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Abundance and patchiness of Chrysaora quinquecirrha medusae from a high-frequency time series in the Choptank River, Chesapeake Bay, USA

DOI:10.1007/s10750-016-3060-8
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Jacqueline Tay at University of Maryland, College Park
Jacqueline Tay
Raleigh R. Hood
Raleigh R. Hood
Raleigh R. Hood
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Abstract and Figures

Despite strong control over marine plankton dynamics and negative impacts on human activities, jellyfish are not well quantified due primarily to sampling difficulties with nets. Therefore, some of the longest records of jellyfish are visual shore-based surveys. As surface counting is inexpensive and simple, it is of interest to determine what can be learned from such records as well as the usefulness of the method. We analyzed a 4-year high-frequency time series of Chrysaora quinquecirrha medusa counts collected using three sampling methods in the Choptank River, Chesapeake Bay. Medusa abundance was modeled by change points and was highly correlated between the sampling methods. The remaining signal was random, and indices of aggregation [fit to the Poisson distribution, Taylor’s Power Law (TPL), and Morisita’s Index] indicated that medusae were aggregated. TPL suggested that patches grew in the number of individuals as abundance increased. Additionally, a simple conceptualization of where the time series sampled in space revealed that the upper bound of patch size was on the order of kilometers. Our results enhance the knowledge of local C. quinquecirrha abundance and patchiness, alluding to processes that generate these patterns. This study also provides direction for improving population monitoring from visual shore-based surveys.
a Chesapeake Bay, USA with the sampling location at Horn Point Laboratory (HPL) in the Choptank River denoted by the dot.b Counts of medusae were collected using three sampling methods—two surface counting (dock and visual) methods and a vertical net haul (net). The values reflect the dimensions that are sampled by each of the methods. To compare the abundances sampled by surface (dock and visual) counts with those sampled by net counts, a minimum, 0.1 m, and maximum, 1 m, depth was used to calculate maximum and minimum abundances, respectively
a Chesapeake Bay, USA with the sampling location at Horn Point Laboratory (HPL) in the Choptank River denoted by the dot.b Counts of medusae were collected using three sampling methods—two surface counting (dock and visual) methods and a vertical net haul (net). The values reflect the dimensions that are sampled by each of the methods. To compare the abundances sampled by surface (dock and visual) counts with those sampled by net counts, a minimum, 0.1 m, and maximum, 1 m, depth was used to calculate maximum and minimum abundances, respectively
… 
a Ratio of medusa numbers sampled from the visual and net count methods separated into morning and evening samples. A higher proportion of medusae are found in the surface in the evening than in the morning (Wilcox = 40610, P = 1.92 e−05). b Medusae counts sampled by the net, showing that the difference in a is not due to difference in water column counts between the morning and evening (Wilcox = 90,102, P = .67). Boxplots for both panels show median, interquartile range, and extreme values
a Ratio of medusa numbers sampled from the visual and net count methods separated into morning and evening samples. A higher proportion of medusae are found in the surface in the evening than in the morning (Wilcox = 40610, P = 1.92 e−05). b Medusae counts sampled by the net, showing that the difference in a is not due to difference in water column counts between the morning and evening (Wilcox = 90,102, P = .67). Boxplots for both panels show median, interquartile range, and extreme values
… 
Twice daily Chrysaora quinquecirrha medusa counts from Horn Point Laboratory from 2005 to 2008 for three different sampling methods (dock, visual, net). Dotted vertical lines represent change points detected using the Segmentor3IsBack package (Cleynen et al., 2014) in R. Numbers refer to segment numbers
Twice daily Chrysaora quinquecirrha medusa counts from Horn Point Laboratory from 2005 to 2008 for three different sampling methods (dock, visual, net). Dotted vertical lines represent change points detected using the Segmentor3IsBack package (Cleynen et al., 2014) in R. Numbers refer to segment numbers
… 
Autocorrelation function for each 2006 segment for dock counts. Lag is in units of sampling points (2 sampling points per day). Blue dashed lines denote significance (P = .05). Most segments had no significant autocorrelation. Segment 2 in 2006 was an exception and showed high correlation at lag 2
Autocorrelation function for each 2006 segment for dock counts. Lag is in units of sampling points (2 sampling points per day). Blue dashed lines denote significance (P = .05). Most segments had no significant autocorrelation. Segment 2 in 2006 was an exception and showed high correlation at lag 2
… 
Linear regressions of abundance as collected by different sampling methods. Dotted line represents 1:1 line that is expected if two methods give the same estimate of abundance. a Regression between abundances in number m⁻² collected by the two surface counting methods. The slope was not significantly different from 1. b Regression between the abundances in number m⁻³ collected by the net count and the surface counting methods. Because the depth to which medusae were observed from surface counting was ambiguous, a minimum, 0.1 m, and maximum, 1 m, depth were used to calculate a maximum (high) and minimum (low) abundance, respectively, for the two surface counting methods. The abundances were significantly related (see text)
+5
Linear regressions of abundance as collected by different sampling methods. Dotted line represents 1:1 line that is expected if two methods give the same estimate of abundance. a Regression between abundances in number m⁻² collected by the two surface counting methods. The slope was not significantly different from 1. b Regression between the abundances in number m⁻³ collected by the net count and the surface counting methods. Because the depth to which medusae were observed from surface counting was ambiguous, a minimum, 0.1 m, and maximum, 1 m, depth were used to calculate a maximum (high) and minimum (low) abundance, respectively, for the two surface counting methods. The abundances were significantly related (see text)
… 
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PRIMARY RESEARCH PAPER
Abundance and patchiness of Chrysaora quinquecirrha
medusae from a high-frequency time series
in the Choptank River, Chesapeake Bay,
USA
Jacqueline Tay .Raleigh R. Hood
Received: 19 May 2016 / Revised: 18 October 2016 / Accepted: 16 November 2016 / Published online: 7 December 2016
ÓSpringer International Publishing Switzerland 2016
Abstract Despite strong control over marine plank-
ton dynamics and negative impacts on human activ-
ities, jellyfish are not well quantified due primarily to
sampling difficulties with nets. Therefore, some of the
longest records of jellyfish are visual shore-based
surveys. As surface counting is inexpensive and
simple, it is of interest to determine what can be
learned from such records as well as the usefulness of
the method. We analyzed a 4-year high-frequency
time series of Chrysaora quinquecirrha medusa
counts collected using three sampling methods in the
Choptank River, Chesapeake Bay. Medusa abundance
was modeled by change points and was highly
correlated between the sampling methods. The
remaining signal was random, and indices of aggre-
gation [fit to the Poisson distribution, Taylor’s Power
Law (TPL), and Morisita’s Index] indicated that
medusae were aggregated. TPL suggested that patches
grew in the number of individuals as abundance
increased. Additionally, a simple conceptualization of
where the time series sampled in space revealed that
the upper bound of patch size was on the order of
kilometers. Our results enhance the knowledge of
local C. quinquecirrha abundance and patchiness,
alluding to processes that generate these patterns. This
study also provides direction for improving population
monitoring from visual shore-based surveys.
Keywords Abundance Aggregation Patchiness
Jellyfish Gelatinous zooplankton Time series
Introduction
There is growing interest in jellyfish, among the
scientific community as well as the general public, as
we learn more about their strong control over marine
plankton dynamics (Richardson et al., 2009; Robinson
et al., 2014) and as their negative impacts on human
commercial and recreational activities increase (Pur-
cell et al., 2007; Purcell, 2012). In Chesapeake Bay,
the scyphozoan medusa, Chrysaora quinquecirrha
(Desor, 1848), is a keystone predator that consumes
crustacean mesozooplankton, fish eggs and larvae, and
ctenophores (Feigenbaum & Kelly, 1984; Purcell
et al., 1994; Purcell & Cowan, 1995; Purcell, 1997;
Purcell & Decker, 2005), strongly impacting the flow
of carbon within the food web (Baird & Ulanowicz,
1989; Libralato et al., 2006). Aside from the conse-
quences for fisheries, C. quinquecirrha is a common
nuisance to swimmers and watermen, and their blooms
Handling editor: Jo
¨rg Dutz
Electronic supplementary material The online version of
this article (doi:10.1007/s10750-016-3060-8) contains supple-
mentary material, which is available to authorized users.
J. Tay (&)R. R. Hood
Horn Point Laboratory, University of Maryland Center for
Environmental Science, 2020 Horns Point Road,
Cambridge, MD 21613, USA
e-mail: jtay@umces.edu
123
Hydrobiologia (2017) 792:227–242
DOI 10.1007/s10750-016-3060-8
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... Due to their gelatinous nature, medusae are difficult to sample by net and may be injured if not handled with care (Tay and Hood, 2017). Some of the longest records of jellyfish abundance are shore-based surveys that may not be representative of the entire water column, especially in deeper water and when there are distinct hydrological features such as pycnoclines that may aggregate or restrict the vertical distribution of medusae (Graham et al., 2003;Rakow and Graham, 2006;Suzuki et al., 2016;Tay and Hood, 2017). ...
... Due to their gelatinous nature, medusae are difficult to sample by net and may be injured if not handled with care (Tay and Hood, 2017). Some of the longest records of jellyfish abundance are shore-based surveys that may not be representative of the entire water column, especially in deeper water and when there are distinct hydrological features such as pycnoclines that may aggregate or restrict the vertical distribution of medusae (Graham et al., 2003;Rakow and Graham, 2006;Suzuki et al., 2016;Tay and Hood, 2017). Many surveys also use fixed stations, that may provide only a limited view of the population as changes in flow will change the observable population, causing observer bias to pick out patterns that may not actually exist (Tay and Hood, 2017). ...
... Some of the longest records of jellyfish abundance are shore-based surveys that may not be representative of the entire water column, especially in deeper water and when there are distinct hydrological features such as pycnoclines that may aggregate or restrict the vertical distribution of medusae (Graham et al., 2003;Rakow and Graham, 2006;Suzuki et al., 2016;Tay and Hood, 2017). Many surveys also use fixed stations, that may provide only a limited view of the population as changes in flow will change the observable population, causing observer bias to pick out patterns that may not actually exist (Tay and Hood, 2017). Long-term records of medusa presence and abundance are necessary to determine whether populations cycles are changing in response to environmental drivers. ...
What Drives Jellyfish Population Cycles? Influence of Climate and Environment on the Complex Life Histories of Scyphozoans
Thesis
  • Jan 2022
Jellyfish population cycles and bloom events occur at global, regional, and local scales. Understanding what causes these cycles now and in the future is a major question in jellyfish bloom research, because of the potential impacts on ecosystem function and services. Most bloom forming scyphozoan jellyfish have complex life histories involving a long-lived asexually reproducing benthic polyp and a sexually reproducing pelagic medusae. Environmental and climate factors affect each life stage, but we do not fully understand how these variables drive life stage transition, or how demographic differences in survival, growth and fecundity translate into visible jellyfish outbreaks. We undertook a comprehensive laboratory and field-based study of the physicochemical conditions that control survival, fecundity and phase transition of the different life stages of scyphozoan jellyfish. Through this research, we examine the effects of environmental drivers on jellyfish population cycles and life stage transition. Modifications to estuaries through the construction of barrages alter the natural dynamics of inhabitant species by controlling freshwater inputs into those systems, driving the presence and absence of medusae from estuaries. As well as this, we explore how environmental conditions translate into reproductive success or failure in temperate populations from the medusa to the polyp life stage, demonstrating that early polyp growth rates are strongly linked to their thermal environment and highlighting a potential marine heatwave event. We examine not only the effects of temperature and other climate drivers on scyphozoan jellyfish growth, survival and reproduction, but also whether epigenetic transgenerational effects can drive acclimation to warmer summer temperatures in the short term in the context of a warming ocean. No parental effects were observed in the first or second generation, and in the third generation the transgenerational effects of temperature were subtle and appeared most strongly in cooling scenarios. Finally, within the setting of anthropogenically-driven climate change, we demonstrate for the first time that A. aurita polyps require a minimum period of cooler temperatures to strobilate, contradicting claims that jellyfish populations will be more prevalent in warming oceans, specifically in the context of warmer winter conditions. To answer these questions, we chose the common, or moon jellyfish Aurelia aurita as our primary experimental organism. However, we expanded our research to other species to demonstrate how they may vary in both environment and response to forcing factors as compared to a ‘typical’ model species. This thesis highlights the importance of examining each population within the context of their environment, and advances our understanding of how the climate and environment affect jellyfish life stage transition.
... Time series of abundance (Breitburg & Fulford, 2006;Feigenbaum & Kelly, 1984;Sexton et al., 2010;Tay & Hood, 2017) reveal that both C. chesapeakei and A. aurita become abundant during summer when temperatures rise above 17°C and are largely absent in the winter (Table 6.1). In the case of C. chesapeakei, the appearance of medusae in early summer is related to temperature-controlled triggering of strobilation of benthic polyps (Decker et al., 2007;Loeb, 1972), whereas the disappearance in the fall is related to temperature-controlled declines in pulsation rate below 15°C, which causes the medusa to Aurelia aurita * *** *** ** * Chrysaora chesapeakei + + + + + + *** *** *** ** ** Cyanea capillata ** ** ** ** ** Nemopsis bachei *** *** ** Mnemiopsis leidyi ** ** ** ** *** *** ** ** *** ** ** ** Beroe ovata ** ** ** *** sink (Sexton et al., 2010). ...
... Rhopilema verrilli and S. meleagris are both uncommon visitors to lower CB from coastal waters during fall and winter (Calder, 1972). Interannual to decadal time series of C. chesapeakei from the estuarine reaches of the Patuxent River (Breitburg & Fulford, 2006;Cargo & King, 1990) and Choptank (Sexton et al., 2010;Tay & Hood, 2017) reveal strong episodic and interannual variability in medusa abundance that appear to be related to freshwater flow, with high-flow years often associated with lower overall medusa abundance (Cargo & King, 1990). Observations from 2018 reveal a complete collapse of the C. chesapeakei medusa population in CB, which could be related to unusually high precipitation and freshwater flow in late spring and early summer (R. Hood, unpublished observations). ...
... Rhopilema verrilli and Stomolophus meleagris are found only in the polyhaline reach. In addition, the 4-year Choptank River time series has been used to identify aggregation behavior and quantify patch size of C. chesapeakei (Tay & Hood, 2017). Indices of aggregation calculated from the time series indicate that medusae were aggregated and suggested that patches grew in the number of individuals as abundance increased. ...
Mesozooplankton and Gelatinous Zooplankton in the Face of Environmental Stressors
Chapter
  • Dec 2020
Mesozooplankton and gelatinous zooplankton communities in Chesapeake Bay (CB) and the northern Adriatic Sea (NAS) have been subject to similar stressors over recent decades, including warming waters, overfishing, urbanization, and eutrophication. Direct comparisons between the systems are clouded by the lack of standardized and sustained long‐term monitoring programs in both, which have covered different temporal and spatial scales, and employed different methodologies. Data that are available show that the systems differ in community composition, with CB having fewer species compared with the more diverse NAS. Both systems have seen an altered gelatinous zooplankton community over recent decades. In the NAS, these changes in part have been due to the recent introduction of nonindigenous species, a phenomenon not yet documented in CB. Chesapeake Bay has seen a long‐term decline in the abundance of the dominant copepod taxa, attributed to increases in ctenophore abundance and/or increased seasonal hypoxia. Given the importance of mesozooplankton and gelatinous organisms in marine food webs, it is imperative that future ecosystem‐based management efforts for marine resources include coordinated, consistent, and standardized monitoring of mesozooplankton and gelatinous zooplankton. Such data would allow for the development of robust indices to help achieve management goals for water quality, ecosystem health, and marine resources.
... Time series of abundance (Breitburg & Fulford, 2006;Feigenbaum & Kelly, 1984;Sexton et al., 2010;Tay & Hood, 2017) reveal that both C. chesapeakei and A. aurita become abundant during summer when temperatures rise above 17°C and are largely absent in the winter (Table 6.1). In the case of C. chesapeakei, the appearance of medusae in early summer is related to temperature-controlled triggering of strobilation of benthic polyps (Decker et al., 2007;Loeb, 1972), whereas the disappearance in the fall is related to temperature-controlled declines in pulsation rate below 15°C, which causes the medusa to Aurelia aurita * *** *** ** * Chrysaora chesapeakei + + + + + + *** *** *** ** ** Cyanea capillata ** ** ** ** ** Nemopsis bachei *** *** ** Mnemiopsis leidyi ** ** ** ** *** *** ** ** *** ** ** ** Beroe ovata ** ** ** *** sink (Sexton et al., 2010). ...
... Rhopilema verrilli and S. meleagris are both uncommon visitors to lower CB from coastal waters during fall and winter (Calder, 1972). Interannual to decadal time series of C. chesapeakei from the estuarine reaches of the Patuxent River (Breitburg & Fulford, 2006;Cargo & King, 1990) and Choptank (Sexton et al., 2010;Tay & Hood, 2017) reveal strong episodic and interannual variability in medusa abundance that appear to be related to freshwater flow, with high-flow years often associated with lower overall medusa abundance (Cargo & King, 1990). Observations from 2018 reveal a complete collapse of the C. chesapeakei medusa population in CB, which could be related to unusually high precipitation and freshwater flow in late spring and early summer (R. Hood, unpublished observations). ...
... Rhopilema verrilli and Stomolophus meleagris are found only in the polyhaline reach. In addition, the 4-year Choptank River time series has been used to identify aggregation behavior and quantify patch size of C. chesapeakei (Tay & Hood, 2017). Indices of aggregation calculated from the time series indicate that medusae were aggregated and suggested that patches grew in the number of individuals as abundance increased. ...
Mesozooplankton and Gelatinous Zooplankton in the Face of Environmental Stressors.
Chapter
  • Jul 2020
... Results from our study revealed similar patterns of C. chesapeakei abundance and seasonality compared to previous studies conducted in the Patuxent River tributary (Cargo and Schultz 1966, Cones and Haven 1969, Loeb 1972, Calder 1974, Baird and Ulanowicz 1989, Purcell 1992, Suchman and Sullivan 1998, Brown et al. 2002, Breitburg and Fulford 2006, Decker et al. 2007, Breitburg and Burrell 2014, Tay and Hood 2017. Fig. 8. Relative Chrysaora chesapeakei density noted between years and across transects. ...
... This was not the case during the peak week of 18 July 2017, when a relatively similar number of medusae were found in the creek and channel. The difference in the observed dispersion patterns is not clear, and advective factors such as wind, river discharge, and geomorphology of sites may have resulted in more dispersal out of the source regions (Purcell et al. 2000, Graham et al. 2001, Suchman and Brodeur 2005, Decker et al. 2007, Hamner and Dawson 2009, Kaneshiro-Pineiro and Kimmel 2015, Tay and Hood 2017. However, there were no significant differences in Patuxent River discharge from June to August when comparing 2016 to 2017. ...
Multi-scale spatial dynamics of the Chesapeake Bay nettle, Chrysaora chesapeakei
Article
Full-text available
  • May 2020
Untangling organisms' multi-scale spatial distributions is challenging due to their interactions with environments at multiple spatial and temporal scales. We deployed an Adaptive Resolution Imaging Sonar (ARIS) in a Chesapeake Bay sub-estuary to investigate multi-scale spatial distributions of the bay nettle (Chrysaora chesapeakei) in May-September of 2016 and 2017. Nettles were found to be dispersed in aggrega-tions of multiple individuals. The average density of bay nettles in 2017 was higher than in 2016. Small aggre-gations (<5 m) were persistent in both years but only contributed <10% of total observed nettles. Large patches (>30 m) contributed~40% of the total observed nettles. Large patches were more common in creek habitat where nettle density was higher. Nettle density was found to hit a peak value once in 2016, while there were two density peaks in 2017. Different aggregation patterns were observed during the second peak period in 2017 in which the number of large patches increased dramatically. Within the surveyed waterscape, the spatial patterns were consistent over time with higher abundance in the source creek than in the river channel, which underscores that C. chesapeakei requires hard substrate in shallow creeks for its benthic polyp stage. Using the ratio between nettles in the creek and near creek mouth as a proxy for dispersal rate, more nettles were transported out of the creek in 2017 than in 2016. The increase in patch size and high dispersion rate in peak periods in 2017 suggests that individuals were moving out of the creek habitat as density increased. Results highlight the complex spatial structure of bay nettles, which has major impacts on density estimates and subsequently affects our understanding of jellyfish population dynamics and long-term trends.
Multigene phylogeny of the scyphozoan jellyfish family Pelagiidae reveals that the common U.S. Atlantic sea nettle comprises two distinct species ( Chrysaora quinquecirrha and C. chesapeakei )
Article
Full-text available
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Background Species of the scyphozoan family Pelagiidae (e.g., Pelagia noctiluca , Chrysaora quinquecirrha ) are well-known for impacting fisheries, aquaculture, and tourism, especially for the painful sting they can inflict on swimmers. However, historical taxonomic uncertainty at the genus (e.g., new genus Mawia ) and species levels hinders progress in studying their biology and evolutionary adaptations that make them nuisance species, as well as ability to understand and/or mitigate their ecological and economic impacts. Methods We collected nuclear ( 28S rDNA) and mitochondrial (cytochrome c oxidase I and 16S rDNA) sequence data from individuals of all four pelagiid genera, including 11 of 13 currently recognized species of Chrysaora . To examine species boundaries in the U.S. Atlantic sea nettle Chrysaora quinquecirrha , specimens were included from its entire range along the U.S. Atlantic and Gulf of Mexico coasts, with representatives also examined morphologically (macromorphology and cnidome). Results Phylogenetic analyses show that the genus Chrysaora is paraphyletic with respect to other pelagiid genera. In combined analyses, Mawia , sampled from the coast of Senegal, is most closely related to Sanderia malayensis , and Pelagia forms a close relationship to a clade of Pacific Chrysaora species ( Chrysaora achlyos, Chrysaora colorata , Chrysaora fuscescens , and Chrysaora melanaster ). Chrysaora quinquecirrha is polyphyletic, with one clade from the U.S. coastal Atlantic and another in U.S. Atlantic estuaries and Gulf of Mexico. These genetic differences are reflected in morphology, e.g., tentacle and lappet number, oral arm length, and nematocyst dimensions. Caribbean sea nettles (Jamaica and Panama) are genetically similar to the U.S. Atlantic estuaries and Gulf of Mexico clade of Chrysaora quinquecirrha . Discussion Our phylogenetic hypothesis for Pelagiidae contradicts current generic definitions, revealing major disagreements between DNA-based and morphology-based phylogenies. A paraphyletic Chrysaora raises systematic questions at the genus level for Pelagiidae; accepting the validity of the recently erected genus Mawia , as well as past genera, will require the creation of additional pelagiid genera. Historical review of the species-delineating genetic and morphological differences indicates that Chrysaora quinquecirrha Desor 1848 applies to the U.S. Coastal Atlantic Chrysaora species (U.S. Atlantic sea nettle), while the name C. chesapeakei Papenfuss 1936 applies to the U.S. Atlantic estuarine and Gulf of Mexico Chrysaora species (Atlantic bay nettle). We provide a detailed redescription, with designation of a neotype for Chrysaora chesapeakei , and clarify the description of Chrysaora quinquecirrha . Since Caribbean Chrysaora are genetically similar to Chrysaora chesapeakei , we provisionally term them Chrysaora c.f. chesapeakei . The presence of Mawia benovici off the coast of Western Africa provides a potential source region for jellyfish introduced into the Adriatic Sea in 2013.
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Understanding the population dynamics and complete life cycle of bivalves is important for effectively manage them. Most of the literature and research to date has focused on juvenile and adult bivalves, much less is known about larvae. The larval stage of the bivalve life cycle has been difficult to study due to the lack of a rapid automated approach for identifying species. However, a new technique, called ShellBi, has emerged that utilizes color patterns on the larval shell under polarized light to identify bivalve larvae. The objective of this chapter was to review the scientific basis for ShellBi and to apply it to bivalve larvae in Choptank River with the goal of distinguishing C. virginica from seven other species that spawn at the same time. A digital camera and polarized light microscope were used to capture images of the shells of bivalve larvae under standard and cross-polarized light. Images of C. virginica were distinguishable from other species based on these patterns, especially at later stages of development. These images could serve as a visual guide to identify C. virginica collected from the Choptank River and other tributaries with similar species in Chesapeake Bay.
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Bias and Dispersion of Overlap Indices: Results of Some Monte Carlo Simulations
Article
We have used computer simulations to determine the sampling distributions of four indices of overlap or similarity: the coefficient of community, Morisita's index, Horn's information theory index, and Euclidean distance. Estimates of overlap were systematically biased downward when sample size was small and when expected values were close to 1. The standard deviations of samples of indices were greatest when expected values were intermediate between 0 and 1, and sample sizes were small. In studies having sample sizes of 25, 50, or 100, one could expect the standard error of an estimated index of similarity to fall between 0.05 and 0.10, provided that samples were truly drawn from homogeneous populations. We suggest that simulations be used to estimate confidence limits on similarity and overlap indices where hypothesis testing is required. In addition, efforts should be made to develop indices of overlap for which statistical measures of dispersion and bias can be derived analytically.
Spatial Patterns and Movements in Coprophagous Beetles
Article
  • May 1980
Spatial distribution in two groups of dung-inhabiting beetles, Aphodius (Scarabaeidae) and Hydrophilidae, was analysed at two spatial levels, between and within pastures. Long-distance movements in the strictly coprophagous species of Aphodius were studied by trapping beetles in the centre of a town, away from the pastures. In both groups of beetles, and at both spatial levels, a linear relationship was found between log spatial variance and log mean abundance. Between-field variation in numbers was shown to be negatively correlated with the intensity of long-distance movements (interspecific comparison), and between-field variance moreover declined during the seasonal flight period in most species of Aphodius. There was an indication of a negative correlation between spatial variance and the proportion of mature females in the annual catches (Aphodius), which is interpreted as a consequence of interspecific differences in egg-laying habits both in space and time. In species showing little long-distance movements, females predominated among the "migrants" (in the centre of a town), and among the female "migrants" mature individuals were over-represented, compared with the proportion in the pastures. Long-distance movements occurred seasonally in relation to the numbers of beetles in the pastures, which supports the view that in these species there is no important difference between the short-distance and long-distance movements. Modelling of processes important in the dynamics of spatial patterns is discussed, a simple model is proposed, and the advocated universality of the model by Taylor and Taylor is questioned. /// Пространственное распределение двух групп обитающих в навозе жуков Aphodius (Scarabaeidae) и Hydrophilidae, проанализировано на двух пространственных уровних - при сравнении 2-х пастбищ и в пределах одного пастбища. Дальние миграции у видов Aphodius, строгих копрофагов, исследовали путем отлова жуков в центре города, вне пастбищ. В обеих группах жуков и на обоих пространственных уровних найдена линейная зависимость между логарифмом величины пространственных различий и логарифмом величины среднего обилия. Показано, что различия численности на разных участках имеют обратную зависимость с интенсивностью дальнюх миграций (межвидовые сравнения); различия на 2-х участках снижаются в течение периода лета у большинства видов Aphodius. Имеются признаки обратной корреляции между пространственными различиями и оиношением подовозрелых самок в годичных отловах (Aphodius), что рассматривается следствие междидових различий в местах и сроках яйцекладки. У видов с короткими миграциями среди "мигрантов" (в центре города) преобладают самки, а среди мигрирующх самок половозрелые особи составляли большую долю, чем на пастоищах. Далвние миграции наблюдаются в определенные сехоны, в зависнмости от численности жуков на пастобищах, что поддерживает точку зрения, о что у этих жуков не сущечтвует разлисий между короткими и дальными миграциями. Обсуждается моделирование процессов имеющих важное значение в димамике прочтранственного распределения. Предложена простая модель, ставится под сомнение защищамая универсальная модель Тэйлора и Тэйлора.