Showing papers on "Species richness published in 1979"
TL;DR: In this article, the distribution of tree abundance and dispersion in a tropical deciduous (dry) forest was analyzed and the generalization that tropical trees have spaced adults did not hold.
Abstract: Patterns of tree abundance and dispersion in a tropical deciduous (dry) forest are summarized. The generalization that tropical trees have spaced adults did not hold. All species were either clumped or randomly dispersed, with rare species more clumped than common species. Breeding system was unrelated to species abundance or dispersion, but clumping was related to mode of seed dispersal. Juvenile densities decreased approximately exponentially away from adults. Rare species gave evidence of poor reproductive performance compared with their performance when common in nearby forests. Patterns of relative species abundance in the dry forest are compared with patterns in other forests, and are explained by a simple stochastic model based on random-walk immigration and extinction set in motion by periodic community disturbance.
1,185 citations
TL;DR: The effects of disturbance on local species diversity were investigated in an algal- dominated intertidal boulder field in southern California and suggest that disturbances which open space are necessary for the maintenance of diversity in most commu- nities of sessile organisms.
Abstract: The effects of disturbance on local species diversity were investigated in an algal- dominated intertidal boulder field in southern California. In this habitat, the major form of disturbance occurs when waves, generated by winter storms, overturn boulders. These natural physical distur- bances open space, interrupt successional sequences, and determine local levels of species diversity. Because small boulders are more frequently overturned than larger ones, the plants and sessile animals of boulder fields are distributed in a patchwork of successional stages. Boulders which are subjected to intermediate disturbance frequencies are usually less dominated than those which are very frequently disturbed, and always less dominated than those which are seldom disturbed. In all seasons most small boulders have fewer species than those of intermediate size. Large boulders also usually have fewer species, except in the spring, when defoliation of the algal canopy during the previous winter has opened space for colonization. Species richness on these boulders declines during summer months, and is less than that on boulders of intermediate size in the fall. Small boulders, with a shorter disturbance interval, support only sparse early successional com- munities of the green alga, U/va, and barnacles. Large, infrequently disturbed boulders are dominated by the late successional red alga, Gigartina canaliculata. Intermediate-sized boulders support the most diverse communities composed of U/va, barnacles, several middle successional species of red algae, and Gigartina canaliclaata. Comparison of the pattern of succession on experimentally sta- bilized boulders with that on unstable ones confirms that differences in the frequency of disturbance are responsible for the above patterns of species composition. The frequency of disturbance also determines the degree of between-boulder variation in species composition and diversity. Small boulders which are frequently overturned sample the available pool of spores and larvae more often. As a result, a greater number of different species occur as single dominants on these boulders. Boulders with an intermediate probability of being disturbed are most variable in species diversity. Assemblages on these boulders range from being dominated by a single species to being very diverse while most communities on boulders which are frequently or seldom disturbed are strongly dominated. Observations on the local densities of three species of middle successional red algae over two year-long periods indicate that most of these are variable in time. More local populations went extinct or became newly established on boulders than remained constant in size. These species persist glob- ally in the boulder field mosaic by colonizing recent openings created by disturbances. These results lend support to a nonequilibrium view of community structure and, along with other studies suggest that disturbances which open space are necessary for the maintenance of diversity in most commu- nities of sessile organisms.
1,010 citations
01 Jan 1979
TL;DR: A review of experiments in which large, epibenthic predators are excluded from soft-sediment marine benthic communities in unvegetated portions of estuaries and lagoons and a comparison of grassbeds, where predators on the infauna are less effective, demonstrate that such soft- sediment systems, when freed from predation, usually exhibit an increase in total density, a increase in species richness, and no tendency toward competitive exclusion by some dominant species as mentioned in this paper.
Abstract: A review of experiments in which large, epibenthic predators are excluded from soft-sediment marine benthic communities in unvegetated portions of estuaries and lagoons and a comparison of unvegetated areas with nearby grassbeds, where predators on the infauna are less effective, demonstrate that such soft- sediment systems, when freed from predation, usually exhibit 1) an increase in total density, 2) an increase in species richness, and 3) no tendency toward competitive exclusion by some dominant species. The currently accepted model of community organization, developed from experimental work in marine rocky intertidal communities, would predict that significant simplification of the community should occur as a consequence of intense competition in such a system where density had increased substantially following the removal of predators.
364 citations
TL;DR: Overall predation rate and ant species richness were found to be positively correlated on a latitudinal scale, but this relationship broke down at the level of habitats and microhabitats.
Abstract: Predation by ants on wasp larva baits was assessed at five latitudes from 43°N to 2°S. Rates of predation were significantly greater in the tropics; that is, a food item was exploited by ants in significantly less time in the tropics than in the temperate zone. It was also found that predation rates were higher in low second—growth vegetation than in forests and higher on the ground than on vegetation, and that these differences were more pronounced in the temperature zone than in the tropics. Rates of predation occuring on buildings were lower than in natural situations at every latitude. The number of ant species taken at the baits increased from 22 at the northernmost locality to 74 at the southernmost. In all localities but the northernmost the forest habitat produced a greater diversity of species than the field habitat. There was greater degree of microhabitat specificity among ants in the tropics than in the temperate zone. The proportion of forest canopy specialists also increased toward the tropics. Overall predation rate and ant species richness were found to be positively correlated on a latitudinal scale, but this relationship broke down at the level of habitats and microhabitats.
290 citations
TL;DR: Partial correlation analysis of grouped data from early-, mid-, and late season suggests that influential factors change with season, and in the early season, prey abundance and temperature variation account for most of the variation in spider species richness, while in mid-season, litter complexity and moisture fluctuations appear to influence richness.
Abstract: Spider communities were sampled over an artificial gradient of litter depth (created by raking) and compared to those of two other forests exhibiting natural variation in litter depth. More species of spiders were present in areas of greater depth and/or complexity in all sites. Relative abundance of Lycosidae decreased, while relative abundance of Clubionidae, Thomisidae and Gnaphosidae increased over gradients of increasing depth and complexity. Similarity of species composition between areas within a forest was related to site differences in litter depth and structure.
289 citations
201 citations
TL;DR: It is argued that savannah P. anubis has a higher rate of exchange of individuals between groups than has been recorded for the rain forest primates under consideration, and the differing rates of exchange are due to disease-related selection against traits which result in high rates of individual exchange among rain forest primate groups.
Abstract: The intestinal protozoan faunas of 11 social groups of Cercocebus albigena, 3 groups of Cercopithecus mitis, 3 groups of Cercopithecus ascanius, 2 groups of rain forest and 4 groups of savannah Papio anubis are documented. All individuals in a particular social group exhibit identical protozoan faunas. All social groups of each species, except the savannah P. anubis, exhibit intergroup differences in the composition of their protozoan faunas. The number of intestinal, protozoan species in Cercocebus albigena social groups is a function of group size. The similarity between the protozoan faunas of different C. albigena groups is related to the density of social groups and types of land tenure in particular localities. Past social history of C. albigena groups may have some influence on the level of similarity of different groups' faunas. Entrance of a nongroup member into a group of Cercopithecus mitis resulted in an increase in the species richness of the group's protozoan fauna. Group fission may result in reduction of a group's protozoan species richness. All groups of savannah Papio anubis exhibit identical protozoan faunas. I argue that this is because savannah P. anubis has a higher rate of exchange of individuals between groups than has been recorded for the rain forest primates under consideration. I hypothesize that the differing rates of exchange are due to disease-related selection against traits which result in high rates of individual exchange among rain forest primate groups. Primate social groups are functionally biological islands; the species richness of their protozoan faunas changes according to group size and levels of protozoan migration between groups.
181 citations
TL;DR: It is proposed that the greater size and morphological complexity of trees than shrubs, and than herbs in turn, accounts for these patterns in pest species richness; larger more complex hosts present a greater diversity of pest niches.
Abstract: Trees tend to have more pest species than do shrubs, which in turn have more than herbs, per unit area of geographical distribution. These patterns are shown by species/area analyses of the insect associates of 215 genera of British plants and the fungal parasites of 323 United States plant species. Within these growth-form categories some comparisons show no discernible differences in pest species richness: Angiosperm trees have approximately the same number of fungal parasites as gymnosperms, and monocot herbs have about the same number of fungal parasites as do herbs in general, in the United States. British sedges, grasses, all monocots, composites, and bog plants do not support discernably different numbers of insect species than herbs in general, per unit host range. However, other comparisons within the herb-shrub-tree categories do show differences: Ferns support fewer insect species than other herb genera in Britain, and weedy herbs support fewer fungal parasite species than climax and subclimax ...
172 citations
TL;DR: One group of insects, the bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae), are less host-specific in the tropics than in temperate regions, even though there are considerably more species present in the Tropics.
Abstract: Many groups of animals show a gradient of increasing species richness from polar to equatorial regions1,2. Theory3,4 suggests that species should be more specialised ecologically in the tropics. Most of the evidence for this comes from studies on birds5–10. Birds appear to subdivide the habitat more finely and specialise more in their food in the tropics. It has been suggested11 that tropical Papilionidae (Lepidoptera) are more specialised in their hosts than temperate species, but host specificity was considered only at the level of the plant family, and more detailed studies of a wide range of butterflies12 suggest that they are little (if at all) more specialised in their food plants in the tropics. Similarly, monogenean trematode parasites of fish show no change in the degree of host specificity at different latitudes13. Here it is shown that one group of insects, the bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae), are less host-specific in the tropics than in temperate regions, even though there are considerably more species present in the tropics. The ‘reverse’ latitudinal gradient in host specificity can be related to the greater proportion of relatively non-specific xylomycetophagous species (ambrosia beetles) in the tropics and to the greater heterogeneity of tropical forests which will make host specialisation more difficult.
162 citations
TL;DR: The niche pattern observed for this community is consistent with an inference of competitive coexistence, and measures of niche position, niche breadth and population abundance are incorporated into an analysis of community "niche pattern".
Abstract: This study examines the relationships among 4 small mammal species in 2nd-growth mesic forest on Walker Branch Watershed in eastern Tennessee, USA. Populations of Bltarinna brev- icauda, Peromyscus leucopus, Ochrotomys nuttalli and Tamias striatus were live-trapped on 9 0.36- ha grids during the summer of 1973. Eight measures of physical habitat structure were used in dis- criminant analysis of the microhabitats occupied by these 4 species. Three statistically significant discriminant functions were calculated. Each discriminant function is represented as an axis in a 3- dimensional discriminant space. These 3 axes are interpreted as vegetation type, vegetation structure and litter-soil surface characteristics. The positions of the species in the discriminant space charac- terize the microhabitat configurations of the species relative to the ecological properties attributed to the axes. Each species differs significantly from every other species on at least 1 axis. The observed species differences are conservative estimates of microhabitat (structural niche) segregation. We propose measures of niche position (i.e., exploitation specialty) and niche breadth based on the discriminant analysis. Species i is represented by a cloud of ni sample points in the discriminant space. Sample point j for species i lies the distance dij from the origin of the space. The average of these distances (di) represents the average "position" for species i relative to the origin. Because this origin represents the average of the microhabitats sampled on the watershed, and because the microhabitats actually occurring on the watershed are assumed to vary continuously, the likelihood of a species encountering favored microhabitat on Walker Branch decreases as d increases. This d is, thus, interpreted as an index of niche position relative to the average of the microhabitats sampled. Variability among the dij values for species i (vi) measures degree of specialization, a direct measure of niche breadth for species i. Our data indicate that d and v are inversely related: breadth decreases as position becomes increasingly specialized. We incorporate measures of niche position, niche breadth and population abundance into an analysis of community "niche pattern." This niche pattern characterizes the 4 species as follows: Peromyscus is an abundant generalist, well-adapted to the watershed as a whole. Ochrotomys, the only other mouse, is a relatively rare specialist, poorly adapted to the watershed. Tamias occupies an intermediate position between Peromyscus and Ochrotomys, and exhibits intermediate abundance. Although we have little data for Bl/arinna, this rare species appears to be poorly adapted to the watershed. Species differences in niche breadth appear to be determined more by the relative fre- quencies and carrying capacities of the species exploitation specialties than by the relative efficiencies with which the species exploit some critical limiting factor(s). Although we have no experimental evidence, the niche pattern observed for this community is consistent with an inference of competitive coexistence. The niche parameters of transient species which are infrequently encountered on Walker Branch are briefly discussed.
161 citations
TL;DR: Both total biomass and species richness were reduced after the 1979 winter, but the decline was only slight and greatest reductions were observed in areas low in the intertidal.
TL;DR: In this paper, the authors examined the species richness of bees and flower-visiting wasps in seasonal neotropical habitats in Costa Rica and found that within-habitat species richness was higher in tropical forests than in the temperate forests previously described.
Abstract: This study examines the species richness of bees and flower visiting wasps in seasonal neotropical habitats in Costa Rica. A total of 9231 individuals were netted at flowers. These repre- sented 192 species of bees and 138 species of wasps. Over 50W of the bee individuals were eusocial Apidae, but there were only 12% of the bee species. There was less dominance among the wasp families. Most of the species in both groups were uncommon: 50W of the bee species were represented by fewer than 8 individuals, and over 50W of the wasp species had only I or 2 individuals. Previous comparisons of the species richness of bees in tropical and temperate areas have been complicated by different sample sizes and a lack of distinguishing within- and between-habitat diver- sity components. Here, comparisons are made of within-habitat species richness for structurally similar habitats. The within-habitat species richness of bees was higher in tropical forests than in the temperate forests previously described. The tropical grassland had lower bee species richness, and it is postulated that the coevolutionary history of a habitat is an important component of bee diversity. The higher species richness of tropical forests was correlated with the abundance and diversity of animal-pollinated plants. Tropical bees were not more temporally specialized despite the longer flowering seasons, so diversity and temporal specialization were not correlated. The average flight season of tropical species was 3 times longer than that reported for bees in most temperate areas, and the turnover in species was also similar. Seasonality was correlated with the degree of species' sociality: eusocial bees were essentially aseasonal. Most seasonal bee species were encountered in the dry season. Flower visiting wasps were much more diverse in the tropical habitats than reported for temperate habitats, and they overlap with bees in resource use. Many other taxa also fed at flowers, and such diversity among competitors may be a factor in limiting bee diversity in the tropics.
TL;DR: The ichthyofauna of the Panamanian seagrass beds is significantly richer than that of similar habitats which have been studied in the Gulf of Mexico, which appears to be due in part to the influence of nearby coral reefs, which add an additional structural dimension to the habitat.
Abstract: Collections of fishes from seagrass meadows along the coast of the Republic of Panama and the Canal Zone during 1974–1975 revealed that juveniles of reefassociated predators are common in this habitat. There are also important diurnal changes in species composition: members of the families Pomadasyidae, Lutjanidae, Sciaenidae, Apogonidae and Muraenidae were noticeably more abundant in the seagrass meadows at night. Although there were significant differences in species composition and abundance among sampling sites, seasonal differences within sites appeared to be insignificant. The ichthyofauna of the Panamanian seagrass beds is significantly richer than that of similar habitats which have been studied in the Gulf of Mexico. This difference in species richness appears to be due in part to the influence of nearby coral reefs, which add an additional structural dimension to the habitat.
TL;DR: Lowering the herbivore levels may cause an intensification of exploitative competition among phytoplankton, which favors edible species and a few inedible algae like Synedra at the expense of many inedibles species that are eliminated.
Abstract: The hypothesis that herbivory plays a major role in the maintenance of high algal diversity was tested over a e-year period in polyethylene enclosures at Heney Lake, Quebec. Reduction of grazing pressure resulted in a significant decrease in the number of inedible species, whereas the diversity of edible algae remained unaffected. Lowering the herbivore levels may cause an intensification of exploitative competition among phytoplankton, which favors edible species and a few inedible algae like Synedra at the expense of many inedible species that are eliminated.
TL;DR: It was suggested that mediation of predator behavior by physical structure in seagrass meadows may play an important role in the regulation of species richness and abundances.
Abstract: The amphipod species consumed by Lagodon rhomboides represented only a small subset of the amphipod assemblage available at three seagrass habitats in Apalachee Bay, Florida (USA). Predatory preferences were related most closely to the microhabitat of prey species and were unrelated to amphipod abundances. Important prey species were all epifaunal types. Consumption of preferred amphipod species was non-selective at a site with sparse macrophyte cover, but selectivity increased with macrophyte biomass. The amphipod species that were preferentially selected as prey by pinfish correspond with those that have been suggested as being limited by fish predators. It was suggested that mediation of predator behavior by physical structure in seagrass meadows may play an important role in the regulation of species richness and abundances. Species-specific identification of prey is recommended for food-habit studies.
TL;DR: It is suggested that the number of agromyzid species on many common and widespread umbellifers is considerably below the number that could finally evolve to exploit these plants, and that guilds of specialized leaf-miners are not 'equilibrium assemblages'.
Abstract: (1) The number of species of larval agromyzids (Diptera: Agromyzidae) mining plants in the family-Umbelliferae within the British Isles is reviewed. (2) A regression of the number of agromyzid species (S) on the geographical range of each plant (measured in 10 km squares, A) (leS + 1 vs leA) is highly significant, but explains only 32% of the variance. Several other 'species-area' curves are similar in this respect. (3) Geometric mean size of the plants, leaf-form (both measures of plant 'architecture'), and whether or not they grow in aquatic habitats explains some of the residual variation, but approximately 50% remains unexplained. (4) A wide variety of other characteristics of the plants, and their associated fauna (potential competitors and natural enemies) had no detectable influence on the number of Agromyzidae. Factors examined include taxonomic isolation, whether the plants were annual, biennial or perennial, the number of species of potentially competing microlepidoptera, and the number of species of parasitoids. (5) We suggest that the number of agromyzid species on many common and widespread umbellifers is considerably below the number that could finally evolve to exploit these plants, and that guilds of specialized leaf-miners are not 'equilibrium assemblages'.
TL;DR: The first extensive empirical data on the relationship between connectance (defined as the fraction of the pairs of species which directly interact) and species richness in biological communities are presented.
Abstract: BIOLOGICAL communities differ in the number of species that they contain; in the number of interactions between species (primarily feeding and competitive relationships); and in the intensity of their interactions. We present here the first extensive empirical data on the relationship between connectance (defined as the fraction of the pairs of species which directly interact1,2) and species richness in biological communities. Our results show that connectance may decline considerably as the number of species increases.
TL;DR: Considerable evidence supported the hypothesis that environmental (climatic) unpredictability increases northwards and mainly causes the phenomenon observed, and tests suggested that low diversity is not an important cause of northern instability.
Abstract: European data from 15 long-term censuses of breeding land bird communities were analysed in order to measure community stability. Stability was here operationally defined as year-to-year persistence of community structure (total density, number of species, diversity, evenness of the species-abundance distribution, species list, and frequencies of species). Central Europe and southern Scandinavia formed a zone of fairly stable communities, but more northern communities were fairly unstable. This result contrasts with several recent arguments, but accords well with the classic dogma that instability of biological communities increases northwards in the northern hemisphere. Three theoretical explanations for the difference in stability between northern and southern communities were explored, and causal mechanisms underlying the hypotheses were specified and tested. Considerable evidence supported the hypothesis that environmental (climatic) unpredictability increases northwards and mainly causes the phenomenon observed. Gradients in productivity may, perhaps in interaction with unpredictability, also contribute to geographical differences in stability, but tests suggested that low diversity is not an important cause of northern instability.
TL;DR: It was shown that congeneric species coexist more frequently in the same habitats than could be expected from a random distribution of the available species over habitats, in agreement with the conclusion of BIRCH (1979) from a review of the field evidence.
Abstract: The history of the "principle of competitive exclusion" is briefly reviewed. Next, it is shown that taxonomically closely related (carabid) species, i.e. species in the same genus, can indeed be considered to be also ecologically closely related. This opened the possibility to test whether or not exclusion plays a demonstrable role in the distribution of species belonging to the same or to different genera over different habitats. The method used was proposed by SIMPSON (1949) and applied for the first time by WILLIAMS (1951). With the help of the pitfall-catches of 149 carabid species during nine years and in 73 different habitats, and by using three, different "values" it could thus be shown that congeneric species coexist more frequently in the same habitats than could be expected from a random distribution of the available species over habitats. This "coexistence principle" was further illustrated by two examples from habitats studied during a number of years. It could also be shown that interaction groups of coexisting congeneric (carabid) species do not die out more frequently than those of species belonging to different genera, not even in the course of a century. These findings are thus in agreement with the conclusion of BIRCH (1979) from a review of the field evidence, that "competitive exclusion" must be considered an only exceptional outcome of the possible interactions between species. The most parsimonious hypothesis for understanding the findings discussed in this paper therefore is: Taxonomically closely related (carabid) species are also ecologically closely related, and will thus more often than not be found coexisting in the same habitats.
TL;DR: Total within stand diversity and beta diversity were highest in the tropical forests and a higher percentage of temperate species were classified as colonizers as opposed to the tropical species where the majority were noncolonizers; but tendency to colonize appears to be inversely related to the amount of litter present in a habitat.
Abstract: Species richness and diversity of litter mites were measured in 3 vegetative stands in Wyoming and in Costa Rica (a pine forest, a broad-leaved forest and a field) by sampling the natural litter and by experimentally manipulating the type (pine, broad-leaved and field litter) and amount (100 g dry weight/600 cm2 plot) of litter present within each stand. Within sample species richness of the experimental plots was the same in all 4 forests (12-14 species/100 g litter) but the 2 fields supported significantly fewer species (5/100 g). In the natural forest litter, within sample richness ranged from 13 species (Costa Rica forest) to 27/600 cm2 sample (Costa Rica pine); but again both fields were significantly less rich (4 and 6 species). Mite diversity (H') in the fields also was < the forests in both natural and experimental litter. Total within stand diversity and beta diversity were highest in the tropical forests. Also, a higher percentage of temperate species were classified as colonizers as opposed to the tropical species where the majority were noncolonizers; but tendency to colonize appears to be inversely related to the amount of litter present in a habitat.
TL;DR: Host plants and animals and the parasite species which attack them have recently been shown to conform to the species-area relation consistent with the theory of island biogeography, and it is suggested that parasite species richness asymptotically approaches an upper limit established mainly by host "island" size.
Abstract: Host plants and animals and the parasite species which attack them have recently been shown to conform to the species-area relation consistent with the theory of island biogeography (Dritschilo et al., 1975; Opler, 1974; Seifert, 1975; Strong, 1974a, b; Strong and Levin, 1975; Strong et al., 1977; Tepedino and Stanton, 1976). This pattern, supplemented by additional statistical analysis in some examples (Dritschilo et al., 1975; Strong, 1974q, b; Strong et al., 1977) has suggested that parasite species richness asymptotically approaches an upper limit established mainly by host "island" size and that recent evolutionary age has an insignificant effect on the number of species which attack the host. Although a logarithmic fit to the species-area relation cannot be taken as a confirmation of the equilibrium theory per se (Lynch and Johnson, 1974; Simberloff, 1974, 1976), and although there are some minor statistical deficiencies in the data presentation (Haas, 1975; Kuris and Blaustein, 1977), this relation is a robust empirical generalization with wide application. Host island studies have been of two types based on what is defined as an island and the time scale involved in approach to the asymptote. In one type, each individual host or a small patch of hosts is taken as an island with the species pool being all of those species known to attack that host in that part of its range (Brown and Kodric-Brown, 1977; Price, 1976; Seifert, 1975; Simberloff, 1976a; Strong, 1974b, 1976; Strong et al., 1977; Tepedino and Stanton, 1976; Ward and Lakhani, 1977). Area effects are due to the size of individual hosts or host patches, and distance effects are due to the distance between hosts or patches. All species on an individual host or patch for a given sampling episode must be assessed; and if equilibrium is established, turnover would occur in ecological time. Often, particularly in areas with high seasonality, the condition of the host changes through time, and an asymptote is never reached before the end of the season, for example in cushion plants in Wyoming (Tepedino and Stanton, 1976), in soybeans in Illinois (Price, 1976), and in small salt marsh islands in Florida (Rey and McCoy, pers. comm.).
TL;DR: Between-habitat faunal changes in summer were primarily clinal, following a gradual change in sediment texture, and a strong correlation between the Shannon-Weaver diversity and sediment texture existed in summer, with diversity increasing due to decreasing species dominance and increasing species richness as sediments became coarser.
TL;DR: Mngazana is a rich estuary dominated by mangroves and containing a diversity of both invertebrates and fish, which has affinities with the tropics in summer, while in winter many warm-temperate species increase in numbers.
Abstract: Mngazana is a rich estuary dominated by mangroves and containing a diversity of both invertebrates and fish. Its richness is mainly due to favourable physical conditions. The invertebrate fauna includes temperate, tropical, and subtropical species, predominating in the lower reaches, middle reaches and head respectively. The fish have affinities with the tropics in summer, while in winter many warm-temperate species increase in numbers. In comparison with the fauna of soft substrates, that of rocks has a higher percentage of stenohaline and estuarine forms, and a more restricted distribution. The rocky habitat in estuaries favours greater specialization with respect to salinity tolerance. A high percentage of the biomass of invertebrates in soft substrates consists of detritivores, and the biomass is related to the organic content of the substrate. Mangrove mud has the hlghest organic content and supports the highest biomass, but few species can tolerate the conditions there. Mangroves are probably the ma...
TL;DR: Overall, the bird community structure in different types of forests was similar and the proportion of residents was higher and tropical migrants lower in coniferous than in nearby deciduous forests.
Abstract: Eight forest plots were studied, some of them for five years. Bird community population densities fluctuated from year to year, but the density differences between habitats remained approximately the same. Densities and bird species richness of different forest plots were closely correlated. Both bird community densities and species richness were most successfully predicted from the proportion of the basal tree and shrub area standing dead. Vertical foliage structure and/or number of species of trees and shrubs were minor additional factors. It is suggested that vertical foliage structure is correlated with ecosystem productivity. Food availability is suggested as the ultimate determinant of variations in local bird species richness and community density. The proportion of Turdinae decreased and that of Sylviidae increased with increasing total bird population density. Overall, the bird community structure in different types of forests was similar. The proportion of residents was higher and tropical migrants lower in coniferous than in nearby deciduous forests. Only about 10% of the bird individuals in the coniferous forests were tropical migrants in contrast to about 60% in northeastern North America.
TL;DR: A simple null hypothesis is suggested as an alternative to time-stability; that a species-area relationship is sufficient to account for the observed pattern of species richness.
Abstract: The data base and four basic assumptions underlying Sanders' formulation of the stability-time hypothesis are re-examined. We present data and analyses which suggest that: (1) the sampling techniques varied among the regions; (2) recalculation of the rarefaction curves, including the variance asso- ciated with an expected number of species, blurs any distinctions that existed among the regions; (3) the variation in the polychaete-bivalve fraction of the total fauna in the samples is so high as to cast doubt on general conclusions drawn from any comparisons of differences in species richness among these two groups; and (4) the percentage of silt and clay in the sediments from which the samples were drawn is highly variable and the distribution of polychaetes and bivalves is patchy; there is a significant negative correlation between percent silt and polychaete species numbers. Both of the preceding suggest that more than a single habitat was sampled. We suggest a simple null hypothesis as an alternative to time-stability; that a species-area relationship is sufficient to account for the observed pattern of species richness. Areal extent of the estuary, bay, shelf and deep sea regions of the Gay Head-Bermuda transect accounts for as much as 99% of the variation in polychaete species numbers. Two possible mechanisms underlying an area effect (variation in habitat heterogeneity and a sampling phenomenon) are probably important in the benthic environment.
TL;DR: In this paper, the authors investigated the flowering plant species richness of twenty-six vacant urban lots which varied in age, size, isolation from other lots, and in intensity of 'weed control' (sporadic seasonal mowing), in the light of equilibrium island biogeographic theory.
Abstract: The flowering plant species richness of twenty-six vacant urban lots which varied in age, size, isolation from other lots, and in intensity of 'weed control' (sporadic seasonal mowing), was investigated in the light of equilibrium island biogeographic theory. Species richness for all lots increased logarith- mically with lot age. The species richness of lots 40 months and older, each of which had been mown at least once, did not increase with age, and was posi- tively related to lot area and negatively related to measures of lot isolation. These results suggest that species richness had reached or was nearing equilibrium in these older-mown lots, possibly due to mowing and immigration-extinction phenomena, and that other lots are significant sources of colonists. That the slope of a plot of log-species richness against log-area for the older-mown lots is similar to that for oceanic islands suggests that these lots have immigration- extinction rates similar to those of true islands.
TL;DR: The effects of 2-lane and 4-lane highways on forest birds were examined along Interstate 95 in northern Maine during 1975-77 to determine whether highway use caused a change in bird populations in forest habitat outside the ROW, and which species were adversely or favorably affected by the highway.
Abstract: The effects of 2-lane and 4-lane highways on forest birds were examined along Interstate 95 (1-95) in northern Maine during 1975-77. Total numbers of breeding birds in forest areas near the highway were not significantly different from those at greater distances. Four species were less abundant near the highway, after accounting for variations in habitat, and 6 other species were more abundant. Addition of species nesting along the forest-right-of-way (ROW) edge caused a slight increase in species richness and diversity. The ROW and median strip along 4-lane highway supported half as many breeding birds as an equal amount of forest habitat. Densities of breeding birds in the ROW along 2-lane highway were 79% of those in forest habitats. J. WILDL. MANAGE. 43(2):421-427 The influence of a highway on wildlife begins with destruction of habitat, as pavement and grass replace existing plant communities. Where these are forest communities the change is dramatic, and for forest wildlife the area may no longer be suitable. Subsequent use of the highway may disturb certain species of wildlife in areas near the road, rendering additional habitats unsuitable. On the other hand, habitats created in the rightof-way (ROW) and developing along the forest-ROW edge may support species not present in forest communities. This study examined the effects of 1-95 on breeding bird populations in forest habitats in northern Maine. The objectives were to determine: (1) the size of the population lost through removal of forest habitat encompassed by the highway and ROW; (2) whether highway use caused a change in bird populations in forest habitat outside the ROW; and (3) which species, if any, were adversely or favorably affected by the highway. I am grateful to the Maine Department of Transportation for financial and technical assistance. V. B. Richens, M. W. Coulter, R. B. Owen, Jr., and R. C. Eckhardt, of the University of Maine at Orono, provided editorial assistance. The following persons helped collect field data: Nona Famous, Norman Famous, Linda Wright, Wesley Wright, and Deborah Palman. This paper is a contribution of the Maine Cooperative Wildlife Research Unit: U.S. Fish and Wildlife Service, Maine Department of Inland Fisheries and Wildlife, University of Maine, and Wildlife Management Institute, cooperating.
TL;DR: In this paper, the authors describe the forest vegetation along an altitudinal transect running from 158 m to 1220 m (treeline) in the Mount Field National Park, Tasmania.
Abstract: The aim of this study was to describe the forest vegetation along an altitudinal transect running from 158 m to 1220 m (treeline) in the Mount Field National Park, Tasmania. Eighteen 1 ha plots were sampled along this transect, using a modified point-centred quarter method for species composition and density. Size frequency distributions were used to calculate basal areas. Estimates of relative density, frequency and basal area for each species were combined in to an importance value. The altitudinal ranges of all woody species were determined. The altitudinal temperature lapse rate was measured, and data on soil pH obtained.
The initial ‘direct gradient’ analysis revealed relatively well marked discontinuities in the vegetation which were further examined by ordination and classification techniques. The latter provided a simple threefold classification into altitudinal zones. The lower zone reaches from the Park entrance (158 m) to between 600 and 670 m, and comprises tall open forest dominated by Eucalyptus regnans and/or E. obliqua and with a ‘wet sclerophyll’ understorey characterized by Olearia argophylla. The middle zone stretches from c. 670 to 940 m and comprises closed rainforest or ‘mixed’ forest (i.e. with senescent emergent eucalypts) dominated by Nothofagus cunning hamii and Atherosperma moschatum. This zone is characterized by the absence of O. argophylla and the presence of Phyllocladus aspleniifolius. The upper part of this zone constitutes an interdigitating transition to the subalpine forests, usually dominated by E. coccifera and occurring on suitable sites between c. 880 m and the timberline. The transition to subalpine forests is associated with a marked decline in basal area.
Species richness (of woody plants) increases with altitude to reach a peak in the sub-alpine zone. This trend is the reverse of that normally encountered elsewhere in the world, and is mainly due to relatively high α and β diversities in the shrub stratum of this zone.
The significance of fires, aspect and substrate is discussed in relation to the variations in composition within each zone. The low diversity of Nothofagus-dominated rainforest is thought to be due, in part, to the intense competitive thinning in the eucalypt re-growth phase following burning, and the subsequent ‘capture’ of the Eucalyptus niche by Nothofagus. It is speculated that, in Tasmania, the downhill migrations during the cooling phases of the Pleistocene were associated with extinctions of lowland forest taxa, while uphill migrations during warming phases were associated with speciation on the plateaux of the present subalpine zone. This hypothesis implies that the relative proportions of land area available at different altitudes, now and in the past, have determined the relative rates of speciation and extinction, and hence the altitudinal gradients of species richness.
TL;DR: It appears that the Panamanian sea grass meadows are effectively more structurally complex than those in Florida, due to the presence of nearby coral reefs which support several invertebrate and many fish species which treat the coral reef - seagrass habitat as a single entity.
Abstract: Monthly data on motile epibenthic macroinvertebrates inhabiting subtidal tropical (Panama') and warm temperate (U.S.A.) turtlegrass (Thalassia testudinum) meadows were gathered to test the hypothesis that structurally similar habitats will support similar numbers of species, regardless of latitude. Taken at face value these data do not support the hypothesis; species richness was significantly greater in Panama'. However, based on observational evidence as well as previously published natural history information it appears that the Panamanian sea grass meadows are effectively more structurally complex than those in Florida. This is primarily due to the presence of nearby coral reefs which support several invertebrate and many fish species which treat the coral reef - seagrass habitat as a single entity. In addition, many more vagrant species were taken in the tropical collections, as a result of the proximity of many other distinct habitats in Panama. Differences in total macroinvertebrate abundance between the two study areas seem to reflect differences in seasonal fluctuations of their fish predators, and in the species composition and biological activities of the fishes themselves. The predation and disturbance hypotheses can also be advanced to explain the results of this study. Although neither one of them seems to be correct, both are compatible with the data presented here. This suggests caution in accepting the mechanisms implied by hypotheses making very general predictions on community organization, when no independent information exists to verify them.
TL;DR: The mean annual concentration of oxidants (which averaged 18 parts per 100 million on the 11 most polluted sites) is statistically indicated as the most likely causal factor for the reduced cover of native species of coastal sage scrub in certain southern Californian sites.
Abstract: Causes for the reduced cover of native species of coastal sage scrub in certain southern Californian sites wvere sought among 43 habitat variables. The mean annual concentration of oxidants (which averaged 18 parts per 100 million on the 11 most polluted sites) is statistically indicated as the most likely causal factor. Sites of high oxidant levels in the region are also characterized by declining species richness and equitability.