Showing papers on "Species richness published in 1982"

Tropical forests: their richness in coleoptera and other arthropod species

Abstract: Extrapolation from data about canopy insects collected by fogging methods together with estimates of tropical plant host specificity indicate that one hectare of unrich seasonal forest in Panama may have in excess of 41,000 species of arthropods. Further extrapolation of available data based on known relative richness of insect Orders and canopy richness leads to the conclusion that current estimates of Arthropod species numbers are grossly underestimated; that there could be as many as 30 million species extant globally, not 1.5 million a, usually estimated. Since the early days of naturalists, there has been the question of how many species there were in the forests of the tropics. Bates (1892) wrote of collecting more than 700 species of butterflies within an hour's walk of his home in Para, Brazil. Many have guessed that the arthropod fauna of the world today contains between 1.5 to 10 million species. No hard data are available however, and these estimates are less than reliable and as a result misleading. In a recent paper, Erwin and Scott (1980) provided the first hard data with regard to the Coleoptera fauna of a single species of tree in the tropical seasonal forest of Panama. Also recently, Peter Raven of the Missouri Botanical Gardens wrote me with the same inquiry that Bates had pondered-"How many species are there in one acre of rich tropical forest?" With the hard data available from the Panama study, I set out to give as close an estimate as possible and was shocked by my conclusions. The tropical tree Luehea seemannii is a medium-sized seasonal forest evergreen tree with open canopy, large and wide-spaced leaves. The trees sampled (n = 19) had few epiphytes or lianas generally, certainly not the epiphytic load normally thought of as being rich. These 19 trees over a three season sampling regime produced 955+ species of beetles, excluding weevils. In other samples now being processed from Brazil, there are as many weevils as leaf-beetles, usually more, so I added 206 (weevils) to the Luehea count and rounded to 1,200 for convenience. There can be as many as 245 species of trees in one hectare of rich forest in the tropics, often some of these in the same genus. Usually there are between 40 to 100 species and/or genera, so I used 70 as an average number of genus-group trees where host-specificity might play a role with regard to arthropods. No data are available with which to judge the proportion of host-specific arthropods per trophic group anywhere, let alone the tropics. So conservatively, I allowed 20% of the Luehea herbivorous beetles to be host-specific (i.e., must use this tree species in some way for successful reproduction), 5% of the predators (i.e., are tied to one or more of the hostspecific herbivores), 10% of the fungivores (i.e., are tied to fungus associated only with this tree), and 5% of the scavengers (i.e., are associated in some way with only the tree or with the other three trophic groups) (Table 1).

Patterns of neotropical plant species diversity.

Abstract: Diversity has been given a central role in attempts to develop a general theory of ecology (Johnson and Raven, 1970). Much attention has been focused on large-scale trends, such as the increase in species diversity with decreasing latitude (Pianka, 1966; Mac Arthur, 1965; Fischer, 1960; Tramer, 1974), but there is surprisingly little documentation of the equally striking changes in diversity within the tropics. Moreover, additional information on tropical plant species diversity patterns is critically needed because of their potential importance in resolving some of the fundamental and theoretically significant differences of opinion as to the nature and manner of regulation of species diversity.

Fish community structure and function along two habitat gradients in a headwater stream

Abstract: The stream continuum concept suggests that the physical structure of the stream chan- nel coupled with the hydrological cycle and energy inputs results in a consistent pattern of community structure and function along a stream. I evaluated this concept in a headwater fish community along two physical gradients: upstream to downstream and riffle to pool. Habitat diversity and volume increased from upstream to downstream, and from riffle to pool. Temporal variation in habitat diversity was greater upstream. Upstream, and in riffles, habitat volume tended to vary more with time. Fluctuations in rainfall regime caused annual variation in habitat, especially in volume. Benthic insect density was highest from autumn (October-November) through spring (May-June). Following emergence of adults in late spring, invertebrate densities were low in summer in areas with riparian vegetation, but were not lower where riparian vegetation was absent and stable substrates were present. Along a gradient of substrates from silt-sand to gravel-rock, insect production increased, as indicated by adults and pupae in the drift. Peak resource availability for insectivore-piscivore fishes occurred in late summer and autumn, due to increased abundance of young-of-the-year fish. Pool and raceway-pool habitat guilds and insectivore and insectivore-piscivore trophic guilds con- tained the largest number of species. Increases in species richness were primarily associated with the addition of deeper habitats. Species richness of the pool insectivore-piscivore guild was es- pecially variable over time. Biomass in shallow areas consisted predominantly of generalized insec- tivores. In deep, stable habitats, generalized insectivores were replaced as the predominant trophic group by insectivore-piscivores and large benthic insectivores. Immigration of fish occurred in spring and autumn, the periods of highest resource availability. Immigration between midriver and headwater regions primarily involved older age classes (111+), and was associated with changes in flow regime, habitat structure, and seasonal dynamics of the resource base of particular trophic groups. Flow regime and habitat volume appeared to be important factors limiting immigration in autumn, especially in pool species. Habitat diversity (depth, current, and substrate; DCS) was significantly correlated with fish species diversity (FSD). However, considerable variation occurred in the relationship between the two vari- ables, including: (1) FSD decreased, in winter in shallow, less diverse habitats due to emigration, and increased in spring due to recolonization; (2) FSD increased in spring and autumn when resource availability increased; (3) FSD was least predictable from DCS in autumn, when flow regimes were low and large numbers of fish recruits were present; and (4) DCS did not predict FSD as accurately in temporally variable upstream areas where large numbers of small fish dominated the community, especially in areas with human disturbance. Young age groups (0-11) were primarily found in shallow, temporally variable areas upstream and in riffles. Relative growth rates were highest during summer months. However, growth rates did not increase as much between spring and summer as would have been predicted from the seasonal increase in water temperature, suggesting that resource limitation may have occurred during summer periods. Centrarchids had substantially higher growth rates than cyprinids during early life stages. Net pro- duction for age 0-11 fish was highest in upstream and riffle areas because of high densities of young, generalized insectivores. Net production of insectivore-piscivores was highest in downstream and pool habitats. Development of large, stable pools and raceways resulted in decreased fish production due to shifts in age structure toward fewer, large individuals with slower relative growth rates (age III+). Temporal variation in reproductive success and survival of younger age groups (0-I) was associated with random variation in high flow regimes and appeared to be a major factor determining spatial and temporal variation in production. These patterns of fish community structure and function support the qualitative aspect of the stream continuum concept: consistent shifts in community organization are associated with spatial or temporal changes in channel morphology and resource availability. However, for the stream con- tinuum concept to be useful as a quantitative predictor, the ultimate mechanism(s) regulating fish community organization need to be more rigorously established. I hypothesize that in upstream or riffle areas, where younger age classes predominate, recolonization dynamics, the effect of gradual changes in physical conditions on competitive interactions, and temporal variation in reproductive success, are more important than competitive exclusion and predation as determinants of community organization.

Patterns in the Species Composition and Richness of Fish Assemblages in Northern Wisconsin Lakes

Abstract: Fish assemblage structure, and factors and mechanisms appearing important in the ecological maintence of these structures, were examined for 18 small lakes in northern Wisconsin during summer and winter. The study was focused around the following questions. Are there discrete, repeatable groups of fish assemblages? If so, are they temporally stable? What are the relations between fish assemblage structure and habitat complexity, physical disturbance, biotic interactions and the insular nature of small lakes? A comparative approach was used to generate hypotheses and propose explanations concerning the roles of these factors in structuring the assemblages. Multivariate classification, ordination, and discriminant analyses helped discern two assemblage types: Umbra—cyprinid and centrarchid—Esox. Each had a distinctive species composition and seasonal change in composition. Environmental characteristic of the lakes occupied by each assemblage type also differed consistently. The type of assemblage present in a lake appeared related to oxygen concentrations in winter, interacting with the availability of refuges from either a severe physical environment (low oxygen during winter) or from large pisvivores. Centrarchid—Esox assemblages occurred in lakes with high winter oxygen levels, and also in lakes with low oxygen if a stream or connecting lake could provide a refuge from these conditions in winter. When no refuge was present, low winter oxygen lakes lacked piscivorous fishes, but contained Umbra—cyprinid assemblages. The relationships between species richness in summer and environmental factors were generally similar for the two assemblage types, but the relative importance of individual factors differed. In winter, richness relationships in centrarchid—Esox assemblages for most environmental factors were reversed from those of summer. No significant seasonal change occurred in the Umbra—cyprinid assemblages. Habitat complexity factors, particulary vegetation diversity, were significantly related to summer species richness in both assemblage types. Lake area was also related to summer richness for both types, but the slope of the species—area regression was much steeper for Umbra—cypinid assemblages than for those in centrarchid—Esox lakes. Species richness relationships with winter oxygen concentration were negative in both seasons in Umbra—cyprinid lakes, but the relationship was positive for centrarchid—Esox assemblages in winter. A measure of lake connectedness was related to summer richness in centrarchid—Esox lakes. These patterns suggest that centrarchid—Esox assemblages are in ecological equilibrium but that a disturbance—induced disequilibrium occurs in Umbra—cyprinid assemblages.

Effects of Urbanization on Avian Community Organization

Abstract: -The avian community of a mature residential area was studied and compared with an undisturbed climax beech-maple forest. Urbanization was presumed to be responsible for decreasing species richness and diversity, increasing biomass and density, and favoring dominance by a few species. Foraging guilds shifted from forest insectivores that were canopy foliage gleaners or bark drillers to urban ground gleaners. Analyses of habitat structure showed that although urban foliage height diversity was like that of the forest, the urban area contained only one-third of the total percent vegetative cover. As compared to the forest, urban vegetative cover was: (1) significantly less in all but the middle layer; (2) replaced by man-made structures, ground cover and ornamental vegetation in the low and middle layers but dominated the high layer; and (3) highly discontinuous, existing as isolated strata. Differences in avian community organization between the forest and urban area are discussed in relation to urban habitat manipulation and population-suppressing factors. Bird communities of residential and urban areas contain higher bird densities than outlying natural areas (Graber and Graber 1963, Emlen 1974), with only forest edge communities supporting greater densities in temperate zones. In addition to the factors controlling natural communities (Lancaster and Rees 1979) the diversity of birds in urban areas is affected by the age of the neighborhood (Lucid 1974) type of housing (Geis 1974), and degree of urbanization (Batten 1972). Few studies have compared the avifauna of cities with that of outlying natural areas and have measured habitat structure in both communities. The difficulties arise in selecting comparable study areas and quantifying the synthetic urban habitat in relation to natural parameters. In this study, we determined how urbanization affected avian community organization by comparing the ecological characteristics of the birds of a mature residential area with those of the regional vegetative climax, an outlying forest.

Randomness, Area, and Species Richness

Abstract: Thorough censuses have been made of breeding birds on islands in Pymatuning Lake, a reservoir at the Pennsylvania-Ohio border Analysis of the censuses yields the conclusion that for these islands the variation of the number of resident avian species with island size is that which one would expect if the birds were distributed randomly, with the probability of a breeding pair residing on an island proportional to the area of the island and independent of the presence of other pairs This type of random placement of individuals can yield species-area relations which differ from those commonly employed for analysis of biogeographic data

Relationships between Temperate Forest Bird Communities and Vegetation Structure

Abstract: General patterns of density, species richness, and relative abundance of breeding birds are examined in a wide variety of North American forests. Taking data from censuses published in American Birds, we use rarefaction to ordinate the species richness of communities in terms of samples of equal numbers of individuals. By this criterion young forests in secondary succession and mature deciduous forests can be equally rich in bird species; coniferous forests and dense successional stands having only one or two species of trees have the fewest species of birds. For our data set the density of birds is higher in mature deciduous forests than in successional stands. The species/area relationship (sla) is a function of both this species/individuals relationship (s/n) and the individuals/ area relationship (n/a). According to the Jonckheere-Terpstra statistic there is a statistically significant pattern to the order in which bird communities fall with regard to s/n and n/a. To see these relationships in terms of the structure of the vegetation, we present the positions of 56 stands in a graphic space determined by principal components. Tree species richness and canopy cover dominate the first axis, and variation in canopy height the second. Tree density has a somewhat independent pattern of variation and is expressed by the third axis. In the bivariate space of principal components one and three, a SYMAP contour diagram of the number of bird species expected in 10 ha (sla) shows maximal values in mature deciduous forests, but not in those that have the highest tree species richness, canopy height, or tree density. The number of individual birds/10 ha (n/a) shows a similar pattern except that maximal density occurs at maximal values of tree species richness and canopy height. By this criterion both bird species richness and density are minimal in coniferous forests characterized by high tree density, low canopy, and few species of trees. These patterns are not discernible by the classic bird species diversity/foliage height diversity method proposed by Mac Arthur and Mac Arthur in 1961. They are masked by correlation coefficients, partly because the coefficients are insensitive to nonlinear relationships. We recommend rarefaction, principal components analysis, and contour diagrams to display relationships among communities.

The distribution of abundance. I. Measurements

Abstract: We investigated the spatial distributions of densities within the geographical ranges of species of carabid beetles, birds and plants. Unselected data of hundreds of species from censuses in sampling areas of varying size and location in northwestern Europe were analysed. The geographical distribution of species abundance is as a rule heterogeneous, with the highest abundances occurring near the centres of the species ranges and the lowest at the margins. As this trend was found in a great number of unselected species belonging to quite different biological taxa, we feel that this trend may be considered as a general biogeographical rule. We obtained this result mainly from indirect measurements, meaning that we deduce the geographical trend within species ranges from correlations of local frequencies of occurrence with the distance of the sampling area to the range centre for each species. The picture may be com- plicated by such biological properties as the species' feeding habits that also greatly affect their density, but within each of the groups distinguished we found that the same general rule applies. The interpretation of such peaked distributions in terms of two-dimensional ecological tolerance or optimum response surfaces in geographic space is discussed in a second paper.

The richness, abundance and biomass of the arthropod communities on trees.

Abstract: (1) The invertebrate fauna of six tree species in both Britain and South Africa was sampled using pyrethrum knockdown. Two of the tree species in Britain and three in South Africa were introduced; the rest were native. (2) Average faunal diversities were similar in South Africa and in Britain. (3) The South African arthropod community consisted of fewer, heavier individuals than the British ones and tended to have a more uniform, larger biomass overall. (4) Faunal diversity was similar for native and introduced trees for all guilds except the phytophages, which showed a lower diversity on introduced trees. (5) On every native tree, the most abundant species was an hemipteran; on four of the five introduced trees other orders provided the most abundant species. (6) Total species richness was correlated with tree abundance for both native and introduced trees in Britain. (7) Arthropod abundance increased with species richness-as communities became richer in species, they became more tightly packed. (8) The biomass and numbers of individual arthropods, classified by guild, was not clearly related to structural and other features of the individual trees sampled. (9) There was a positive correlation between the biomass of chewing phytophages and a measure of defoliation.

Dynamics and organization of a rocky intertidal fish assemblage: the persistence and resilience of taxocene structure

Abstract: This paper examines characteristics of a rocky intertidal fish taxocene in central California. Seasonal and annual changes in taxocene structure, diversity, and recruitment were described and attempts were made to correlate these parameters with environmental variables. In addition, the persistence and resilience of taxocene structure were examined to determine whether this assemblage was regulated through deterministic or stochastic processes. A series of tidepools were defaunated 15 times over 29 mo. Sampling did not grossly affect taxocene structure in the study site and recolonization from surrounding areas was rapid. Three types of abundance patterns were observed: (1) species present year round (residents), (2) species present seasonally, and (3) species occasionally present. Productivity appeared to be the main environmental factor affecting taxocene structure because there were significant correlations between it and: (1) diversity, (2) species richness, (3) numerical abundance, and (4) recruitmen...

Patterns and determinants of monkey densities in Peru and Bolivia, with notes on distributions

Abstract: A comparative study of species assemblages and population densities was conducted on Amazonian monkey communities in 16 areas, ranging from 3°S latitude in northern Peru to 18°S latitude in southern Bolivia. The habitats ranged from several types of tropical rain forest in the more northern latitudes to dry, deciduous forest in the southernmost study area. The monkey populations of three of the study areas have historically received light hunting pressure; the rest have been moderately to heavily hunted. A transect census technique was used to estimate the relative and absolute densities of all diurnal monkey species except Cebuella pygmaea. The number of coexisting monkey species ranged from 4–6 in the southern areas to 12–14 in the northern areas. The reduction in species richness in central and southern areas of Bolivia is probably attributable to several inimical habitat factors. Predation by humans was found to be the single most important factor affecting monkey densities. Monkey densities, and especially biomasses, were much lower in areas not protected from hunting than in protected areas. Hunting did not affect all species equally. Larger-sized species are hunted more and have severely reduced numbers in unprotected areas, whereas the densities of smaller species are not noticeably diminished in unprotected areas. Large, herbivorous monkey species contributed the major proportion of the total monkey biomass in protected areas. The strong influence of hunting has largely obscured the effects of other factors on population densities.

Vacant niches and unsaturated communities: a comparison of bracken herbivores at sites on two continents.

Abstract: (1) Communities of herbivorous insects feeding on the above-ground parts of bracken (Pteridium aquilinum (L.) Kuhn) were compared at matched open and woodland sites in the north of England (Skipwith Common) and the Sacramento Mountains, New Mexico (Sierra Blanca). (2) General supporting surveys of herbivores were also conducted throughout Britain and the south-western U.S.A. (Arizona and New Mexico). (3) Twenty-seven species of insects feed on the above-ground parts of bracken fronds in Britain, with another eight possibly or occasionally doing so. Only five species were found on bracken in New Mexico, with two more in Arizona. (4) This difference in faunal richness between Britain and the south-western U.S.A. is consistent with predictions based on standard species-area relationships, given the areas within which bracken grows in the two regions. (5) The small pool of species in Arizona and New Mexico means that local communities of bracken herbivores in this region are also species-poor. Compared with communities in Britain, bracken in New Mexico has a large number of apparently vacant niches, i.e. totally unutilized, or underutilized plant-parts. (6) Despite containing a markedly impoverished number of species, there is no clear evidence either for niche-expansion, or for density compensation in the New Mexico communities. Two possible exceptions to this generalization are enigmatic. (7) These results for bracken are probably representative of phytophagous insect communities in general, in that such communities appear rarely to be saturated with species, and are not structured to any major extent by interspecific competition.

Species richness and endemism in the Usambara mountain forests, Tanzania

Abstract: The East Usambara Mountain forests constitute what is probably one of the richest biological communities in Africa in terms of plant and animal species numbers and endemic taxa. This review presents brief accounts of the flora and of three invertebrate and four vertebrate groups and shows the percentage endemic taxa to vary from 2% (mammals) to 95% (millipedes) as a proportion of the true forest species. Notes are given on the geology, soils, climate and present land use of the Usambaras. Biological richness is considered to be due to long periods of isolation and geological stability coupled with periods of species immigration during times of re-establishment of a continuous forest cover. The nature of the endemic elements is briefly discussed. Evidence is given to show that the forests are subject to increasing pressure from legal and illegal encroachment due to agriculture (tea, cardamon, subsistence) and forestry timber operations. Air photograph analysis shows a forest decrease of some 50% in the vicinity of Amani from 1954 to 1976. The low conservation status of most forest reserves and the lack of detailed knowledge on the distribution, status and biology of the endemic species means present conservation efforts are poor and haphazard. This review calls for greatly increased research inputs and a complete halt to all exploitation of natural forest areas until a long term conservation land use plan can be implemented.

Seasonal and Site Variation in Costa Rican Euglossine Bees at Chemical Baits in Lowland Deciduous and Evergreen Forests

Abstract: By attracting male euglossine bees with cineole, eugenol, methyl salicylate, methyl cinnamate, and benzyl acetate in Costa Rican lowland deciduous forest and rain forest, we found no indication of change in the composition and numbers of rain forest attractable bee species during different seasons, but within the deciduous forest both abundance and species richness declined in the dry season. Within each major forest type there were substantial differences in the abundance and species composition of attractable bees among habitats: baits in estuarine swamp forest and open pasture in the rain forest attracted very few bees as compared with nearby forest understory sites. In the deciduous forest, at least 15 species of male euglossine bees were attracted that apparently do not have breeding populations in this forest and that do not visit orchids in this forest; we hypothesized that they normally find females and chemical resources elsewhere in distant habitats or forest types.

Macrobenthos of the subtidal Wadden Sea: revisited after 55 years

Abstract: During the years 1923–1926 Hagmeier & Kandler (1927) sampled the macrofauna of subtidal shallows and channels of the Wadden Sea close to the Island of Sylt (German Bight, North Sea) Reinvestigating this study area in 1980, a substantially altered faunal composition was recorded An approach is made to quantify the comparison in terms of abundance, species richness and diversity of invertebrate taxa Human interference is assumed to be responsible for the major changes Natural oyster beds have been overexploited and the local population ofOstrea edulis has been driven to extinction Subsequently, mussels(Mytilus edulis) spread in the entire region, promoted by shell fishery Particularly barnacles and many polychaetes took advantage of the expansion of mussel banks which is substantiated by correlation analysis Reefs of the colonial polychaeteSabellaria spinulosa stood in the way of shrimp trawling and became destroyed together with the associated fauna A subtidalZostera marina bed was wiped out in 1934 by a natural epidemic disease but never succeeded in reestablishing itself The associated fauna disappeared Large epibenthic predators and scavengers (crabs, snails and starfish) survived all these changes The total number of species remained approximately at the same level but molluscs experienced losses and polychaetes diversified Overall abundance increased with a disproportionately large share of a few species(Mytilus edulis, Balanus crenatus, Cerastoderma edule, Scoloplos armiger) The subtidal fauna of the Wadden Sea proved to be vulnerable to human disturbance; thus, the present community can no longer be viewed as the outcome of entirely natural processes

Quantitative Reef Assessment Studies in Bermuda: A Comparison of Methods and Preliminary Results

Abstract: To compare in quantitative terms both ecological characteristics of the stony coral fauna at various reef sites in Bermuda and available assessment methodologies, we present a study of four separate methods at each of three reef sites. Three plotless (Intersected-length, Quarter point, Point) and one quadrat (Belt-quadrat) methods were employed. Each technique gave similar results but had inherent advantages and disadvantages which involve trade-offs in quantity and type of information generated and time required for use. Pooling of method results revealed that total coral coverage was highest at North Rock (26%), intermediate at Three Hill Shoals (17%), and lowest at South shore (13%). Diversity statistics were highest at Three Hill Shoals, intermediate at North Rock, and lowest at South shore. At all three sites the most dominant species in terms of coverage was Dip/aria sfrigosa; six coral species accounted for 90% of the total coral coverage. This study represents a quantitative comparison of the results and performance of common reef assessment methodologies and the first truly quantitative data on coral coverage, diversity, and distribution for selected reef sites in Bermuda. The importance of detailed knowledge about the ecological characteristics of coral and other benthic communities of coral reefs is now recognized and has been recently stressed by Loya (1978). Quantitative, as opposed to qualitative, methodologies allow more standardized and accurate descriptions of the desired reef community to be made. In this way meaningful intercomparisons of different reef areas as well as of various zones on a single reef or reef complex become feasible. Ecological parameters such as species richness, abundance, diversity, coverage, density, and zonation are common statistics of comparison and become available through quantitative methods. Classical studies on coral reefs prior to the 1970's (see reviews by Stoddart, 1969; 1972) have been primarily qualitative. Although many have utilized quadrats in various ways as data sampling units, it has been difficult to compare between methods and results. Generalizations based on such data are therefore tenuous. More recently, as interest in quantification of aspects of reef ecology has grown, two general classes of methodologies have emerged: (I) plot techniques, utilizing quadrats as sampling units either randomly or arranged belt fashion along a transect line for guidance; and (2) plotless techniques, essentially an outgrowth of the methodology of terrestrial plant ecologists, utilizing a distance (and/or other measurements) from or on a sampling structure, which is usually a transect line of specified length but with no breadth. Loya (1978) provides a comprehensive review of existing plotless methodologies and suggests new procedures for coral reefs which have had success in terrestrial plant ecology. The only previous comparison of reef survey methodologies known to us is by Goodwin et al. (1976) who compared grid, transect and random quadrat methods to total samples in a 400-m2 grid on Grenadine reefs. They concluded that a series of parallel line transects was adequate to delimit dominant species but 4-m2 quadrats were preferable for recognition of less abundant species. We present here results using four different assessment methods to characterize

Species Removals From a First‐Year Old‐Field Plant Community

Abstract: The three models of succession described by Connell and Slatyer (1977) were tested by removing selected species from a 1st—yr old field in southwestern Ohio. The facilitation model, which is a restatement of the traditional view of succession, was rejected as inapplicable to the community investigated. Evidence favored the tolerance model over the inhibition models; however, it was concluded that more than one model of succession may apply in the same field at the same time, reflecting the spatial heterogeneity which characterizes old—field communities. The observation that community richness and diversity decreased with species removal contrasts with previous studies and is related to time of field abandonment. See full-text article at JSTOR

Comparison of benthic macroinvertebrate fauna and substratum composition in riffles and pools in the impounded River Elan and the unregulated River Wye, mid‐Wales

Abstract: SUMMARY. The macro-invertebrate fauna and substrate were studied in a riffle and pool from a regulated (Elan) and an unregulated (Wye) river in summer. There were some differences in the substrate particle size distribution of the two rivers and between the riffle and the pool on the Wye. There was more detritus in pools than in riffles in both rivers and generally more in the Elan than the Wye. Deposits on the bed of the Elan were rich in iron and manganese. On the Wye. there was a greater density of invertebrates in the riffle than in the pool, but species richness was similar. Most species showed some preferences for either the riffle or the pool. The riffle contained a substantial number of Ephemeroptera, Trichoptera, Plecoptera and Simuliidae (52%) whilst the pool was dominated by chironomids (71%). Compared with the Wye, total invertebrate density and species richness were reduced in the Elan. Some species characteristic of riffles were reduced or absent on the Elan. Invertebrate density on the Elan was similar in the riffle and pool; species richness was greater in the riffle. The distribution and abundance of invertebrates is discussed in relation to such environmental factors as water velocity through the substrate and dissolved oxygen supply in interstitial habitats.

Seasonal patterns in species richness of herbivores: macrolepidopteran larvae on Finnish deciduous trees.

Abstract: . 1. The seasonal distribution of macrolepidopteran species richness on Finnish deciduous trees vaned from positively skewed (peak in spring) to negatively skewed (peak in autumn). 2. The skewness values of species richness had a significant negative correlation (r = - 0.98) with the duration of the seasonal shoot-growth period of the tree species. 3. Trees which complete their shoot growth early in the season (Quercus type) produce new leaves only during spring, while trees whose shoot growth continues to autumn (Populus type) do so throughout the summer. 4. Consequently, there is a difference in the number of available resources in the late summer foliage of different tree species, Trees ceasing leaf production early such as oak (Quercus robur) and bird cherry (Prunus padus) have one major resource type (mature leaves) in late-season foliage while trees like birches and alders have two Ooung and mature leaves). 5. Because young leaves formed late in the season are preferred to mature ones by some species of herbivores and because other species prefer mature leaves at the same time, the species richness of Populus-type trees is higher later in the season than the species richness of Quercus-type of trees, which have just one type of resource available.

The assessment of arboreal insect fauna: comparisons of knockdown sampling and faunal lists

Abstract: . 1. A comparison is made between the fauna of six British tree species sampled by pyrethrum knockdown and the faunal lists in the literature for the same tree species. 2. Conspecific trees vary both in abundance of arthropods and their proportional distribution across taxa, but there are important overriding differences between tree species. 3. The percentage similarity in faunal composition between tree species reflects the ecological specificity of the arthropod groups used for the comparison. 4. The similarity in species composition between tree species is least for phytophages, the guild most closely associated with particular tree species, The two species of Salix are most similar in their fauna for most guilds. 5. About 40% of the entirely phytophagous species in the faunal lists for native trees were found in the knockdown samples. 6. The proportion of individuals of predominantly phytophagous taxa collected that belong to the relevant faunal lists ranges from 0.39 to 0.99. 7. Those species found in the knockdown samples which are not included in faunal lists none the less contribute to the trophic web of the tree. 8. The relative species richness of arboreal faunas assessed from knockdown samples parallels that derived from faunal lists. 9. The two approaches to the categorization of arboreal faunas, knockdown sampling and faunal lists, provide comparable data.

Ecological Correlates of a Neotropical Mutualism: Ant Assemblages at Costus extrafloral Nectaries

Abstract: The species richness and composition of ant assemblages at the extrafloral nectaries of four Costus spp. (Zingiberaceae) in Panama were quantified to determine (1) the relative specificity of these ant—plant mutualisms, and (2) the ecological factors that influence ant assemblages. Although inflorescences of Costus spp. commonly produce extrafloral nectar for several months (species means 1—2 mo, range to 4 mo), there was little turnover in ant—species composition on individual inflorescences. A total of 34 ant species in five subfamilies were observed, but plant species varied significantly in ant species richness. The number of ant species expected from equal sampling (40 inflorescences per Costus sp.) was 9 for C. pulverulentus, 13 for C. scaber, 15 for C. allenii, and 20 for C. laevis. Among—species differences in ant species richness were not a function of plant distribution, the volume or composition of extrafloral nectar, or the duration of nectar flow. The number of ant species was positively correlated with inflorescence height, which varied from 0.6 to 2.0 m. The differences in ant species richness with inflorescence height were due primarily to the addition of arboreal ants, which increased from 3 species representing 3% of all ant species observations on the shortest plant, C. pulverulentus, to 12 species representing 62% of all ant observations on the tallest plant, C. laevis. The number of terrestrial ant species varied only from six to eight. Cumulative ant—species curves as a function of number of inflorescences sampled (N = 41—80) did not plateau for any Costus sp., indicating that a large number of ant species can utilize extrafloral nectar in this system. The high ant species richness and the similarity in nectar characteristics among Costus spp. suggest these are relatively generalized mutualisms with limited coevolution between the plants and their attendant ants. The brief period of extrafloral nectar production (° = 36—55 d), coupled with spatial variation in ant species distributions, probably limit the degree of specialization among mutualists. This is in contrast to more specialized ant—plant mutualisms where plants are relatively predictable sources of food and/or nest sites for ants.

On the use of measures of structure and diversity in applied diatom ecology

Abstract: Water managers ask for simple ecological indices as a tool for measuring the effectiveness of their activities. Diversity indices are often used as such tools. The concept of diversity is closely related to the nature of species-abundance distributions. There is empirical and theoretical evidence that diatom-assemblages have a species-abundance distribution of log-series type. Then the most appropriate diversity index is the dominance,i.e. the relative abundance of the commonest species. The number of species in a sample of fixed size of the assemblage is a useful additional index. It appears from some examples that these indices have no consistent relationships with the degree of water pollution. This in contrast to the species composition of the assemblages. (Complete paper published in: HAKANSSON, H. and J.GERLOFF, Eds., (1982). Festschrift Niels Foged. Diatomaceae III. Beiheft zur Nova Hedwigia

Species-area and species-distance relationships of terrestrial mammals in the Thousand Island Region.

Abstract: The species-area and species-distance relationships of terrestrial mammals in the Thousand Island Region of the St. Lawrence River are totally consistent with the basic predictions of the equilibrium theory of island biogeography. The power model provides the best fit for the species-area relationship, and the z-value of 0.305 does not differ significantly from Preston's canonical value (0.26). Distance (D) is a normal determinant (Sαe -D 2) of mammalian richness, and 93% of the variability in richness is accounted for by island area and isolation. The high z-values and poor species-distance correlations reported in previous studies of mammalian island biogeography, rather than evidencing non-equilibrium, are predictions consistent with the equilibrium theory for distant archipelagoes or, equivalently, poor immigrators such as mammals.

The Influence of Host Plant Growth Form and Phenology on the Life Strategies of Finnish Macrolepidopterous Larvae

Abstract: The species numbers, seasonal pattern of species richness, and degree of food specialization of Finnish macrolepidopterous larvae on different plant growth forms was analyzed. There is a significant positive correlation between the commonness of the plant and the number of associated lepidopterous species within all plant growth forms. The number of species on trees and shrubs is higher than on forbs and grasses. On dwarf shrubs the lepidopterous species richness is quite evenly distributed throughout the growing season, but on forbs there is a tendency towards the late summer. On trees the species richness pattern varies greatly. On the trees with a short shoot-growth period the larval species pattern is skewed towards the early summer while on the trees with longer shoot-growth period the majority of macrolepidopterous larvae occur in mid or late summer. It is suggested that the quality of tree leaves along with the direct climatic factors is the central factor determining the seasonal species richness pattern of the larvae. The proportion of specialized feeders is highest in those macrolepidopterous groups where the diet mainly consists of herbs. The proportion of lepidopterous species overwintering as larvae is higher on forbs than on trees and shrubs.

The use of ground flora to indicate edaphic factors in upland ecosystems of the McCormick Experimental Forest, Upper Michigan

Abstract: Groups of ground-flora species indicating similar habitat conditions, termed ecological species groups, were studied over the rather narrow range of upland environmental conditions of the Cyrus H. McCormick Experimental Forest, north-central Upper Michigan, United States. Nonparametric and multivariate statistical techniques were used to analyze frequency of occurrence data and contrast the relative indicator value of the groups and species. Species distributions were finely adapted to the local environmental situation. It was possible to identify specific soil drainage, texture, and fertility levels using the ecological species groups with a known probability of error. For example, presence of the Osmunda species group indicated a 90% probability of soil mottling within the upper 40 cm. By observing the presence and absence of the Clintonia and Osmunda species groups it was possible to classify soil drainage (moist conditions) at the 5% level of significance. Similarly, presence of the Viola species grou...

A Nonequilibrium Theory for the Rate-Control of Speciation and Extinction and the Origin of Macroevolutionary Patterns

Abstract: Cracraft, J. (Department of Anatomy, University of Illinois at the Medical Center, P.O. Box 6998, Chicago, Illinois 60680, and Division of Birds, Field Museum of Natural History, Chicago, Illinois 60605) 1982. A nonequilibrium theory for the rate-control of speciation and extinction and the origin of macroevolutionary patterns. Syst. Zool., 31:348-365.-Macroevolutionary analysis focuses on the explanation of general patterns of diversity among monophyletic groups. Three general patterns can be recognized: radiation diversity in which species richness increases through time, reduction diversity in which richness decreases, and steadystate diversity in which it remains relatively constant. Most clades show some combination of these three patterns. Clades also exhibit a pattern of phenotypic change that can be superimposed on the pattern of diversification. With speciation, descendant species can become either markedly apomorphic or remain plesiomorphic relative to the ancestral condition. There is no necessary correlation between a particular phenotypic pattern and a specific pattern of diversity. Explanations of macroevolutionary patterns have been of two principal types: adaptationist and species selectionist. The adaptationist approach has explained patterns of diversity in terms of the occupation of "adaptive zones," driven by natural selection. "Adaptive zones" are tautological constructs and lack ontological status. The other macroevolutionary explanation, species selection, is a pattern of species survival through time and as such is neither a process nor a theory of macroevolutionary change. A deterministic theory of macroevolution lies in explaining inter-cladal diversity patterns by variation in the rate-controls of speciation

Early Spring Herb Communities in Mesophytic Forests of the Great Lakes Region

Abstract: Herb composition in early spring (before leafout of hardwood overstories) was sampled quantitatively in 60 little-disturbed mesophytic hardwood stands in the Great Lakes region, USA. Disturbed hardwood stands and stands containing evergreens (hemlock) in the overstory were de- scribed by relev6. Importance of strictly vernal growth forms, early spring annuals and ephemeroid perennials, was correlated with total cover of herbs. In places with nutrient-poor mineral soil, slow rates of litter decomposition, compressed growing season, or evergreen shade, populations of vernal herbs were generally sparse, with summergreen and semi-evergreen taxa relatively important. In mesophytic woods occupying physiographically similar sites, the most significant regional dif- ferences in species importance are associated with differences in soil fertility rather than climate. Superimposed on the soil-related, specific compositional differences were gradual, more general, southeast to northwest decreases in species richness, total cover of herbs, and importance of strictly vernal growth forms (annuals and ephemeroids) relative to herbs with summergreen shoots. Within stands, the most significant influences on vernal herb composition were soil drainage and microtopography. Plants with a large proportion of shoots of recent seed origin (annuals and "weedy" perennials) were often strongly dominant in areas with recently exposed mineral soil, as at the edges of receding vernal pools. Plants with large subterranean organs were rare in such sites. Cover of vernal herbs tended to be high on soil mounds and very low in pits, but differences in species composition were not as well defined as they are in large-area uplands vs. broad poorly drained areas. Species abundant on large patches of bare soil (as at the edges of receding vernal pools) also tended to be common in disturbed stands. Long-lived perennials with large storage organs tended to be uncommon in disturbed stands.