Geographic Areas

Physiographic Layout

Covering large geographic areas of eastern Rajasthan and southwestern Uttar Pradesh, the Bundelkhand Craton is a rocky terrain of low-altitude hillocks worn down considerably by weathering. Bordering the cratonic block in the west, a Precambrian mobile belt stands out as high hill and mountain ranges known as the Aravali (Plate 9.1). The Aravali Ranges extend southwest from Delhi to Palanpur in Gujarat and then bend gradually southeastward, ending against the ENE–WSW-trending ~ 1000 km long graben in which flows the Narmada, the river that discharges into the Arabian Sea in the west. The Aravali ranges are 400–600 m high in the northeast, but they rise to an elevation of more than 1000 m in the southwest. Among the high peaks are the 1772-m Gurushikhar near Mount Abu, the 1431-m Jaga, and the 1225-m Bhorat northwest of Udaipur.

Plate 9.1. The shaded relief map shows the physiography of the cratonic Bundelkhand surrounded by the undulating terrain of the Vindhyan in the east and the hill ranges of the Aravali in the west and of the Satpura in the south.

(Reproduced with permission from: AridOcean/Shutterstock. Annotation by authors.)

East of the Bundelkhand cratonic block lies the 100- to 300-km-wide Vindhyan terrane characterized by a series of hill ranges that trend ENE–WSW in Madhya Pradesh and NNE–SSW in eastern Rajasthan. These hill ranges do not rise more than 600 m above the mean sea level. The rivers and streams draining eastwards and northwards flow gently in their wide winding courses. However, in the northern part of this terrane, rivers such as the Chambal and the Betwa have made conspicuous incisions in their valleys just before joining the Yamuna River. Here, a large swathe of the land has become a badland.

The Aravali is the water divide between the rivers that join the Yamuna of the Ganga system discharging into the Bay of Bengal and the rivers that flow southwest to empty themselves into the Arabian Sea.

2 The agricultural landscape as a unit of management and conservation

Landscapes are geographic areas to which human beings attribute considerable value and would like to conserve. The aesthetic, spiritual and heritage value of biodiversity as an attribute of landscape has long been recognised (Tribot et al., 2018). Increasingly, it is the management of the functional value of biodiversity, as a source of ecosystem services and functions necessary for human well-being that is becoming the focus of attention (Guerry et al., 2015; IPBES, 2019) and toward which much of the financial and policy support is directed (EU, 2021; Hristov et al., 2020).

Agricultural landscapes are made up of a mosaic of cultivated fields and grasslands, and these structures are intermingled with semi-natural habitats, such as woods, moorland and rivers, and areas of urbanisation, including villages and roads. Some arthropod species make use of only one of these structural elements, but many utilise more than one type and will cycle through them depending upon their resource preferences, life history stage and the phenological conditions of the structure (e.g., Holland et al., 2005; Nardi et al., 2019). Consequently, the management applied in any one structure can affect the arthropod biodiversity of the whole landscape (Nardi et al., 2019). There is, therefore, a real benefit in evaluating biodiversity at landscape scales because it explicitly integrates the management of the different component structures of the landscape into the evaluation. Networks of sensors arranged at high spatial resolution throughout the landscape, could be used to sample all habitat components to indicate landscape-scale arthropod biodiversity and the contribution of particular field or landscape structures and their configuration. In principle, this might include metrics for the contribution of each agricultural field and its management to biodiversity, thereby achieving the most important criterion for a switch to obligation of results payments; that of the measurement of the landscapes would provide big data tied to real time sensors for comparing different farms and landscapes and upscaling to regions and countries.

In addition to these potential financial benefits for individual farmers, landscape-explicit biomonitoring of biodiversity could also have potentially very important social benefits. For example it could help to shift the defined socio-cultural role of the farmer from a food producer to an environmental steward producing a wide range of ecosystem benefits in addition to food. Currently, anecdotal evidence suggests that many farmers see conserving biodiversity outside of their field of expertise and as not part of their job (Bohan et al., 2022). Indeed, those farmers that do feel a connection to the biodiversity on their land or actively conserve it seldom receive payment for their efforts. Farmland biodiversity is mostly considered as a non-marketable good, but simultaneously regarded as important for agricultural production, but rarely explicitly budgeted for as an agricultural input, and agroecosystem functioning (Bommarco et al., 2013; IPBES, 2019). Landscape-scale biomonitoring using simple sensors would help to demonstrate how much individual management by farmers and the biodiversity in their fields, interacts with the biodiversity of surrounding structures to contribute to overall landscape biodiversity. If appropriately coupled to the aesthetic, spiritual and heritage value of biodiversity (Griffiths et al., 2020), the contribution of the management adopted by farmers to overall well-being within the landscape could also become a significant source of pride for those farmers. This would couple the well-being of individual farmers to other people residing in the landscape and wider society and might help circumvent some of the problems of stigmatisation of farmers for their perceived poor management of the environment, which currently limit efforts to conserve biodiversity (Bakker et al., 2021; Chèze et al., 2020; Kleijn et al., 2020).

Religion

Given the large geographic area of the Indus cities and the hierarchy of settlements, it is surprising that distinctive shared symbols and distinctive ritual objects are found in all major settlements. These symbols are thought to reflect a shared ideology that in conjunction with economic strategies helped to integrate the many different communities living in the major cities and surrounding settlements. Some of the more common artifacts and symbols are similar styles of terracotta figurines of animals that may have been used for symbolic sacrificial purposes. Human figurines of males and females with ornaments and elaborate headdresses may represent fertility or other specific deities (Figure 11) Various geometric symbols such as the stepped cross, swastika, endless knot, and intersecting circle motif are found on pottery as well as pendants and seals. Narrative scenes on seals depict outdoor ceremonies that took place under the sacred pipal or fig tree, worship of deities in trees or seated in yogic position on a throne, processions with sacred animals, the practice of animal sacrifice, and possibly even human sacrifice. Other scenes depict what may be important myths and stories. Local cults may have been practiced in specific regions while a more established state religion appears to have emerged in the major cities. At Mohenjo-daro and Dholavira, stone sculptures of male figures have been found that may represent clan leaders. In the past, these were incorrectly called ‘priest-king’ images.

Figure 11. Harappan figurines and sculpture. (a) Terracotta female figurine, Mohenjo-daro; (b) terracotta female Figurine, Harappa; (c) bronze female figurine, Mohenjo-daro; (d) steatite ‘priest-king’ figure, Mohenjo-daro; (e) terracotta male figurine, Harappa.

The most direct evidence for ritual practice is found in the cemetery burials at major sites such as Harappa, Dholavira, and Mohenjo-daro, as well as some smaller settlements such as Lothal, Rupar, and Kalibangan. Most burials were made in a north–south-oriented rectangular pit with the head to the north. The body was placed in a wooden coffin or wrapped in a shroud, and laid out on top of or surrounded by burial pottery and other offerings needed for the after-life (Figure 12). Although these burials do not contain large amounts of material wealth, they do contain distinctive pottery and ornaments that would not have been available to common people. The health status and mature age profiles of the buried individuals also indicate that they were a privileged class. The delicate shell bangles found buried with many of the women also indicate that over time they became less and less involved in manual labor, clearly an indication of elite status. Although there are no ‘royal burials’, the recent excavation of a burial complex at Dholavira suggests that some individuals were interred with gold ornaments, a tradition that was not practiced in the major cities and towns. Cemeteries that have been discovered represent only a small portion of the population, and the rest of the urban population would have been disposed of by other means that have left no archaeological trace. This burial pattern is one more indication of social differentiation and hierarchy.

Figure 12. Harappa burials with pottery and ornaments.

Glaciers: Origin and Dynamics

Glaciers arise in geographic areas where annual snow accumulation exceeds annual snowmelt. If this imbalance is sustained for a significant number of years (decadal–centennial timescales), the accumulated snow compresses under its weight and squeezes out any embedded air pockets. The snow then becomes firn (which is a granular state between snow and ice) and then, upon further compaction, ice is formed. The more net snowfall, the more ice is produced, and ultimately a glacier is formed. It takes decades for this process to occur. The mature glaciers of our planet have therefore existed for thousands of years. Our Greenland and Antarctic ice sheets are even older and have existed for over a hundred thousand years (Greenland) and millions of years (Antarctica).

Glaciers are therefore subject to all the factors that determine snow accumulation and snowmelt. These include latitude, altitude, net incoming shortwave radiation, the topographic environment, tectonic movement, and importantly for glaciers in the Anthropocene, atmospheric greenhouse gases (which regulate temperature).

Though perhaps counterintuitive, ice is a fluid and flows accordingly, though on longer timescales than the usual fluids we think of, like water. But ice obeys the physics of a visco-elastic substance. Most importantly, it flows downhill under gravitational acceleration.

Downhill glacier flow brings ice into warmer atmospheric temperatures so glaciers flow from an elevation in which they grow into elevations where they melt. The global average rise in temperature per kilometer of descent is 6.5°C in the free atmosphere. Temperature lapse rates along a topographic surface such as a mountainside, however, vary depending on the surface energy balance, but the envelope of free air lapse rates is between ~ 2 and 9.8°C km^− 1.

Through physical inertia, and because it takes a large amount of energy to melt ice, glaciers tend to flow well below the elevation where net accumulation equals net melting, an elevation called the equilibrium line altitude (ELA). The ELA depends on temperature, precipitation, and radiation and hence varies geographically with the topographic environment. The ELA on a windward topographic slope, for example, tends to be lower than the ELA on the lee slope. Altitudinal changes in the ELA over time determine whether a glacier grows or diminishes. A descent of the ELA would in general be beneficial to a glacier. A rise of the ELA would be detrimental to a glacier. Unfortunately for glaciers in the Anthropocene, a major determinant of the ELA is temperature: the higher the temperature, the higher the ELA. If the ELA exceeds the highest topographic elevation in the region, a glacier simply cannot exist.

One complicating factor is orographically induced snowfall. In a warmer climate, the air has more moisture so accumulation increases at higher elevations. The competing factors of increasing temperature (which is bad for glaciers) and increased accumulation (which is good for glaciers) have therefore been the subject of a number of numerical studies (e.g., Pollock and Bush, 2013; Janes and Bush, 2012), the conclusions of which are that by the end of the century, the temperature effect is dominant and only glaciers at the highest elevations will exist.

Introduction

Every species has a geographic area beyond which they are no longer found—that geographic area is that species’ range. Ranges can be bound by geographic features such as rivers, mountains, or oceans, but many are bound by environmental limits like temperature and precipitation, known as the species’ “niche.” The edge of the range is known as the range limit, and populations there often experience unique environmental pressures compared with more central parts of the species range. The unique environments at range limits allow scientists to understand the evolution of tolerance to environmental pressures, the ability of species to adapt or not adapt to varying conditions, and in a more contemporary sense, how changing climates can impact species at the limits of their climate niche.

The range limit is the area beyond which a species can no longer produce viable individuals, whether due to reduced fitness or other factors that limit colonization. Populations at geographic range limits are often called “marginal,” “peripheral,” or “edge” because they exist at the margins of the species range. Note that these terms are sometimes applied to populations existing at the environmental extremes of a species’ distribution or niche, but not necessarily at geographic margins (e.g., very high elevations in the center of a species’ range). In this article, we focus mainly on geographic species range limits. Species ranges can be disjointed, but marginal populations are those at the furthest limit of the range. Ranges can be said to be at equilibrium, indicating that their borders are not shifting (Gaston, 2003), but perturbations and evolutionary adaptation can cause ranges to contract or expand, in a process called range shift. Climate change (global warming) is facilitating range shifts– making some parts of the range uninhabitable while opening new areas for colonization Araújo et al. (2005).

The areas where a range is expanding, or where conditions are becoming favorable even if expansion has not yet occurred, are known as the leading edge of the range. The areas where contraction is more likely, or where conditions are becoming potentially less favorable, are known as the rear edge. For example, in montane species the leading edge is often the higher elevation edge of the species range, and the lower edge of the range is the rear edge (Fig. 1). The different edges are hypothesized to have different characteristics—the rear edge may be more impacted by heat-related stress and may show strong local adaptation (Hampe and Petit, 2005), whereas the leading edge is impacted by cold stress, is expected to exhibit population growth, and is more likely to be populated by founder events and to be the source of dispersal leading to range expansion (Hampe and Petit, 2005).

Fig. 1. A cartoon depiction of a species range. The color gradient represents temperature, warmer at the rear edge and cooler at the leading edge. Rear edge populations are characterized by warmer temperatures—as such, as climate changes there is the potential for range contraction at this edge. The interior range can have higher gene flow as a result of increased habitat connectivity. Populations can be more stable due to less extreme environments. At the leading edge populations experience cold stress, but as climate changes, these areas may warm and open up new habitat, allowing for range expansion. It should be noted that environmental patterns vary not only from north to south but from east to west as well. Depending on the geographic area a species covers, east-to-west climate gradients may also be important in setting range limits.

In this chapter, we highlight major methods in studying range limits, what we have learned so far from range limits studies, and new topics in range limits research. By the end of this chapter, the reader should understand how populations at range limits may differ from more interior populations and how the inclusion of marginal populations can enhance a research program. 1.

3.16 Pinnacle Point

Pinnacle Point refers the geographic area around a small headland in the coast of the Indian Ocean, about 10 km from the Mossel Bay point in the Western Cape Province (Figs. 1 and 2). This area has a series of caves and rock shelters formed at the eroded fault breccias of the shear zones in the highly structurally deformed Skurweberg Formation of the Table Mountain Group Sandstones (quartzitic sandstones) (Fig. 12A and B; Bar-Matthews et al., 2010). A series of caves and rock shelters on the same cliff face can be grouped together into a complex, and at the tip of the Pinnacle Point there is Site 13 complex (PP13 A-G). Pinnacle Point Cave 13B (PP13B) has preserved the earliest archaeological evidence of modern humans using marine shellfish and pigments, and the manufacture of bladelets around 164 ka (Marean et al., 2010). The stratigraphy of PP13B, described by Marean et al. (2010), differs laterally within the cave and three sequences of the lightly cemented MSA (LC-MSA) deposit, and two eastern and western areas of non-LC-MSA deposits have been studied. They were found to differ markedly, suggesting a complex history of deposition, erosion and alteration. The stratigraphy of Marean et al. (2010) starts with the lowest (LC-MSA Lower) deposited on top of the Table Mountain Sandstone (TMS) bedrock. This layer is the least cemented of all LC-MSA but contains the most archaeological evidence including materials that humans altered using fire. Three OSL dates of LC-MSA Lower yielded a mean age of 162 ± 5 ka. The succeeding layer is LC-MSA Middle, which is mostly ash with multiple lenses of charcoal and in situ hearths, and high densities of marine shellfish. It has been dated to 125 ± 5 ka using OSL. LC-MSA Upper overlies the anthropogenic LC-MSA Middle layer as three heavily cemented layers. The lower LC-MSA Upper layer is an indurated sandy-silty layer with multiple lenses of organic material. The middle layer is a sandy horizon with a lens of shellfish and multiple lenses of organic material. It was dated with four OSL samples that yielded a mean age of 126 ± 4 ka. The top layer is a capping cemented dune that sealed the cave to human occupation around 93 ± 4 ka. The LC-MSA Flowstone with a thickness up to 5 cm is the final unit of LC-MSA deposits that started precipitating immediately after the dune sealed the cave. It is a laminated brown-yellow flowstone that was dated using U/Th and six samples yielded ages from 92 ka to 39 ka.

Fig. 12. Photos of some sites outside the Cradle. The site of Pinnacle Point is a series of caves and rock shelters formed by shear zones in quartzitic sandstones of the Table Mountain Group (A and B). Sibudu rock shelter contains an extensive cultural sequence that spans pre-Still Bay to Iron Age (C and D). Wonderwerk cave is phreatic tube in the dolomitic hills of Kuruman and contains a lithic sequence that spans the Early Stone Age to the Late Stone Age (E).

Photo credits: Matt Caruana (A, B and D), Andy Herries (C and E).

In the eastern area excavation, seven layers were observed starting with the Lower Roof Spall Facies deposited directly on top of the TMS bedrock. This layer is a clast-supported pebbly breccia to the south and pebbly sandstone to the north dated to 110 ± 4 ka using OSL dating of two samples. Overlying the Lower Roof Spall Facies is three layers of Upper Roof Spall (URS) and Shelly Brown Sand (UBS) Facies. The URS and UBS occur as individual layers in some places and as inseparable layers in some areas. Generally, the URS comes first, followed by a blended URS-UBS before the UBS on its own. OSL ages of the individual URS and UBS layers overlap in the range 98-91 ka, but the age (ca. 115 ka) of the blended URS-UBS does not overlap. The URS and UBS Facies contain well-preserved hearths with distinct bands of ash, charcoal and baked sediments, and can have lithic artifacts and fauna inside and around them. The URS is overlain by the Truncation Fill, which is a dark, rocky and organic-rich horizon dated using radiocarbon on a sample of charcoal from the boundary with the URS. Then there is the Re-Deposited Disturbance layer of disturbed and re-deposited material from modern activities as evidenced by modern bird feathers and modern artifacts such as cigarette butts. Fine-grained surface sediments are the top layer. In the western area excavation, the deposits seem to resemble a midden or dump compared to the eastern area. The deposit starts with a Boulder Facies, which is an unconsolidated sediment with large boulders and a silty loam matrix. Then a series of Laminated Facies sediment ca. 1 m thick overlies the Boulder Facies. This unit is mostly sterile grayish-brown sand and silt sediment dated between 414 and 349 ka. Then follows the Light Brown Silt Facies dated between 349 and 152 ka. The overlying Dark Brown Sand Facies is a series of sandy layers with a low to moderate density of lithic and faunal material. The OSL ages of these layers range from 159 ± 7 ka to 98 ± 4 ka. Surface sediments are also the top layer in the western area.

A TROPHIC POLYMORPHISM AND ENVIRONMENTAL FLUCTUATION

Field studies in relatively localized geographic areas have led to the recognition of polymorphisms within or between populations related to the acquisition and processing of dietary resources. The patterns encountered may arise from developmental plasticity (Section III.C, preceding) or from selection in fluctuating environments over a protracted time span.

One example of trophic polymorphism within populations is seen in ambystomatid salamanders. Ambystoma macrodactylum columbianum (the Central long-toed salamander) expresses a cannibal morph in the larval phase that is characterized by hypertrophied vomerine teeth and a longer, wider head, when compared with the noncannibal morph (Walls et al., 1993a). Although feeding on conspecifics enhances the morphological differences between the cannibal and noncannibal morphs, initiation of the cannibal morph is mediated through environmental triggers (Walls et al., 1993b).

A similar phenomenon occurs in the tiger salamander (Ambystoma tigrinum), where cannibalistic larvae (usually males) have hypertrophied vomerine teeth, large bodies, and wide heads, when compared with noncannibals. The cannibalistic larvae are macrophagous carnivores, whereas the noncannibal morphs are omnivorous planktivores (Lanoo and Bachman, 1984; Lannoo et al., 1989). Cannibalistic individuals metamorphose earlier than typical morphs. Pedersen (1991) investigated the morphological differences between the cannibal and noncannibal morphs and found that the former had longer, recurved teeth, distortion of the underlying vomer, and hypertrophied muscles associated with the feeding apparatus. He postulated that heterochrony between the skull, dentigerous bones, and dentition may be a feature of the cannibal morphs and noted that the morphology develops before cannibalistic behavior is initiated. Pedersen (1991) regarded these morphs as essentially representing functionally different species in a trophic context. The growth of the skull in small cannibals is accelerated (Pedersen, 1993) and is compensatory for the demands of macrophagy.

Aspects of trophic polymorphism are also evident in the larvae of the Southern spadefoot toad (Spea multiplicata). Tadpoles of this species occur as a carnivorous and an omnivorous morph, and they occupy different trophic niches (Pfennig, 1992). The carnivorous morph consumes shrimp, and the omnivorous morph detritus. Carnivores arise facultatively through the ingestion of shrimp and the morphological differences—an enlarged orbitohyoideus muscle and a shorter, wider gut—are reversible. The ephemerality of the pond, and thus the number of shrimp, induces the carnivorous morph. Carnivores develop faster but have a smaller size at metamorphosis, fewer fat reserves, and lower survivorship. The closely related Plains spadefoot (Spea bombifrons) develops similarly to the Southern spadefoot, but carnivory is further translated into cannibalism (Pfennig et al., 1993). The carnivorous/cannibalistic morph has beak-shaped mouthparts as opposed to flattened, keratinous jaws, hypertrophied jaw depressor muscles, and a morphologically wider and shorter gut and tends to exhibit solitary, rather than gregarious, behavior.

Reversible responses in trophic morphology have also been demonstrated in the cichlid fish Cichlasoma managuense (Meyer, 1987) when exposed to different feeding regimens (Figure 17-2). Differences in diet, and possibly in feeding mode, induced phenotypically plastic changes of the feeding apparatus, brought about through retardation of the normal developmental rate. Similar between-population differences in trophic morphology in other cichlid species were documented by Witte et al. (1990). Populations feeding habitually on soft foods have delicate pharyngeal jaws and numerous, slender teeth, whereas those feeding on hard food, such as snails, have massive jaws, and heavy, blunt teeth. It is possible that some of the morphological plasticity is triggered by nutritional differences in the diet, as well as by differing mechanical demands of the various foot types (Wimberger, 1993).

FIGURE 17-2. Radiographs of two specimens of Cichlasoma manguense fed on different diets for eight months. The upper illustration (A) exhibits the acutorostral morphology, whereas the lower one (B) depicts the obtusorostral form.

Reprinted with permission from Meyer (1987).Copyright © 1987

In the three-spined stickleback (Gasterosteus aculeatus), observed polymorphic variation is heritable, although there is still some plasticity in response to diet (Robinson, 2000). In a study of four populations representing anadromous, stream, lacustrine planktivorous, and benthic feeding groups, Caldecutt and Adams (1998) revealed statistically significant morphological differences between them, as assessed through landmark-based geometric morphometric analysis. The differences in skull form, representing geometric assessment of jaw morphology, were consistent with functional morphological predictions based upon habitat type and dietary data.

More dramatic polymorphism associated with the trophic apparatus has been demonstrated in the teleost fish Astyanax mexicanus, which exists as an eyeless cave-dwelling morph and a sighted, surface-active morph (Wilkens, 1988). Eye formation is initiated in the cave-dwelling forms, but subsequently stops, and the eye degenerates (Yamamoto and Jeffery, 2000). Inductive signals from the lens are involved in the surface-dwelling fish's eye formation. Transplantation experiments indicate that the surface fish lens is sufficient to rescue eye development in cave fishes. The differences between surface dwellers and cave dwellers is trophically related and results in a trade-off manifested through modification of developmental pathways. The cave-dwelling forms have larger teeth and more taste buds (Vogel, 2000; Pennisi, 2002), which enhance feeding abilities in the cave environment. Yamamoto and Jeffery (2000) report that the eyed and eyeless forms of this species probably diverged from one another in the last million years and have been able to exploit food resources in environments requiring different sensory modalities. Eye loss need not be explained simply as a result of neutral mutation or drift, but instead seems to be related to a relaxation of stabilizing selection and the favoring of smaller eyes, larger teeth, and more taste buds in the cave-dwelling forms. The result is polymorphism and a stepped cline.

Selection in the field in the context of trophic polymorphism has also been the subject of intense study of Darwin's finches on the Galapagos islands. Inherent variation in heritable characteristics, such as beak morphology in Geospiza, permit selection to act in response to rapid changes in food availability associated with climatic extremes, such as droughts (Grant, 1991). The intensity of selection in these situations is enhanced by small population sizes. In certain situations, where environmental changes are dramatic, this inherent variability can lead to more firmly established and divergent patterns of form. For G. conirostris on Isla Genovesa, genealogies of family groups were established and heritability of traits studied (Grant and Grant, 1979, 1989). Feeding patterns of as many birds as possible throughout their life span were quantified and the relationship of beak size to survival and reproduction established. Size and proportions of the beak were found to be highly heritable and directly correlated with the capacity to feed on particular foods; slender bills were more effective at penetrating soft fruit and feeding on nectar, whereas the most massive bills were associated with cracking open cactus seeds and stripping bark from trunks to search for insects. In periods of stable climate, adult survivorship was generally unrelated to phenotype, but in extreme drought conditions and associated vegetational changes, there was strong selection on bill size and shape. A clear functional relationship between bill type and food manipulation was demonstrated. Had the drought conditions persisted, eventual fixation of the alleles producing the largest possible sized beaks may have resulted. Variation in structural features, such as bill size, and the functional associations thereof, thus appear to permit survival in fluctuating environments.

Abstract

Regionalization is the discipline that groups geographic areas of the world into regions based on predetermined criteria. While these may be abiotic criteria (e.g., climate), in biogeography the term (more specifically referred to as bioregionalization), has essentially come to mean that regions are defined on the basis of distribution patterns in living organisms. Most often this has been done using species of tetrapod vertebrates and vascular plants, with other studies considering other taxa, or shared branch lengths in the phylogenies for these groups. This process was initially performed intuitively, but currently, this is achieved using increasingly sophisticated algorithms. The results for approaches using different methods and looking at different taxa tend to converge towards common global schemata which can be explained using past and present climate, plate tectonics, and the evolution of life on Earth. Preserving distinctive assemblages of living organisms, as illustrated in regionalisation exercises, is increasingly viewed as one important facet of biodiversity conservation.

Level of Resolution 1: Broad-Scale Multispecies Ranges

Understanding variability in population distribution among geographic areas and habitats is important when attempting to generalize data from one locality to another. The first prerequisite for aggregating distribution patterns of multiple species is knowledge of species occurrence at several scales to prevent local-scale research on population dynamics from being generalized to places where a species does not occur in its typical habitat. At continental scales, range-wide maps of species distributions are available in field guides or other reviews. Because the geographical extent and sampling intensity of surveys varies by taxa, using general geographic information provides some preliminary comparability among taxa by excluding some distribution details that are important only at finer scales. Large-scale, comprehensive distribution data are available for taxa such as birds (e.g., Price et al. 1995), fish, and trees. Atlases and other comprehensive distribution data are being assembled for other vertebrates, plants, and invertebrates (Johnson and Sargeant 2002).

Because only the most common species are found in all places within their range and suitable habitats (e.g., data in Brewer et al. 1991, Corace 2007), a tabulation of known species presence by regional landforms, ecosystems, cover types (e.g., forest, shrubland, grassland), or disturbance history is an important step in any broad assessment of species conservation status (e.g., Probst and Thompson 1996). At Level 1, species distributions are developed to a degree that might allow them to be matched to land covers from remote sensing and species distribution maps (e.g., Jennings 2000) without supplementary field observation or knowledge of habitat gradients within land cover types. At scales intermediate between regional and local, patterns of presence and absence within a species' geographical range is apparent, and some species may be absent where other species with the same or similar habitat preferences might be present. For example, upland sandpiper (Bartramia longicauda) is infrequent in southeast Michigan openlands, whereas grasshopper sparrow (Ammodramus savannarum) is not found in a majority of the counties in Michigan's Upper Peninsula (Fig. 7-1). These differences may be due to range limits, landscape structure, or more specific habitat preferences than just “openland” or “grassland” (see Level 2).

Fig. 7-1. Breeding Bird Atlas distribution of four species of openland birds in Michigan, USA

adapted from Brewer et al. 1991.

Environmental Factors Spreading Bilharzia and Geohelminths in Kenya

The global burden of schistosomiasis and STH infections is enormous. The transmission of schistosomiasis is associated with lack of safe water for domestic use and poor sanitary facilities that are often present in poor communities with low socioeconomic conditions. Such conditions are rampant in many developing countries of the world. Many environmental factors are associated with transmission of these diseases. Irrigation projects that are put in place to boost food production often bring with it health-related problems including the spread of bilharzia as seen in Mwea Irrigation Scheme. Current estimates show that more than 3 million Kenyans are infected with either one or both species of the parasites that cause schistosomiasis (Schistosoma mansoni causes intestinal schistosomiasis and Schistosoma haematobium causes urinary schistosomiasis), and more than 10 million people living in the rural areas are at risk of acquiring schistosomiasis. About a decade ago, morbidity due to schistosomiasis was the fourth most frequently noted infection in the Coast Province, the fifth in Eastern and Nyanza provinces, sixth in the North Eastern Province, and 10th in the Central Province. The scenario has not changed much today. Approximately 17 000 cases were reported in hospitals as chronic mild morbidity due to either intestinal or urinary schistosomiasis. Severe morbidity often leading to mortality is focal and less common, but sufficient to be a public health concern.

Only intestinal schistosomiasis is found in Mwea division, central Kenya. Heavy infection of S. mansoni can be seriously debilitating. Heavy egg loads, sometimes more than 500 per g of stool, may lead to hepatosplenomegaly. The infection by schistosomiasis follows an age-dependent trend with heaviest infections occurring in adolescents. Infections, especially of the S. mansoni form, are prevalent in men than women. In a case study in Mwea involving 2244 person whose stool samples were examined for S. mansoni, 21% were positive with significantly more men than women infected. The infection prevalence also differed when the data was analyzed by agroecological zones (higher in the rice irrigation zone (32.1%) than nonirrigation zone 14.4%). Also in a study of 1737 school-age children (aged 8–20 years) in 25 schools in Budalangi, a flood-prone area in Funyula division, Busia district, Kenya, in 1998, revealed an overall STH infection of 89%. The prevalence ranged from 70% to 100% in different schools. Hookworm infection was 77% (8.6% heavy infection), Ascaris 41.9% (4.5% heavy infection), and Trichuris (6.9% heavy infection). In total, 19.8% of the children were infected with both STH and S. mansoni (ranging from 1.4% to 77.7%), with the highest prevalence found in lakeside schools. Microgeographical characteristics influence both the prevalence and the intensity of S. mansoni infection. This brings into focus the importance of geography and varying environmental parameters when targeting control efforts to specific sites of focal transmission. This is necessary so that the costs involved are minimized. Such geographical variation that influences infection depends on activities that expose people to frequent or prolonged contact with contaminated water. Irrigation of rice is one activity that increases the risk of infection because of the long hours the farmers have to be in contact with contaminated water. Such wet fields of rice are ideally suitable for the growth of snails because the growing rice modifies the water temperature and provides a suitable microhabitat for parasite transmission. Rice farming, therefore, increases the chances for the development of schistosome parasite and causes an increase in the prevalence and intensity of schistosomiasis.

Some of the major areas in Kenya where seasonal flooding occurs or were swampy have seen the development of irrigation schemes. Some of the major irrigation areas in Kenya are in Central Province where rivers and streams from Mount Kenya flood the low-lying lands; others are in Western Province around the Lake Victoria basin and in the Coast Province near the Athi River basin. In these areas, there are serious problems with transmission of schistosomiasis. For example, one area would be discussed in central Kenya – the Mwea–Tebere Irrigation Scheme. Mwea (Figure 1) is located approximately 100 km northeast of Nairobi. It has an area of 513 km² and a population of 126 000 persons according to the 1999 national census. The division is divided into three agroecological zones: the rice irrigation zone, which was until a few years ago supported by the National Irrigation Board and the other part of it is outside the support of the irrigation board and falls under the nonirrigation zone. The rice irrigation scheme covers approximately 13 640 ha of the division and produces 90% of the country's rice output. A well-designed canal water network serves the rice irrigation scheme. With the recent liberalization of rice farming from the irrigation board, there has been a steady development of new irrigation fields for both unplanned rice farming and farming of horticultural produce like beans and tomatoes. This zone is sometimes referred to as an unplanned rice/horticulture zone and is found in the twilights, surrounding the rice irrigation zone. The nonirrigation zone is drier than the other zones and therefore may appear conducive for coffee growing and other subsistence agricultural activity.