutually exclusive, and others merely offer
different levels of explanation. To account fully for a latitudinal gradient in species richness, in this chapter, we examine the ecological and evolutionary outcomes of the
origins and maintenance of tropical biodiversity to try to understand “why tropic regions have the highest biodiversity?” We begin by summarizing the differences
between tropic, temperate, and polar regions, and then turn to the pattern of biodiversity, “why are there so many different kinds of organisms in the tropics?” and
finally to latitudinal gradients in species richness diversity and their hypothese.
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