Environmental change and biological diversity Present, past and future

A S. Raghubanshi, J. S. Singh & B. S. Venkatachala

Raghubanshi, A. S., Singh, ]. S & Venkatachala, B. S 1991. Environmental change and biological diversity: Present, pasl and future Palaeobotanist 39( 1) : R6·109.

The present paper reviews lhe current dislribulion and faclors delermining lhe level of biological diversity. Past c1imale changes causing mass eXlinclions, lessons drawn from lhese past events, and lhe impact of future climate change on biological diversity in ilS broadesl sense are also considered. lArge scale changes in vegetalion zones and composilion, over eXlensive pans of lhe globe are indicaled. Displacement of isolherms due 10 rise in global lemperalures would necessitale very rapid shiflS which may be possible only with human assistance except for propagaled by spores or dUSl seeds. Rates of migralion and behaviour of lhe migraling species will delermine lheir range shift capabililies Differences in migralion rales may resull in new combinalions of species because of dissocialion of communities into their component species. Species rigidly associated to a panicular sel of environmental condilions may well become eXlinct Characterislics such as large population size, broad geographical dislribulion and high dispersal pOlenlials will prolecl species from eXlinclion. Increased pressure from invaders, increased frequency of epidemics and alleration of productivity and species distribulions are indicaled. Elevaled sea WaleI' lemperalures may badly damage sea flora and fauna as is exemplified by present day EI nino effecls. DestruClion of coastal habilals due 10 sea level rise may affecl birds and fishes using sail marshes, eSluaries and islels as breeding ground. Island species will be severely affecled bOlh due 10 reduced area and Iimitalions of latitudinal migralion. Changes in precipitalion pauern may resull in reduced avian and mammalian populalions in many pans of lhe world. Key-words-Climalic change, Greenhouse effeCl, Biological diversity, Mass , Species turnover, Past c1imalic change.

A. S. Raghubanshi & j. S. Singh, Department of Botany, Banaras Hindu University, Varanasi 221 005, India. B. S. VenkatCichala, Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow 226 007, India. riu

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H6 RAGHUBANSHI et al.-ENVIRONMENTAL CHANGE AND BIOLOGICAL DIVERSI1Y 87

emerged due to the concern over the imminent fundamental descriptions of the nature of a of thousands of species as a result of community, is a measure of its diverSity: the number pollution and (Soule & Wilcox, of different species of organisms and their 1980; Ehrlich & Ehrlich, 1981; Ricklefs, 1987). The abundance, generally in terms of individuals, but current frenzy of environmental degradation is sometimes as genets or modules (Harper, 1981) or unprecedented with deforestation, desertification, biomass (Southwood, 1987) However, despite and destruction of wetlands and coral reefs considerable interest, a generally accepted occurring at rates comparable to or greater than the definition of diversity has nOt emerged (Peet, 1974). major catastrophes in the fossil records and Hurlbert (1971) contended that diversity per se does threatening to eliminate most tropical forests and nOt exist and suggested abandoning the term millions of species in our lifetime (Soule, 1985). because of multiplicity of meanings and The exacerbating anthropogenic forcing and interpretations attached to it. MacArthur (1972) also environmental degradation seem to have ushered in considered the term had outlived its usefulness, and an era of mass extinctions. According to the Eberhardt (1969), Austin (1964) and McIntosh estimates of Myers (1988), from the "hot spot" (1967) all complained of the lack of a definition. localities of tropical forests which combine Eberhardt (1969) considered that diversity mostly exceptional levels of biodiversity, endemism and suggests a considerable confusion of concepts, threats of imminent destruction, some 17000 definitions, models, and measures (or indices). endemic species (135% of all plant species of DiverSity in essence, has always been defined by the tropical forest) and 350,000 animal species might indices used to measure it and this has not led to the soon be lost. In the next few decades 25 per cent of uniformity which allows a clear statement of ideas the 250,000 higher plant species will probably and hypotheses (Peet, 1974). disappear, and in the remaining period of 21st The concept of diversity has developed from the century another 25 per cent might be lost (Myers, study of species-abundance relations and from 1990) attempts to answer questions such as (i) \Xfhy are Several authors have considered the significance there so many kinds of organisms?, and (ii) \Xfhy are of future climatic change on species survival (Ford, there certain numbers of each kind (Morrison & 1982; Norse & McManius, 1980; Wilcox, 1980; Yarranton, 1973). DiverSity thus incorporates aspects Brubaker, 1986). Peters and Darling (198'») have of number of species per unit area, and the discussed the possible impact of greenhouse gases distribution of individuals among the species. These and related global warming on the diversity of aspects were separately considered by Williams species inhabiting biosphere reserves. (1964), who derived a statistic expressive of the It is difficult to assess the consequences of a mathematical distribution of any element over sharp reduction in biological diversity for natural anOther Margalef (1958) proposed that the amount resources and for the intrinsic stability of natural of information contained in its floristic or faunistic systems. Many consider, with justification, these structure is an appropriate measure of the consequences to be potentially disastrous (Ricklefs, community'S diversity. 1987). The ability to predict the change in system A community is said to have high diversity if it function after biological depauperation, requires an has many species and the distribution of individuals understanding of the processes responsible for is fairly even among species_ Conversely, diversity is generating and maintaining diversity in biological low when the species are few and their abundances communities. We must try to understand how the uneven (Pielou, 1969). Dependence on twO rather biological diversity is distributed globally, what independent properties of a community results into factOrs determine the level of biological diverSity, ambiguiry. Therefore, a community with few species and how was it impacted by the past climatic but high evenness could have the same level of changes. diversity as another with many species but low evenness. In general, the diversity of a sample is WHAT IS DIVERSI1Y? minimal when all the individuals belong to a single species, and maximal when each individual belongs Variability of natural communities is well to a different species. Whirraker (1972) known. For example, the molluscs of a rocky shore disringuished three levels of diversity: in a cold climate may consist of only a few species Alpha diversity-Within-habitat or within­ whereas the trees in a tract of tropical rain forest may community diversity. have hundreds of species. Among the most Beta diversity-between -habitat or 88 THE PALAEOBOTANIST intercommunity diversity, defined as the change in functioning in face of such disruptive processes as species composition along environmental gradients, acid rain. or species turnover. Gamma diversity-diversity of the entire CURRENT SPECIES DIVERSITY GRADIENTS landscape or a rar>ge of communities in a location (i.e., a combination of alpha and beta). Variations in species diversity have been These forms are not always easily distinguished examined with respect to geography, climate and (Peet, 1974). Many alpha-diversity measurements are SOil..Species diversity increases from the poles to the influenced by habitat variations, which could be tropics as documented for a variety of organisms -interpreted equally well as beta diversity. The first including mammals, birds, fishes, insects, other two (alpha and beta-diversities), nevertheless have invertebrates and plants (Abbott, 1968; Black et al., proved particularly useful. The concepts of alpha 1950; Darlington, 1959; Fischer, 1960; MacArthur & diversity and equitability have been successfully Wilson, 1967; Pianka, 1966; Price, 1975; Simpson, used in understanding the benthic foraminiferal 1964; Stehli, 1968; and others); diversity is greater changes in the northern Indian ocean across the on continents than islands (MacArthur & Wilson, Oligocene-Miocene boundary and during the 1967); in temperate regions there is an increase in Quaternary (Gupta & Srinivasan, 1989, 1990c). diversity from maritime to continental climates Further, the degree to which diversity is alpha or (Whittaker & Niering, 1965; Whittaker, 1960, 1965); regional (beta or gamma) is found to have Monk (1965, 1967) has reported higher diversities considerable implications for extinction processes on calcareous soils than on acidic soils; and (Sepkoski, 1988). According to Sepkoski (1988) the Frydman and Whittaker (1968) found that diversity within-habitat diversity doubled from the was correlated with soil fertility. Resource based to the , and remained relatively steady models of community structure predict that species thereafter; beta diversity also increased subsequent richness should be higher in fields with greater to the Cambrian and remained approximately steady range of resource availability (Tilman, 1982). thereafter. The alpha and beta diversities, each In certain narrowly defined groups, the account for one-sixth of the early Paleozoic increase latitudinal gradient in species diversity is reversed in global diversity. According to Niklas (1986) and with species richness increasing poleward within a Niklas et al. (1985), there occurred striking increases latitudinal belt before decreasing again at still higher in angiosperm gamma diversity through the latitudes; for example, in penguins in the southern and Cenozoic. Southwood et al. (1979) hemisphere and in alcids in the northern studied the vegetation along a gradient of a hemisphere (Stehli, 1968); and also, in the secondary succession in southern England and sublittoral and shallow shelf infaun;J. (Thorson, found that alpha-diversity increased and then 1957). Fresh water planktonic communities are more decreased with succession age, whereas the beta­ diverse in the temperate regions compared to their diversity was proportional to the successional age counterparts in the tropics. Ichneumonid wasps are differences, age being on a logarithmic scale. This more diverse in the temperate regions than in the suggested that the turnover of plant species declined tropics (Owen & Owen, 1974), the same seems to be logarithmically with successional age. true also for burroWing animals (Klopfer, 1962). Biodiversity may range from genetic variation at Species diversity tends to decrease with the population level, through alpha, beta and patch elevation. However, this pattern is by no means diversities to regional community complexity. In the universal (Diamond, 1988a). For example, the present paper we take a broader view of species diversity of plant species along the Western Andean diversity by considering turnover of kinds of species slopes of northern circle is extremely low at sea and their assemblages in addition to species level, increases from middle to high elevations, and numbers and abundances. A broader view may be then decreases at still higher elevations. In the more conducive to investigations for assessing the Mediterranean zone of California the species role of biological diversity in ecosystem functioning. diversity reaches a maximum at middle elevations Schindler (1988) has reviewed literature on the (Cody, 1975). effects of acid rain on fresh water ecosystems to Levels of alpha diversity appear to be similar in show th~1tsignificant changes in lake metabolism did tropical alpine, temperate alpine and arctic not occur although changes in species of communities (Hanselman, 1975). Nevertheless, phytoplankton were dramatic in acidified lakes. among mountains, regional or gamma diversity There is lack of knowledge on mechanism through appears to be greater in tropical alpine than in which this biological diversity sustains ecosystem temperate alpine or arctic regions. This is evident RAGHUBANSHI et al.-ENVIRONMENTAL CHANGE AND BIOWGlCAL DIVERSI1Y 89 from relatively high levels of endemism and (ii) Diversity usually decreases up the slope of a vicarious species complexes on tropical mountains mountain. (Smith & Young, 1987) (iii) Terrestrial communities normally have greater Another apparent gradient in the diversity of diversity per unit area compared tQ marine terrestrial species groups is from a high diversity in communities. large continental landmasses to a low diversity in (iv) Islands usually have lower diversity per unit small oceanic islands (MacArthur & Wilson, 1967). area compared to continents. Species richness in mammals in the interior of North (v) Habitats with extreme environmental America is greater compared to that in the conditions such as hotsprings, deserts and peninsulas around the periphery of the continent polar deserts usually have very low species (Simpson, 1964) This peninsular effect is also diverSity. shown by the deciduous trees of Canada; there are (vi) In benthic communities in the oceans, shallow 31 species in the Atlantic provinces and 50 species in regions have low diversity while deeper a comparable area at the same latitude (north of regions have high diversity. 435°N) in Ontario (Hosie, 1969). Species diversity in marine animals, in bivalves and in polychaetes of soft sediments decreases from FACTORS CONTROLLING SPECIES DIVERSITY tropical shallow seas, through succeSSively lower It is important to understand the factors that values in the deep sea on the continental slope, in govern diversity gradients as any change in the tropical estuaries, in boreal shallow seas and in climate is likely to affect the causal factors. Several boreal estuaries (Sanders, 1968). A diversity contrast explanations have been offered within the past three between boreal shallow water communities of these decades to explain the observed patterns in the animals occurring in a continental climate (off the distribution of species diversity (Connell & Orias, new England Coast) where diversity is low and in a 1964; Darlington, 1957, 1959; Dobzhansky, 1950; maritime climate (off the State of Washington) Dunbar, 1960; Fischer, 1960; Hutchinson, 1959; where diversity is comparatively high was reported MacArthur, 1965; Pianka, 1966; Whittaker, 1972, by Sanders (1968). 1977; Ricklefs, 1979; Rosen, 1981; Thiery, 1982; Study of the relationship of species diversity to Cracraft, 1985; Turner ef al., 1988). Most of these environmental conditions has not led to widely usually explain only the patterns observed in a acceptable generalities, however (Whittaker, 1972), particular situation. Complex biological patterns in some cases diversity is highest in more mesic such as those of diversity hardly result from Single communities, in others it is not. In forest-grazing causal factor. The effect of one factor may be land of parts of Kumaun Himalaya, Saxena and Singh overridden or modified by others. Diamond 0988a) (1980) reported maximum floral diversity on the has argued that some of the determinants of species aspects which had intermediate temperature and diverSity, such as , herbiVOry, disturbance, moisture conditions and it declined towards the seasonality, and environmental predictability, cooler (and wetter) and warmer (and drier) control diversity in a nonmonotonic way, so that an exposures. Whittaker (1975) has reported that increase in those factors may yield either an increase maximum diversities are in the middle part of the or a decrease in diversity. moisture gradient for larger vegetation units in the There appear to be nine more or less distinct temperate zone. Terborgh (1973) also stated that the hypotheses regarding observed patterns of species general case in temperate North American vegetation diversity. is to have greatest species numbers in the middle part of moisture gradient, rather than in wetter or 1. Time hypothesis drier areas. But several contradictions are also available (Whittaker, 1972; del Moral, 1972). Zobel The history of geological disturbances indicates et al. (1976) reported increase in plant diversity in that all communities tend to diversify in time, and forest communities of the Central Western Cascades therefore older the community more species it is of Oregon away from the moderate environmental likely to have. Biotic diversity is a product of conditions, towards both cooler and more xeric evolution and therefore is dependent on the length environments. of time through which the biota has developed in an A few broad trends which emerge from the uninterrupted fashion (Fischer, 1960). Communities literature survey can be summarized as below: have been evolving in the tropics for a very long (i) A gradient of increasing diversity is usually time without interruptions. Thus a constant seen from the poles to the equator. favourable environment and a relative freedom from 90 THE PALAEOBOTANIST

climatic disasters like glaciation has led to greater Pianka (1966) distingUishes twO sub·categories diversity in warm, humid tropics. On the other hand of this hypothesis, one on a macro- and the other on glaciation and other catastrophic climatic events a micro-scale. Simpson (1964) has shown that the have repeatedly destroyed biota in the temperate highest diversities of mammals in the United States region. There has thus been relatively little time for occur in the mountain areas of high tOpographic communities to evolve in the higher latitudes. relief These areas contain many different habitats The time stability hypothesis is difficult to test and hence more species. Also, mountainous areas (Peters, 1976; Abele & Walters, 1979) The evidence experience more IOpographic isolation of relating to this hypothesis as summarised by Elton populations and so may promote (Krebs, (1958) and discussed by Deevey (1949), however, 198')). MaCArthur (1965) has argued that there may indicates that most continental habitats are be more land bird species in the tropics both ecologically saturated. Some palaeontological data because of an increase in the number of species per support the time hypotheSiS. Planktonic fossil habitat as well as increase in the number of habitats foraminifera exhibit a declining trend in species per unit area. richness from equator to the poles for at least 270 Microspatial heterogeneity, on the other hand, million years (Stehli et aI., 1969). Evidence for this operates on a more local scale and the si ze of hypothesis also comes from a study of the number of environmental elements correspond roughly to the insect species associated with different tree species size of the organisms populating the region (Pianka, in Britain. There appears to be a fairly strong 1966). Elements of the environmental complex in positive correlation between the number of insect this class might be soil particle size, rock and species associated with a tree species and the time boulders, karst topography, or the pallern and for which the tree species has been growing in compleXity of vegetation. Habitats with a more Britain after recolonisation follOWing the last complex or variegated structure contain more glaciation (Birks, 1980). Lake Baikal in USSR is also species than do Simpler habitats. Thus, within any an example which supports time hypothesis. There group of taxa there are generally fewer species in a are 580 species of benthic invertebrates in the deep rock desert than in an adjacent grassland, fewer in waters of this lake (Kozhov, 1963). A comparable grassland than in an adjacent savanna, and fewer in Jake in glaciated northern Canada, Great Slave lake, the savanna than in an adjacent tropical rain forest contains only four species in the same zone (Diamond, 1988a). MaCArthur and MaCArthur (1961) (Sanders, 1968). measured hird species diversity on a series of sites Simpson (1964) has argued that the warm and allempted to relate this to foliage height temperate regions have remained undisturbed long diverSity. Foliage height diversity is a measure of enough (from the Eocene to the present) to become stratification and evenness in the vertical both ecologically and evolutionarily saturated. distribution of vegetation, and according to However, there are fewer species in this zone than MacArthur and MaCArthur (1961), foliage height in the tropics, indicating that factors other than time diversity is a good predictOr of bird species diversity. stability are needed to explain differences between Structural diverSity of habitats tends to increase tropical and temperate diversities. For North from the poles to the equator with polar ice caps and American mammals, the recently glaciated zone the equatorial tropical rain forest forming the shows a fairly flat diversity profile, in contrast to a extreme ends of the gradient. However, vegetation steep gradient in species diversity expected from the spatial heterogenei~y'is clearly dependent on other evolutionary time theory (Simpson, 1964). Further, factOrs and explanation of animal species diversity in Newell (1962) stresses that temperate areas at terms of vegetation complexity at best puts the intermediate latitudes were simply shifted laterally question of the control of diverSity back to the along with their flora and fauna during the glaCial control of vegetation diversity (Pianka, 1966). periods and therefore they may have had as long a time to adapt as have the nonglaciated areas. 3. The competition hypothesis

2. Spatial heterogeneity hypothesis As advocated by Dobzhansky (1950) and Williams (1964), the natural selection in the AccC1rding to this hypothesis, more spatially temperate zones is controlled mainly by the complex environments favour coexistence of more exigencies of physical environment, whereas species. In other words, the more heterogeneous biological competition is a more important and complex the physical environment, the more component of evolution in the tropics (Pianka, complex and diverse will be the plant and animal 1966). As competition increases, organisms become communities. more specialized and niche sizes decrease causing RAGHUBANSHI et a/.-ENVIRONMENTAL CHANGE AND BIOLOGICAL DIVERSIlY 91

the species diversity to increase (MacArthur, 1965, relative constancy of resources than do areas with 1972). The evolutionary impetus to reduce more erratic climatic regimes. This also results in competition results in more niche overlap and thus smaller niches and more species occupying the unit higher diversity (Klopfer & MacArthur, 1960). Niche habitat space. Thus more stable the environmental theory predicts that when species coexist, their parameters, the more species will be· present. niches should either become narrower or the Biological communities would be evolving faster in overlap become greater compared to the allopatric the wet tropics because of the uniformly suitable situations. Coexistence of species is made possible conditions for life throughout the year. However, because of niche shift also called character rainfall and temperature can be shown to vary less in displacement (Fenchel, 1975; Giller & McNeill, the humid tropics than in the temperate zones, but 1981; Nilsson, 1965), reduction in niche width or rigorous correlation with faunal diversity has not yet increase in niche overlap. Roughgarden (1974) been possible (Pianka, 1966). Climatic factors thus showed decrease in niche breadth in species rich could determine directly the vegetation complexity, communities of Anolis lizards. while being only indirectly related to the faunal According to Dobzhansky (1950), in the humid diversity of the area. tropics catastrophic mortality (density­ The factor of climatic stability can be combined independent), such as that due to drought and cold, with the time factor, with which it has much in seldom occurs. Catastrophic mortality usually causes common. The stability-time hypothesis (Sanders, selection for increased fecundity and/or accelerated 1968) states that the longer a community has development and reproduction, rather than selection maintained stability and not been subject to major for competitive ability and interactions with other disturbances the more species will accumulate. species. Therefore, tropical species will be more highly evolved and possess finer adaptations than 6. The productivity hypothesis temperate species, due to their more density­ dependent mortality and the increased importance It has been suggested that combined with the of competitive interactions. factor of climatic stability, increased productivity The importance of interspecific competition, would increase species diversity (Connell & Orias, however, is being seriously questioned in recent 1964). The productivity hypothesis states that years (see Shoener, 1983; Connell, 1983; Strong et everything being equal, as environments increase in ai., 1984) especially by those working with insects productivity, diversity will increase. However, many where competition does appear to be relatively weak different relationships exist between species and unimportant. numbers and the productivity of their resources (Ricklefs, 1979; Krebs, 1985; Begon etai., 1986), and 4. Predation hypothesis a variety of theoretical explanations have been According to this hypothesis, as predators advanced to support different relationships between increase in numbers, they reduce population sizes of resource productivity and species diversity (Connell their prey, thus allowing for more prey species to & Orias, 1964; Pianka, 1972; Riebesell, 1974; Tilman, coexist (Paine, 1966; Janzen, 1970). Paine (1966) 1982). In at least one case, the same data have been argues that there are more predators and paraSites in used to support both increasing and decreasing the tropics than elsewhere and these hold down relationship between productivity and species their prey populations to such low levels that diversity. Brown and Gibson (1983) interpreted the competition among prey organisms is reduced. The data of Whiteside and Harmsworth (1967) on Chydorid Cladocera to mean that species diversity reduced competition allows additions of more prey and productivity have a negative correlation, while species, which in turn support new predators. It is interesting to recall the review on extinct terrestrial Krebs (1985) using the same data indicated vertebrates by Webb (1987). It was suggested that otherwise. the extinction of large herbivores in mid-Cretaceous Productivity-diversity relationships may be led to that of the large carnivores. However. classified broadly into two types: increasing, and reassembly was from the top down and each new unimodal (Abrams, 1988). Since a certain level of dynasty emerged from insectivors or small carnivores resource productivity will allow some consumers to which gave rise to wholly new groups of dominant exist, diversity must increase with productivity for herbivores. low levels of productivity. As productivity continues to increase, diversity may remain the same or 5. Climatic stability hypothesis increase (both called increasing productivity­ Stable climates allow the evolution of finer diversity relationship), or diversity may decrease, specializations and adaptations because of the resulting in a unimodal relationship. There are cases 92 THE PALAEOBOTANIST

in which diversity increases with productivity over "an, increased probability of extinction to an the range of productivities measured; see for increase in the gradient of environmental harshness example Pianka's (1967) data relating number of The latter is a measure of the physiological stress to lizard species to length of the growing season, which populations are exposed" Since rate of Brown's (1975) analysis of North American desert biological diversification is a function of balance rodent communities, and Belovsky's (1986) between rates of speciation and extinction, summary of generalist herbivore species number vs. lithospheric complexity together with environmental productivity. Kirchner (1977) found that fertilizing a harshness is responsible for species diversity shortgrass prairie with nitrogen or increasing gradients. Latitudinal and longitudinal gradients of productiVity by watering increased plant species diversity (Simpson, 1964; Wilson, 1974; MacArthur, diversity. Tilman (1982) presents data on several 1969; Cook, 1969) parallel the gradients in plant communities illustrating unimodal topographiC compleXity which is taken to be an productivity-diversity relationships. A similar pattern approximation of lithospheric (geomorphological) was observed by Abramsky and Rosenzweig (1983) compleXity and environmental harshness. An for diversity in desert rodent communities. increased diverSity with increasing depth in benthic Richerson and Lum (1980) on the other hand, found invertebrates is related to opportunities that no evidence for an effect of productiVity on diversity compleXity creates for geographiC isolation and in an extensive analysis of California land plant differentiation. communities (Abrams, 1988). The theory does not claim to explain all observations, neither it attempts to account for the 7. Temporal heterogeneity hypothesis greatest amount of variance seen in large scale Pianka (1966) has argued tha t the longer diversity gradients (Cracraft, 1985). But Cracraft growing season of tropical regions allows the supports testability of the theory because it has component species to partition the environment considerable empirical support. temporally as well as spatially, thereby permitting the coexistence of more species. Such temporal 9. Species-energy hypothesis partitioning of environmental resources is also Recently, Turner et at. (1988) have tried to exhibited by the warm and cool season plants of explain the steep decline in the number of species mixed-grass prairie (Singh et al., 1983). Different from tropics to pole by 'the weather', that is, photosynthetic adaptation of plants to cool and latitudinal decline in the input of solar energy. They moist (C3) and to warm and dry (~)conditions proposed a new hypotheSiS, the species-energy permits temporal separation of species into warm hypothesis, which predicts that species richness season and cool season guilds. This confers upon correlates with the available solar energy as the constituent species the ability to avoid measured by temperature and sunshine hours. Such competition. This seasonal expression causes plant a correlation has been demonstrated for birds diversity to vary with time, the mid season, (Wright, 1983), butterflies and moths (Turner et al., experiencing maximum diversity as the recruitment 1987) and terrestrial vertebrates (Terentev, 1963). of the community is completed and the resource Plant diversity (Richerson & Lum, 1980) and tree tends to be more equitably shared among the diversity (Currie & Paquin, 1987) are found to be constituent species at that time. related with temperature and rainfall, or with evapotranspiration, which is a function of these two. 8. lithospheric complexity and environmental Turner et al. (1988) argued that if their harshness hypothesis hypothesis were correct, "the correlations should Cracraft (1985) presented an alternative exist only during those parts of the year when conceptualization of biological diversification and organisms are actively absorbing energy, and should its causes. He considers "the rates of speciation and disappear if energy absorption ceases, .... or even extinctions are diversity independent. The rate of become negative if irreplaceable energy is being speciation is hypothesized to be mediated by the expanded, as when an insect hibernates". They rate-change of lithospheric evolution operating provide data for distribution of small insectivorous through' geomorphological complexity. Increased birds in Britain and show that the diversity of complexity presents more opportunities for summer visitors correlates only with summer vicariousness and long-distance dispersal to produce temperature and the same of winter visitors with isolation and differentiation". He further formulates winter temperature only. a deterministic theory of extinction which relates The relationship between energy and species RAGHUBANSHI et al.-ENVIRONMENTAL CHANGE AND BIOLOGICAL DIVERSIlY 93 richness is explained by giving a simple stochastic from generic data. They inferred that extinctions are theory, "Given the observed constant rurnover driven by some environmental process (implicating (colonization and extincrion) of species in anyone eX'traterrestrial or geophysical driVing mechanisms) area, regions where populations are larger will have with a periodicity of approximately 26 Ma. However, more species at equilihrium, as smaller populations proposed cyclic nature of extinctions has generated become ex'tinct more often ". "Greater energy a lor of debate (Davis et al., 1984; Quinn, 1987, supplies might increase populations of birds Quinn & Signor, 1989; Patterson & Smith, 1989) indirecrly, through overall produerivity, or direerly which is still inconclusive. on account of the lower metabolic energy required Major extinerions have occurred at geologic to maintain body functions when the air is warmer". time boundaries, such as Frasnian/Fammennian, Ordovician/, /, PAST CLIMATIC CHANGES AND DIVERSITY Triassic/ and Cretaceous/Tertiary Plants seem ro have survived the great mass extinction The present biological diversity on the Earth has events bener than animals; for example, at the taken a long time ro evolve. Signor (1990) has Triassic/Jurassic boundary, gyrnnosperms of similar reviewed the hisrory of diversity ro morphology dominated the vegetation on either side show that the appearance of seed plants as did the angiosperms across the Cretaceous/ accelerated the diversificatiqn ro a Late Devonian TenialY (KIT boundary) (Ricklefs et aI., 1990). peak of over 40 genera; thereafter following a slight During each mass extinCtion episode 25-> 75 per decline, the di\'ersification resumed in the cent of the extant taxa were lost. The course of , and the number of species increased Gondwana floral development in India in relation ro ro over 200. The increase in the number of plant piT boundary furnishes an interesting example. species occurred gradually between the mid­ A glacigene event initiated the Permian flora in Carboniferous and the end of the Permian. The India. The advent of Glossopteris association in the slight reduction (about 20%) in diversity at the end earliest Permian thus witnessed a great stress on of the Permian was followed by a rapid increase to environment because of extensive glaciation on the pre-Mesozoic levels, subsequently diversity Gondwana supercontinent. The cold conditions increased slowly ro about 250 species in the Early under which sediments of Talchir Formation were Cretaceous. Coniferophytes, cycads and cycadeoids laid allowed limited diversification of plant species replaced the previously dominant groups and in number as well as kind. Major floral elements of dominated the plant biota until the Middle this period are represented by leaves of the genera Cretaceous. The mid-Cretaceous coincided with the Gangamopteris and Noeggerathiopsis. Slightly later final phase of plant diversification and the appeared the Glossopteris with nearly six appearance of angiosperms. The latter, having the species and the only reported is highest rate of diversification among the major plant Paranocladus. The palynological fossils found groups, diversified slowly at first but more rapidly in dispersed in these sediments also reflect low the Cenozoic, and they now constitute more than diversification. Out of nine genera of palynofossils. 80% of the plant species on earth. According ro five refer to saccate pollen, three to a trilete·bearing Knoll (1984), there were about 25,000 species of and one alete spore type (Lele, 197::;). These floral flowering plants in the Early Cretaceous, this elements appear to be organizationally related with number swelled to 100,000 species by the Late some of the Late Carboniferous pollen group and Cretaceous, and roday there are about 200,000 could have evolved from that stock (Vijaya & Tiwari: species. However, extinerions and reconstitution of Ms, 1991). biotic communities have repeatedly occurred in the With the amelioration of the climatic conditions, geological past as illustrated through the following the flora diversified and some new elements, viz., examples. There is a specrrum of minor extinction BOliychiopsis, };'lIryphylllll11, Rlibidgea and Bliriadia events, many of which indicate the biological system appeared in the late Early Permian (Karharbari being in profound stress, in addition to five major "Formation"). Species of the genera extinction events during past 600 million years Noeggerathiopsis, Gangamopteris and Glossopteris (Raup, 1986) Apparently, relatively long periods of also increased in number (Bajpai, 1990). By the end stability alternated with shorr·lived extinCtion of Karharbari the number of palynotaxa almost events. Raup and Sepkoski (1984, 1986) analysed the doubled, the species multiplied four-fold, numerical patterns of extinction in the marine fossil pteridophyric spores contributing ro about one third record and identified 10 mass extinctions since the of the population. Late Permian from family data and 8-12 extinctions By the ea rly Midd Ie Perm ian (Ba raka r 94 THE PAlAEOBOTANIST

Formation), the Noeggerathiopsis-Gangamopteris some of the older disaccate-stria[e taxa (Maheshwari association declined and was succeeded by a & Banerji, ]975, Tiwari & Singh, 1986) The Glossopteris dominated association_ The genera megaflora shows a continuum in characteristic Botrychiopsis, Rubidgea and Buriadia, which elements, such as Schizonellra gondwanensis, deve loped onIy loca lly became o:t inc£. Two new Glossopteris spp. and Rhabdotaenia sp Even the elements, vi z., Rhabdotaenia and Walkomiella sphenophyll Trizygia ~peciosahas heen reponed appeared, the larrer taxOn is known through only (Bhattacharyya, 1963). one record. A well marked change in palynofloral Some of the Lower Triassic forms, ego composition at the Karharbari/Barakar boundary has Playjordiaspora, Lundbladispora, Llinatisporites, etc been recorded; the Earl y Permian monosaccate made sporadic appearance in [he uppermost Upper predominance suddenly declined, the diversiry in Permian strata, while a few of [he dominant Upper species of the pteridophytic (inc Iuding lycopsid) Permian forms, e.g., Strialopodoca/piles and such spores increased many-fold and the gymnospermous others continued, in diminishing order of disaccate striate and nonsrriate pollen dominated diversification, into the Lower Triassic (Vijaya & numerically (Tiwari & Tripathi, 1988) Floral Tiwari, 1987; Srivastava & Jha, 1990) The early pan elements suggest a mesic environmenr that was of the Lower Triassic is marked by 84 distinct species probably warm temperate with ample water supply which were either absent in the Upper Permian or and sufficienr light inrensity (Maheshwari et al., in appeared inconsistently only at itS closing phase. Press). The flora of upper Middle Permian (Kultj Among the new-comers of Triassic palyno Formation) is poorly known. assemblage, pteridophytic spores are represenred b\' The Late Permian (Raniganj Formation) had the 48 species and the gymnospermous pollen by only peak development of Glossopteris and some other 36 species. The taeniate pollen perhaps increase ge nera, vi Z., Rhabdotaenia, Palaeouitta ria, consistently at the cost of striate pollen (Tiwari. Belemnopteris, etc (Maheshwari, 1970). The fossil personal communication). wood shows well-marked annual rings (Maheshwari, Thus a major change is recorded in [he pollen 1972). The climate was warm-temperate with heavy spore constituents and, implicity. in the vegetation rainfall. On the basis of palynofossil species also, it at the PIT boundary. It is necessary [0 work Out leaf has been confirmed that the climax of Gondwana floras with this objective to record clima[ic vegetation was arrained in the Late Permian Raniganj signatures both at the transition as ,,-rell as in the Formation. At the terminal Permian (uppermost Early Triassic. Raniganj Formation) the megafossils indicate a The mass extinction at the K/T boundary has rather impoverished vegetation in which leaves had been a subject of numerous studies. There are those a reduced surface and open venation (Bajpai, 1987, who believe in a gradual extinction (thousands to Bajpai & Tewari, 1990) million of years) through long-term global cooling Relatively more diversified palynofossil­ and marine regression, while others advocate assemblage of the Raniganj Formation reflects the catastrophic (months [0 years) e)..1inction. The three multiple lines of evolutionary trends in pollen and most commonly cited causes of mass extinction are: spores. The paJynofossil-assemblage is dominated by (i) change in sea level, (ii) climatic deterioration, striate-disaccate pollen Striatopodocarpites, and (iii) collision with extraterres[rial bodies. Protohaploxypinus, Crescentlpollenites, Striatites and Alvarez et al. U980, 1984b) proposed that the Densipollenites. The rotal number of spore-pollen impact of a 10 km diameter asteroid caused mass species recorded in Raniganj is 175, out of which 39 extinction at the end of the Cretaceous The dust species have pteridophytic affinity. 137 species clouds blocked out solar radiation, phorosynthesis disappeared in the Lower Triassic that included 76 was checked, and eanh's surface was cooled to lethal per cent of pollen and 24 per cenr of pteridophyric limits. Massive wildfires were also caused by the spore species However, six species of spores and 32 impact (Sairo et aI., ]986; Wolbach et al., 1988) of pollen conrinued ro survive, from Late Permian ro Evidence cited in suppon of asteroid impact Early Triassic, as shown in Table] (after Tiwari & hypOthesis includes a worldwide layer of clay Tripathi, ]99], MS). deposits enriched with siderophilic elements, At the beginning of the Early Triassic (Panchet mainly iridium, osmium isorope ratios, shocked Group ).a change is noticed in the basic composition quanz and spherules inrerpreted [0 be microraktites of the palynoflora. The spore pollen genera (Bohor et al., 1987; Kerr, 1988) Hut et al. (987) consistent in their occurrence in the Early Triassic have postulated multiple small impacts, instead. are Klausipollenites, Lunatisporites, Lundbladispora, The KIT seems to have been Densoisporites, Playjordiaspora, Alisporites, and preceded by several million years of global cooling RAGHUBANSHI et aI-ENVIRONMENTAL CHANGE AND BIOLOGICAL DNERSITY 95

Table I-Distribution of spore-pollen taxa through Permo-Triassic period of India

PALYNOTAXA!AGE PERMIAN TRIASSIC Acanlholrileles filiformis Alisporiles gracilis Allimonoleles flavalus Anapiculalisporiles consonus Anapiculalisporiles verilas Apiculalisporis inconspicuus Apiculalisporis levis Apiculalisporis secrei us Barakariles dubius Brevitriletes communis Calamospora aplala Calamospora exila Corisacciles alulas Corisacciles dislinclus Crescenlipolleniles ampulus Crescenlipolleniles gondwanensis Crescenlipolleniles hirsulus ·Crescenlipolleniles implicalllS Crescenlipo/leniles sellingi Cunealisporites eXiguus Cunealisporiles raniS Cyciobaculisporiles indicus Cyc/obaculisporiles minimus Cyciobaculisporites minulus Densipolleniles brevis Densipolleniles densus Densipo/leniles magnicorpus Densipolleniles minimus DiSlriamonocolpiles ovalus DiSlrialiles bilaleris Dislrialiles insolilus Dislriomonosacciles oualis Diuarisaccus invasus Divarisaccus lelei Ephednpiles elliplicus EupunClisporiles grabus Fusacolpiles fusus Ghoshiasporites didecus Ginkgocycadophylus cymbalus Gnelaceaepolleniles grandis Gnelaceaepolleniles sinuosus Gondisporiles raniganjensis Gondisporiles reltculalus GOlldwanaeplicales bharadwajil GUI/ulapo/lenites hannonicus Hamiapolleniles inceslus Hennellysporiles divers/form is Hindipolleniles globossus Hindipolleniles indicus Hindipolleniles rajmahalensis Hindipolleniles oblongus Horridilrileles brevis Ibisporiles diplosaccus Indospora clara Indospora laeuigala Indospora macula Lacinitrileles badamensis Laeviga losporite; colliensis Laevigalosporiles punclalllS Labiriles a Itt/as Lahiriles a nguslUS Lahiriles kajoraensis Lahiriles lepidus Lahiriles minulUS Labirites parvus Lahiriles rolundus Lahiriles singularis LeiOlrileles brevis LopbOlrileles frequensis LophOlrileles novus Mammialeles mammus Marsupipolleniles Slrialus Marsupipolleniles Iriradialus Microbaculispora gondwanensis Microfoueolalispora foueolala Pilyosporiles papillionis Plicattpolleniles reliculalus Plicattpolleniles Iriangularis POlonieisporiles raniganjensis Praecolpaliles sinuosus Punclalosporiles morosus Raniganjiasacciles ovalUs Rhizomaspora eOSla Rbizomaspora fimbriala Rbizomaspora indica Ricaspora granulala Scheuringipolleniles ovalus Sirialiles rbombicus Siriapolleniles obliquus Siriapolleniles saccalus Siriasporis slrialLlS Sirialiles alius Sirialiles barakarensis Sirialites ganjerensis Sirialiles multislrialus Sirialites nOlus Sirialiles obliquus Sirialiles obl/ISUS Sirialiles ornal/IS Sirialiles rbombieus Sirialiles sublilis Sirialiles leclus Sirialiles lenlulus Striatopodocarpiles copiosus Striatopodocarpiles crassislrialus Siriatopodocarpites ovalis Sirialopodocarpites ovatus Strialopodocarpites subcircularis Strialopodocarpiles liwarii Slriatopodocarpites wjmensis Strialosporites braziliensis Striomonosacciles ovatus Tbymospora raniganjensis Trochosporiles Inpus Tumoripollenites baculaIUs Varireliculales varius Verrucosisporiles diversus Verrucosisporites donarii Verticipollenites crassus Verticipollenites debilis Vertic/polleniles finilimus Verlicipollenites gibbosus Verlicipolleniles oblongus Verticipollenites secrel/IS Verticipolleniles subcircularis Vesicaspora dislincla Vesieaspora Itt/ens Vesicaspora ovala Vesttgisporiles diseclus Vesligisporites monosaccalus Virkkipollenites meblae Virkktpollenites obscurus Virkkipolleniles triangu/aris \'(/elwilscbiapites extansus We/wilschiapiles lenuis Weylandites lucifer Brevilriletes unicus Callumispora gretensis Crescenlipollenites fuscus Crescentipollenites sanlhalensis Cuneatisporites mirabilis Cyclogranisporites gondwanensis Densipolleniles indicus Densipollenites invisus Faunipollenites perexiguus Faunipollenites varius Horriditrileles curvibaculosus Inaperturopollenites nebulosus Lahiriles incerlus Labirites raniganjensis Lahirites rarus LophOlriletes rectus Parasaccites korbaensis Platysaccus fuscus Plicatipollenites indicus Scheuringipolleniles barakarensis Scbeuringipollenites maximus Strialopodocarpiles brevis Sirialiles communis Sirialiles solitus Sirialites varius Sirialopodocarpiles decorus Strialopodocarpites d/ffus/./s Slrialopodocarpites labrus SlrialOpodocarpites magnificus Strialopodocarpiles ob/ongalus Sirialopodocarpites perfeci/./s Sirialopodocarpites rarus Striatopodocarpites rOlundus Strialopodocarpiles venustus Slriomonosaccites circularis Verrucosisporites gondwanensis Virkkipollenites densus Weylandites indicus Alisporites asansolensis Alisporites dam udicus Alisporites grobus Alisporites indicus Alisporites landianus Alisporites plicatus Aratrisporites fischeri Birelisporiles dubius Birelisporites sp. Callumispora fungosa Chordasporiles raniganjensis Convertubisporites conlactus Converlubisporites densus Crescentipollenites bengalensis Cyathidites australis Cycadopites follicularis Cyclogranisporites triletus Decisporis pancbetensis Decisporis mdis Decisporis variabilis Densoispol'iles complicatus Densoisporites contactus Densoisporites playfordii Decisporites triassieus Dictyophyllidites dews Dictyotriletes invisus DivaripUllclites bifurcalus Divanpunctites globosus Divaripunctites plicatus Falcisporiles nuthalensis Falcisporites slabilis Faunipo/leniles microcarpus Goubinispora indica Goubinispora morondauensis Granuloperculatipollis flavalus Granuloperculatipollis problematicus Guttatisporites ambiguus Indotriradites cLlspidus Indotriradites mammilalus lndotriradites wargalensis Klaus/pollenites scbaubergeri Klausipollenites sulcatus Labirites levistriatus Lahirites triassicus Laricoidiles inlragranulos/./s Lopholri/etes minimus Lunatisporites asansoliensis Lunalisporites damudicus Lunatisporites diJf/./sus Lu natispol'ites noviaulensis Lunatisporiles ouatus Lu natisporites pellucidus L/./natisporites rhombicus Lundbladispora baculata Lundbladispora brevieula Lundbladispora densispinosa Lundbladispora microconata Lu ndbladispora obsolela Lundbladispora raniganjensis Lundbladispora warli Orbella indica Osmundacidites senectus Pilasporites plurigenus Pinuspolleniles Iboractus Playfordiaspora cancellosa Prelricolptpollenites bbaradwajii Pyramidosporiles racemosus Rhizomaspora biharia Rbizomaspora divaricala Rbizomaspora Iriassica Rimaspora plicata Simeonospora kblonovae Striatiles levistriatus Striatites panchetensis Strialopodocarpites multislrialus Sirialopodocarpites raniganjensis Subverrusporis rudis Verrucosisporites bosei Verrucosisporites densus Verrucosisporiles morulae Verrucosisporites narmianus Verrucosisporites triassicus Verrucosisporiles warli Weylandites circularis

(After Tiwari & Tripathi, 1991 : MS). 96 Tift: PAIAEOROTr\NIST

Table 2-Distrlbution of fossil spore and pollen taxa through Eocene-Oligocene Epoch in India

PAlYNOTAXA!AGE EOCENE OLIGOCENE Araliaceolpolleniles rugulalus Arecipites indicus Asperilricolporiles pi/osus Caprzjoliipites deseretus Cupanieidiles jlabelltjormis Dicolpopollis kalewensis Pauitn'colporites ornatus Neocouperipollis cymbatus Palmaepollenites baculatus Proteacidites dehaanii Retibreuilricolpites joueolatus Relitricolpiles jlorentinus Rholpites baculzjerus Rhoipites communis Schizosporis rugulalus Spinainaperlurites densispinus Stephanocolpites globalus Striatricolporites obscuris Symplocoipolleniles graci/is Tricolpiles breuicolpus Tricolpiles jissilis Triorites pseudoreticulatus Triorites I uhljerus Araliaceoipollenites matanomadhensis Areclpites bellus Bakslpollis primitiua Cupulijeroipolleniles oualus Dandotiaspora plicala Dermalobreuicolporiles dermalus Dracaenoipollis circularis Intrapunclisporis apunclis Lakiapollis ouatus Neocouperzpollis breuispinosus Neocouperipollis kutchensis Osmundacidites kutchensis Palmaepolleniles nadhamuniz Palmaepolleniles ouatus Palmaepolleniles plicalus Pelliciemipollis langenheimii Polybreuicolporites nadhamunii Pseudonothojagidites kutchensis Retistephanocolpites jlauatus Ret,lelrabreuico/porites globatus Retilribreuicolporites malanomadhensis Seniasporiles uerrucosus StriacOlporites cephalus Striacolporites oualus Sympolocoipolleniles kutchensis n-icolpites reliculalus Umbel/ijeroipolleniles ouatus Verrucolporites uerrucus Cricotriporites cauueriensis Paleocaesalpiniaceaepites miocenicus Proteacidiles bel/us Relitrico/pites hispidus Stephanocolpites letracolpiles Trico/piles pi/osus Marginipollis kutchensis Pauitricolporites magnus Symploco,pollenites punctatus Psi/alricolporites operculatus Proxapertiles operculalus

Anac%sidites tri/obatus Cupanieidiles j/accidijormis Engelhardlioidites minutijormis Myricaceoipol/eniles dubius Polyco/piles pedaliaceoides Proteacidites te,-razus Proxapertites hammenii Psi/odipontes hammenii Rho,piles conalus Pauitricolporites magnus lugopollis lelraporoides Spinizonocolpiles echinallis

Palmaepol/eniles kUlchensis

Araliaceoipol/enites mannarglldii

Tricolpiles longicolpallis ------_._._.~~_._._._._._. Ma rgocolporiles silholeyi ------_._._.~~_._._._._._. MaII riliidiles densispinus

...... _._._._~_._._._._._. Slrialupol/is belilis ------_._._.~~_._._._._._. Tricolpites Inargocolpiles ------_._._._.~_._._._._._. Cal)'apolleniles callueriensis _._._. --41_._._._._._. Ma rgimpol/is co ncinn liS

Myricipiles harrisii Palaeocoprosmadiles arcotense Biretisporites convexus Cheilanlhoidspora monolela Cyathidiles auslralis Cyalhidiles minor La euigalosporiles lakiensis Lygodiumsporites lakiensis Palaeomalvaceaepollis mammilalus Pa/eosamalaceaepiles minulUS Proxaperliles microreticulalus Sirialri/etes microuerrucosus SI,-ialriletes susannae Todisporiles kUlchensis 2'Joftocosti~ , amotlt1'e Margocolporites sahnii Proteacidites granulalus Sapolaceotdaepolleniles obscunls Sublnporopollis scabralus Araliaceoipolleniles deserelus Bombacacidiles Iriangu/alus Compositoipollenites tricolporatus Graminidites granulatus Leptolepidiles chandrae Palaeomaluaceaepollis rudis Podocarpidiles cognatus Po/ypodiaceaesporites chauetjii Polypodiisporiles conslrictus Polyporina mull/porosa Proxapertites scabralus Punclatisporiles sarangwarenSiS Rel/lricolpites delica IUS Toroisporis dulcis Tnporopolleniles exaclus Trisynco/piles ramanujamii Verrupolyporiles g/obosus

Legends: Cauvery Basin Kutch Basin Godavari Basin Ranges Extended on the basis of their occurrence in Miocene Dara after. Venl<.arachala (1973), Venkarachala & Rawat (1972, 1973), Kar (1985), Venkarachala & Sharma (1984), RAGHUBANSHI et a/.-ENVIRONMENTAL CHANGE AND BIOWGlCAL DIVERSIlY 97 and substantial sea·level lowering. Hallam (1987) suggested that extinction was biological and has argued, on the other hand, in favour of terrestrial resulted from predation. causation of end·Cretaceou~mass extinction event. Among the terrestrial vertebrates, dinosaurs He concludes that these extinctions were not a were one of only a few groups to be seriously geologically instantaneous event and were selective affected by the extinction event. The demi3e of the in character. According to Hallam (1987), the last dinosaurs probably made possible the Early Tertiary few hundred thousand years of the Cretaceous were evolutionary radiation of mammals. In terrestrial marked by environmental changes more dramatic habitats marsupial mammals were hard hit (Raup, than experienced for a long time previously or 1986). Species not exterminated during these subsequently. A substantial and rapid fall of sea level extinction events included land plants, crocodiles, could have had both direct and indirect influence on snakes, mammals and many kinds of invertebrates the organic world, e.g., marine invertebrate mass (Lewin, 1986). Thus a sort of selectivity characterises extinction episodes occurring in the Phanerozoic the major extinctions, however, Raup and Boyajian due to reduction in neritic habitat area. Sea-level fall (1988) have found evidence for a suprisingly could also have caused increases in seasonal uniform extinction pattern in certain marine extremes of temperature on the continents, thereby organisms (Lewin, 1988). increasing the environmental stress. Increased For extinction trends during the Palaeozoic, volcanic activity over an extended period and on a Sepkoski (1987) opined that whole communities large enough scale would lead to the production of exhibit increasing extinction offshore but the genera immense amounts of acid rain, reduction in within individual taxonomic classes tend to have alkalinity and pH of the surface ocean, global their highest extinctions onshore. Earlier atmospheric cooling resulting from expelled ash, generalisation that extinction intensity tends to and ozone layer depletion (Hallam, 1987). Crowley increase offshore from shallow to deep marine and North (1988) have suggested that terrestrially environments, result from a concentration of genera induced climate instability may be a viable in classes with low characteristic extinction rates in mechanism for causing rapid environmental change nearshore environments (Sepkoski, 1987) Observed and biotic turnover in earth's history. Moses (1989) rate of extinctions of the genera within individual has reviewed and compared the impact and tectonic taxonomic classes is consistent with the ecologic explanations. He has suggested that extraordinary expectation that the organisms inhabiting tectonism, including volcanism, sea floor spreading unpredictably fluctuating environments should and sea level changes which took place prior to and suffer more extinction than counterparts living at the KIT boundary, caused changes in under more predictably equitable conditions. biogeochemical cycles and climate leading to mass Kurten (1971> has emphasised the worldwide extinctions. trend toward glacial conditions during Miocene. Plant fossils recorded from the Miocene sediments During mass extinction event at the KIT do not support Kurten's view atleast for India. The boundary, roughly half of the existing genera Miocene flora in Kerala-Lakshdweep, Cauvery, perished (Alvarez et al., 1990; Ganapathy, 1980). ]aisalmer, Cambay, Assam-Arakan and Bengal basins These included microscopic floating animals and and the Lower and Middle Siwalik was constituted plants, calcareous planktoniC foraminifera, overwhelmingly of tropical evergreen elements, calcareous nanoplankton and marine reptiles. The presently known from Indo-Malayan region most striking feature of the extinction was indicating warm and humid conditions (see Awasthi, disappearance of the planktonic forms and 1974, 1982a, b, 1984; Awasthi & Panjwani, 1984; coccolithophorids in the oceanic realm. In this Lakhanpal et aI., 1981; Lakhanpal et al., 1984). realm, approximately 13 per cent of marine families However, cooling and dry trends occurred in the and about 50 per cent of marine genera died out post-Miocene time as a result of collision of the completely in the Maestrichtian, the final stage of Indian Plate with the Asian plate, appearance of the Cretaceous; the loss may even be as high as 60­ several physical barriers increased continentality, 75 per cent (Raup, 1986). According to Hallam reduced precipitation, and further rise of the (1987), the sudden extinction event in bottom-living Himalaya. The sudden decline of the rich savanna organisms at the end of the Cretaceous could be ungulate fauna in North America during the Miocene related to either the loss of food supply or suggests that the same cooling and drying trends that destruction of chalky substrate habitat. From a study produced savanna fauna, when carried further, led to of planktonic foraminifera at KIT transition in its demise (Webb, 1987). Deterioration of Cenozoic Meghalaya, India, Pandey et al. (1990) have climates during the last few million years when 98 THE PALAEOBOTANIST glaciers began ro form in the northern Hemisphere, decline in preCIpitation prompted the expansion of occurred and the mid-continental North America low-biomass, openland and arid land vegetation, and experienced the final transition from savanna ro the evolution of open-land plant taxa. Arid and semi­ steppe as the predominant biome. Desertification arid land vegetation which hitherto occupied occurred over a considerable expanse of Mexico and limited, dry locations thus expanded into areas at the south-western United States. In the north a the lower spectral end of the precipitation gradient unique steppe-tundra biota developed across the in the low and middle latitudes. During warmer and land area now partly beneath the Bering Sea but also wetter interglacials tree vegetation was able ro including adjacent parts of northern Asia and encroach into areas formerly occupied by openland northern North America. vegetation at both high and low latitudes resulting in Studies on plankronic foraminifera from Indian the advance in tree lines polewards and into former Ocean deep-sea cores have revealed that major deserts during interglacials. The reverse happened epoch boundaries are marked by characteristic during glacial when openland, treeless herbaceous species: Pliocene/Pleistocene, the last appearance of vegetation returned (Singh, 1988) Glohigerinoides jistulosus; Miocene/Pliocene, Numerous large·scale climatic fluctuations appearance of Glohorotalia tumida; Oligocene/ causing a succession of glacial/interglacial cycles, Miocene, the appearance of Glohoquadrina occurred during Quaternary. These climatic dehiscens (Srinivasan, 1989). The intervals of major oscillations were particularly severe and their impact faunal turnover reflected global climatic events on biota was drastic particularly in western Europe coincident with regional tecronism. Quantitative (Coope, 1987). During shorter interludes the climate foraminiferal clata integrated with oxygen and of England was occasionally warm enough ro carbon isotopic record revealed intervals of major suPPOrt a warm·temperate vegetation. The palaeoceanographic events during 22 Ma, 14 Ma, 12­ glacial/interglacial cycles during the Quaternary also 10 Ma, 6.2-5.2 Ma, and 1.8 Ma (Srinivasan, 1989; changed drastically the distribution and abundance Srinivasan & Chaturvedi, 1990). Gupta and Srinivasan patterns of benthic foraminiferal assemblages in (1990b) have examined the response of northern northern Indian Ocean (Gupta & Srinivasan, 1990a). Indian Ocean deep-sea benthic foraminifera to In general, the Early Quaternary was characterised by global climatic changes during Pliocene/Plei­ relatively less diverse assemblages, unstable bottom stocene. Four intervals of major faunal and climatic water conditions, and cooling of bottom waters. The turnovers are recognised: 5.2-5.1 Ma (Widespread transition between Early and Late Quaternary was antarctic glaciation, bottom water cooling, increased marked by warming of bottom waters and more upwelling, highest Uvigerina abundance and eqUitable and more diverse assemblages. In Late intensified bottom water circulation), 3.9-3.2 Ma Quaternary the benthic foraminiferal assemblages (wanner bottom waters, decreased Uvigerina and were more diverse, more equitable but less increased Cihicides abundance), 3.2-31 Ma (bottom abundant reflecting a more uniform and less water cooling, possible initiation of glaciation in the intensified bottom circulation perhaps due to less Northern Hemisphere), and 3.1-recent (major glacial activity in Antarctic regions. changes in benthic foraminiferal assemblages, The climatic changes during Late Quaternary warm/cold cycles, major glacial/interglacial were abrupt and intense and episodes of wholesale intervals, increase in polar ice volume). The extinction must have been almost synchronous with Oligocene/Miocene transition resulted in lower the events that caused them; namely the sudden rise alpha diversity of benthic foraminiferal assemblages and fall of the regional temperature (Coope, 1987). in northern Indian Ocean (Gupta & Srinivasan, On the other hand, species recolonizing these areas 1989) and reflected significant increase in Antarctic show a lag in their response to the climatic stimulus ice. and as a result recovery was rather protracted and Turnover of palynotaxa through Eocene/ gradual (Coope, 1987). Coope (987) has also Oligocene in Cauvery, Godavari and Kutch basins in suggested that individual species adjust to changing India is illustrated in Table 2 (after Kar, 1985, conditions by tracking the appropriate environment Venkatachala & Rawat, 1972, 1973; Venkatach;l1a & geographically rather than by evolutionary change, Sharma, 1984). and species ecologically tied ro one another by Singh ("1988) has summarized the hisrory of arid mutual dependence must have moved at the speed land vegdation and climate. The lowering of world of the slowest member. We have to bear this in mind temperature during the Late Cretaceous, Palaeogene while speculating on the future climatic change and and Neogene, reduced precipitation levels all over its impact on biota. the globe, curtailing the high rainfall areas. The Ritchie (1985) has described the vegetational RAGHUBANSHI et a/.-ENVIRONMENTAL CHANGE AND BIOLOGICAL DIVERSI1Y 99 changes in Lower Mackenzie Basin of north west PhoeniX, Polyalthia, Homalium, Hydnocarpus, Canada. During the late glacial the vegetation was Mesua, Garcinia, Ailanthus, Sterculia, Grewia, relatively stable, consisting of sparse herb tundra on Bursera, Walsura, Euphoria, Terminalia, Syzygium, uplands in a slowly warming climate (Ritchie & Lagerstroemia, Sonneratia, Barringtonia, Leea, Hare, 1971; Ritchie & Cwynar, 1982). During Early Phyllanthus, Cinnamomum, Artocarpus, FiCUS, etc. Holocene thermal conditions were about 10 per cent (Bande et al., 1988; Lakhanpal et' at., 1984) warmer than present, a change from tundra Miocene-Pliocene: Polyalthia, Mesua, woodland at most sites occurred. This was largely Calophyllum, Garcinia, Kayea, Dipterocarpus, brought about by the efficiently dispersed Populus. Anisoptera, Dr)'obalanops, Shorea, Hopea, Sterculia, Relatively rapid changes in regional vegetation Herifiem f>terospermum, Schleichera, Euphoria, occurred during 11,800-6,500 years BP; Juniperus Bursera, LizlPbus, Mangijera, Gluta, Swintonia, invaded the poplar woodlands, and later the slower­ Lannea, Buchanania, Dracontomelum, Albizia, dispersed Picea arrived and formed stands on Ajzelia·/ntsia, Cassia, Bauhinia, Cynometra, alluvial sites, largely replacing the poplar. At about Sindora, Dialium, Millettia, /soberlinia, Pongamia, 7,500 years BP Butea papyrijera spread to the o ugein ia, Pa rina ria, Ca rallia, Termina lia, uplands. The accumulated fuel load perhaps caused Syzygium, Barringtonia, Careya, Lagerstroemia, an increase in fire frequency, which in turn Sonneratia, Duabanga, Alangium, Chrysophyllum, maintained arboreal birch in the area. Fire opened Sideroxylon, DiosPYros, Leea, Cordia, Phyllanthus, up the woodlands locally and prompted the spread Artocarp us, Holoptelea, etc. (Awasthi, 1974, 1982a, of Alnus crispa (Ritchie, 1985). 1982b; Awasthi & Panjwani, 1984; Lakhanpal et al., Vishnu-Mime (1984) suggests that during the 1981, 1984 ). mid-Miocene there existed an incipient latitudinal The Miocene orogeny and perhaps planetary zonation of vegetation in the Himalaya, then only dynamics led to mark climatic changes involving the 2200-2400 m high. There occurred wet tropical pluvial cycles, i.e., the repetition of cold (and dry) forests on the lower slopes, wet temperate forests on and warm (and mesic) phase during the Pliocene. the higher slopes, with wet subtropical in berween. These cycles brought about drastic changes in The palearctic genera occurred in the top two zones physiogamy and in vegetation, which include the as they do today in the eastern Himalaya. There was disappearance of some forest types (e.g. tropical wet nor much difference in the generic composition evergreen Dipterocarpus-Anisoptera forests from the berween the Neogene floral assemblages of eastern western Himalaya), arrival of species from extra· and western Himalaya. However, the specific Himalayan regions, relative increase and decrease in affinities of the taxa differentiating these floral the area occupied by different biomes such as forest assemblages are only tentative; indications are that and steppe, etc. It is, however, difficult either to they had a number of common species (Vishnu· interpret the sequences of such changes precisely, or Mittre, 1984). At that time the tropical wet evergreen to suggest at what rate and at which time the forests of the western Himalaya consisted vegetational changes occurred (Vishnu-Mime,1984). overwhelmingly of Malayan and southeastern By the end of the Miocene (Lower Siwalik), the elements (e.g., Dipterocarpus, Cynometra, tropical African elements, such as Zizyphus Anisoptera, Gluta, Diospyros, Elaeocarpus, Sterculia, mauritiana had reached the lower slopes of the Bursera), while the temperate forests consisted of a western Himalaya (Lakhanpal, 1965; Lakhanpal & number of palearctic genera (e.g., Pinus, Abies, Awasthi, 1984). In subtropical and temperate belts of Picea, Alnus, Betula, Magnolia). The tropical wet Kashmir, a continuous flux berween the forests of evergreen vegetation of the eastern Himalaya had Quercus-Carya, Larix, Quercus, Engelhardtia, somewhat different species (Awasthi, 1974; Mohan, Quercus-Alnus, and Pinus roxburghii on the one 1933). Some of the present-day common tree taxa hand, and steppe (Poaceae with or without Cheno­ with which older taxa had affinities were amaranth and Artemisia) on the other, occurred Calophyllum, Dipterocarpus, Shorea, Kayea and from 3.5-2.47 million years B.P. The steppe attained Gluta, etc. It may be pOinted out that only the preponderance during the cooling-phase and the eastern Himalayan region still contains a wet forests during the warming phase. Cedrus deodara, a evergreen tropical forest. Several of the modern Mediterranean species, immigrated during the species, however, were also present during the Pliocene. During Pliocene in the Kashmir valley, Miocene. subsequent to the decline of Cedrus-Quercus The following important genera are recorded in: forests, Pinus wallichiana arrived and expanded. Palaeocene-Eocene: Araucaria, Podocarpus, Pinus wallichiana declined subsequently to be Musa, Pandanus, Nipa, Cocos, Areca, Hyphaene, replaced by Picea-Cedrus-Quercus forests. 100 THE PALAEOBOTANIST

The subalpine and alpine conditions developed force controlling global diversity, both in the marine in the Himalaya after the final uplift. At the time, and terrestrial realms; and (iv) climate and sea level Quercus semecarptfolia and Betula utilis were the undoubtedly played a role in the short term but are chief subalpine and apline forest-forming species. unlikely to control diversity in the long term. During the last glaciation (about 0.7 million years Several insights can be drawn from ago), the steppes encompassed most of the areas in palaeoecology which are relevant to future global higher elevations (above 3000 m), but the change. Davis (1989) emphasised on four of these: subsequent warm-phase led to the expansion of (i) Species respond to climate individualistically; junipers in dry areas and of Q. semecarpijolia and the individual range shifts have caused changes in Betula utilis in relatively mesic areas. Similar the composition of plant and animal communities alternations were found between steppe and through time; (ii) Biological responses to climatic Ephedra communities in arid parts. change often occur with time lags; each species and During the Pliocene·Early Pleistocene as many ecosystem component has its own time constant of as 25 species in subtropical and temperate zones change; (iii) Disturbance regimes are an aspect of were found which occur today in the Sino-Japanese climate that changes as climate changes; a change in region. Abies spectabilis, Betula utilis, Quercus disturbance regime can amplify the results of semecarpijolia, Q. glauca, Cinnamomum tamala, climatic change arnd produce a much larger change juglans regia, Machilus duthiei, Pinus wallichiana, in vegetation; (iv) Multiple impacts will be Acer oblongum, Alnus nepalensis, Cupressus important, producing effects that are different from torulosa, Litsea elongata and Mallotus philippensis any we see around us today. Ricklefs et al. (1990) are example of trees. have concluded that, "It is clearly in our best More recently, berween about 8,000 and 4,500 interest at this point to increase our resolution of years ago, a warm phase Which resulted in massive past mass extinction events so that we may answer snow-melting and concomitant increase in the sea­ such questions as to their causes, time courses, the level coincided with the invasion of chir pine (Pinus attributes associated with extinction/survival, the roxburghii) forests by oaks (Quercus spp.) in the types of refuges within which life forms persisted, central Himalaya (VishnU-Mime, 1984). At this time, and the return of the global systems to pre-event in fact, oaks predominated in the entire subtropical levels of biomass, diversity, and ecological and temperate belts of the western Himalaya. In complexity" some regions, such as the Kashmir Valley (within about the last 500 years) and Himachal Pradesh FUTURE CLIMATE CHANGE AND (during 1,400·500 years ago) oaks disappeared or SPECIES DIVERSITY were pushed to sheltered areas within the conifer regimes. The present flora of Kashmir Valley is Although man has been altering the devoid of either oaks or P. roxburghii (Puri et al., environment for nearly two million years, it is only 1983). In Kashmir, at higher elevations (2000-3000 recently that the influence has approached global m), Pinus walltchiana (the blue pine) was the main proportions with almost inevitable changes in the pine species, while in Himachal Pradesh and climate (Hansen et al., 1981). Current predictions Kumaon in the lower elevations, the pine was mainly (Manabe & Stouffer, 1980; Manabe and Wetherald, P. roxburghii. 1975; Hansen et al., 1984) indicate a steady state It is interesting that the oaks predominated and increase in glooal temperatures of 1.5 to 4.5 ° C by invaded the pine forests during the warm-phase of the year 2030 and 6 to 10° C increase between 50 and the climate, because at present the oak forests are 60° N over the continents (Manabe & Wetherald, located 3t higher elevations (hence cooler 1986; Mitchell, 1983). The earth's climate has not environment) than the chir pine (p. roxburghii) varied more than 1 or 2° C in the past 10,000 years. forest (Singh & Singh, 1987). Thus warming expected in the next 50 years or so While reviewing the geologic history of biotic will exceed any climatic change experienced in diversity, Signor (1990) has concluded: (i) human history. evolutionary change leading to increased alpha As discussed earlier, entire biomes have shifted diversity in marine and benthic communities in response to global temperature changes in the contrib~teddirectly to increased diversity on past. Profound changes in response to global regional and global scales; (ii) coevolutionary warming are suggested in the distribution of major interactions between terrestrial plants and animals biomes, particularly those of north temperate and led to increased species richness in terrestrial boreal regions (Emanuel et al., 1985). It has been communities; (iii) continental drift has been a major suggested that shifts similar to those during RAGHUBANSHI et aI.-ENVIRONMENTAL CHANGE AND BIOLOGICAL DIVERSIlY 101

Pleistocene and past Holocene would occur, and colonise suitable habitats. Species having slow vegetation belts would move hundreds of kilometres migration rates or experiencing geographical towards the poles (Frye, 1983). Peters and Darling barriers may not survive and become extinct. Even (1985) assume a 300 kilometre shift towards poles behaviour of a species is important for the rate of on the basis of models (Miller et al., 1986) and on migration. Many tropical deep forest birds, for the positions of vegetation zones during analogous example, simply do not cross even very small warming periods in the past (Dorf, 1976; Furley et unforested areas (Diamond, 1975). This is also true al., 1983). Using two general circulation models, for the chaparral birds. These bird species are highly GISS model of NASA and GFDL model of NOAA, M. sedentary and refuse to cross strips of nonchaparral Davis and C. Zobinski predicted 500-1000 kilometre habitat wider than 50-100 meters (Diamond, 1988b). northward range shifts for eastern hemlock, yellow Here lies the importance of contiguity of habitat. birch, beech and sugar maple (see Roberts, 1989). The current rate at which protected or undisturbed Under milder GISS scenario, their predictions biomes are being fragmented, poses severe showed that in the middle of the century sugar problems for future. A direct relationship between maple would disappear across the southern edge of fragmentation of ecosystem and many of global its current range in 200 to 600 kilometre wide belt. changes that have been detected in last few decades Under the more severe GFDL scenario, sugar maple seems undeniable. In all cases of major would die out throughout its entire range, except fragmentation of ecosystem, changes in species diversity and species composition are found the Maine, eastern Qu~becand Nova SCotia. Similar patterns are also predicted for yellow birch and (Wilson, 1988). Certainly, fragmentation will result hemlock but beech would be most affeCted species in fewer pathways for species migration towards under either scenario. Under the GISS model beech favourable habitats (CGC, 1988). would die out over a 1500 kilometre region in the Given the low rates of plant dispersal, eastern United States. vegetation would not be able to change its CGC (1988) speculates 500 km displacement of geographical distribution as fast as the changes in isotherms of North America for every 50 C rise in suitable habitat (CGC, 1988). As a result, there global temperature. This change could occur within would be lags of decades in adjustment of ecological 100 years (jaeger, 1988). Fossil records have been systems to rapidly changing climatic conditions. useful in assessing the rates at which tree species CGC (1988) concludes that lags in the match were able to advance across the landscape during between climate and vegetation will become the Holocene. The rates measured by the appearance apparent in the mid-continent long before doubling of pollen in quantity at different latltudes average of carbon dioxide has occurred. Quaternary 10-45 km per century over long time periods palaeorecords show that species do not react en bloc (Firbas, 1949; Davis, 1981; Huntley & Birks, 1983). to the climatic change but have responded to change The fastest range adjustment exhibited by spruce individualistically (Coope, 1987; Davis, 1981). into northwestern Canada at 200 km per century Species will perhaps alter their geographical range (Ritchie & McDonald, 1986). Dispersal rate for as each will find conditions intolerable or new beech was about 20 km a century. In the event of territories for colonization. As a result, ecosystems several hundred-kilometre poleward shift in that are of limited spatial extent today may have temperate belts during the next century, localized been much mOre expensive in the past. CGC (1988) populations currently living near their maximum gives example of oak savanna, which today forms the thermal tolerance levels would have to shift narrow ecotone between prairie and forest in North northward at a rate of several kilometres per year to America, but which covered an area hundreds of avoid being left behind in areas too warm for kilometres wide during the mid -Holocene survival (Peters & Darling, 1985). If the current (McAndrews, 1967). Species that are rare or predictions of rates of species shift of 700 to 900 geographically localized today, such as bristlecone kilometres per century are correct, beech would pine (Pinus aristata), were abundant in the past, have to migrate 40 times faster than it did 15,000 while ponderosa pine (p. ponderosa), the dominant years ago (see Roberts, 1989). Although some tree over large regions of the Rocky Mountains species, such as plants propagated by spores or dust today, was very rare during the last glacial period seeds, may be able to assume this rate (Perring, (Spaulding et al., 1983). Spruce which now 1965), many species would not disperse fast enough characterises the vast boreal biome, was sparse to escape the expected climatic change without throughout North America in the Early Hoiocene human assistance (Peters & Dar! ing, 1985). (Webb, 1987). Dispersal rates are crucial to species ability to The above examples show that existing biomes 102 THE PAlAEOBOTANIST will not remain intact under future changes of global (Ritchie & Hare, 1971; Ritchie & Cwynar, 1982; climate. Differences in the rate of migration of Uimb, 1982) The moist and wet boreal forest will be constituent species will dissociate communities into expected to move northward and will be replaced on their component species. The fossil records its southern flank by cool temperate forest. In reviewed in this paper show clearly that Central Canada, except in the far north, large tracts communities may be disassembled and species of the boreal forests will be replaced by cool reassembled in new combinations in response to temperate steppe (Harrington, 1987). new climatic conditions (Davis, 1981; Graham, 1986; According to a recent report by EPA, spruce and Coope, 1987). The resulting new combinations of northern pine would decline in the southern parts of vegetation, climate, and soil can result in altered their range in the east side of United States and spatial patterns of such fundamental processes as net expand northward (see Roberts, 1989). New England primary production (Pastor & Post, 1988). More coniferous forests would be replaced by hardwoods, subtle, but still important processes such as evolved especially by oak while southern pine might shift host·pathogen relationships may also be disrupted into hardwood forests of eastern Pennsylvania and by the stress of new conditions, resulting in New Jersey. In the southeast, some 18 rree species increased frequency of epidemics (Leonard & Fray, may become locally extinct, and forest land may 1986). become converted into scrub and savanna. In the According to Coope (1987), species that could west side of United States, Douglas fir, ponderosa not track the changing positions of suitable pine and western hemlock can disperse upslope in environments muSt have become extinct when major the Rockies. In California and Oregon the Douglas climatic oscillations began in the Uite Tertiary. Rigid fir would shrink in the lowland and be replaced by association with a particular latitude, for instance western pine. In the case of regional drought and photoperiodic dependence, would make a species a increased fire due to change in climate, forest area likely candidate for extinction. For example, the in the west could be dramatically reduced and some endomychid beetle, Stenofarsus rotendus, in species would go locally extinct. For the United Panama is programmed, mainly through its response States as a whole, the EPA report foresees a marked to day-length, to terminate diapause in April, at the loss of healthy forest area and a net reduction in beginning of rainy season (Wolda & Denlinger, forest productiVity for several centuries. 1984). Without changes in its physiology the species Climatic changes resulting from increase in could not live in places where the timing of atmospheric carbon dioxide are expected to alter response to day-length and the beginning of the forest productivity and species distributions. rainy season did not coincide (Wolda, 1987). Williams (1985) estimates that a doubling of CO 2 Existing data on exotic species may prove will increase productiVity in northern Alberta while particularly useful in predicting species responses to reducing it in the dry southeastern part of the environmental change (CGC, 1988). For example, province. For Finland, Kauppi and Posch (] 985) ,he population dynamics of successful invaders have estimated that a climatic warming will lead to (Harper, 1977) may provide information needed to the greatest absolute increase in yield from the predict which species will spread and expand in boreal forest in warm southern and maritime regions response to changed future environment. Species but the greatest relative increase in north. may feel pressure from invaders that find the new Using a linked forest productivity soil process climatic regime to their liking (Peters & Darling, model with climate model predictions 1985). For example, Melaleuca quinquenervia, a corresponding to a doubling of CO2 , Paster and Post bamboo-like Australian eucalypt, has invaded the (1988) have assessed the possible responses of Florida Everglades, forming dense monotypic stands north eastern North American forests to a warmer where drainage and subsequent fires have disturbed and generally drier climate. Their model prediction the natural marsh community (Courtenay, 1978; were: (i) on soils where there was no decrease in Myers, 1983). Such Invasions may become common soil water availability with a doubling of CO 2 , the place in response to large scale climatic changes. current mixed spruce-fir-northern hardwood forest Estimates of vegetation changes in Canada show was replaced by a more productive northern a large effect of global warming (Warrick et at., 1986; hardwood forest, and (ii) with increase in the Gates, 1985). The warming would return Canada to proportion of the growing season with soil water warmer summer condit:ions than those of the below wilting point, the simulated mixed spruce­ climatic optimum over North America about 6000 fir/northern hardwood forests were replaced by a years ago (Han:ington, 1987). At that time the boreal stunted pine·oak forest. forest extended far north of its present range Peters and Darling (1985) have shown that small RAGHUBANSHI et al.-ENVIRONMENTAL CHANGE AND BlOWGICAL DIVERSIlY 103 ecological reserves may be especially vulnerable to mortality in sea-urchins during the periods of high the effects of climatic change. A likely result will be temperature. The severe El Nino of 1982/83 caused the extinction of species that such reserves were extensive damage to the fishing industry and to the established to preserve. While discussing the effect sea birds and other organisms (Feldman et at., 1984; of global warming on natural reserve species, Peters Schreiber & Schreiber, 1984; Glantz, 1985; Jordan, and Darling (1985) identified nine types of species 1985). Extensive coral mortality occurred all over and communities which may be particularly affected the eastern pacific (Glynn, 1983, 1984). A.<;a result of by warming trends over the next hundred years. nutrient depletion caused by elevated temperatures These include (i) peripheral populations located Macrocystiscanopies were reduced and considerable near the edge of a species range, (ii) geographically mortality and reduced growth rates occurred in kelp localised species such as island species, (iii) forest communities. During the 1982-83 El Nino genetically impoverished species having very small event in Chile, the northern populations of the alga populations and ecotypes, (iv) specialized species Durvillea disappeared and have not yet recolonized requiring narrow range of environmental conditions, (Tomicic, 1985). The kelp, Laminaria japonica, is (v) poor dispersers, (vi) annuals, (vii) montane and grown extensively in warm waters (Tseng, 1981) and alpine communities, (viii) arctic communities, and their sporophytes are temperature sensitive and (ix) coastal communities. Characteristics such as probably near the limit of the temperar.ures in which large population size, broad geographic distribution they can survive. An increase in water temperature of and high dispersal potential should help protect only a few degree could eliminate the entire species and higher taxa from extinction. population of this alga. Palaeorecords show that large body size appears to A rise in sea level resulting from thermal be a disadvantage, at least for terrestrial animals. No expansion of sea water and melting of glaciers and tetrapode greater than 10 kg survived the Late polar icecaps has been widely discussed (Hansen et Cretaceous (Pad ian & Clements, 1985). at., 1981; Hoffman et at., 1983; NRC, 1983). The Survival of specialist species may be strongly Villach conference on the Greenhouse effect in dependent on a single host. A loss or departure of Austria in 1985 predicted a rise in sea level between that host due to climatic change will certainly lead to 20-140 cm in the next 50 years. However, recent destruction of the specialized species. For example, estimates predict a sea level rise in the range in fig wasps, whose reproduction is closely tied to 30 ± 20 cm (Thom, 1989; Gaughan, 1989). The the plant in which they hatch, each of the 750 effect of expected rate of sea level rise in the next species can grow only on its own species of fig century may be somewhat analogous to the effects of (Kjellberg et at., 1987). Similarly Everglades kite sea level rise that occurred at the end of the last ice (Rostrhamus sociabitis) dep~ndson the apple snail age, 80 m over an interval of 14,000 years (Bloom, (Pomacea catiginosa) for its food. The snails are 1988) During deglaciation, major dislocations in themselves localised in distribution, and a decrease estuaries, marshes, and nearshore ecosystems in their abundance due to drying of the Everglades occurred (CGC, 1988). Available information has threatened the kite with extinction in the United suggests that the predicted rates of sea level rise are States (Bent, 1961) Large herbivores were the most near the upper bound of possible rates of intertidal susceptible to disruption during the revolutions in marsh growth (Bormann et at., 1984). Consequently, land plants, notably the Carboniferous-Permian rise sea level rise in the next century is likely to drown 0f seed plants and the early to mid-Cretaceous rise many if not all salt marsh systems except in areas of flowering plants (Webb, 1987). where the land is rising and reducing the rate of Elevated ambient temperatures may affect land relative sea level change (CGC, 1988). bird fauna through the negative response of :f predictions of sea level rise are correct, nestlings to elevated temperatures (Murphy, 1985; coastal habitats, such as salt marshes and islets used Tomback &'Murphy, 1981; Barrett & Runde, 1980; by nestling birds, may be inundated or eroded. Salt Salzman, 1982). Possible effects of elevated sea marshes and estuaries are very important for many temperature on marine flora and fauna can be birds and fishes as a breeding ground. Any surmised by taking examples from El Nino events. destruction of these areas will lead to extinction of Temperature controls the sea water denSity and is many of these species. Freshwater lowlands along related to nutrient concentrations, for example, a the coast are likely to suffer from the intrusion of strong negative correlation exists between salt water. The cypress trees of the US Gulf Coast, for temperature and nitrate, there are negligible example, do not tOlerate salt water, yet they grow amounts of nitrate above 15°C Oackson, 1977, only slightly above sea level (Titus et at., 1984) 1983). Tegner and Dayton (1987) observed mass Island species are one of the most threatened 104 THE PALAEOBOTANIST communities as latitudinal migration of these Austin, M. P. 1964. Relationships among functional properties of species are limited (Peters & Darling, 1985). If California grassland. Nature 217 : 1163. latitudinal migration required by them exceeds the Awasthi, N. 1974. Neogene angiospermous woods. In: Surange, K. R., Lakhanpal, R. N. & Bharadwaj, D C. (eds)-Aspects and size of the island, a climate change would leave little appraisal of Indian palaeobotany, pp. 3-i I· 35H. Birbal Sahni alternative but extinction. Institute of Palaeobotany, Lucknow. The projected increase in temperature would Awasthi, N. 1982a. Studies on some carbonisecl woods from Ney· cause widespread changes in precipitation pattern veli Lignite deposits. India. Geopbytolo/!,y 14: H2·95 Awasthi, N. 1982b Tertiary plant megafossils from the Himalaya­ (Hansen et al., 1981; Kellog & Schware, 1981). It is a review. Palaeobotanist 30 : 25-i·267 suggested that there will be an increase in Awasthi, N. & Panjwani, M. 1984. Studies on some more carbo· precipitation over India, and decrease in central and nised woods from the Neogene of Kerala Coast. India. Palae· south central USA and over much i.l Europe and obotanist 32: 326,336. Russia ~Wi~eyet al., 1980). Summer dryness may Bajpai, Usha 1987 Glossopteris shailae, a new leaf from Upper become more frequent over the continents at middle Permian (Raniganj Formation) of India. Palaeobotanist 35 : 159164. latitude in the Northern Hemisphere. Some models Bajpai, Usha 1990. r-Ioristics, age and stratigraphical position of suggest a 40 per cent decrease in rainfall in fossiliferous band in Chitra Mine Area, Saharjuri Outlier, American Great Plains by the year 2040. In some Deogarh Coalfield, Bihar. Palaeobotanist 37 : 306·315. areas, increased temperature could exacerbate Bajpai, Usha & Tewari, Rajni 1990 Plant fossils from upper beds of Raniganj Formation in Jharia Coalfield. Palaeobotanist regional drying (Manabe et al, 1981) Breeding 38: 43·49. success in certain birds may strongly depend on Rande, M. B., Chandra, A, Venkatachala, B. S. & Mehrotra. R. C. rainfall intenSity as shown by Sterna birundo in 1988. Deccan Imertrappean Ooristics and its stratigraphiC Germany (Becker & Finck, 1985). The same is true implications. In: Maheshwari, H. K. (Ed. )-Palaeocene of India, pp. 83·123. Indian AsseX'iation of Palynostratigraphers, for birds in tropical dry forests in Puerto Rico Lucknow. Presently the age of the Deccan Traps is considered (Faaborg et al, 1984). Drought in the interior of as 67·65 my (at the KIT boundary). Australia is shown to strongly reduce the number of Barrett, R. T. & Runde, O. J. 1980. Growth and survival of nestling suitable rabbit warrens and number of rabbits Kittiwakes Rissa tridactyla in Norway. Ornis Scandinav. 11 : (Myers & Parker, 1975) Similarly red kangaroos, 228·235. Becker, P. H. &- Finck, P. 1985. Witterung and Ernahrungssitua· Megaleia ntfa, are greatly reduced in numbers by a tion als entscheidence Faktoren des Bruterfolges del' Flus· long drought (Newsome et al, 1967) In relatively seschwalke (Sterna hirundo). I Ornith. 126: 393·404. dry years the size of butterfly populations may be Begon, M., Harper, J. L. & Townsend, C. R. 1986. 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