Species Diversity Within and Among Ecosystems - Ecological Systems - page 261

between 12% and 34% are currently threatened with extinction. The highest species
richness of threatened marine fishes is found in the Indo-West Pacific, Central
Indo-Pacific, South China, Coral, Caribbean, and Mediterranean Seas, and the
highest species richness of threatened freshwater fish species is found in Southeast
Asia [ 38 ].
The available data for the LPI for freshwater fish indicates a rapid and steady
decline in population abundance approaching a 65% reduction. Marine data are
limited, but indicate a gradual decrease of 20% in the number of marine fish
populations [ 38 ]. The main threat to fish species is overexploitation
and pollution; aquatic habitats are routinely treated as limitless sources for human
consumption [ 53 , 54 ]. Over 85% of the world's fisheries are either recovering or
fully or partially overexploited [ 55 ]. In addition, freshwater fish have been particu-
larly negatively affected by pollution and habitat alteration caused by damming and
water management activities such as abstraction for agriculture [ 56 ].
Reptiles
While reptiles are the dominant vertebrate of arid systems, like other vertebrates,
the highest species richness is found in tropical forests. Indonesia and the Congo
Basin have the highest species richness of reptiles. Marine reptiles, such as sea
snakes, turtles, and crocodiles, are found in the highest concentrations in the West
and Central Indo-Pacific and the South China and Coral Seas. An assessment of
a representative sample of species suggests that between 18% and 32% of reptile
species are threatened with extinction, although this varies greatly between groups
[ 38 ]. For example, a high proportion of crocodilians are threatened compared with
a relatively lower number of snakes [ 57 ]. The highest species richness of threatened
reptiles is found in Southeast Asia and the Ganges basin [ 38 ].
The available trend data for the LPI for reptile species indicates that the number
of reptiles has declined by 7% [ 38 ]. However, this figure for the whole class may
mask the decline in certain orders such as turtles and tortoises, which have seen
large declines in regional-scale analysis [ 57 ]. Habitat loss is the greatest threat to
reptiles and is principally in the form of agricultural expansion, logging, and urban
development. Hunting, trapping, and overharvesting for consumption and the pet
trade are particular threats, especially to turtles and tortoises [ 58 ]( Fig. 14.3 ).
Link Between Species and Ecosystem Function
A key topic in ecology is investigating how the diversity and composition of species
in an ecosystem is related to its function. Considerable research has gone into
answering this question [ 59 ] and ecological theory supports the notion that ecosys-
tem function, and the resultant goods and services, depends on biodiversity. It is