`star` Latitudinal gradients
`star` Species Richness in Rainforests
`star` Species-Area relationships


● The `color{violet}("diversity of plants")` and `color{violet}("animals")` is not uniform throughout the world but shows a rather uneven

● For many group of `color{violet}("animals")` or `color{violet}("plants")`, there are interesting patterns in `color{violet}("diversity")`, the most well- known being the `color{brown}("latitudinal gradient")` in `color{violet}("diversity.")`

● In general, species `color{violet}("diversity decreases")` as we move away from the equator towards the poles.

● With very few exceptions, tropics (`color{violet}("latitudinal range of 23.5° N to 23.5° S")`) harbour more species than `color{violet}("temperate or polar areas.")`

● Colombia located near the equator has nearly `color{violet}("1,400 species of birds")` while New York at `color{violet}("41° N")` has `color{violet}("105 species")` and Greenland at `color{violet}("71° N")` only `color{violet}("56 species.")`

● India, with much of its land area in the `color{violet}("tropical latitudes")`, has more than `color{violet}("1,200 species of birds.")`

● A forest in a `color{violet}("tropical region")` like `color{violet}("Equador")` has up to 10 times as many species of vascular plants as a forest of equal area in a `color{violet}("temperate region")` like the Midwest of the USA.

● The largely `color{violet}("tropical Amazonian rain")` forest in South America has the `color{violet}("greatest biodiversity")` on earth- it is home to more than `color{violet}("40,000 species of plants, 3,000 of fishes, 1,300 of birds,")` `color{violet}("427 of mammals, 427 of amphibians")`, `color{violet}("378 of reptiles and of more than 1,25,000 invertebrates.")`


● `color{violet}("Scientists estimate")` that in these rain forests there might be at least two million insect species waiting to be
`color{violet}("discovered")` and `color{violet}("named.")`

● `color{violet}("Ecologists")` and `color{violet}("evolutionary biologists")` have proposed various hypotheses; some important ones are:

`star` `color{brown}("Speciation")` is generally a function of time, unlike `color{violet}("temperate regions")` subjected to frequent glaciations in the past, `color{violet}("tropical latitudes")` have remained relatively undisturbed for millions of years and thus, had a long evolutionary time for `color{violet}("species diversification")`

`star` `color{brown}("Tropical environments")`, unlike temperate ones, are less `color{violet}("seasonal, relatively ")`more constant and predictable. Such constant environments promote niche `color{violet}("specialisation")` and lead to a greater species `color(violet}("diversity.")`

`star` There is more `color{brown}("solar energy")` available in the `color{violet}("tropics,")` which contributes to `color{violet}("higher productivity")`; this in turn might contribute indirectly to `color{violet}("greater diversity.")`


● During his `color{violet}("pioneering")` and `color{violet}("extensive explorations")` in the wilderness of South American jungles, the great
German naturalist and geographer `color{brown}("Alexander von Humboldt")` observed that within a region species
richness increased with increasing explored area, but only up to a limit.

● In fact, the relation between species richness and area for a wide variety of `color{violet}("taxa (angiosperm plants, birds, bats, freshwater fishes)")` turns out to be a `color{violet}("rectangular hyperbola.")`

● On a `color{violet}("logarithmic scale")`, the relationship is a `color{violet}("straight line")` described by the equation
`color{violet}("log S = log C + Z log A")`
`color{violet}("S=")` Species richness
`color{violet}("A=")` Area
`color{violet}("Z =")` slope of the line (regression coefficient)
`color{violet}("C = Y")`-intercept

● `color(violet}("Ecologists")` have discovered that the value of `color{brown}(Z)` lies in the range of `color{brown}(0.1)` to `color{brown}(0.2)`, regardless of the taxonomic group or the region (whether it is the `color{violet}("plants in Britain")`, `color{violet}("birds in California")` or `color{violet}("molluscs")` in New York state, the slopes of the regression line are amazingly similar).

● But, if we analyse the species-area relationships among very `color{violet}("large areas")` like the entire continents, we will
find that the `color{violet}("slope of the line")` to be much steeper (`color{violet}(Z)` values in the range of 0.6 to 1.2).

● For example, for `color{violet}("frugivorous (fruit-eating) birds")` and `color{violet}("mammals")` in the `color{violet}("tropical forests")` of different continents, the slope is found to be 1.15.