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Latitudinal Diversity Gradient (latitudinal + diversity_gradient)
Selected AbstractsLatitudinal diversity gradients for brachiopod genera during late Palaeozoic time: links between climate, biogeography and evolutionary ratesGLOBAL ECOLOGY, Issue 4 2007Matthew G. Powell ABSTRACT Aim, The latitudinal diversity gradient, in which taxonomic richness is greatest at low latitudes and declines towards the poles, is a pervasive feature of the biota through geological time. This study utilizes fossil data to examine how the latitudinal diversity gradient and associated spatial patterns covaried through the major climate shifts at the onset and end of the late Palaeozoic ice age. Location, Data were acquired from fossil localities from around the world. Methods, Latitudinal patterns of diversity, mean geographical range size and macroevolutionary rates were constructed from a literature-derived data base of occurrences of fossil brachiopod genera in space and time. The literature search resulted in a total of 18,596 occurrences for 991 genera from 2320 localities. Results, Climate changes associated with the onset of the late Palaeozoic ice age (c. 327 Ma) altered the biogeographical structure of the brachiopod fauna by the preferential elimination of narrowly distributed, largely tropical genera when glaciation began. Because the oceans were left populated primarily with widespread genera, the slope of the diversity gradient became gentle at this time, and the gradient of average latitudinal range size weakened. In addition, because narrowly distributed genera had intrinsically high rates of origination and extinction, the gradients of both of these macroevolutionary rates were also reduced. These patterns were reversed when the ice age climate abated in early Permian time (c. 290 Ma): narrowly distributed genera rediversified at low latitudes, restoring steep gradients of diversity, average latitudinal range size and macroevolutionary rates. Main conclusions, During late Palaeozoic time, these latitudinal gradients for brachiopods may have been linked by the increased magnitude of seasonality during the late Palaeozoic ice age. Pronounced seasonality would have prevented the existence of genera with narrow latitudinal ranges. These results for the late Palaeozoic ice age suggest a climatic basis for the present-day latitudinal diversity gradient. [source] Body size determines the strength of the latitudinal diversity gradientECOGRAPHY, Issue 3 2001Helmut Hillebrand In most groups of organisms, the species richness decreases from the tropics to the poles. The mechanisms causing this latitudinal diversity gradient are still controversial. We present data from a comprehensive weighted meta-analysis on the strength of the latitudinal gradient in relation to body size. We sampled literature data on the correlation between species richness and latitude for a variety of organisms, ranging from trees to protozoa. In addition, own data on the presence of large-scale diversity patterns for diatoms were included, both for local and regional species richness. The strength of the latitudinal gradient was positively correlated to the size of the organisms. Strongest decreases of species richness to the poles was found for large organisms like trees and vertebrates, whereas meiofauna, protozoa and diatoms showed weak or no correlations between species richness and latitude. These results imply that latitudinal gradients are shaped by non-equilibrium (regional) processes and are persistent under conditions of dispersal limitation. [source] Temporal dynamics within a contemporary latitudinal diversity gradientECOLOGY LETTERS, Issue 9 2008Jonathan A. D. Fisher Abstract Poleward declines in species diversity [latitudinal diversity gradients (LDG)] remain among the oldest and most widespread of macroecological patterns. However, their contemporary dynamics remain largely unexplored even though changing ecological conditions, including global change, may modify LDG and their respective ecosystems. Here, we examine temporal variation within a temperate Northwest Atlantic LDG using 31 years of annual fisheries-independent surveys and explore its dynamics in relation to a dominant climate signal [the wintertime North Atlantic Oscillation (NAO)] that varies interannually and alters the latitudinal gradient of Northwest Atlantic continental shelf bottom water temperatures. We found that the slopes of the annual LDG vary dramatically due to changes in geographic distributions of 100+ species, variations that are concealed within the cumulative, static LDG. These changes are strongly associated with changes in NAO sign and strength. This is the first illustration of temporal dynamics in a contemporary LDG and the first demonstration of the speed at which local environmental variations can alter an LDG. Our findings underscore the need to investigate factors that modify LDG separately from those that contribute to their origins. [source] The tropics: cradle, museum or casino?ECOLOGY LETTERS, Issue 7 2008A dynamic null model for latitudinal gradients of species diversity Abstract Several ecological and evolutionary hypotheses have been proposed to explain the latitudinal diversity gradient (LDG), but a general model for this conspicuous pattern remains elusive. Mid-domain effect (MDE) models generate gradients of species diversity by randomly placing the geographic ranges of species in one- or two-dimensional spaces, thus excluding both evolutionary processes and the effect of contemporary climate. Traditional MDE models are statistical and static because they determine the size of ranges either randomly or based on empirical frequency distributions. Here we present a simple dynamic null model for the LDG that simulates stochastic processes of range shifts, extinction and speciation. The model predicts higher species diversity and higher extinction and speciation rates in the tropics, and a strong influence of range movements in shaping the LDG. These null expectations should be taken into consideration in studies aimed at understanding the many factors that generate latitudinal diversity gradients. [source] Area and the latitudinal diversity gradient for terrestrial birdsECOLOGY LETTERS, Issue 6 2001Bradford A. Hawkins We tested the hypothesis that area represents the primary explanation for the latitudinal diversity gradient using breeding terrestrial birds of North America, the northern Palearctic, Australia and the Afrotropics as our focal group. We tested two propositions inherent to the area hypothesis: (1) tropical biomes are larger than extra-tropical biomes, and (2) there is a significant species-area relationship for birds at the biome scale of resolution. Using a more realistic definition of biomes which incorporates the effects of both energy and water, we find no support for either proposition, leading us to conclude that the area per se does not explain terrestrial latitudinal diversity gradients. [source] Latitudinal diversity gradients for brachiopod genera during late Palaeozoic time: links between climate, biogeography and evolutionary ratesGLOBAL ECOLOGY, Issue 4 2007Matthew G. Powell ABSTRACT Aim, The latitudinal diversity gradient, in which taxonomic richness is greatest at low latitudes and declines towards the poles, is a pervasive feature of the biota through geological time. This study utilizes fossil data to examine how the latitudinal diversity gradient and associated spatial patterns covaried through the major climate shifts at the onset and end of the late Palaeozoic ice age. Location, Data were acquired from fossil localities from around the world. Methods, Latitudinal patterns of diversity, mean geographical range size and macroevolutionary rates were constructed from a literature-derived data base of occurrences of fossil brachiopod genera in space and time. The literature search resulted in a total of 18,596 occurrences for 991 genera from 2320 localities. Results, Climate changes associated with the onset of the late Palaeozoic ice age (c. 327 Ma) altered the biogeographical structure of the brachiopod fauna by the preferential elimination of narrowly distributed, largely tropical genera when glaciation began. Because the oceans were left populated primarily with widespread genera, the slope of the diversity gradient became gentle at this time, and the gradient of average latitudinal range size weakened. In addition, because narrowly distributed genera had intrinsically high rates of origination and extinction, the gradients of both of these macroevolutionary rates were also reduced. These patterns were reversed when the ice age climate abated in early Permian time (c. 290 Ma): narrowly distributed genera rediversified at low latitudes, restoring steep gradients of diversity, average latitudinal range size and macroevolutionary rates. Main conclusions, During late Palaeozoic time, these latitudinal gradients for brachiopods may have been linked by the increased magnitude of seasonality during the late Palaeozoic ice age. Pronounced seasonality would have prevented the existence of genera with narrow latitudinal ranges. These results for the late Palaeozoic ice age suggest a climatic basis for the present-day latitudinal diversity gradient. [source] Does biogeographical history matter?AUSTRAL ECOLOGY, Issue 1 2005Diversity, distribution of lotic midges (Diptera: Chironomidae) in the Australian Wet Tropics Abstract We examined broad scale patterns of diversity and distribution of lotic Chironomidae (Diptera) within the Wet Tropics bioregion of northern Queensland, Australia. Field surveys across broad latitudinal and altitudinal gradients within the Wet Tropics revealed a fauna of 87 species-level taxa in 49 genera comprising three main elements: a small genuinely tropical fraction, and larger cosmopolitan and Gondwanan components. The latter group originated when Australia, as part of the ancient Gondwana supercontinent, was situated over Antarctic latitudes with a cooler, wetter climate than today. In the Wet Tropics, cool Gondwanan taxa occurred predominantly in upland and shaded lowland sites, but no species appeared narrowly temperature restricted, and there was no faunal zonation with altitude. Most chironomid species occurred at all latitudes within the Wet Tropics, with no evidence for an enduring effect of the historical rainforest contractions on current-day distribution patterns. These findings contrast with those for aquatic faunas elsewhere in the world and for the terrestrial Wet Tropics fauna. We relate this to the generally broad environmental tolerances of Australian chironomids, and comment on why the latitudinal diversity gradient does not apply to the Australian chironomid fauna. [source] Does biogeographical history matter?AUSTRAL ECOLOGY, Issue 1 2005Diversity, distribution of lotic midges (Diptera: Chironomidae) in the Australian Wet Tropics Abstract We examined broad scale patterns of diversity and distribution of lotic Chironomidae (Diptera) within the Wet Tropics bioregion of northern Queensland, Australia. Field surveys across broad latitudinal and altitudinal gradients within the Wet Tropics revealed a fauna of 87 species-level taxa in 49 genera comprising three main elements: a small genuinely tropical fraction, and larger cosmopolitan and Gondwanan components. The latter group originated when Australia, as part of the ancient Gondwana supercontinent, was situated over Antarctic latitudes with a cooler, wetter climate than today. In the Wet Tropics, cool Gondwanan taxa occurred predominantly in upland and shaded lowland sites, but no species appeared narrowly temperature restricted, and there was no faunal zonation with altitude. Most chironomid species occurred at all latitudes within the Wet Tropics, with no evidence for an enduring effect of the historical rainforest contractions on current-day distribution patterns. These findings contrast with those for aquatic faunas elsewhere in the world and for the terrestrial Wet Tropics fauna. We relate this to the generally broad environmental tolerances of Australian chironomids, and comment on why the latitudinal diversity gradient does not apply to the Australian chironomid fauna. [source] Temporal dynamics within a contemporary latitudinal diversity gradientECOLOGY LETTERS, Issue 9 2008Jonathan A. D. Fisher Abstract Poleward declines in species diversity [latitudinal diversity gradients (LDG)] remain among the oldest and most widespread of macroecological patterns. However, their contemporary dynamics remain largely unexplored even though changing ecological conditions, including global change, may modify LDG and their respective ecosystems. Here, we examine temporal variation within a temperate Northwest Atlantic LDG using 31 years of annual fisheries-independent surveys and explore its dynamics in relation to a dominant climate signal [the wintertime North Atlantic Oscillation (NAO)] that varies interannually and alters the latitudinal gradient of Northwest Atlantic continental shelf bottom water temperatures. We found that the slopes of the annual LDG vary dramatically due to changes in geographic distributions of 100+ species, variations that are concealed within the cumulative, static LDG. These changes are strongly associated with changes in NAO sign and strength. This is the first illustration of temporal dynamics in a contemporary LDG and the first demonstration of the speed at which local environmental variations can alter an LDG. Our findings underscore the need to investigate factors that modify LDG separately from those that contribute to their origins. [source] The tropics: cradle, museum or casino?ECOLOGY LETTERS, Issue 7 2008A dynamic null model for latitudinal gradients of species diversity Abstract Several ecological and evolutionary hypotheses have been proposed to explain the latitudinal diversity gradient (LDG), but a general model for this conspicuous pattern remains elusive. Mid-domain effect (MDE) models generate gradients of species diversity by randomly placing the geographic ranges of species in one- or two-dimensional spaces, thus excluding both evolutionary processes and the effect of contemporary climate. Traditional MDE models are statistical and static because they determine the size of ranges either randomly or based on empirical frequency distributions. Here we present a simple dynamic null model for the LDG that simulates stochastic processes of range shifts, extinction and speciation. The model predicts higher species diversity and higher extinction and speciation rates in the tropics, and a strong influence of range movements in shaping the LDG. These null expectations should be taken into consideration in studies aimed at understanding the many factors that generate latitudinal diversity gradients. [source] Area and the latitudinal diversity gradient for terrestrial birdsECOLOGY LETTERS, Issue 6 2001Bradford A. Hawkins We tested the hypothesis that area represents the primary explanation for the latitudinal diversity gradient using breeding terrestrial birds of North America, the northern Palearctic, Australia and the Afrotropics as our focal group. We tested two propositions inherent to the area hypothesis: (1) tropical biomes are larger than extra-tropical biomes, and (2) there is a significant species-area relationship for birds at the biome scale of resolution. Using a more realistic definition of biomes which incorporates the effects of both energy and water, we find no support for either proposition, leading us to conclude that the area per se does not explain terrestrial latitudinal diversity gradients. [source] Can the tropical conservatism hypothesis explain temperate species richness patterns?GLOBAL ECOLOGY, Issue 4 2009An inverse latitudinal biodiversity gradient in the New World snake tribe Lampropeltini ABSTRACT Aim, A latitudinal gradient in species richness, defined as a decrease in biodiversity away from the equator, is one of the oldest known patterns in ecology and evolutionary biology. However, there are also many known cases of increasing poleward diversity, forming inverse latitudinal biodiversity gradients. As only three processes (speciation, extinction and dispersal) can directly affect species richness in areas, similar factors may be responsible for both classical (high tropical diversity) and inverse (high temperate diversity) gradients. Thus, a modified explanation for differential species richness which accounts for both patterns would be preferable to one which only explains high tropical biodiversity. Location, The New World. Methods, We test several proposed ecological, temporal, evolutionary and spatial explanations for latitudinal diversity gradients in the New World snake tribe Lampropeltini, which exhibits its highest biodiversity in temperate regions. Results, We find that an extratropical peak in species richness is not explained by latitudinal variation in diversification rate, the mid-domain effect, or Rapoport's rule. Rather, earlier colonization and longer duration in the temperate zones allowing more time for speciation to increase biodiversity, phylogenetic niche conservatism limiting tropical dispersal and the expansion of the temperate zones in the Tertiary better explain inverse diversity gradients in this group. Main conclusions, Our conclusions are the inverse of the predictions made by the tropical conservatism hypothesis to explain higher biodiversity near the equator. Therefore, we suggest that the processes invoked are not intrinsic to the tropics but are dependent on historical biogeography to determine the distribution of species richness, which we refer to as the ,biogeographical conservatism hypothesis'. [source] Revisiting Jablonski (1993): cladogenesis and range expansion explain latitudinal variation in taxonomic richnessJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2007P. R. MARTIN Abstract The increase in diversity towards the equator arises from latitudinal variation in rates of cladogenesis, extinction, immigration and/or emigration of taxa. We tested the relative contribution of all four processes to the latitudinal gradient in 26 marine invertebrate orders with extensive fossil records, examined previously by David Jablonski. Coupling Jablonski's estimates of latitudinal variation in cladogenesis with new data on patterns of extinction and current distributions, we show that the present-day gradient in diversity is caused by higher rates of cladogenesis and subsequent range expansion (immigration) at lower latitudes. In contrast, extinction and emigration were not important in the creation of the latitudinal gradient in ordinal richness. This work represents one of the first simultaneous tests of the role of all four processes in the creation of the latitudinal gradient in taxonomic richness, and suggests that low tropical extinction rates are not essential to the creation of latitudinal diversity gradients. [source] | ||||||||||