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Showing papers on "Species richness published in 1987"


Journal ArticleDOI
09 Jan 1987-Science
TL;DR: Observations suggest that regional and historical processes, as well as unique events and circumstances, profoundly influence local community structure and ecologists must broaden their concepts of community processes and incorporate data from systematics, biogeography, and paleontology into analyses of ecological patterns and tests of community theory.
Abstract: The species richness (diversity) of local plant and animal assemblages—biological communities—balances regional processes of species formation and geographic dispersal, which add species to communities, against processes of predation, competitive exclusion, adaptation, and stochastic variation, which may promote local extinction During the past three decades, ecologists have sought to explain differences in local diversity by the influence of the physical environment on local interactions among species, interactions that are generally believed to limit the number of coexisting species But diversity of the biological community often fails to converge under similar physical conditions, and local diversity bears a demonstrable dependence upon regional diversity These observations suggest that regional and historical processes, as well as unique events and circumstances, profoundly influence local community structure Ecologists must broaden their concepts of community processes and incorporate data from systematics, biogeography, and paleontology into analyses of ecological patterns and tests of community theory

2,230 citations


Journal ArticleDOI
TL;DR: A survey of 22 old fields at Cedar Creek, Minnesota, showed that total and available soil nitrogen increased during succession and that major species had individualistic, fairly Gaussian distributions along this temporal nitrogen gradient as discussed by the authors.
Abstract: In 1982, experimental nitrogen gradients were established on both existing and disturbed (disked) vegetation in three fields (abandoned 14, 25, and 48 yr) and on existing vegetation in native oak savannah. Each of these seven gradients contained five or six replicates of each of nine treatments that differed in the annual rate of nitrogen addition. In none of the fields did plant biomass, height, species richness, or light penetration respond to addition of P, K, Ca, Mg, S, and trace metals. In contrast, plant biomass and height increased significantly, and light penetration and species richness decreased significantly, with added nitrogen along all seven gradients. On average, >60% of the species had been displaced from high—nitrogen treatments by 1985. Nitrogen addition led to a period of transient dominance by certain species. Species that reached peak relative abundance in high—nitrogen treatments in 1982 tended to be rare in all but the low—nitrogen treatments by 1985. In contrast, the relative abundances of most species that dominated the high—nitrogen treatments in 1985 did not increase along the nitrogen gradients in 1982. The relative or absolute abundances of most common species changed significantly along the experimental gradients in at least 1 yr. By 1985, many common species were differentiated in their distributions along the seven gradients. In general, early successional annuals and short—lived perennials and plants of short stature at maturity reached their peak abundance in low—nitrogen plots, whereas plots, receiving high rates of nitrogen addition were dominated by long—lived herbaceous and woody species that are taller at maturity. A survey of 22 old fields at Cedar Creek, Minnesota, showed that total and available soil nitrogen increased during succession and that major species had individualistic, fairly Gaussian distributions along this temporal nitrogen gradient. The distributions along the experimental gradients of most of the common species were consistent with the pattern observed in the old—field survey, demonstrating that nitrogen influences the pattern of secondary succession at Cedar Creek. The major exception was Agropyron repens, and early successional grass that dominated high—nitrogen treatments on six of the seven gradients. Comparisons of species responses on the disturbed plots with those on plots of existing (undisturbed) vegetation showed that, by 1985, most species responded similarly to the nitrogen gradients despite great differences in their initial abundances. For instance, Agropyron repens, an initial dominant of Field A but rare in Fields B and C, was dominant in the high—nitrogen treatments in both the disturbed and undisturbed plots of these three fields. It invaded into and rapidly increased in abundance in numerous high—nitrogen plots from which it was initially absent. Schizachyrium scoparium declined along the nitrogen gradients both in undisked plots in which it was initially dominant and in disked plots in which it was initially rare. Such similarities suggest that the outcome of interspecific interactions among old—field plants is highly dependent on nitrogen supply rates, but fairly independent of initial plant abundances.

1,020 citations


Journal ArticleDOI
24 Sep 1987-Nature
TL;DR: In this paper, the authors examined the spatial distributions of trees in North America to determine which characteristics of the environment are most closely related to the species richness of different regions and found that topography and proximity to the sea are significantly related to residual variation, whereas seasonal climatic variability and glacial history are not.
Abstract: Biologists have long recognized the striking geographical variability of species richness1. A primary goal of contemporary ecology is to identify the factors responsible for this variability2. We have examined the spatial distributions of trees in North America to determine which characteristics of the environment are most closely related to the species richness of different regions. Realized annual evapotranspiration, which is correlated with primary production and is therefore a measure of available energy, statistically explains 76% of the variation in species richness. Topography and proximity to the sea are significantly related to the residual variation, whereas seasonal climatic variability and glacial history are not. Tree richness in Great Britain and Ireland can be accurately predicted from these North American patterns. Our data are best explained by the hypothesis that contemporary available energy limits species richness3,4.

671 citations


Journal ArticleDOI
TL;DR: The first complete samples of all plant species and individuals for any lowland tropical forest in the world are reported, finding that the wet forest sample is by far the most species-rich such sample yet recorded and would remain so even if all tree species were excluded from the data.
Abstract: We report the results of the first complete samples of all plant species and individuals for any lowland tropical forest in the world. The three forests sampled are in western Ecuador; Rio Palenque, Jauneche, and Capeira are, respectively, wet, moist, and dry forests. In each forest we sampled all vascular plants in a 0.1-ha area. At wet forest Rio Palenque, nontree habit groups make up most of the sampled species and individuals. Over a third of the species and almost half the individual plants are epiphytes, 13 percent of the species are terrestrial herbs, 10 percent are shrubs, and 9 percent nonepiphytic climbers. The moist and dry forest samples have many fewer species, largely due to many fewer epiphytes. The new data are compared with the most diverse 0.1-ha samples from elsewhere in the world. Our wet forest sample is by far the most species-rich such sample yet recorded and would remain so even if all tree species were excluded from the data. ALTHOUGH IT IS WIDELY ACCEPTED that tropical rain forests are the world's most species-rich plant communities (e.g., Cain & Castro 1959, Walter 1971), the data base for this assertion is weak and almost entirely restricted to trees. Recently it has been suggested that certain nontropical plant communities, rather than tropical rain forests, may be the most species-rich vegetation types in the world (Richards 1969, Naveh & Whittaker 1979), at least for small sample plots (Parsons & Cameron 1974). Others have suggested that various types of nonforest vegetation are the most diverse in the world, at least for plants of particular habits, e.g., shrubs or herbs. Such claims have been made for the fynbos of the South African Cape region (Richards 1969, Taylor 1978), the Australian sclerophyllous forests (Richards 1969, Milewski 1983; see also Rice & Westoby 1983, Lamont et al. 1977), and the Mediterranean shrublands and maquis (Naveh & Whittaker 1979). The cerrado of Brazil, also sclerophyllous, typically has more species per 0.1 ha (or 1 ha) than any vegetation of Mediterranean-type climates (Eiten 1978, pers. comm.), but the species-rich types of cerrado include many trees (usually 30-60 species/ha) and may be better considered as a distinctive type of open-canopied tropical woodland (Eiten 1972, 1978). The highest recorded plant species diversities for samples of ?0.1 ha in each of these vegetation types are recorded in Table 1 and Figure 1. Direct comparisons of the species richness of different plant communities are greatly complicated by problems of scale (Rice & Westoby 1983). One reason for the lack of comparisons of plant diversity between tropical and other vegetations is that nearly all the available data on tropical forest diversity are restricted to trees. Sample areas Received 23 September 1985, revision accepted 30 December 1985. of 1 ha are needed to adequately measure tree species diversity. Since few individual trees are included in small plots, the great richness of tropical forest tree species is not apparent in samples comparable to the 0.1-ha ones commonly used to census other growth forms (e.g., Naveh & Whittaker 1979; Cowling 1983; Rice & Westoby 1983; Shmida, in press and included references). Even when only trees are considered, 1-ha samples of tropical forest may have as many as 300 species of 10 cm DBH in Amazonia (Gentry 1987), 227 in Malesia (Cousens 1951, Whitmore 1975), and 223 in Borneo (Proctor et ad. 1983). Other tropical forests on each continent have many fewer tree species, often only 50 or 100/ha. We may conclude from these figures, and from the very different shapes of the tropical and nontropical species area curves in Figure 1, that for relatively large areas of 1 ha, the richest closedcanopy tropical forests have more tree species than the richest nonforest communities have species of all plants. However, for smaller sample areas of <0. 1 ha, the richest sclerophyllous vegetations are apparently as species rich as are the majority of tropical forest communities when only the latter's trees are considered. Whether tropical forests, as a general rule and even for sample plots of < 1 ha, have more plant species than these rich nonforest communities depends on how rich tropical forests are in the rarely censused nontree habit groups. Lianas are one nontree component of tropical forests that contribute significantly to their diversity. One of us has recently published data that focus on the species richness of tropical forest lianas (Gentry 1982b, 1983, 1985a). In a series of 0.1-ha samples of plants -2.5 cm DBH in a broad series of lowland Neotropical forests, lianas (including some hemiepiphytic climbers; see definitions in Gentry 1985b) constituted 19 percent of the species in dry and pluvial forests, 22 percent in wet forests, and 23 BIOTROPICA 19(2): 149-156 1987 149 This content downloaded from 207.46.13.122 on Thu, 19 May 2016 04:17:50 UTC All use subject to http://about.jstor.org/terms TABLE 1. Plant species richness of 0. 1-ha samples in different vegetation types. Only the most species-rich sites (and some ranges of normal variation) for each vegetation type are included. Range (ave.) for Site or vegetation Reference 0.1 ha 0.1-ha plots Herbsa Woodya Mediterranean climate South African fynboschb Tussen die Riviere Werger 1972 64 Cape Province fynbos Naveh & Whittaker 1979 52-128 (ave. 75) 39.8 35.3 Tygerberg Cowling 1983 103 68 30 Cape Town Cowling 1983 99 71 28 Subtropical transitionalthicket Cowling 1983 98 48 50

521 citations


Journal ArticleDOI
01 Oct 1987-Ecology
TL;DR: The dissimilar effects of different natural disturbances on grass- land species, growth form characteristics, and community structure are documented.
Abstract: A field study was conducted to address the roles of fire, cattle grazing, and the interaction of these two disturbances on plant species abundance and community structure in a tallgrass prairie. In 1985 and 1986, species composition was sampled in three replicates of the following grassland treatments: ungrazed + unburned (undisturbed), grazed + unburned, ungrazed + burned, and grazed + burned. Cover of the matrix-forming species Andropogon gerardii was significantly greater, while cover of the nonmatrix species Bromus tectorum was significantly lower, on the burned treatments than on the unburned treatments. The number and cover of annuals were significantly higher on the grazed treatments than on the ungrazed treatments. Species richness increased with increasing disturbance intensity. Diversity, however, was lowest on the ungrazed + burned treatment and highest on the grazed + burned treatment. Burning significantly reduced species diversity on ungrazed treatments, and grazing significantly increased diversity on the burned treatment. This study documented the dissimilar effects of different natural disturbances on grass- land species, growth form characteristics, and community structure. In addition, the results emphasize the important role of interaction among disturbances on plant community structure in grasslands.

388 citations


Journal ArticleDOI
01 Dec 1987-Ecology
TL;DR: Results from Illinois support previous conclusions that species that breed in forest interior habitat and winter in the tropics are most likely to be adversely affected by a reduction in forest habitat and show that bird communities in isolated tracts of forest are not random assemblages, but rather that species found in smaller woodlots are subsets ofspecies found in larger forests.
Abstract: We investigated breeding bird communities of isolated woodlots (1.8-600 ha) in east-central Illinois during three summers (1979-1981) to compare the influence of area and habitat on community structure. Woodlots supported from 9 to 43 species and composition was relatively constant among years. Ecological generalists dominated small woodlots, while more specialized species increased in importance with area. Area accounted for most variation (86-98%) in total species number in each year and the species-area relationship did not change significantly among years. The amount of variance accounted for by area was greater than in previous studies. Neither habitat nor woodlot isolation explained significant additional variation in total species richness after area. Area accounted for most variation in number of species in different migratory and breeding habitat cate- gories, except for short-distance migrants, which correlated most strongly with habitat. Variation in habitat was not related to woodlot area and habitat accounted for additional variation in bird species numbers in most cases. Abundances of one-third to one-half of species examined correlated with woodlot area, but a greater proportion (66-72%) were influenced more strongly by habitat variables. Results from Illinois support previous con- clusions that species that breed in forest interior habitat and winter in the tropics are most likely to be adversely affected by a reduction in forest habitat. Results also show that bird communities in isolated tracts of forest are not random assemblages, but rather that species found in smaller woodlots are subsets of species found in larger forests.

336 citations


Journal ArticleDOI
01 Feb 1987-Ecology
TL;DR: Patterns suggest that while soil nitrogen is an important determinant of local species composition and abundance, dispersal and colonization, which are dependent on field age, determine which species are present in a field.
Abstract: Vegetation and soils were sampled in 22 old fields ranging in age from 1 to 56 yr since abandonment. Soil nitrogen concentration increased significantly with field age. Vegetation cover, total aboveground plant biomass, and litter cover increased significantly with soil nitrogen. Light penetration to the soil surface was negatively correlated with total plant biomass. Field age and soil nitrogen concentration were used as independent variables in simple regression and partial correlation analyses to determine the relative importance of such time-dependent processes as dispersal vs. the availability of a limiting resource (nitrogen) as predictors of patterns in species richness or the abundance of various plant groups. Species richness per field and within-field heterogeneity in species composition increased with field age. Local species richness decreased with increasing soil nitrogen. Cover of annuals and introduced species decreased with field age and nitrogen; however, annuals contributed an important part of total vegetative cover even in 25-yr-old fields. Cover of perennials and woody species increased with soil nitrogen and field age. Although the fields were bordered by woods, woody species contributed <15?/o cover even in the oldest fields. For several plant groups the relationship between cover and soil nitrogen within individual fields was the opposite of that among all fields. These patterns suggest that while soil nitrogen is an important determinant of local species composition and abundance, dispersal and colonization, which are dependent on field age, determine which species are present in a field.

332 citations


Journal ArticleDOI
TL;DR: Based on pre-fragmentation data collected in 1982 and 1983, the population of male euglossine bees was homogeneous in the continuous forest and forest fragments of different sizes, indicating there was little potential for forest pollination by these clearing species.
Abstract: At sites near Manaus, Amazonas, Brazil we measured the impact of forest fragmentation on populations of male euglossine bees. The visitation rates of 15 species of male euglossine bees to three chemical attractants were determined for continuous forest; isolated 1, 10, and 100 ha forest fragments; and a cleared area. For most species, visitation rate declined with fragment size, even though openings separating fragments and continuous forest tended to be narrow (as little as 100 m). Preand post-isolation comparisons for individual fragments exhibited the same trend. Bee species attracted to scents in the clearing differed from those of the forest indicating there was little potential for forest pollination by these clearing species. These results are discussed with respect to the impact of forest fragmentation on plant species richness and the design of natural and commercial forest reserves. EUGLOSSINE BEES ARE KNOWN TO BE important pollinators of neotropical orchids and other plant families (Williams & Dodson 1972, Braga 1976). The greatest species richness occurs in forest habitats, but species are present in open habitats (Zucchi et al. 1969). Strong fliers, euglossines range over large areas (Janzen 1971, Ackerman et al. 1982) and have diverse home range structures (Janzen 1981). Male euglossine bees use chemicals from orchid fragrances, probably as building blocks for pheromones that attract females (Kimsey 1980, Williams & Whitten 1983). Commercially available chemicals can be used to attract male euglossine bees, thus making it possible to measure precisely the relative population densities of the numerous species that occur in a given locality and that are attracted to chemical baits. Therefore, male euglossine bees are ideally suited to study population dynamics in forest fragments. In this study, we used three chemical scents to quantify relative population densities of male euglossine bees in continuous forest and forest fragments of different sizes. Methyl salicylate and cineole are known to attract a wide variety of euglossine species (Williams & Dodson 1972) and along with vanillin were chemicals that had been used in studies in Brazil (Braga 1976). Based on pre-fragmentation data collected in 1982 and 1983, the population of male euglossine bees was homogeneous in the continuous forest. In 1983 following fragmentation of the forest, the male euglossine bee populations were monitored in I Received 20 June 1985, revision accepted 27 November 1985. 176 BIOTROPICA 19(2): 176-179 1987 relation to habitat size and were found to be lower in small forest fragments.

327 citations


Journal ArticleDOI
TL;DR: The species richness at Chamela, Jalisco (average annual rainfall 748 mm, with a 4-month wet season), exceeded that of other Neotropical dry forests with more than twice its annual rainfall.
Abstract: The species richness at Chamela, Jalisco (average annual rainfall 748 mm, with a 4-month wet season), exceeded that of other Neotropical dry forests with more than twice its annual rainfall. Transect samples totaling 0.3 ha included 176 species and 1352 plants -2.5 cm DBH. The mean number of species per 100-m2 transect was 22.7. Upland and arroyo sites were similar in species number, but the latter included greater percentages of species of vines (11% vs 21%) and trees 10 cm DBH (24% vs 31%). The only species that were both common and ubiquitous were Trichilia trifolia, Caesalpinia eriostachys, and Cordia alliodora. Upland sites were typified by species of Croton, Lonchocarpus, and Cordia, and arroyo sites were typified by Thouinidium decandrum and a variety of vines. Families with the most species were Leguminosae, Euphorbiaceae, Rubiaceae, and Bignoniaceae. Total basal area averaged 0.24 m2/100 m2 in uplands but 0.52 m2/100 m2 in arroyos; most of the difference was due to trees -30 cm DBH. In all sites, over 50 percent of the stems were < 5 cm DBH, but vines and large trees were more abundant in arroyos. Stem densities averaged about 45/100 m2 in both sites.

313 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe a tallgrass prairie from Konza Prairie, Kansas, USA with respect to plant species compositional changes over a five-year period in response to fire and topography.
Abstract: Native unploughed tallgrass prairie from Konza Prairie, Kansas, USA is described with respect to plant species compositional changes over a five year period in response to fire and topography. The principal gradient of variation in the vegetation is related to time since burning. Species show an individualistic response in terms of relative abundance to this gradient. Both the percentage of and cover of C4 species and all grasses decrease as the prairie remains unburnt. Forb and woody plant species numbers and abundance increase along this gradient. A secondary gradient of variation reflects topography (i.e. upland versus lowland soils). Upland soils support a higher species richness and diversity. Upland and lowland plant assemblages are distinct except on annually burnt prairie. The interaction between burning regime, topography and year-to-year climatic variation affects the relative abundance of the plant species differentially. The most dominant species overall, Andropogon gerardii, was affected only by year-to-year variation (i.e. climate). Its position at the top of the species abundance hierarchy was unaffected by burning regime or soil type. The other dominant species showed a suite of varying responses to these factors.

294 citations


Journal ArticleDOI
TL;DR: It is suggested that the level of understory fertility may provide a simple indicator of overall ecosystem productivity and predictable patterns of change in plant community composition across such environmental gradients as annual precipitation are shown.
Abstract: We compare levels of flowering and fruiting in 55 samples of Neotropical forest understory from 13 sites in 6 countries. Each sample consists of a census of fertile understory plants along a transect. Changes in species richness and density of fertile understory plants are correlated with rainfall and soil fertility. Areas with weak (or no) dry seasons and intermediate to rich soils average 64 fertile plant species and 174 individuals per sample, whereas areas with poor soil and a strong dry season average only 5 fertile species and 8 fertile individuals. Areas with either strong dry seasons and good soils or weak dry seasons and very poor soils have intermediate values. Taxonomic composition of the understory also changes predictably with rainfall and soil fertility. In increasingly stressed forests changes are found in understory structure, with sequential loss of terrestrial herbs, epiphytes, understory shrubs, and lianas. The understory of the poorest soil site consists almost entirely of young trees. The effects of seasonal differences at a given site are small compared with between-site differences. We suggest that the level of understory fertility may provide a simple indicator of overall ecosystem productivity. THE UNDERSTORY OF A TROPICAL RAIN FOREST iS composed of a different set of species than is the canopy. The understory, though often neglected, is an integral and important part of the plant community. For example, understory species constitute 25 percent of the species and 24 percent of the individuals sampled in 1000 m2 at a wet-forest site in western Ecuador (Gentry and Dodson 1987). In a coastal Ecuador moist forest, 2 1 percent of the species and 44 percent of the individuals in a similar sample are restricted to the understory. The importance of understory plants is evident from local species lists: 46 percent of the Rio Palenque species (Dodson and Gentry 1978), 43 percent of the Barro Colorado Island, Panama species (Croat 1978), and 47 percent of the Jauneche (Dodson et al. 1985) species are herbs, shrubs, and small trees. These figures are overestimates, since a number of the species included in such lists are weedy and found rarely, if at all, inside the closed forest, but the overall importance of the understory to rainforest plant diversity is clear. The understory supports a different fauna than does the canopy. Many species of insects, birds, and mammals are restricted to the understory, and understory plants are major food sources for this biota. For example, hermit hummingbirds, major pollinators for many plant taxa, are exclusively understory birds. Such frugivores as birds of the family Pipridae and bats of the genus Carollia are largely dependent on understory fruits (e.g., Snow 1965, Stiles 1981, Fleming 1985). Temperate zone studies have shown that response of the forest understory to environmental gradients can differ from that of the canopy (summary in Whittaker 1977). For the tropics, we now have data that show predictable patterns of change in plant community composition across such environmental gradients as annual precipitation (Gentry 1982a, 1987, in press). Surprisingly little attention has been focused on the easily accessible understory, and few data are available for comparing the structure or floristic composition of the rainforest understory in differ-

Book ChapterDOI
TL;DR: In this paper, a procedural model for vegetation analysis is presented and the shape and distribution of species response curves are examined along a temperature gradient using 750 sites in eucalypt forests.
Abstract: A procedural model for vegetation analysis is presented. Suggestions are made that analysis methods can test theory as well as examine vegetation-environment correlations. Gauch and Whittaker’s propositions regarding species behavioural properties expected for an individualistic continuum are tested on a eucalypt forest data set. The data set is carefully stratified to control environmental heterogeneity. The shape and distribution of species response curves are then examined along a temperature gradient using 750 sites. The conclusions are: (1) Bell shaped response curves to environmental gradients are not universal (2) Positive-skewed curves are characteristic of major canopy species in eucalypt forest in southern New South Wales (3) Species richness increases with temperature along the gradient (4) Tests of other propositions regarding species modes and ranges are confounded by the change in species richness along the gradients (5) More rigorous statistical analysis and analyses on other vegetation types are needed.

Journal ArticleDOI
TL;DR: The results indicate that maintenance of a diversity of forest-interior birds will require preservation of large areas of forest, and forest area is the best predictor of the density and species richness of Forest-interIOR birds for small forests, while isolation is thebest predictor for large forests.

Journal ArticleDOI
TL;DR: The results suggest that crayfish play an important role in structuring the macrophyte and invertebrate communities that exist in northern Wisconsin lakes and decline in species richness and comparison of species abundance over time suggested thatcrayfish grazed selectively.
Abstract: We conducted five 4- to 12-wk in situ enclosure–exclosure experiments in four macrophyte assemblages in three northern Wisconsin lakes to test the impact of grazing by the crayfish Orconectes rusti...

Journal ArticleDOI
TL;DR: Spores of Gigaspora and Scutellospora species predominated in the root zones of three major plant species growing in the barrier dunes extending from northern New Jersey to Virginia, and Dominance by a single fungal species was inversely correlated with distance south and with temperature parameters.
Abstract: Spores of Gigaspora and Scutellospora species predominated in the root zones of three major plant species growing in the barrier dunes extending from northern New Jersey to Virginia. Similarity in edaphic factors, vegetation, daylength during the growing season, and precipitation along a 355 km transect permitted study of the composition of the VAM fungal community in response to temperature. Twenty-three species of VAM fungi were recovered. Dominant species along the transect were G. gigantea, Acaulospora scrobiculata, and S. dipapillosa. Some species were more abundant in the northern (cooler) regions of the transect and others were more abundant in the southern regions. Average VAM fungal species richness was positively correlated with distance south along the transect and with temperature parameters. Temperature effects on the VAM fungal community may be separated into two components, a direct effect on the fungi and an indirect effect mediated through the host plant. Plots of rank/log Importance Value depicted the structure of the VAM fungal community and were of use in identifying severe habitats where heat stress appeared to be the controlling factor. Dominance by a single fungal species was inversely correlated with distance south and with temperature parameters. It was most pronounced in northern sites and in the root zones of heat-stressed Ammophila breviligulata plants growing near the species' southern limit.

Journal ArticleDOI
01 Apr 1987
TL;DR: Observations indicate that patches of semidisturbed riparian woodland provide refuges from which populations of I. humilis may invade adjacent agricultural land, and vice versa, and the species richness of native ants is markedly reduced at riparian forestry sites occupied by I. Humilis.
Abstract: This study was designed to determine the extent to which the introduced Argentine ant (Iridomyrmex humilis), a pest in urban and agricultural environments, has invaded natural habitats in the lower Sacramento Valley, and its effects on the native ant fauna. Of four natural habitats surveyed (valley riparian woodland, foothill riparian woodland, blue oak-digger pine woodland, and chaparral), at 46 sites in Yolo and Solano counties, only valley riparian woodland was found to have been colonized by I. humilis. Riparian woodland sites occupied by I. humilis have permanent sources of water and tend to be environmentally degraded. Populations of I. humilis are common but patchily distributed along four principal riparian systems in Yolo and Solano counties (Ulatis Creek, Putah Creek, Cache Creek, and the Sacramento River). Observations indicate that patches of semidisturbed riparian woodland provide refuges from which populations of I. humilis may invade adjacent agricultural land, and vice versa. The species richness of native ants is markedly reduced at riparian woodland sites occupied by I. humilis. Among the common native ants, epigaeic (aboveground foraging) species are more susceptible to displacement by I. humilis than are hypogaeic species. The three most adversely affected species (Liometopum occidentale, Tapinoma sessile, and Formica occidua [ = moki]), which are absent from sites colonized by I. humilis, are dominant epigaeic ants; two of the three least displaced species (Stenamma diecki and S. californicum) are timid, cryptobiotic ants that forage in soil and leaf litter.

Journal ArticleDOI
TL;DR: Changes in the lowland dipterocarp forest structure and composition are described for a 34-year period between 1947 and 1981 in Sungei Menyala Forest Reserve, Peninsular Malaysia, and eight of the 32 commoner species showed significant changes, all unidirectional.
Abstract: Changes in the lowland dipterocarp forest structure and composition are described for a 34-year period between 1947 and 1981 in Sungei Menyala Forest Reserve, Peninsular Malaysia Although tree density declined by about 10%, basal area changed little, averaging 324 m 2 ha −1 Size class distributions in 1947 and 1981 were not significantly different Mortality rates were independent of size class Mortality exceeded recruitment during the first 16 years to 1963, but was thereafter almost exactly balanced by recruitment Recruitment rate increased significantly for the latter part of the study Mortality was greater than average for understorey species and lower for emergents Pioneer and late seral species together showed significantly higher mortality rates Amongst the commoner species, emergent, late-seral and pioneer species showed the highest annual diameter growth rates with species averages over all size classes exceeding 3 mm yr −1 ; rates for main-canopy species were between 15 and 25 mm yr −1 , and understorey species generally less than 2 mm yr −1 Species richness was almost identical in 1947 and 1981 (243, 244 species), but a clear decline (to 229 species) between 1953 and 1971 was recovered by 1981 Most species showed little net change in density over the 34-year period, but eight of the 32 commoner species showed significant changes, all unidirectional These changes in species composition are not negligible, but further analysis is needed to determine if, for example, they are related to disturbance of part of the plot in 1917

Journal ArticleDOI
TL;DR: Mammalian species richness within patches decreased with increasing percentage of barren ground per patch, with proximity to buildings, and with patchiness in the total vegetation cover, but increased with increasing density of vegetation in the layer 21-50 cm above ground.
Abstract: (1) Species of terrestrial mammals, reptiles and amphibians were surveyed in patches of semi-natural and disturbed vegetation within the City of Oxford. The patches were delimited by roads, walls or other artificial barriers, and ranged from 0 16 ha to 20 ha. (2) A total of twenty species of mammals was recorded, two to seventeen species occurring per patch. Mammalian species richness (the number of species) within patches decreased with increasing percentage of barren ground per patch, with proximity to buildings, and with patchiness in the total vegetation cover, but increased with increasing density of vegetation in the layer 21-50 cm above ground. (3) Five species of amphibians and four species of reptiles were recorded, zero to seven species occurring per patch. The richness of these taxa within patches increased with patch area, but declined away from sources of permanent water. (4) More species of mammals, amphibians and reptiles were retained in two small habitat patches than in one large patch equal to their combined area. (5) For mammals, excluding large species such as deer, species richness in the urban environment can be preserved by maintaining a system of small (>0 65 ha) patches of undisturbed woodland throughout the city area. The richness of reptiles and amphibians can probably be preserved by maintaining patches of )0 55 ha that provide permanent water.

Journal ArticleDOI
TL;DR: Species richness as well as sample size decreased gradually with increasing altitude over a 100–2200 m range, in contrast to data from the literature which demonstrated a maximum at intermediate elevations.
Abstract: Sample size and species richness of a series of light-trap samples taken in a number of localities in the Republic of Panama are given. Species richness as well as sample size decreased gradually with increasing altitude over a 100–2200 m range, in contrast to data from the literature which demonstrated a maximum at intermediate elevations. It is suggested that differences in technique, especially the continuous nature of the sampling in the present case are responsible for this discrepancy. Moderate human disturbance, which leaves a relatively high tree species diversity in the area has a surprisingly little, if any, effect on insect diversity. A large perturbation of the environment does, however, decrease species richness of the insect fauna.

Journal ArticleDOI
TL;DR: Any apparent “structure” in this assemblage seems to be the result of the summation of individual responses to changing algal physical structure during succession, as a larger sample of the available pool of individuals is collected and more species are found in a given area of algal mat when the structure is more complex.

Journal ArticleDOI
01 Apr 1987-Nature
TL;DR: Host insects' feeding niche, geographical extent of study, the architecture of plants on which hosts occur and the taxonomic isolation of host insects each significantly affects the number of associated parasitoid species per host species, but only the first two variables were significant in the multiple regression.
Abstract: Variation in the number of phytophagous insect species associated with different plant hosts has been examined for many insect and plant groups1–7. Here we extend such analyses to focus on the number of parasitoids and hyperparasitoids attacking British phytophagous insects. First, we examine a number of variables describing characteristics of the herbivores and their host plants. Then we construct a multiple regression model to order the variables and determine how much of the variance in parasitoid species richness we can account for. We find that host insects' feeding niche, geographical extent of study ('range'), the architecture of plants on which hosts occur and the taxonomic isolation of host insects each significantly affects the number of associated parasitoid species per host species, but only the first two variables were significant in the multiple regression. The final model accounts for 22% of the variance in parasitoid richness.

Journal ArticleDOI
TL;DR: The authors compared the abundance and floristic composition of seeds from these two sources at a Costa Rican site by germinating seeds from the soil, measuring seed inputs for 3 years, and monitoring the earliest colonists in a forest clearing.
Abstract: Soil seed banks and current seed inputs each play a role in tropical succession We compared the abundance and floristic composition of seeds from these two sources at a Costa Rican site by germinating seeds from the soil, measuring seed inputs for 3 yr, and monitoring the earliest colonists in a forest clearing There were an estimated 6800 viable seeds/m2 in the soil of 33-yr-old vegetation, 9500 seeds/m2 in 11-yr-old vegetation, and 7000 seeds/m2 in a 75-yr-old forest An estimated 10100 seeds/m2 fell on the soil surface of the young successional vegetation during 3 yr and 3700 seeds/m2 fell during that same time in the forest Locally produced seeds accounted for about 75% of the seed input to the soil surface early in succession Seeds dispersed out of young successional vegetation increased the quantity and species richness of the seed input and storage in an adjacent forest Much of the species richness of the young successional vegetation resulted from seeds dispersed there from other communities by animals Deforestation stimulated germination of most seeds in the surface soil of the old forest, including seeds of the dominant canopy tree The recruitment of seedlings from the soil seed bank numerically overwhelmed that from post-disturbance seed rain and sprouts We evaluated patterns of soil seed storage during succession and predicted the ability of vegetation of differing ages to respond to disturbance Immediately after disturbance the number of seeds in the soil plummeted due to mortality, low inputs, and germination As the vegetation regrew, the soil seed bank increased to a peak after 4 to 7 yr, then gradually decreased to its pre-disturbance size High-frequency pulses of disturbance should result in reduced species richness, dominance by species with long-lived seeds, and fast recovery by seedling recruitment from the soil seed bank

Journal ArticleDOI
01 Dec 1987-Ecology
TL;DR: This study demonstrates that the authors must understand patterns of soil nitrogen availability and processes affecting nitrogen availability in addition to water availability, in order to understand productivity and species composition of Chihuahuan Desert annual plants.
Abstract: We examined the effects of water supplementation and nitrogen amendment on biomass, cover, and density of annual plants on a termite-free and a termite-present area in the Chihuahuan Desert. Soil moisture was higher in the termite than in the termite-free plots, and in the watered than in the unwatered plots during the spring and summer. There were no differences in soil moisture among plots during the winter. Soil nitrogen was higher in the termite-free than in the termite plots. There were no differences in total plant biomass produced in termite and termite-free areas. There were significant differences in relative abundances of species among treatments. natural rainfall was sufficient for maximum spring-annual biomass development on all plots except for the termite-free unfertilized, unwatered plots. These were the driest plots but had high soil nitrogen. Most of the herbaceous species responded to the water amendments by lengthening growing seasons, increasing density, or increasing biomass. When there was sufficient water for most of the spring annuals, high soil nitrogen levels favored increased densities and biomasses of Descurainia pinnata and Lepidium lasiocarpum. The absence of C4 summer annuals in the high-nitrogen plots suggests that relatively high soil nitrogen adversely affected the summer annuals. Termite-free watered plots had higher soil moisture than the termite-unwatered plots, but summer annuals were relatively abundant on the latter. Water amendments had a greater effect on the species abundances in the termite-free area than in the one with termites. In the area with termites, nitrogen amendments had a greater effect on species abundances. Species diversity and richness were affected by fertility as was species composition. This study demonstrates that we must understand patterns of soil nitrogen availability and processes affecting nitrogen availability in addition to water availability, in order to understand productivity and species composition of Chihuahuan Desert annual plants.

Journal Article
TL;DR: In this paper, it is proposed that recurrent diversity in the Gondwanan shrubland is a driving force in the massive specil evolution and that strong disruptive selection would result in the rapid evolution of isolated populations into distinct and specialized species.
Abstract: The floras mediterranean south-western Australian shrublands (kwongan) and south-western Cape jynbos have evolved under conditions low soil nutrients and recurrent The vegetatiOn oj both regions, here termed Gondwanan shrublands, is broadly convergent in structure and junctioning. In particular these shrublands have high species diversity at all levels. Fire has played an important role in the evolution oj traits and life histories on both continents. Populations respond difjerentially to varying components oj the fire regime and post-jire population extinction is not uncommon. Since each fire is a event, high alpha richness could be maintained by the creation oj fire-induced transient niches resulting in difjerential establishment. Under this jorm oj 'lottery' recruitment, competitive are weakened and many species same guild can coexist. It is postulated that recurrent jire is a driving jorce in the massive specil.1tion the Gondwanan shrubland Small demes would be isolated in peculiar habitats ajter jire-induced population. jragmentation. Strong disruptive selection would result in the rapid evolution oj isolated populations into distinct and specialized species. Some tests jar these hypotheses are presented and the implications jar conservation are Iy discussed.

Journal ArticleDOI
01 Jun 1987-Ecology
TL;DR: In this paper, the effects of invasion sequence on community structure were evaluated using aquatic microcosms using 30 400mL beakers inoculated with replicated subsets of species from a species pool consisting of green, blue-green, and golden algae, ciliates, a rotifer, a dinoflagellate, and euglenoids.
Abstract: The effects of invasion sequence on community structure were evaluated using aquatic microcosms. Thirty 400—mL beakers were inoculated with replicated subsets of species from a species pool consisting of green, blue—green, and golden algae, ciliates, a rotifer, a dinoflagellate, and euglenoids. These species were added according to four distinct sequences and two different rates over a 23—wk period, resulting in four replicated sets of insular communities. Significant differences in community structure and species richness could be attributed to both sequence of invasion and distance effects. "Priority" effects were found to be important in some but not all instances. Communities could be divided into two primary types that are similar to the two community types previously reported to arise from the assembly of these same taxa according to different invasions schedules.

Journal ArticleDOI
TL;DR: In this article, the authors studied 32 forest islands surrounded by urban development and found that coniferous tree cover was the most important variable in explaining the variation in the number of birds detected at a sampling point (R 2 = 0.26).

Journal ArticleDOI
01 Dec 1987-Ecology
TL;DR: A long-term analysis of coral community development at Tanguisson Reef, Guam, shows that some coral communities have a greater resilience than was once believed.
Abstract: At Tanguisson Reef, Guam, in 1968-1969 a population explosion of the coral-eating sea star Acanthaster planci devastated the coral community. In the wake of this predation, coral species richness, density, and cover were drastically reduced, and the species composition was altered. In two of three reef zones examined, <1% coral cover remained. At the time of disturbance, some considered the magnitude of this and similar Acanthaster disturbances unprecedented, and predicted long recovery times because reefs were viewed as mature, stable communities. This major disturbance offered an opportunity to study the processes and rate of community recovery. Using the data from previous studies in 1970, 1971, and 1974, and my data from 1980-1981, I present a long-term analysis of coral community development. I have focused on coral recruitment, survivor- ship, and species settlement patterns in relationship to the remnant surviving population. The preference of Acanthaster planci for certain prey (e.g., Montipora and Acropora) shifted the species composition to one in which nonpreferred prey predominated (e.g., Porites and Leptastrea). The predominance of nonpreferred prey was short-lived, and by 1980, preferred prey were the primary colonists of two zones. The three biological zones (reef front, submarine terrace, and seaward slope) had their own characteristic species assemblages soon after the disturbance. Nonrandom recruitment or survival of juvenile corals (diameter < 4 cm) established these zones. Although the percentage ofjuvenile corals fell throughout the survey, their highest density was reached after adult colonies were established. In 1980, of the 34 species examined, 79% showed a significant coefficient of association between adult and juvenile conspecifics. This association caused clumped species dispersion patterns to develop within zones. As the result of recruitment, species diversity rose from 84 species in 1970 to 154 species in 1981. As surviving corals and new recruits developed, the distribution of coral growth forms became more diversified. There was a drastic increase in coral cover (e.g., submarine terrace zone, 0.9% in 1970 to 65% in 1981). This increase in cover corresponded to an increase in size and number of the coral colonies. In 12 yr, species richness, cover, and composition reached or exceeded measurements of comparable reefs before the disturbance. The recovery occurred faster than predicted by a stable equilibrium model because long-term successional changes were not required. Recovery was accelerated because Acanthaster did not destroy the structural integrity of reef framework. This rapid recovery from a natural disturbance demonstrates that some coral communities have a greater resilience than was once believed.

Journal ArticleDOI
01 Dec 1987-Ecology
TL;DR: The results demonstrate that herbivorous snails can strongly influence the distribution, abundance, and diversity of freshwater macrophytes, and suggest that the role of herbivores in freshwater Macrophyte communities may be similar to their role in terrestrial and marine communities.
Abstract: The influence of herbivorous snails on freshwater macrophytes was exam- ined both in the laboratory and the field. In the laboratory, 14 macrophyte species grown in the absence of herbivores had growth rates ranging from 1-10%/d. When grown with four densities of herbivorous snails, species that grew fastest in the absence of herbivores were, in general, most negatively influenced by grazing. In food choice tests, snails typically preferred the plant species that grew fastest in the absence of herbivores. Snail densities were manipulated in a small mesotrophic lake, Christmas Lake. In areas where high snail densities were maintained, macrophyte species richness decreased, and the plants remaining were the species least preferred in laboratory choice tests. In surveys of eight additional lakes having a range of snail densities, the relationship between snail density and macrophyte species composition and diversity was consistent with the labo- ratory and Christmas Lake results. The levels of herbivore damage in the lake were mea- sured for one macrophyte species. For the leaves examined, from 6 to 13% of the total leaf area was lost to herbivores. These results demonstrate that herbivorous snails can strongly influence the distribution, abundance, and diversity of freshwater macrophytes, and suggest that the role of herbivores in freshwater macrophyte communities may be similar to their role in terrestrial and marine communities.


Journal ArticleDOI
TL;DR: In this paper, the first two years' results of an investigation into the use of sheep grazing to restore species-rich calcicolous grasslands were reported. But the results were limited to a 10 ha arable field with shallow soils over Jurassic corallian limestone.