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This chapter considers the signal of local dispersal which sits inside maps of the locations of individuals, and introduces spatial statistics as measures of spatial structure. It shows how dispersal plays a fundamental part in local population dynamics. Dispersal is also shown to have important implications for the outcome of local spatial competition between two species, the dynamics of metapopulations, and the structure of multispecies communities. Local dispersal causes clumping, slows down changes in density, and affects the asymptotic state ultimately achieved by a population. When different species compete, dispersal over greater distances gives a species an advantage which can eliminate competitive coexistence which might otherwise occur. However, in the presence of spatial environmental heterogeneity, where too much dispersal can move offspring away from favourable parts of the environment, dispersal over intermediate distances can allow faster population growth than dispersal over either short or long distances.

This chapter reviews models of spatially subdivided populations with explicit stochastic dynamics of local populations. It considers metapopulation models for territorial and nonterritorial species. The final section deals with populations continuously distributed in space, focusing on how spatial environmental autocorrelation and individual dispersal tend to synchronize fluctuations in local populations, and on the influence of this synchrony on the risk of regional extinction.

The study of metapopulation dynamics has had a profound impact on our understanding of how species relate to their habitats. A natural, if naïve, set of assumptions would be that species are to be found wherever there is suitable habitat that they can get to; that species will rarely, if ever, be found in unsuitable habitat; that they will be most abundant in their preferred habitat; that species can be preserved as long as a good-size chunk of suitable habitat is conserved for them; and that destruction of a species’ habitat is always detrimental for its abundance. We will see that none of these reasonable-sounding assumptions is necessarily true. Metapopulation biology is a vast field, so to focus this chapter I will be guided partly by questions relevant to conservation biology. There are two important kinds of metapopulation. The so-called Levins metapopulation idea (Levins, 1970) is illustrated in Figure 4.1. It is imagined that patches of habitat suitable for a species are distributed across a landscape. Over time, there is a dynamical process of colonization and extinction: the colonization of empty patches by occupied patches sending out colonizing propagules and the extinction of local populations on occupied patches. This extinction can occur for a number of reasons. Small populations are prone to extinction just by the chance vagaries of the environment, reproduction, and death—environmental and demographic stochasticity (May, 1974b; Lande et al., 2003). An example of a species for which this is important is the Glanville fritillary butterfly (Melitaea cinxia), which has been extensively studied by Hanski and colleagues (Hanski, 1999). This Scandinavian butterfly lives in dry meadows which are small and patchily distributed. Another reason for local population extinction is that the habitat patch itself may be ephemeral. For example, wood-rotting fungi will find that their patch ultimately rots completely away (Siitonen et al., 2005) and epiphytic mosses will ultimately find that their tree falls over (Snall et al., 2005). The second type of metapopulation consists of local populations connected by dispersal, but without the extinction of the local populations.

This chapter shows that direct habitat loss is recognized as the main cause of species extinction, and how habitat fragmentation is an inherent consequence of habitat loss. This causal relationship has made the analysis of the relative impact of habitat loss and fragmentation on biodiversity more complex, since their effects are quite hard to distinguish. Model-based approaches underscore the necessity of considering the effect of both habitat loss and fragmentation on genetic variation and dynamics of metapopulations, and further experimental designs under controlled conditions should help validate such predictions. The review material that addressed the consequences of habitat fragmentation on biodiversity repeatedly identified the decrease of connectivity among habitat remnants associated with habitat fragmentation as a major driver of extinction.

The paleontological and phylogenetic evidence have shown that the main features ultimately responsible for plant modularity were already present at a very early stage in the evolution of land plants, and are a property shared by the whole lineage. The ecological and evolutionary implications of plant modularity have frequently been highlighted following White's pioneering treatment of plant individuals as metapopulations of repeated modules. One of the consequences of plant modularity is the appearance of a distinctive source of phenotypic variance, that is, the within-plant or subindividual component. Another consequence of the multiplicity of modules is variation in the characteristics of the copies of the same organ produced on different modules of the same plant. A thesis is developed that the multiplicity of homologous structures arising from plant modularity gives rise to a subindividual level of phenotypic differences among organs of the same plant.

Conservation of deserts can be carried out using many different approaches, including the conservation of individual desert species versus a habitat-level approach, reintroductions and recolonizations of endangered species, and revegetation of desert habitats, as well as conserving areas where there are strong genotype by environment interactions among populations of a single species. The last mentioned is important because this is where evolution of new species starts to occur—it may be important to conserve each population separately. Another, equally important issue is that the conservation of deserts must keep the importance of people in mind. It has been stated many times that people (particularly indigenous people) are part of the conservation landscape and need to be considered when conserving landscapes.

Aquatic populations are patchily distributed. The full implications of this statement for the dynamics of these populations depend very strongly on movement and dispersal patterns. The characteristically heterogeneous distribution of exploited aquatic species is of course essential to harvesting strategies employed by fishers. It can also present important challenges to management when species distributions contract to core habitat areas and these concentrations can be readily located and exploited. The types of models described in this chapter, including metapopulation models, provide an initial framework for considering the dynamics of spatially structured populations. Dispersal can provide a stabilizing force by providing a subsidy or rescue effect for depleted populations. Realistic representation of spatial processes in models of aquatic populations is an evolving art. Quantifying movement and connectivity of aquatic species entails special challenges. Spatially explicit models should account for exchange among subpopulations in relation to their size, distance, and degree of separation.

In this chapter, habitat change is broken down into three components: habitat loss, habitat fragmentation, and habitat degradation. For each, the nature and extent of the pressure is described, exactly how it threatens primates, and what is known about how primates respond. Theoretical frameworks (e.g. species–area relationships, metapopulation dynamics) that can be useful in modelling primate declines are covered; only when empirical data are used to build and test such frameworks can primate conservation biologists make specific, useful conservation recommendations. In the real world, all three components of habitat change often act synergistically, leaving us with reduced, fragmented, and degraded primate habitat—often it is hard to ascribe primates’ reactions to a particular force. More work is urgently needed, both to understand how habitat change contributes to primate declines (so that conservation practitioners can guide land-use practices and conservation interventions), and to reduce the rate of habitat change itself.

This chapter develops the concept of “desert” beyond the simple perception of endless sand dunes to describe an extensive heterogeneous dryland habitat. Vegetation types are discussed and specialized habitats such as coastal sabkhas (salt flats) and mangroves are described. Desert phytogeography and the major plant families are reviewed—including the ice plants and other large succulent lineages like the chenopods and amaranths, brassicas and crucifers, caryophs and euphorbs. Mountain regions are important in the Middle East and effects of elevation on plants are discussed, as well as regional patterns of species richness and endemism, problems of landscape connectivity, and other issues pertaining to plant metapopulations and genetic isolation. Finally, the many instances of ecological facilitation (plants “helping” plants) in desert ecology are explored from several different perspectives.

The goal of this chapter is to delineate how abiotic conditions, regional processes, and species interactions influence species diversity at local scales in drylands. There is a very rich literature that bears on this topic, but here we focus on mechanisms that promote or constrain local diversity and ask how these factors apply to deserts. We ask, “What is different about deserts, relative to other habitats, in their patterns of diversity, temporal variability in productivity, and spatial heterogeneity?” We assess how such differences might modify extant theory, and sketch relevant examples. Compared with other biomes, productivity, population densities, and community biomass are much lower in deserts, and temporal heterogeneity is typically higher. Do these differences imply distinct ecological processes and patterns in deserts? Or, do processes operate in deserts in similar ways as in tropical forests or grasslands? For example, it is often assumed that abiotic factors are more important in deserts. If so, how do abiotic factors modify biotic interactions? How do we integrate physical and biotic interactions? More generally, we ask what should be the main goals and approaches of a research program to understand the role of species interactions in determining community structure in drylands, as modified by abiotic factors and regional processes. . . . What Is Different About Drylands? . . . Deserts are traditionally perceived as relatively simple ecosystems harboring low species diversity. Yet increasing evidence suggests that desert communities can be highly diverse and complex. To our knowledge the only systematic analysis of the relative diversity in desert versus nondesert communities was compiled by Polis (1991a). These data suggest that patterns differ widely among taxonomic groups. In some cases, deserts support high diversity, comparable to or even higher than nonarid areas (see Polis 1991b). For example, while avian (Wiens 1991) and anuran (Woodward and Mitchell 1991) diversities are low compared with other biomes, desert annual plants show extremely high species diversity (Inouye 1991). Ants, succulent plants, lizards, scorpions, and tenebrionid beetles also have relatively high diversity in deserts (Polis 1991a–c, Wiens 1991). But, while very high diversity may occur, local diversity varies greatly in space and time (e.g., ants and annual plants: Danin 1977, Inouye 1991, MacKay 1991).

Ecologists generally agree that species diversity is linked to landscape features (Pickett and White 1985, Glenn et al. 1992, Wiens et al. 1993, Rosenzweig 1995, Hoagland and Collins 1997, Ritchie and Olff 1999). We present a conceptual framework for connecting species diversity and landscapes by showing how changes in species assemblages and changes in landscape structure coincide. We focus on the dynamics of the mutual relationship between (1) the frequency of occurrence of the various landscape mosaic components (patches) and their properties in terms of abiotic conditions, resource availabilities, and structural features, and (2) the occurrence and abundance of the species of an assemblage within and among these components. Although we use examples of assemblages of annual plants in semiarid shrubland, we stress the generality of our approach and its applicability to many other groups of organisms and landscapes. Most ecologists would also agree that there are connections between the observations that (1) individuals and populations of organisms are affected by environmental heterogeneity in the landscape, (2) species assemblages (or communities) consist of populations (or parts of them), and (3) changes in the landscape affect species assemblages, and vice versa. In this chapter we explore this often intuitive relationship explicitly. Our basic premise is that species assemblages are collections of populations interacting with the heterogeneity of the landscape. We use the term “assemblage” to preclude assumptions about interactions and proximity or encounters among the organisms. Simple presence in the sampled landscape is the criterion for belonging to an assemblage; the landscape mosaic is an assemblage of patches, which, like species, may or may not interact. We assume that the landscape is heterogeneous, comprising a mosaic of distinct patches, which can be distinguished by some patch property. Our approach does not require a particular size or kind of landscape, but its scale and structure and the definition of patches have to be relevant for the distribution of the organisms whose diversity we study. In this chapter we discuss the functional connection between the dynamics of landscapes and of species assemblages.