Species Diversity Within and Among Ecosystems - Ecological Systems - page 262

2

1.8

1.6

1.4

1.2

1

0.8

0.6

0.4

0.2

0

1970 1975 1980 1985 1990 1995 2000 2005

Fig. 14.3 Living planet index for vertebrates. Index value shown in bold; shaded area shows 95%
confidence limits [ 38 ]

generally predicted that a decrease in biodiversity will result in a reduction of
ecosystem function, which will in turn lead to the loss of ecosystem goods and
services [ 60 - 62 ]. While there is still work to be done to describe the exact nature of
the relationship [ 63 ], evidence suggests that species richness, functional
characteristics, composition, and interactions influence ecosystem function [ 64 ].
The greatest amount of research in this area has focused on the relationship
between species richness and ecosystem function [ 65 ], with the relationship usually
reported as being positive [ 64 ]. Evidence suggests that species-rich communities
have greater interspecific variation in response to changes and provide more
temporally stable ecosystem services [ 66 ]. In experimental systems, it has been
proven that productivity, nutrient retention, and resistance to invasion and diseases,
all tend to increase with increasing species richness [ 67 ].
Interactions among species, such as competition, mutualism, and predation, are
also crucial to ecosystem functioning [ 67 ] and may be more important than species
richness [ 68 ]. Direct interactions between plants and fungi, plants, and animals, and
indirect interactions involving more than two species are essential for ecosystem
processes such as transfer of pollen and seeds, transfer of plant biomass production
to decomposers or herbivores, construction of habitat complexity, or the spread or
suppression of plant, animal, and human pathogens [ 67 ]. Interactions between
different species trophic levels are also key to regulating the provision of ecosystem
services [ 69 ]. Certain combinations of species are complementary in their
patterns of resource use and can increase average rates of productivity and nutrient
retention [ 64 ].
Species' functional characteristics also strongly influence ecosystem properties.
The loss of species such as ecological engineers or keystone species with unique
functional characteristics may have profound effects on ecosystem function [ 71 ].
Species composition also plays an important role in ecosystem processes and