SPATIAL AND TEMPORAL DIMENSIONS OF BIODIVERSITY DYNAMICS
Dethardt Goetze, Ursula Karlowski and Stefan Porembski
Department of Botany, University of Rostock, Germany
Klement Tockner
Department of Limnology, EAWAG Duebendorf, Switzerland
Aparna Watve
Department of Botany, Agharkar Research Institute, India
Klaus Riede
Zoological Research Institute and Museum Alexander Koenig, Germany
Keywords: coevolution, competition, equilibrium processes, evolutionary radiation, extinction, fragmentation, functional group diversity, functional redundancy, gap dynamics, habitat diversity hypothesis, herbivory, hierarchical biodiversity concept, intermediate disturbance hypothesis, island biogeography, keystone species, metapopulation, migration, minimum viable population, mosaic-cycle concept, mutualism, patch-dynamics concept, predation, productivity, resilience, resource availability hypothesis, r-K selection, shifting habitat mosaic, speciation, stability, stepping-stone model, succession.
Contents
2. Temporal dimensions of biodiversity dynamics
3. Spatial dimensions of biodiversity dynamics
4. Dynamics across geological and ecological scales
4. Dynamics across
geological and ecological scales
Understanding the natural dynamics of biodiversity at different spatial and temporal scales is essential for evaluating the impact of humans on diversity dynamics. Knowledge of the underlying processes and mechanisms that govern the generation, maintenance and loss of biodiversity is fundamental for making predictions on the future.
4.1. Geological scale
Between the inception of life, estimated to be about 3.5 to 4 billion years ago, and today, biotic diversity has increased in a process of enormous evolutionary radiation and specialisation. As only the fossil record can give us information about species numbers in past times and most of the soft-bodied organisms did not leave any fossil remains behind, quantitative data on patterns of diversification and extinction throughout geological time are very scarce. Long-term patterns in biodiversity were assessed by compiling the first and last occurrence of every animal genus in the marine-fossil record, revealing that biodiversity increased exponentially through time (or exhibited a logistic increase). Three separate evolutionary faunas (Cambrian, Palaeozoic, and Modern) have been identified, each going through initial diversification, dominance, and decline. Each successive fauna displayed a slower rate of diversification but a higher level of diversification than the preceding one. This increase in biodiversity through time has been sporadically interrupted by brief (less than one million years) events leading to mass extinctions (Figure 5). The great mass extinction at the end of the Permian period led to a reduction in marine families by 50% and in marine genera by 80%. After mass extinctions, diversification is accelerated owing to greater capacities of pioneer species and perhaps also influenced by the added space made available to them. Recently, a distinct 62-million-year wave of rising and falling biodiversity through the past 500+ million years was discovered. This wave is too big to be ignored, with biodiversity shrinking and growing by several hundred marine genera. This rhythmic cycle is supposed to be governed by internal dynamics as well as by rhythmic external forcing.
Major changes in biodiversity also occurred during the Cenozoic, for which more accurate information is available. There is evidence that global diversity today is lower than it was 5 to 15 million years ago. Pulses of mammal extinction, for example, reduced the North American large mammal diversity from at least 120 species to today 25 species. This reduction was most probably caused by rapid changes in climate and by the appearance of humans at the end of the Pleistocene. End-Pleistocene extinctions also occurred in South America, in Eurasia and in Australia, but not in Africa. In Australia major extinctions happened about 40 000 years BP, compared to 9000 to 18 000 years in the Americas. The present era (Holocene), however, is a time of generally and rapidly decreasing biodiversity, correlated with a growing human impact on the Earth and its climate.
Figure 5. Diversity of marine animal families through 77 time intervals of the Phanerozoic.
The bold upper curve shows the total number of families with skeletalised species known from the fossil record, with the principal phases of diversification indicated at the top. Cm, Pz and Md: Cambrian, Palaeozoic and Modern Fauna. Arrows and numbers mark the mass extinction rates of the marine realm (number 5 marks the present event).
Modified after Sepkoski, J. J. jr. (1993). Ten years in the library: new data confirm palaeontological patterns. Palaeobiology 19: 43–51.
4.2. Ecological scale
Most estimates of the total number of species today lie between 5 and 30 million, although the overall total could be higher than 30 million if poorly known groups such as deep-sea organisms, fungi, and microorganisms comprise more species than currently estimated. Species present today only represent 2 to 4% of all species that once occurred on our planet. Extinction is therefore a natural part of Earth’s history. Over the past few hundred years, however, humans have increased the species extinction rate by as much as 1000 times over the background rates typical over the planet’s history (Figure 6).
A fundamental question in evolutionary and conservation theory is: why do some areas contain greater species diversity than others, for biodiversity has developed very differently in different latitudes and altitudes. The general trend for terrestrial environments is an increase of species diversity with decreasing latitude and a decrease with elevation. The energy theory points out that this phenomenon is as well correlated with the energetic element of climate at a global or local scale: high temperature in combination with low evapotranspiration is correlated with high species diversity.
Beside the role of immigration and extinction in relation to area size and proximity to source areas, the role of speciation is recognised as an important factor. Speciation, a key driver of evolution, might be faster in those biomes where no physiological rest period interrupts the genetic processes. Thus the speciation rate could be faster in the tropics compared to regions with a long dry or cold (winter) period. Recent analyses of volcanic islands have shown that species richness is a strong predictor of the level of speciation of both plants and arthropods; which indicates that diversity itself can be a major driver of speciation. Riverine flood plains, to take another example, are key centres of biological diversification. They are assumed to belong to those aquatic ecosystems where biota of lentic areas (standing water bodies) started their evolution. The temporal continuity of riverine systems and their associated disturbance regime allowed the permanent presence of lentic and semi-lentic water bodies throughout time. Therefore, crustacean orders such as Chonchostraca and Notostraca—they are so-called living fossils—are still living in flood plain areas. The speciation of alluvial groundwater crustaceans is also supposed to be favoured by the lateral shifting of river channels that lead to the isolation of former connected channels (e.g. Cyclopids in the alluvial aquifer of the Danube). In contrast to alluvial floodplains, true groundwater ecosystems are less dynamic but they also have a very unique fauna represented by very species-rich groups such as Crustacea. Causes for the high diversity of ground waters are (1) the lack of abundant competitors/predators in the subsurface hydroscape, (2) a high propensity for speciation through isolation, (3) favourable thermal conditions, and (4) a dynamic local palaeogeography.
Figure 6. Species extinction rates.
"Fossil Record" refers to average extinction rates as estimated from the fossil record. "Recent Past–Known Record" refers to extinction rates calculated from known extinctions of species (lower estimate) or known extinctions plus "possibly extinct" species (upper bound). A species is considered to be "possibly extinct" if it is believed by experts to be extinct but extensive surveys have not yet been undertaken to confirm its disappearance. "Projected" extinctions are model-derived estimates using a variety of techniques, including species-area models, rates at which species are shifting to increasingly more threatened categories, extinction probabilities associated with the IUCN categories of threat, impacts of projected habitat loss on species currently threatened with habitat loss, and correlation of species loss with energy consumption. The rate of known extinctions of species in the past century is roughly 50 to 500 times greater than the extinction rate calculated from the fossil record of 0.1 to 1 extinction per thousand species per thousand years. The rate is up to 1000 times higher than the background extinction rates if possibly extinct species are included. Adapted from Millennium Ecosystem Assessment 2005. Ecosystems and human well-being: biodiversity synthesis. World Resources Institute, Washington, DC.
4.3. Rapid biodiversity changes
Recently isolated ecosystems, such as the African Lakes or volcanic archipelagos such as the Galapagos and Hawai’i islands, can be considered as natural laboratories where speciation can be observed in situ. These habitats became isolated in geologically young times, dating back several thousands (African Lakes) to a few millions of years (Galapagos, Hawai’i). The Darwin finches on Galapagos are among the best known examples (see Characterization of Biodiversity).
One of the fastest and most species-rich adaptive radiations is represented by the haplochromine cichlid fish of the East African Great Lakes. Together, the isolated Lake Victoria and Lake Malawi harbour more than 800 species that are not found anywhere else in the world. These are more than all of the freshwater species found in all the waters of both Europe and North America. There is evidence that these flocks evolved in a very short time period from one or a few common ancestors (Lake Victoria: 15 000 to 250 000 years, Lake Malawi: up to five million years). A recent long-term study revealed that adaptation processes are on-going at rapid speed, resulting in morphological and physiological changes already after a few decades. In contrast, the rivers associated with these two lakes show very low haplochromine species richness and morphological diversity. This is believed to be because rivers lack the wealth of ecological opportunity thought to drive adaptive radiation in lakes.
Another well-studied species swarm are Hawai’ian Drosophilids. These fruit flies are genetically well-studied, and therefore reveal insights into genetic mechanims of hybrid incompatibility. Meanwhile, rapidly evolving, highly divergent genes were identified, such as the hybrid male rescue (Hmr) in D. melanogaster, D. mauritania, and D. similans. They evolve rapidly and under strong positive selection, causing differences of 13% between Hmr-proteins of the sister species.
Infectious diseases are also recognised as playing important roles in natural systems by influencing coevolutionary processes. Rapid evolution (on the order of decades or shorter) has been supported by an increasing number of examples from host-pathogen systems. Although pathogens are responsible for spreading new diseases and may pose major risks to endangered species, pathogens can also be a driving force behind species and genetic diversity in natural populations. Similarly, the introduction of exotic species may increase overall diversity and trigger future evolutionary processes, although the impacts of exotic species may vary at different spatio-temporal scales.
At the scale of entire ecosystems, major fluctuations in species diversity may occur at short time periods of months to years. In floodplains, which are disturbance-dominated—even disturbance-dependent ecosystems—major fluctuations of species richness occur as a consequence of periodic floods and droughts. Floodplains are very resilient systems, and within a few months following a severe flood diversity is again as high as it was during pre-flood conditions. The high resilience is a consequence of the adaptation of the populations to survive harsh conditions as well as the presence of refugia from which they can recolonise depauperated habitats.
4.4. Forecasting biodiversity changes
At present we face the sixth mass extinction of species with a 100 to 1000 times faster decline in richness compared to previous events (Figure 6). Since 1600, 484 animal and 654 plant species (mostly vertebrates and flowering species) are recorded as having gone globally extinct. This is certainly an underestimate of the true total. The rate of extinction has increased dramatically during recent decades. The Living Planet Index measured a decline of the freshwater index (decline of selected vertebrate populations) of 55% between 1970 and 2000, compared to 25% for marine and 25% for terrestrial populations. The main reasons of the rapid decline in biodiversity are large-scale land-use changes, global climate change, and invasion by non-native species. Can we forecast future biodiversity trends? Future biodiversity loss is predicted to be 10 to 100 times faster than present loss. Prediction of extinctions are model-derived estimates using a variety of techniques including species-area models, rates at which species are shifting to increasingly more threatened categories, extinction probabilities associated with the IUCN categories of threat, impacts of projected habitat loss on species currently threatened with habitat loss, and correlation of species loss with energy consumption.
Key questions related to the future fate of biodiversity are (i) whether present biodiversity loss patterns are comparable to those in the past, (ii) are declines in diversity gradual or rather do they show a threshold-behaviour and (iii) to which extent human impacts will affect future evolutionary processes and directions. For example, a time lag of several million years often occurs following mass extinction events before the diversity of the surviving biota recovers. During this period, some of the species that survived the extinction gradually decline to extinction, so representing ‘dead clades walking’. Thus, the current extinction event might have consequences lasting for many thousands of human generations.
Naturally occurring dynamics of biodiversity constitute only one aspect of biodiversity which is more sophisticated, still requiring scientific monitoring projects as well as experimental approaches of fundamental research on any aspect mentioned in this chapter. Most of the knowledge gained so far has been derived from data originally obtained for other purposes.
More research is needed on the complex interrelations of biodiversity dynamics, organismic functional groups and ecosystem functioning. In particular, ecosystems under stress may be suited for studying ecosystem key functions under varying diversity. A more quantitative and objective assessment of the role of microbial diversity in ecosystem function should be carried out by studying those processes uniquely or predominantly mediated by microorganisms and on which other organisms ultimately depend. Bacteriologists and mycologists should collaborate with ecologists so that more comprehensive data sets could be obtained on measurable parameters of functional attributes such as rates of nitrification, denitrification, decomposition etc. in combination with diversity data.
As it is often impossible to predict which species may play a major role in key processes like the above-mentioned under changed environmental conditions, and what implications might ensue for biodiversity, the temporal and spatial scales at which critical interactions function are in need of extensive study. One priority is to investigate to what degree the species involved determine the integrity of the community and its unaltered persistence through time, i.e. its stability. This refers to cases where there could be a relationship between dynamics of biological complexity and stability.
Concepts for describing and analysing dynamics of spatial biodiversity patterns are, in general, still to be developed, e.g. related to the patch dynamics concept, the metapopulation theory, or the theory of island biogeography for habitats on the mainland. A number of recent studies in this field have demonstrated that many results obtained from studies of selected model populations and of rather small oceanic model islands cannot readily be transferred to communities in mosaics of complex terrestrial habitats. In this context the problem of scale needs to be addressed in order to be able to refer diversity values to defined ecological entities at organisation levels above the species level. In addition, further concepts for the diversity of these ecological entities themselves, i.e. sites or habitats, physiotopes, and ecosystems, have to be developed to obtain comparable diversity measures at these higher organisation levels.
In consequence of the ratification of the United Nations’ Convention on Biological Diversity, the German Federal Ministry of Education and Research (BMBF) launched the BIOLOG research programme (Biodiversity and Global Change) that comprises the BIOLOG-Europe and BIOTA-Africa programmes doing research on biodiversity dynamics. The BIOTA-Africa programme is an international research project with collaboration of a variety of German and African research institutions. It was started in 2001 and is located at the University of Hamburg. Internet: http://www.biota-africa.org. The BIOLOG research activities are embedded in the worldwide DIVERSITAS network for the support of biodiversity science. This provides an international platform for the communication and promotion of biodiversity research and resulting recommendations and initiatives for the sustainable conservation of biodiversity. The German BMBF is also funding and co-ordinating the German GBIF activities. GBIF is an international initiative for networking the existing worldwide data on biological diversity and making it freely available on the Internet: http://www.gbif.org. The BDFFP is a bi-national, collaborative research project between the Smithsonian Institution, Washington, D.C., and the Brazilian Institute for Research in the Amazon (INPA). It was initiated in 1979 and is located at Manaus. Internet: http://pdbff.inpa.gov.br. The GROMS project was initially supported from 1997 to 2002 by the German Federal Ministry of the Environment (BMU) through the German Federal Agency for Nature Conservation (BfN), and in the following by the Convention on Migratory Species (CMS) and the Museum Alexander Koenig, Bonn. The GROMS project is an initiative supported by the Convention on Migratory Species (UNEP/CMS). It is located at the Museum Koenig, Bonn. Internet: http://www.groms.de. The German Research Association (DFG) supported a number of studies on sigmasociology and community diversity of vegetation complexes.
Click Here To View The Related ChaptersConnell J.H. (1978). Diversity in tropical rainforests and coral reefs. Science 199: 1302–1310. [This introduced the concept of maximisation of species diversity under intermediate levels of disturbance. Since then there have been numerous investigations, the majority of which support this model.]
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Dethardt Goetze was born in Braunschweig, Germany. He studied botany, zoology, limnology, soil sciences and geology at the Universities of Braunschweig and Freiburg/Breisgau and accomplished his doctorate at Darmstadt University of Technology. He developed a method for surveying and analysing biodiversity at different organisation levels of ecological systems in typified landscape sections in southwestern Germany. He also managed conservation projects for an environment protection organisation in central Germany. Currently, he is a postdoctoral assistant at the Department of Botany of the University of Rostock and coordinator of a botanical project of the interdisciplinary BIOTA Africa research programme (Biodiversity Monitoring Transect Analysis in Africa), focusing on the implications of global change on habitat fragmentation to develop guidelines on a more sustainable use of biodiversity in West Africa. His fields of research are the analysis of habitat patterns, landscape metrics, landscape diversity, and their dynamics.
Ursula Karlowski was born in Oberhausen, Germany. She studied Biology at the Universities of Bielefeld and Bonn and her dissertation subject was the secondary succession of old-fields in the afromontane region of Uganda. The influence of animal-dispersal on the regeneration process as well as the implications of her results for the management strategy of Mgahinga Gorilla National Park was one of the focal points of her study. She has been engaged in rain forest conservation in eastern and central Africa since 1988, especially in southwestern Uganda in close cooperation with the Mgahinga Gorilla National Park Project. She continued her vegetation studies and assessments on the conservation status in Kahuzi-Biega National Park and in high altitude regions of the Parc National des Virunga, D.R. Congo.
Currently she is working as a scientific assistant at the Institute of Biosciences at the University of Rostock. As a specialist in vegetation ecology her special interests are studies of vegetation change and nature conservation strategies. She has been given grants from DAAD, FES and from animal and environment protection NGOs like Friends of the Earth, berggorilla®enwald direct aid, and Diane Fossey Gorilla Fund.
Klement Tockner is an Associate Professor for aquatic ecology at ETH (Swiss Federal Institute of Ecology and Technology) and head of the research group "Floodplain Ecology and Biodiversity" at the department of Limnology at EAWAG (Swiss Federal Institute for Aquatic Science and Technology). He received his PhD degree in 1993 at the University of Vienna. After one year of work as a limnology consultant in East Africa, he coordinated the Danube Restoration Project in Austria. In recent years, he has been a visiting scientist at the Tohoku University (Sendai, Japan), the University of Montana (USA) and the Institute of Ecosystem Studies (USA). Klement Tockner has experience of both fundamental and applied scientific investigations of European river systems. In particular, he has worked on several large Alpine river systems, and has been involved in the scientific investigations underpinning restoration of parts of the Danube. He leads an international and interdisciplinary research team at the Tagliamento River in NE Italy, which is a key reference ecosystem of European importance.
Aparna Watve is working at Agharkar Research Institute Pune, India, on a project to document plant communities on rock outcrops in Northern Western Ghats. The rock outcrops are rich in endemic plants which are in immediate need for conservation. The present project aims at identifying appropriate management strategies for conservation of the outcrop habitats. Her doctoral work was on spatial distribution of plant species and communities in the Mulshi area of the Western Ghats. She has worked in Botanical Surveys of India for documenting the floristic diversity of national parks, and became engaged in developing web based electronic catalogues of Indian organisms at the Centre for Biodiversity Informatics. Her main interests are documentation and dissemination of knowledge regarding biodiversity, especially of specialised habitats such as sacred groves and rock outcrops. She is also working as a consultant for non-formal, unsupervised environment education programmes.
Klaus Riede studied zoology and biocybernetics in Frankfurt and Tuebingen, Germany. After his dissertation in Zoology, at the Max-Planck-Institute for behavioural physiology, he studied the species-rich grasshopper fauna of South America. He continued field studies in Malaysia, combining them with neuroethological laboratory experiments about hearing physiology in Orthoptera. Since 1997, he designed and managed two major biodiversity informatics projects at Museum Koenig, Bonn: the "Global Register of Migratory Species" ( www.groms.de) and the "Digital Orthoptera Access" project (www.dorsa.de).
Stefan Porembski was born in 1960, in Berlin (Germany). He studied Biology with Chemistry and Physics at the Freie Universität Berlin and at the University of Bonn, and his dissertation subject was functional aspects of the morphology and anatomy of succulent plants with particular emphasis on Cactaceae.
He was a Postdoctoral and Scientific Assistant at the Botanical Institute of the University of Bonn, and since 1998 has been Professor and head of department at the Botanical Institute and director of the Botanical Garden of the University of Rostock, where he created a working group on terrestrial habitat fragments (inselbergs, miniature dunes, forest islands, and temporary pools).
His main fields of research are tropical ecology and biodiversity (the vegetation of inselbergs, forest fragments, desiccation-tolerant vascular plants, carnivorous plants, succulents, and epiphytes), and systematics of angiosperms. He has concentrated especially on the analysis of spatial and temporal dynamics of plant communities by using permanent plots placed in different tropical ecosystems. Several of his projects are concerned with the consequences of changing land-use activities for the species diversity of tropical ecosystems. He has researched mostly in South America (Brazil), West Africa (Ivory Coast, Benin), and India, and has received grants from, among others, the DFG, BMBF, and DAAD. He is Vice-President of the International Organisation for Succulent Plant Study (IOS).
To cite this chapter (concerning the order of co-authors), please write: Dethardt Goetze, Ursula Karlowski, Klement Tockner, Aparna Watve, Klaus Riede and Stefan Porembski, Spatial and Temporal Dimensions of Biodiversity Dynamics, in the EOLSS Theme: Biodiversity: Structure and Function.
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