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8.4 READING RESOURCES 
Pre-Reading 
A.
This picture shows the population decline of some animal species. What factors do you think led to the 
decline in population? What other animals have declining populations? How can we increase their 
populations? 
Reading #1: The Biodiversity Crisis 
Traditionally, ecologists have measured 
biodiversity
, a general term for the number of species 
present in the biosphere, by taking into account both the number of species and their relative 
abundance to each other. On various scales of living organism organization, biodiversity can be 
estimated. These estimation indices, which derive from information theory, are most helpful when 
used as a first step in quantifying biodiversity between and within ecosystems. However, they are less 
helpful when conservation biologists' primary concern is merely the loss of biodiversity. However, 
biologists are aware that focusing efforts to preserve the biologically or technologically significant 
components of biodiversity may be aided by measures of biodiversity, such as species diversity. 
The Lake Victoria cichlids serve as an illustration for how we can start to comprehend 
biodiversity. When biologists first started studying cichlids in the 1980s, they found hundreds of 
different species, each of which had distinct feeding habits and habitat preferences. For example, 
some cichlid species eat plankton that is floating in the water, while others consume the eggs of other 
cichlid species. The cichlids of Lake Victoria are the product of a complex 
adaptive radiation
. An 
adaptive radiation
is a rapid (less than three million years in the case of the Lake Victoria cichlids) 
branching through speciation of a phylogenetic clade into many closely related species. Typically, 
the species “radiate” into different habitats and niches. With 15 species, the finches of the Galápagos 
Islands represent a modest adaptive radiation. A spectacular adaptive radiation that once included 
about 500 species is the cichlids of Lake Victoria. 

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Some species started to quickly vanish as biologists were making this discovery. The Nile 
perch, a species of sizable predatory fish that fisheries introduced to Lake Victoria to feed the locals 
there, was one of the causes of these declines. The Nile perch was introduced in 1963, but its 
populations did not begin to surge until the 1980s. The perch population grew by consuming cichlids, 
driving species after species to the point of 
extinction
(the disappearance of a species). In fact, there 
were several factors that played a role in the extinction of perhaps 200 cichlid species in Nile perch, 
deteriorating lake water quality brought on by agriculture and land clearing along Lake Victoria's 
shores, and increased fishing pressure are all issues related to this body of water. Since so many 
species were lost and unnamed, scientists had not even cataloged all of the species that were there. 
The diversity has diminished significantly over time. 
The cichlids of Lake Victoria are a brief illustration of the current, rapid extinction of species 
that takes place on Earth and is primarily brought on by human activity. Extinction is a 
macroevolutionary process that happens naturally at a rate of about one species per million per year.
The fossil record reveals that there have been five periods of