180
T. KOhyama et al.
ecosystem measures and species diversity develops through the process of positive
feedback between the energetic efficiency of ecosystems and the functional differentiation among species, on evolutionary time scales.
1 Introduction
Ecologists and evolutionary biologists differ in their understanding of the mechanisms controlling the pattern of species assembly. One of the main concerns of
ecologists is to describe the negative feedback that regulates populations, communities and ecosystems. Communities at the same trophic level are composed of
species competing for an identical set of resources. In the view of this resource
competition, competitive exclusion by one species is a consequence of the basic
multiple-species competition model. Plenty of conditions have been proposed that
relax competitive exclusion among species; however, this is still far from explaining the diversity of species in real communities.
By contrast, taxonomists, paleontologists, and evolutionary biologists share the
view that the biota of the earth has been bringing about irreversible change in
environments, and increasing in composite species diversity with time, beyond occasional interruption by mass-extinction events. This increase in organismic diversity is coupled with the exploitation of resources, and there acts a positive feedback
between the improvement of resource-lise efficiency and the promotion of
biodiversity. However, ecological negative feedback by resource limitation observed
in present ecosystems should have worked throughout the history of biota. This is
thus an interesting question, i.e. how both negative and positive feedbacks explain
the present assembly of species.
Forest ecosystems and forest tree communities are intriguing subjects of examination. Forests, developing in moist and warm climates, are the most complicated
terrestrial ecosystems in terms of biological architecture, biomass density and species diversity. They are also the most stable systems due to cumulative growth habit
and generation-overlapped populations of trees. Forest ecosystems show a prevailing trend of directional change in biomass, productivity and biodiversity from tropical
moist climate to temperate and/or arid harsh climate. The International Biology
Programme (IBP) in the 1970's intensively investigated biomass and productivity
of forests and determined that a clear functional relationship between ecosystem
attributes and climatic parameters existed (Lieth and Whittaker 1975; Kira and
Shidei 1977). Communities of tree species primarily contribute to primary production and represent the complex and persistent architecture of forest ecosystems.
Attributes of tree communities such as species diversity was, though, not explicitly
related to ecosystem attributes during the IBP.
We are now accumulating data of repeated censuses of permanent plots from
various types of forests to monitor the fate of tree individuals and to obtain demographic parameters of each component tree species. Based on these species parameters, we are able to analyze the results of competition using multi-species models
T. KOhyama et al.
ecosystem measures and species diversity develops through the process of positive
feedback between the energetic efficiency of ecosystems and the functional differentiation among species, on evolutionary time scales.
1 Introduction
Ecologists and evolutionary biologists differ in their understanding of the mechanisms controlling the pattern of species assembly. One of the main concerns of
ecologists is to describe the negative feedback that regulates populations, communities and ecosystems. Communities at the same trophic level are composed of
species competing for an identical set of resources. In the view of this resource
competition, competitive exclusion by one species is a consequence of the basic
multiple-species competition model. Plenty of conditions have been proposed that
relax competitive exclusion among species; however, this is still far from explaining the diversity of species in real communities.
By contrast, taxonomists, paleontologists, and evolutionary biologists share the
view that the biota of the earth has been bringing about irreversible change in
environments, and increasing in composite species diversity with time, beyond occasional interruption by mass-extinction events. This increase in organismic diversity is coupled with the exploitation of resources, and there acts a positive feedback
between the improvement of resource-lise efficiency and the promotion of
biodiversity. However, ecological negative feedback by resource limitation observed
in present ecosystems should have worked throughout the history of biota. This is
thus an interesting question, i.e. how both negative and positive feedbacks explain
the present assembly of species.
Forest ecosystems and forest tree communities are intriguing subjects of examination. Forests, developing in moist and warm climates, are the most complicated
terrestrial ecosystems in terms of biological architecture, biomass density and species diversity. They are also the most stable systems due to cumulative growth habit
and generation-overlapped populations of trees. Forest ecosystems show a prevailing trend of directional change in biomass, productivity and biodiversity from tropical
moist climate to temperate and/or arid harsh climate. The International Biology
Programme (IBP) in the 1970's intensively investigated biomass and productivity
of forests and determined that a clear functional relationship between ecosystem
attributes and climatic parameters existed (Lieth and Whittaker 1975; Kira and
Shidei 1977). Communities of tree species primarily contribute to primary production and represent the complex and persistent architecture of forest ecosystems.
Attributes of tree communities such as species diversity was, though, not explicitly
related to ecosystem attributes during the IBP.
We are now accumulating data of repeated censuses of permanent plots from
various types of forests to monitor the fate of tree individuals and to obtain demographic parameters of each component tree species. Based on these species parameters, we are able to analyze the results of competition using multi-species models