To address the idea that the process of interspecific competition can be inferred from data on ge... more To address the idea that the process of interspecific competition can be inferred from data on geographical distribution alone and that evidence from geographical distribution implies an important role for interspecific competition in shaping ecological communities, we reexamine the occurrence of "true checkerboard" distributions among the land and freshwater birds in three Melanesian archipelagoes: Vanuatu, the Bismarck Archipelago, and the Solomon Islands. We use the most recently published distributional records and explicitly include the geography of the distributions of species within each archipelago. We use the overlap of convex hulls to estimate the overlap in the geographic range for each pair of species in each of these archipelagoes. We define a "true checkerboard" to consist of a pair of species with exclusive island-by-island distributions, but that have overlapping geographical ranges. To avoid the "dilution…
The flora and avifauna of the Galapagos Islands are used to reexamine quantitative analyses of sp... more The flora and avifauna of the Galapagos Islands are used to reexamine quantitative analyses of species numbers and compositional similarities. Conflicts in the results of previous analyses of the Galapagos flora are reconciled and are shown to be the result of using different species numbers and physiographic parameter measurements. The idea that Galapagos plant species numbers largely reflect conditions in the archipelago during the Pleistocene glaciations (i.e., that relaxation times are very long) is criticized, and the more parsimonious alternative, that they reflect recent conditions, is proposed. Generalizations about factors determining species numbers that are based on multiple regression and correlation are precarious. The number of botanical collecting trips to each of the Galapagos Islands is a better predictor of species numbers than are area, elevation, or isolation. Two null hypotheses concerning the determination of floral and avifaunal compositional similarities among the Galapagos Islands are proposed and tested, through the application of a new method of similarity analysis employing the "expected number of taxa shared" (Ets) and its variance (VEts). These hypotheses view compositional similarities as resulting from the stochastic dispersal and persistence of a pool of species equally likely to colonize (Null Hypothesis I), and of a pool of species with different dispersal and persistence abilities (Null Hypothesis II). Although both hypotheses are found to be inadequate models of compositional similarity in the Galapagos, the results suggest that a substantial proportion of compositional similarity can be considered a consequence of stochastic processes of dispersal and persistence, and that compositional similarity arises indirectly as a result of similar species numbers rather than directly in a fashion determined by the physical environment or species interactions. Analyses of the distribution of congeneric bird species in the Galapagos, based on similarity analyses, are also criticized.
In a series of papers (Connor and Simberloff 1978, 1979; Simberloff 1978) we asked whether biogeo... more In a series of papers (Connor and Simberloff 1978, 1979; Simberloff 1978) we asked whether biogeographic patterns of species on islands were consistent with the hypothesis that species colonized islands independently of one another. In all the systems we examined, certain species occupied more islands than did other species, and certain islands had more species than did other islands. Given these constraints, we asked if anything in the observed pattern is inconsistent with the hypothesis that whether species 1 occupies an island does not depend on which other species are present. The alternative hypothesis that we examined was that observed patterns were inconsistent with independent colonization and consistent with a large role for interspecific ompetition. At the outset, we emphasized that we were not asking whether competition influenced how many islands a species occupies or how many species an island contains. We asked only whether the cooccurrence patterns were inconsistent with the hypothesis of independence. There are two ways to analyze an r x c binary matrix depicting presence or absence of r species over an archipelago of c islands (Simberloff and Connor 1979). In Q-mode analysis, one examines how similar matrix columns (islands) are in the collections of species they contain. In R-mode analysis, one examines how similar matrix rows (species) are in the collections of islands they occupy. Wright and Biehl (1982) suggested that both our Q-mode and R-mode analyses are inappropriate to test our hypotheses and suggest an alternative R-mode analysis. We (Connor and Simberloff 1983) pointed out problems inherent in their and other R-mode analyses and defended our original method. Here we discuss Wright and Biehl's arguments against our Q-mode analysis.
Page 1. Vol. 118, No. 2 The American Naturalist August 1981 MISSING SPECIES COMBINATIONS Daniel S... more Page 1. Vol. 118, No. 2 The American Naturalist August 1981 MISSING SPECIES COMBINATIONS Daniel Simberloff and Edward F. Connor* Department of Biological Science, Florida State University, Tallahassee, Florida 32306 ...
Ecological restoration, North America, Mar 1, 2012
To restore historical dune vegetation, substantial effort has been made to remove the invasive pl... more To restore historical dune vegetation, substantial effort has been made to remove the invasive plant species, European beach grass (Ammophila arenaria), from coastal dunes of California, USA. However, little effort has been made to examine the response of terrestrial arthropod assemblages to coastal dune restoration. We sampled terrestrial arthropods at 6 dune restoration sites to determine the response of the arthropod communities to vegetation restoration along the central and northern coast of California. Using pitfall traps, we examined restored and adjacent unrestored foredunes and collected reference data from dunes that had not been invaded by European beach grass. Both arthropod abundance and richness were significantly higher on restored and uninvaded dunes than on unrestored dunes. However, we detected no difference in arthropod richness and abundance between restored and uninvaded dunes. The species composition of the arthropod community reflected greater similarity of geographically adjacent sites, rather than similarity within treatments. We conclude that restored dunes provide higher quality habitat for terrestrial arthropods than unrestored dunes dominated by European beach grass, but longer-term studies are needed to determine if restoration efforts will be effective at fully restoring historical arthropod assemblages.
Page 1. OIKOS 41: 455-465. Copenhagen 1983 Interspecific competition and species co-occurrence pa... more Page 1. OIKOS 41: 455-465. Copenhagen 1983 Interspecific competition and species co-occurrence patterns on islands: null models and the evaluation of evidence Edward F. Connor and Daniel Simberloff Connor, EF and Simberloff, D. 1983. ...
... All of Kew This site. ... Detailed result. return to summary results page. Simberloff D, Heck... more ... All of Kew This site. ... Detailed result. return to summary results page. Simberloff D, Heck KL, McCoyED, Connor EF. 1981 There have been no statistical tests of cladistic biogeographical hypotheses. Proc. Vicariance Biogeogr.,: 40-93 (1979 publ. 1981)- illus. En Ref. in Bibliogr. ...
A diverse array of organisms induce plants to form galls. This phenomenon is one of the most stri... more A diverse array of organisms induce plants to form galls. This phenomenon is one of the most striking instances of convergent evolution, yet the underlying mechanism is only well understood in gall-inducing microbes. To determine if gall induction by insects is associated with bacterial symbiosis, we used 16S rRNA gene sequencing to examine the microbiome of a variety of gall-inducing and non-gall-inducing insects. Overall, we did not find any bacterial signature of gall induction among the insect species we surveyed. There were no specific bacterial taxa that were consistently associated with gall induction. Microbiome diversity differed significantly among species of host insects, but not between gall-and non-gall-inducing insect species. Bacterial community composition also differed strongly among insect species, but not in a systematic way between gall-inducing and non-gall-inducing species. Furthermore, two gall-inducing species harbored highly variable microbiomes with relatively few bacterial sequences, characteristics that suggest a lack of abundant bacterial symbionts. Together, these findings argue that gall induction is not consistently mediated by a bacterial symbiont or bacterial community and may be symbiont-independent, at least in some insect species. While symbionts may still contribute to gall induction in specific instances, we suggest that the convergent evolution of gall induction is more typically driven by endogenous mechanisms, with potential contributions from horizontal gene transfer.
The San Francisco Bay Area hosts a diverse insect fauna and a dense cluster of urban areas. The h... more The San Francisco Bay Area hosts a diverse insect fauna and a dense cluster of urban areas. The high diversity of insects in the Bay Area arises for three primary reasons: its location in the California biotic province, the diverse local environment and the entomologist-area effect. The juxtaposition of high insect diversity and an area intensively used by humans led to the first recorded extinction as well as the first efforts to conserve insects in the United States. Habitat loss due to urbanization, agriculture, and invasive species is largely responsible for local extinctions and reduction in abundance of the remaining species. Invasive species such as the Argentine ant and pathogens causing mortality of oaks and pines are poised to have substantial impacts on the insect fauna of the Bay Area in the near future. Understanding which taxa can or cannot persist in remnant habitat patches within an urban or agricultural matrix, and what management practices would encourage persisten...
Page 1. Edward F. Connor Competition, Scientific Method, and Daniel simberioff nuu Models in Ecol... more Page 1. Edward F. Connor Competition, Scientific Method, and Daniel simberioff nuu Models in Ecology Because field experiments are difficult to perform, ecologists often rely on evidence that is nonexperimental and that thereforeneeds to be rigorously evaluated ...
Abscisic acid (ABA) is an isoprenoid-derived plant signaling molecule involved in a wide variety ... more Abscisic acid (ABA) is an isoprenoid-derived plant signaling molecule involved in a wide variety of plant processes, including facets of growth and development as well as responses to abiotic and biotic stress. ABA had previously been reported in a wide variety of animals, including insects and humans. We used high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-(ESI)-MS/MS) to examine concentrations of ABA in 17 species of phytophagous insects, including gall- and non-gall-inducing species from all insect orders with species known to induce plant galls: Thysanoptera, Hemiptera, Lepidoptera, Coleoptera, Diptera, and Hymenoptera. We found ABA in insect species in all six orders, in both gall-inducing and non-gall-inducing species, with no tendency for gall-inducing insects to have higher concentrations. The concentrations of ABA in insects often markedly exceeded those typically found in plants, suggesting it is highly improbable that insects ...
We used repeated sightings of individual birds encountered in community-level surveys to investig... more We used repeated sightings of individual birds encountered in community-level surveys to investigate the relative roles of habitat and biological interactions in determining the distribution and abundance of each species. To analyze these data, we developed a multispecies N-mixture model that allowed estimation of both positive and negative correlations between abundances of different species while also estimating the effects of habitat and the effects of errors in detection of each species. Using a combination of single-and multispecies Nmixture modeling, we examined for each species whether our measures of habitat were sufficient to account for the variation in encounter histories of individual birds or whether other habitat variables or interactions with other species needed to be considered. In the community that we studied, habitat appeared to be more influential than biological interactions in determining the distribution and abundance of most avian species. Our results lend support to the hypothesis that abundances of forest specialists are negatively affected by forest fragmentation. Our results also suggest that many species were associated with particular types of vegetation as measured by structural attributes of the forests. The abundances of 6 of the 73 species observed in our study were strongly correlated. These species included large birds (American Crow (Corvus brachyrhynchos) and Red-winged Blackbird (Agelaius phoeniceus)) that forage on the ground in open habitats and small birds (Red-eyed Vireo (Vireo olivaceus), House Wren (Troglodytes aedon), Hooded Warbler (Setophaga citrina), and Prairie Warbler (Setophaga discolor)) that are associated with dense shrub cover. Species abundances were positively correlated within each size group and negatively correlated between groups. Except for the American Crow, which preys on eggs and nestlings of small song birds, none of the other 5 species is known to display direct interactions, so we suspect that the correlations may have been associated with species-specific responses to habitat components not adequately measured by our covariates.
We examined the relationship between plant species richness and soil moisture in Bear Trap Meadow... more We examined the relationship between plant species richness and soil moisture in Bear Trap Meadows in the Sierra Mountains in July 2004. We initially used both a within- and between-subjects sampling design, but soon realized that a within-subject sampling design was not feasible for our study. We collected additional information on the grazing intensity in each of our sampling plots to determine if grazing intensity was more strongly associated with plant species richness than soil moisture. Based on our preliminary data, we determined that 22 samples would be needed to detect a decline of one species for a 10% increase in soil moisture with α=0.05 and 80% power. Our overall results indicate that plant species richness is higher at drier locations within Bear trap meadow.
To address the idea that the process of interspecific competition can be inferred from data on ge... more To address the idea that the process of interspecific competition can be inferred from data on geographical distribution alone and that evidence from geographical distribution implies an important role for interspecific competition in shaping ecological communities, we reexamine the occurrence of "true checkerboard" distributions among the land and freshwater birds in three Melanesian archipelagoes: Vanuatu, the Bismarck Archipelago, and the Solomon Islands. We use the most recently published distributional records and explicitly include the geography of the distributions of species within each archipelago. We use the overlap of convex hulls to estimate the overlap in the geographic range for each pair of species in each of these archipelagoes. We define a "true checkerboard" to consist of a pair of species with exclusive island-by-island distributions, but that have overlapping geographical ranges. To avoid the "dilution…
The flora and avifauna of the Galapagos Islands are used to reexamine quantitative analyses of sp... more The flora and avifauna of the Galapagos Islands are used to reexamine quantitative analyses of species numbers and compositional similarities. Conflicts in the results of previous analyses of the Galapagos flora are reconciled and are shown to be the result of using different species numbers and physiographic parameter measurements. The idea that Galapagos plant species numbers largely reflect conditions in the archipelago during the Pleistocene glaciations (i.e., that relaxation times are very long) is criticized, and the more parsimonious alternative, that they reflect recent conditions, is proposed. Generalizations about factors determining species numbers that are based on multiple regression and correlation are precarious. The number of botanical collecting trips to each of the Galapagos Islands is a better predictor of species numbers than are area, elevation, or isolation. Two null hypotheses concerning the determination of floral and avifaunal compositional similarities among the Galapagos Islands are proposed and tested, through the application of a new method of similarity analysis employing the "expected number of taxa shared" (Ets) and its variance (VEts). These hypotheses view compositional similarities as resulting from the stochastic dispersal and persistence of a pool of species equally likely to colonize (Null Hypothesis I), and of a pool of species with different dispersal and persistence abilities (Null Hypothesis II). Although both hypotheses are found to be inadequate models of compositional similarity in the Galapagos, the results suggest that a substantial proportion of compositional similarity can be considered a consequence of stochastic processes of dispersal and persistence, and that compositional similarity arises indirectly as a result of similar species numbers rather than directly in a fashion determined by the physical environment or species interactions. Analyses of the distribution of congeneric bird species in the Galapagos, based on similarity analyses, are also criticized.
In a series of papers (Connor and Simberloff 1978, 1979; Simberloff 1978) we asked whether biogeo... more In a series of papers (Connor and Simberloff 1978, 1979; Simberloff 1978) we asked whether biogeographic patterns of species on islands were consistent with the hypothesis that species colonized islands independently of one another. In all the systems we examined, certain species occupied more islands than did other species, and certain islands had more species than did other islands. Given these constraints, we asked if anything in the observed pattern is inconsistent with the hypothesis that whether species 1 occupies an island does not depend on which other species are present. The alternative hypothesis that we examined was that observed patterns were inconsistent with independent colonization and consistent with a large role for interspecific ompetition. At the outset, we emphasized that we were not asking whether competition influenced how many islands a species occupies or how many species an island contains. We asked only whether the cooccurrence patterns were inconsistent with the hypothesis of independence. There are two ways to analyze an r x c binary matrix depicting presence or absence of r species over an archipelago of c islands (Simberloff and Connor 1979). In Q-mode analysis, one examines how similar matrix columns (islands) are in the collections of species they contain. In R-mode analysis, one examines how similar matrix rows (species) are in the collections of islands they occupy. Wright and Biehl (1982) suggested that both our Q-mode and R-mode analyses are inappropriate to test our hypotheses and suggest an alternative R-mode analysis. We (Connor and Simberloff 1983) pointed out problems inherent in their and other R-mode analyses and defended our original method. Here we discuss Wright and Biehl's arguments against our Q-mode analysis.
Page 1. Vol. 118, No. 2 The American Naturalist August 1981 MISSING SPECIES COMBINATIONS Daniel S... more Page 1. Vol. 118, No. 2 The American Naturalist August 1981 MISSING SPECIES COMBINATIONS Daniel Simberloff and Edward F. Connor* Department of Biological Science, Florida State University, Tallahassee, Florida 32306 ...
Ecological restoration, North America, Mar 1, 2012
To restore historical dune vegetation, substantial effort has been made to remove the invasive pl... more To restore historical dune vegetation, substantial effort has been made to remove the invasive plant species, European beach grass (Ammophila arenaria), from coastal dunes of California, USA. However, little effort has been made to examine the response of terrestrial arthropod assemblages to coastal dune restoration. We sampled terrestrial arthropods at 6 dune restoration sites to determine the response of the arthropod communities to vegetation restoration along the central and northern coast of California. Using pitfall traps, we examined restored and adjacent unrestored foredunes and collected reference data from dunes that had not been invaded by European beach grass. Both arthropod abundance and richness were significantly higher on restored and uninvaded dunes than on unrestored dunes. However, we detected no difference in arthropod richness and abundance between restored and uninvaded dunes. The species composition of the arthropod community reflected greater similarity of geographically adjacent sites, rather than similarity within treatments. We conclude that restored dunes provide higher quality habitat for terrestrial arthropods than unrestored dunes dominated by European beach grass, but longer-term studies are needed to determine if restoration efforts will be effective at fully restoring historical arthropod assemblages.
Page 1. OIKOS 41: 455-465. Copenhagen 1983 Interspecific competition and species co-occurrence pa... more Page 1. OIKOS 41: 455-465. Copenhagen 1983 Interspecific competition and species co-occurrence patterns on islands: null models and the evaluation of evidence Edward F. Connor and Daniel Simberloff Connor, EF and Simberloff, D. 1983. ...
... All of Kew This site. ... Detailed result. return to summary results page. Simberloff D, Heck... more ... All of Kew This site. ... Detailed result. return to summary results page. Simberloff D, Heck KL, McCoyED, Connor EF. 1981 There have been no statistical tests of cladistic biogeographical hypotheses. Proc. Vicariance Biogeogr.,: 40-93 (1979 publ. 1981)- illus. En Ref. in Bibliogr. ...
A diverse array of organisms induce plants to form galls. This phenomenon is one of the most stri... more A diverse array of organisms induce plants to form galls. This phenomenon is one of the most striking instances of convergent evolution, yet the underlying mechanism is only well understood in gall-inducing microbes. To determine if gall induction by insects is associated with bacterial symbiosis, we used 16S rRNA gene sequencing to examine the microbiome of a variety of gall-inducing and non-gall-inducing insects. Overall, we did not find any bacterial signature of gall induction among the insect species we surveyed. There were no specific bacterial taxa that were consistently associated with gall induction. Microbiome diversity differed significantly among species of host insects, but not between gall-and non-gall-inducing insect species. Bacterial community composition also differed strongly among insect species, but not in a systematic way between gall-inducing and non-gall-inducing species. Furthermore, two gall-inducing species harbored highly variable microbiomes with relatively few bacterial sequences, characteristics that suggest a lack of abundant bacterial symbionts. Together, these findings argue that gall induction is not consistently mediated by a bacterial symbiont or bacterial community and may be symbiont-independent, at least in some insect species. While symbionts may still contribute to gall induction in specific instances, we suggest that the convergent evolution of gall induction is more typically driven by endogenous mechanisms, with potential contributions from horizontal gene transfer.
The San Francisco Bay Area hosts a diverse insect fauna and a dense cluster of urban areas. The h... more The San Francisco Bay Area hosts a diverse insect fauna and a dense cluster of urban areas. The high diversity of insects in the Bay Area arises for three primary reasons: its location in the California biotic province, the diverse local environment and the entomologist-area effect. The juxtaposition of high insect diversity and an area intensively used by humans led to the first recorded extinction as well as the first efforts to conserve insects in the United States. Habitat loss due to urbanization, agriculture, and invasive species is largely responsible for local extinctions and reduction in abundance of the remaining species. Invasive species such as the Argentine ant and pathogens causing mortality of oaks and pines are poised to have substantial impacts on the insect fauna of the Bay Area in the near future. Understanding which taxa can or cannot persist in remnant habitat patches within an urban or agricultural matrix, and what management practices would encourage persisten...
Page 1. Edward F. Connor Competition, Scientific Method, and Daniel simberioff nuu Models in Ecol... more Page 1. Edward F. Connor Competition, Scientific Method, and Daniel simberioff nuu Models in Ecology Because field experiments are difficult to perform, ecologists often rely on evidence that is nonexperimental and that thereforeneeds to be rigorously evaluated ...
Abscisic acid (ABA) is an isoprenoid-derived plant signaling molecule involved in a wide variety ... more Abscisic acid (ABA) is an isoprenoid-derived plant signaling molecule involved in a wide variety of plant processes, including facets of growth and development as well as responses to abiotic and biotic stress. ABA had previously been reported in a wide variety of animals, including insects and humans. We used high-performance liquid chromatography-electrospray ionization tandem mass spectrometry (HPLC-(ESI)-MS/MS) to examine concentrations of ABA in 17 species of phytophagous insects, including gall- and non-gall-inducing species from all insect orders with species known to induce plant galls: Thysanoptera, Hemiptera, Lepidoptera, Coleoptera, Diptera, and Hymenoptera. We found ABA in insect species in all six orders, in both gall-inducing and non-gall-inducing species, with no tendency for gall-inducing insects to have higher concentrations. The concentrations of ABA in insects often markedly exceeded those typically found in plants, suggesting it is highly improbable that insects ...
We used repeated sightings of individual birds encountered in community-level surveys to investig... more We used repeated sightings of individual birds encountered in community-level surveys to investigate the relative roles of habitat and biological interactions in determining the distribution and abundance of each species. To analyze these data, we developed a multispecies N-mixture model that allowed estimation of both positive and negative correlations between abundances of different species while also estimating the effects of habitat and the effects of errors in detection of each species. Using a combination of single-and multispecies Nmixture modeling, we examined for each species whether our measures of habitat were sufficient to account for the variation in encounter histories of individual birds or whether other habitat variables or interactions with other species needed to be considered. In the community that we studied, habitat appeared to be more influential than biological interactions in determining the distribution and abundance of most avian species. Our results lend support to the hypothesis that abundances of forest specialists are negatively affected by forest fragmentation. Our results also suggest that many species were associated with particular types of vegetation as measured by structural attributes of the forests. The abundances of 6 of the 73 species observed in our study were strongly correlated. These species included large birds (American Crow (Corvus brachyrhynchos) and Red-winged Blackbird (Agelaius phoeniceus)) that forage on the ground in open habitats and small birds (Red-eyed Vireo (Vireo olivaceus), House Wren (Troglodytes aedon), Hooded Warbler (Setophaga citrina), and Prairie Warbler (Setophaga discolor)) that are associated with dense shrub cover. Species abundances were positively correlated within each size group and negatively correlated between groups. Except for the American Crow, which preys on eggs and nestlings of small song birds, none of the other 5 species is known to display direct interactions, so we suspect that the correlations may have been associated with species-specific responses to habitat components not adequately measured by our covariates.
We examined the relationship between plant species richness and soil moisture in Bear Trap Meadow... more We examined the relationship between plant species richness and soil moisture in Bear Trap Meadows in the Sierra Mountains in July 2004. We initially used both a within- and between-subjects sampling design, but soon realized that a within-subject sampling design was not feasible for our study. We collected additional information on the grazing intensity in each of our sampling plots to determine if grazing intensity was more strongly associated with plant species richness than soil moisture. Based on our preliminary data, we determined that 22 samples would be needed to detect a decline of one species for a 10% increase in soil moisture with α=0.05 and 80% power. Our overall results indicate that plant species richness is higher at drier locations within Bear trap meadow.
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