Proportional Abundance Of Species Research Articles

Deposited sediment influences occurrence of functional traits of stream fishes

AbstractTo better understand stream‐fish sensitivity to fine sediment, we documented assemblage‐wide responses by selected traits along a sedimentation gradient. We then discuss the management implications of these ‘dose–response’ relations in the contexts of biotic assessments and conservation of sediment‐sensitive species. We identified a spatial gradient in sediment deposition among streams within the upper Piedmont of the Roanoke River basin in North Carolina and Virginia. We assessed fine‐sediment sensitivity of 81 species based on eight species traits stratified by four attributes: food preference, feeding location, spawning substrate and spawning behaviour. We then ranked each trait and scored each species with respect to its sediment sensitivity. Using data from electrofishing surveys during 2018–2019, we calculated proportional abundances of traits observed at 30 sites throughout the study area and grouped species by their aggregate sensitivity scores. We assessed relations between embeddedness and silt cover and occurrences of species and traits using a combination of regression and ordination approaches. All traits tested responded to embeddedness or silt cover, or both. Feeding traits exhibited the strongest responses to embeddedness, while reproductive traits exhibited the strongest responses to silt cover. Our findings indicate that negative responses of the probability of presence for high‐sensitivity traits to embeddedness and silt cover were linear, with no apparent thresholds. Additionally, proportional abundances of species with multiple high‐sensitivity traits were inversely related to embeddedness and silt cover. Overall, our findings regarding population‐level responses to sedimentation were consistent with our findings for trait‐specific responses. Our analysis of species sensitivity to fine sediment corroborated the patterns we saw in our trait‐specific analyses, indicating that population responses to sedimentation can be predicted from combinations of species traits. The ‘dose–response’ relations we documented may be applicable to managing sediment impacts on fishes, especially in the contexts of biotic assessments and conservation of sediment‐sensitive species.

On the proportional abundance of species: Integrating population genetics and community ecology

The frequency of genes in interconnected populations and of species in interconnected communities are affected by similar processes, such as birth, death and immigration. The equilibrium distribution of gene frequencies in structured populations is known since the 1930s, under Wright’s metapopulation model known as the island model. The equivalent distribution for the species frequency (i.e. the species proportional abundance distribution (SPAD)), at the metacommunity level, however, is unknown. In this contribution, we develop a stochastic model to analytically account for this distribution (SPAD). We show that the same as for genes SPAD follows a beta distribution, which provides a good description of empirical data and applies across a continuum of scales. This stochastic model, based upon a diffusion approximation, provides an alternative to neutral models for the species abundance distribution (SAD), which focus on number of individuals instead of proportions, and demonstrate that the relative frequency of genes in local populations and of species within communities follow the same probability law. We hope our contribution will help stimulate the mathematical and conceptual integration of theories in genetics and ecology.

Quantifying Assemblage Turnover and Species Contributions at Ecologic Boundaries

Not all boundaries, whether stratigraphical or geographical, are marked by species-level changes in community composition. For example, paleodata for some sites do not show readily discernible glacial-interglacial contrasts. Rather, the proportional abundances of species can vary subtly between glacials and interglacials. This paper presents a simple quantitative measure of assemblage turnover (assemblage turnover index, ATI) that uses changes in species' proportional abundances to identify intervals of community change. A second, functionally-related index (conditioned-on-boundary index, CoBI) identifies species contributions to the total assemblage turnover. With these measures we examine benthonic foraminiferal assemblages to assess glacial/interglacial contrasts at abyssal depths. Our results indicate that these measures, ATI and CoBI, have potential as sequence stratigraphic tools in abyssal depth deposits. Many peaks in the set of values of ATI coincide with terminations at the end of glaciations and delineate peak-bounded ATI intervals (PATIs) separated by boundaries that approximate to glacial terminations and to transgressions at neritic depths. These measures, however, can be used to evaluate the assemblage turnover and composition at any defined ecological or paleoecological boundary. The section used is from Ocean Drilling Program (OPD) Hole 994C, drilled on the Blake Ridge, offshore SE USA.

Variation in beetle community structure across five microhabitats in Australian tropical rainforest trees

Abstract Beetles (Coleoptera) are the most species‐rich and ecologically diverse group of organisms in tropical rainforest canopies. This study reports on the distribution of the beetle community on five discrete canopy microhabitats (mature leaves, new leaves, flowers, fruit, and suspended dead wood) on 23 tree species in an Australian tropical rainforest. We tested the hypothesis that the beetle fauna will vary in community structure between microhabitats based on differences in the quantity, quality as a food source and availability of different canopy microhabitats. There was substantial variation in dominant beetle families in terms of abundance between microhabitats. All assemblages contained a high number of rare species, with flowers supporting most of the more abundant species. Consequently, the flower‐visitor assemblage was more heterogeneous than expected by chance, whereas the mature leaf assemblage was more even in the proportional abundances of species than expected. The distribution of singletons was also non‐random and flowers, which are spatially and temporally restricted, supported fewer singletons than expected by chance, whereas mature leaves and dead wood supported more. These differences were insensitive to beetle feeding guild, and are most likely related to variation in microhabitat distribution and availability, which influenced relative sampling efforts and the probability of random microhabitat/beetle associations. High dissimilarity in species overlap between microhabitats suggests that each microhabitat attracts a unique beetle assemblage, which has an additive effect on canopy‐wide species richness patterns. Consequently, biodiversity studies that focus on single microhabitats may inadvertently omit a large proportion of canopy species.

SURVEYING NATURAL POPULATIONS: QUANTITATIVE TOOLS FOR ASSESSING BIODIVERSITY.: By Lee-Ann C. Hayek and Martin A. Buzas. Columbia University Press, New York, USA, 2nd edition, ISBN 978-0-231-14620-3, 590 p. US$85.00.

Ecology and paleoecology have over the past 40 or so years undergone a profound quantitative revolution, and techniques for assessing biodiversity have not been excluded. It is no longer adequate to assess the diversity of a community by stating only the number of species it contains; such a statistic gives equal weight to both common and rare species and ignores the effect of sample size on species numbers. Likewise, two or more communities cannot be compared on the basis of their number of species alone. Instead, one has at least to ask how the proportional abundances of species at the two sites compare. This begs the question, how can the structural differences between two communities be quantified? Also, what is the ecological significance of the difference between two community structures? Consequently, anybody entering (paleo)ecology nowadays must be comfortable not only with ecological concepts but also with at least the basic statistical techniques for measuring biodiversity. As noted by McKillup and Dyar (2010), such statistical methods can be used both to test and generate hypotheses. Older publications explaining statistical measures of diversity are many and not always easy to use. Magurran (1988, 2004) did sterling …

Diversity patterns in macrobenthos across a continental slope in the NE Atlantic

Different estimates were used to assess the diversity of the total macrofauna and its major taxonomic groups separately from a broad bathymetric range at a site in the NE Atlantic. In the Goban Spur region, a transect was sampled from the shelf to the abyssal plain over a depth range from ∼200 to ∼4500 m and in the Porcupine Sea Bight two stations were sampled (at 3670 m and 4115 m). Species diversity (the number of species per number of individuals) increased with increasing water depth, both when expressed as Hurlbert's E(S n ) and as Shannon's H′ log e . The expected number of species in a 100-individual sample E(S 100) of total macrofauna increased from 30 on the shelf to 68 on the abyssal plain. Evenness (the proportional abundance of species), estimated with Shannon's J′, also increased with water depth from 0.66 to 0.91, whereas dominance (Simpson's D) decreased from 0.09 to 0.01. Species richness (the number of species per unit of area), however, showed a parabolic pattern with a peak at the upper slope. The largest number of species was found at the slope station at 1425 m (232 species within 0.66 m 2). It is argued that species richness is not a synonym of species diversity, but that species richness depends both on species density (which decreases with increasing water depth) and on species diversity. Across the whole bathymetric range (∼200 to ∼4500 m) a total of 696 species within 8327 specimens in a total sampled area of 4.12 m 2 were counted, yielding mean values of ∼12 individuals per species and ∼169 species per m 2. Different communities were found to exist on the shelf, slope and abyss. It is suggested that this could have been caused by different selection processes. Differences in life-history strategies and organic-matter supply could (at least partly) explain the different community structures and diversity patterns found along the depth gradient.

A Calibrated Index for the Measurement of Evenness

Until now, Alatalo's modified Hill's ratio F2,1 has been the most adequate evenness index for general application, because: (a) it is little affected by sampling bias and chance variations in the number of species appearing in the samples; and (b) its values depend only and unambiguously upon evenness. In this paper, it is postulated that only for two-species communities it is always possible to know a priori the exact expected evenness values, and a simulated gradation of two-species communities showing all possible species-abundance relationships is used to evaluate F21. The evaluation showed that F2,1 has two major shortcomings, namely: (1) the index markedly overvalues evenness; and (2) the index's values show a decidedly nonlinear relationship to evenness. Therefore, it is proposed that F2r1 be replaced by a calibrated version of the same index, to be named G2 1, that is written as G2,I (arcsin F2,1/90)F2 1, when F2,1>V/1/2; and as G2,1 = F213, when F2,1 Vl/2; where F2,1 = (N2-1)1(Nl-1), where N2 = 1// and N1 -= exp H', where A = 2p2 and H' = -Epi In Pi, where Pi = proportional abundance of species i. G2,1 retains the advantages of F2 ,1, but lacks its two major shortcomings. Because G2,1 is independent of species richness, the calibration based on two-species communities holds valid for communities of more species. Applied to gradations of species-richer communities, G2,1 also shows a superior behavior. In addition, for those needing very accurate values of G2,1, an algorithm to accomplish such an objective is provided.

Precipitation and the relative abundances of desert winter annuals: a 6-year study in the northern Mohave Desert

The relationship between winter annual plants and the amount and timing of precipitation was studied for 6 years in Rock Valley, Nevada, U.S.A. Sixty-two annual species, whose year-to-year densities commonly varied 100-fold, were encountered in sampling quadrats. While dominance–diversity curves varied markedly between years, the similarity in relative abundances of annuals between years was correlated with differences in September–October precipitation of the previous fall; thus, in a comparison of years, the more similar the amount of precipitation in the early fall months, the more similar the relative abundances of annuals. Between-year differences in the total amount of fall and spring precipitation, or in precipitation in November-December or January-February, were not related to compositional similarity. Annual composition was not related to that of the previous year. The proportional abundance of species varied less than did their absolute abundances. These results suggest that compositional dynamics of annual plants in the Mohave Desert are keyed to processes that affect germination.