[1] Discovered by Alexander von Humboldt in 1799, it has remained one of the key questions in Evolutionary Ecology. biotic hypotheses contributing to latitudinal diversity gradient. For example, low species diversity is known to occur often in stable environments such as tropical mountaintops. The theory of spatial heterogeneity Ecology 3. To address this issue, previous LDG studies have usually relied on correlations between environmental variables and species richness, only considering evolutionary processes indirectly. the latitudinal gradient of species richness (Rohde 1992, Rosenzweig 1995, Brown and Lomolino 1998, Willig 2000, Schemske 2002). This pattern is a one of the most and oldest primary trends concerning life's species on earth. 2 The latitudinal gradient. Abstract. Nonetheless, notable exceptions to the general pattern exist, and it is well recognized that patterns may be dependent on characteristics of spatial scale and taxonomic hierarchy. A latitudinal gradient in biodiversity has existed since before the time of the dinosaurs, yet how and why this gradient arose remains unresolved. 1996, 3, 10-13. 1. spatial heterogeneity hypothesis 2. competition hypothesis 3. predation hypothesis 4. mutualism and coevolution hypothesis. Expert Answer. this hypothesis, dispersal is higher out of than into the tropics, thus acting ''against'' the latitudinal diversity gradient. The time and area hypothesis holds that tropical climates are older and historically larger, allowing more 2003a). Title: The latitudinal gradient in species diversity 1 The latitudinal gradient in species diversity. It is evident that an increase in biological 2003) Source Encyclopedia of biodiversity and Willig et al. area-affect hypothesis, at least for latitudinal gradients in marine systems. In: Journal of Biogeography . A variety of hypotheses have been proposed to explain the latitudinal gradients of biodiversity, among which the diversification rate hypothesis argues that generational turnover and speciation . Latitudinal gradients of biodiversity are biogeographic patterns that quantify the ways in which taxonomic, phylogenetic, functional, genetic, or phenetic biodiversity change with latitudinal position on the surface of the earth (Fig. [2] A similar pattern has been postulated for marine biota. Key words. The time theory Ecology and evolution 2. [Google Scholar] Rohde, K. Rapoport's rule is a local phenomenon and cannot explain latitudinal gradients in species diversity. Figure 1 An example of the modern latitudinal biodiversity gradient, showing the distribution of living terrestrial vertebrate species, with the highest concentration of diversity found in equatorial regions (red end of the colour spectrum) and declining polewards (blue end) to form the modern pattern. 1998 ; Vol. Some of the . [Google Scholar] Therefore, the ecological explanations proffered are usually specific to the group in question. We examined the applicability of three versions of the energy hypothesis, the habitat heterogeneity hypothesis, and historical contingency to the gradient of terrestrial birds. 1). Moreover, the main focus has been on vertebrate taxa and higher plants, and a ma-jority of studies originated from the Americas. By modulating interactions between species, latitudinal gradients may also shape food-web structure. the latitudinal diversity gradient. Am. On the local scale, the spatial heterogeneity hypothesis suggests that the tropics contain more habitat subdivisions (i.e. Introduction. Oikos 1992, 65, 514-527. With this notation, it can easily be seen that a latitudinal gradient in richness, with D T 9 D E, and ecological causes of the latitudinal diversity gradient and to test the major predictions of the tropical conser-vatism hypothesis. The productivity version of the energy hypothesis, tested using actual . The time and area hypothesis holds that tropical climates are o The evolutionary dynamics underlying the latitudinal gradient in biodiversity have been controversial for over a century. Climate is widely recognised as an important determinant of the latitudinal diversity gradient. A latitudinal diversity gradient towards the tropics appears as one most recurrent patterns in ecology, but the mechanisms underlying this pattern remain an area of controversy. habitats (Pianka, 1966a). tropical conservatism hypothesis). We combine a diversity of analytical approaches (e.g., phylogenetics, ancestral area reconstruc-tion, divergence date estimation, analysis of diversication rates, ecological niche modeling) and focus on New . Using marine bivalves as a model system and drawing on other systems where possible, we review paleobiologic . In the second hypothesis, known as the "tropical niche conservatism" hypothesis, lineages originate in the tropics and have difficulties to disperse and adapt into temperate regions, thus accumulating in . The time theory Ecology and evolution 2. Contrary to the anti-tropical diversity pattern of modern articulated brachiopods, Paleozoic terebratulides show a latitudinal diversity gradient that peaks in the Tropics. The latitudinal diversity gradient Key concepts The latitudinal diversity gradient Mid-domain eect Niche conservatism and niche evolution Biotic theories Introduction Figure 1: New World birds, including hummingbirds, exhibit higher species richness in tropical latitudes @article{osti_1357327, title = {A latitudinal diversity gradient in terrestrial bacteria of the genus Streptomyces}, author = {Andam, Cheryl P. and Doroghazi, James R. and Campbell, Ashley N. and Kelly, Peter J. and Choudoir, Mallory J. and Buckley, Daniel H.}, abstractNote = {We show that Streptomyces biogeography in soils across North America is influenced by the regional diversification of . It was documented e.g. The pattern of having lots of species at the equator with diversity dwindling off towards the poles is known as the Latitudinal Diversity Gradient "latitudinal" meaning how far north or south of the equator, "diversity" meaning the number of species, and "gradient" meaning the transition between high and low. The latitudinal cline of the diversity (i.e. The latitudinal diversity gradient describes the phenomenon in which the diversity of species inhabiting biomes is higher near the equator and lower near the poles. In fact, well over 30 hypotheses / environmental, evolutionary, and stochastic / have been advanced to account for empirical patterns in the latitudinal gradient of diversity (Willig et al. Lett. the highest numbers of species in the tropics and gradual decrease poleward) is a well-recognized and long established pattern in terrestrial ecology. The latitudinal diversity gradient is the largest scale, and longest known, pattern in ecology. hypothesis for the bird latitudinal diversity gradient derived from the effects of niche conservatism in the face of global climate change over evolutionary time. The time and4 area hypothesis holds that tropical climates are older and historically larger, allowing more The habitat heterogeneity hypothesis, on the contrary, assumes that as new habitats are added, the number of unique species in- If particular higher taxa are monophyletic and of tropical origin and diversify along latitudinal gradients according to a historical process such as the one presented, then the ve aforementioned predictions should hold with respect to distance from gradients in species richness (e.g. Introducing the LDG. The latitudinal diversity gradient is the largest scale, and longest known, pattern in ecology. The time theory: Ecology and evolution 2. 36 The latitudinal diversity gradient is the dominant pattern of life on Earth, but a consensus 37 understanding of its origins has remained elusive. microhabitats). The existing hypotheses explaining this phenomenon are summarized and the evidence that tends to favor one of these is presented. 5. The "Age of the Tropics" hypothesis argues that the tropics have more species because young, ecologically dominant, tropical clades have not had sufficient time to disperse and adapt to colder climates . The competition hypothesis . We argue that the reasons for this are the verbal nature of existing hypotheses, the failure to mechanistically link interacting ecological and evolutionary processes to the LDG, and the fact that empirical patterns are often consistent . We examined the applicability of three versions of the energy hypothesis, the habitat heterogeneity hypothesis, and historical contingency to the gradient of terrestrial birds. The fact that many of the species-rich tropical marine environments are high in temperature but relatively low in productivity suggests that kinetic mechanisms play a primary . 2003. 2006 Evolutionary and ecological causes of the latitudinal diversity gradient in hylid frogs: treefrog trees unearth the roots of high tropical diversity. An abundance of microhabitats allows taxa to partition each Since the tropics are so much larger than any other extra-tropical biome, one would predict the latitudinal gradient to resemble a step . INTRODUCTION One of the most striking of large-scale biotic patterns is the latitudinal gradient in species diversity, peaking in the tropics and tailing o towards the poles. The competition hypothesis . Here we review two major hypotheses for the origin of the latitudinal diversity gradient. However, most existing studies make no distinction between direct and indirect effects of climate . One hypothesis to explain the latitudinal gradient in species diversity is the geographic area hypothesis. Latitudinal gradients in species diversity Species richness, or biodiversity, increases from the poles to the tropics for a wide variety of terrestrial and marine organisms, often referred to as the latitudinal diversity gradient (LDG) [1].The LDG is one of the most widely recognized patterns in ecology [1].The LDG has been observed to varying degrees in Earth's past.
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latitudinal diversity gradient hypothesis