For many taxa birds, butterflies, rodents, reptiles, vascular plants, and more species richness in habitat fragments is positively correlated with fragment size. This is widely known as the species-area relationship. Thus, when habitats are fragmented into smaller pieces, species are lost; and the likely extent of this loss can be predicted from the species-area relationship. Further, species richness in ...
Small populations are vulnerable to local extinction, but a species has a greater likelihood of persistence where there are a number of local populations interconnected by occasional movements of individuals among them. Such a set of subdivided populations is often termed a “meta population” (Hanski 1999). Two main kinds of meta population have been described. A mainland-island model is ...
The size of any population is determined by the balance between four parameters: births, deaths, immigration, and emigration. Population size is increased by births and immigration of individuals, while deaths and emigration of individuals reduce population size. In fragmented landscapes, these population parameters are influenced by several categories of processes. Deterministic processes Many factors that affect populations in fragmented ...
Many studies have described the occurrence of species in fragments of different sizes, shapes, composition, land-use and context in the landscape. For species that primarily depend on fragmented habitat, particularly animals, fragment size is a key influence on the likelihood of occurrence. As fragment size decreases, the frequency of occurrence declines and the species may be absent from many ...
Removal of large tracts of native vegetation changes physical processes, such as those relating to solar radiation and the fluxes of wind and water (Saunders et al. 1991). The greatest impact on fragments occurs at their boundaries; small remnants and those with complex shapes experience the strongest “edge effects”. For example, the micro climate at a forest edge adjacent ...
The theory of island bio geography (MacArthur and Wilson 1967) had a seminal influence in stimulating ecological and conservation interest in fragmented landscapes. This simple, elegant model highlighted the relationship between the number of species on an island and the island’s area and isolation. It predicted that species richness on an island represents a dynamic balance between the rate ...
Humans have transformed a large fraction of the Earth’s land surface. Over the past three centuries, the global extent of cropland has risen sharply, from around 2.7 to 15 million km2, mostly at the expense of forest habitats (Turner et al. 1990). Permanent pasture lands are even more extensive, reaching around 34 million km2 by the mid-1990s (Wood et ...
A second way to assess habitat loss is by contrastingmajor biomes or ecosystem types. Today, tropical rainforests (also termed tropical moist and humid forests) are receiving the greatest attention, because they are being destroyed so rapidly and because they are the most biologically diverse of all terrestrial biomes. Of the roughly 16 million km2 of tropical rainforest that originally ...
Some regions of the Earth are far more affected by habitat destruction than others. Among the most imperiled are the so-called “biodiversity hotspots”, which contain high species diversity, many locally endemic species (those whose entire geographic range is confined to a small area), and which have lost at least 70% of their native vegetation (Myers et al. 2000). Many ...
One of the most vital and immediate services of ecosystems, particularly of forests, rivers and wetlands, is the provisioning and regulation of water resources. These services provide a vast range of benefits from spiritual to life-saving, illustrated by the classification of hydrologic services into five broad categories by Brauman et al. (2007): improvement of extractive water supply, improvement of ...
Ecosystem services start at the most fundamental level: the creation of the air we breathe and the supply and distribution of water we drink. Through photosynthesis by bacteria, algae, plankton, and plants, atmospheric oxygen is mostly generated and maintained by ecosystems and their constituent species, allowing humans and innumerable other oxygen-dependent organisms to survive. Oxygen also enables the atmosphere ...
In our increasingly technological society, people give little thought to how dependent they are on the proper functioning of ecosystems and the crucial services for humanity that flow from them. Ecosystem services are “the conditions and processes through which natural ecosystems, and the species that make them up, sustain and fulfill human life” (Daily 1997); in other words, “the ...
Just as biodiversity has varied markedly through time, so it also varies across space. Indeed, one can think of it as forming a richly textured land and seascape, with peaks (hotspots) and troughs (cold spots), and extensive plains in between. Even locally, and just for particular groups, the numbers of species can be impressive, with for example c.900 species ...
The Earth is estimated to have formed, by the accretion through large and violent impacts of numerous bodies, approximately 4.5 billion years ago (Ga). Traditionally, habitable worlds are considered to be those on which liquid water is stable at the surface. On Earth, both the atmosphere and the oceans may well have started to form as the planet itself ...
Given the multiple dimensions and the complexity of the variety of life, it should be obvious that there can be no single measure of biodiversity. Analyses and discussions of biodiversity have almost invariably to be framed in terms of particular elements or groups of elements, although this may not always be apparent from the terminology being employed (the term ...
The third group of elements of biodiversity encompasses the scales of ecological differences from populations, through habitats, to ecosystems, ecoregions, provinces, and on up to biomes and biogeographic realms. This is an important dimension to biodiversity not readily captured by genetic or organismal diversity, and in many ways is that which is most immediately apparent to us, giving the ...
Organismal diversity encompasses the full taxonomic hierarchy and its components, from individuals upwards to populations, subspecies and species, genera, families, phyla, and beyond to kingdoms and domains. Measures of organismal diversity thus include some of the most familiar expressions of biodiversity, such as the numbers of species (i.e. species richness). Others should be better studied and more routinely employed ...
Some understanding of what the variety of life comprises can be obtained by distinguishing between different key elements. These are the basic building blocks of biodiversity. For convenience, they can be divided into three groups: genetic diversity, organismal diversity, and ecological diversity. Within each, the elements are organized in nested hierarchies, with those higher order elements comprising lower orderones. ...
Biological diversity or biodiversity (the latter term is simply a contraction of the former) is the variety of life, in all of its many manifestations. It is a broad unifying concept, encompassing all forms, levels and combinations of natural variation, at all levels of biological organization (Gaston and Spicer 2004). A rather longer and more formal definition is given ...
Although conservation biology has been an organized field only since the mid-1980s, it ispossible to identify and summarize at least several salient trends that have shaped it since.Implementation and transformation Conservation biologists now work in a much more elaborate field than existed at the time of its founding. Much of the early energy and debate in conservation biology focused ...
