bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determinants of macroinvertebrate diversity in headwater streams: regional and local influences
Authors: Heino Jani , Muotka Timo , Paavola Riku 
Published: May 2003

Summary

Multiscale determinants of diversity and the relationship between regional (RSR) and local richness (LSR) have recently attracted increased attention, yet such studies on stream organisms remain scarce. We studied the relationships among RSR, β‐diversity, LSR and local environmental variables in 120 headwater streams in Finland. Approximately similar‐sized areas of eight drainage systems were defined as regions, and 15 stream riffles (= locality) per region were sampled.
RSR showed a strong positive relationship with mean LSR (R2 = 0·686), and there was no sign of curvilinearity within the observed range of RSR. RSR was also positively, although non‐significantly, related to β‐diversity (r = 0·662).
In stepwise regression, RSR was the first variable to enter the model, and a model incorporating RSR and stream width explained 32·5% of variation in LSR. If RSR was omitted from the model, then stream width emerged as the most important variable, followed by water pH, which together accounted for 20·6% of variation in LSR.
At the within‐region scale, different variables were important in accounting for variation in LSR. Factors correlated with LSR reflected either stream size, spatial heterogeneity, adverse water chemistry conditions (pH), or a limiting resource base for macroinvertebrates (nutrient concentrations).
The major role of RSR in setting the upper limit to LSR suggests that macroinvertebrate assemblages of boreal headwater streams are unsaturated. This finding is supported by evidence from experimental studies, where it has been shown that competitive interactions among stream macroinvertebrates are effective only at very small spatial scales, and competitive exclusion is prevented typically by frequent disturbances. However, although RSR was generally the most influential variable contributing to LSR, it is far from clear whether RSR consistently sets the limits to LSR, or vice versa. For instance, uniformly adverse water chemistry conditions across a region may lead to low levels of local richness and low species turnover among sites, leading eventually to an impoverished regional species pool.
These findings do not deny the importance of local factors, but emphasize that understanding the organization of stream benthic communities requires simultaneous examination of factors prevailing at multiple spatial scales.
The relative impact of local and regional processes on macro‐invertebrate species richness in temporary pools
Authors: Kiflawi M. , Eitam A. , Blaustein L. 
Published: May 2003

Summary

Freshwater temporary pools constitute insular habitats that can vary extensively in the richness of their macro‐invertebrate fauna, even within small spatial scales. While strictly statistical analyses may identify variables that account partially for this variation, they do not address explicitly the mechanisms that generate it.
Here we show how a simple island‐biogeographical model explains 62% of the variation in local species richness of 47 neighbouring pools, based solely on pool size and permanence. A regression of the observed richness on that predicted by the model did not indicate any systematic biases, and left residuals that were distributed according to the expected.
The model provides a robust working hypothesis, to which we apply a novel approach of quantifying the relative impact of local and regional factors on the species richness of individual pools. Using elasticity analysis of model parameters and invoking elasticity as a measure of parameter ‘importance’ we show, for example, that the impact of regional species richness on the richness of noninteractive communities should always exceed that of the probability of local extinction.
The analysis exposes potential difficulties in generalizing which factor – local or regional – has the greater relative importance, and to what extent, as the answer can depend on: (i) the specific factors being compared, and (ii) particular habitat characteristics of individual localities.
Size matters: competition within populations of the limpetPatella depressa
Authors: Boaventura Diana , Da Fonseca Luís Cancela , Hawkins Stephen J. 
Published: May 2003

SummaryCompetitive interactions within and between size‐classes of the limpetPatella depressaPennant were investigated in central Portugal. Experimental enclosures of 25 × 25 cm containing marked limpets were set up at mid‐tidal level on the shore. Twelve treatments with different combination of densities and size‐classes were assigned to the plots, with three replicates of each. Mortality was recorded every 15 days and length was measured monthly during the approximately 6 months of the experiment.At the end of the experiment limpets were collected for determination of length, height, dry weight, sex and gonad development. The availability of food was assessed indirectly by determination of chlorophyll concentration with spectrophotometric analysis of rock chips. Reduced density treatments showed very low mortality and substantially increased growth. Both size‐classes of limpets showed increased mortality and reduced growth in increased density treatments. This effect was, however, more marked for large than small limpets when caged separately.Although both size‐classes could negatively affect each other, the effect of large limpets on small was greater than the reverse. Large limpets are superior competitors that may modulate the abundance of small limpets on the shore. It is unlikely, however, that they will totally exclude small limpets due to intensity of competition within the large size‐class. Niche differentiation and high recruitment at low shore levels are other possible factors that can contribute to reduce competition between the size‐classes.
Importance of species identity and number for process rates within different stream invertebrate functional feeding groups
Authors: Jonsson Micael , Malmqvist Björn 
Published: May 2003

Summary

The effects of decreasing species richness on process rates were investigated in laboratory experiments within three different stream invertebrate functional feeding groups: filter feeders, grazers and predators.
We found significant effects in all groups; however, the direction and magnitude varied. The effects were not due to species richness per se as species identity was the only significant factor in all analyses.
Filter‐feeding collectors showed a decreasing filtration rate with decreasing species richness in a first experimental trial while a second one showed no trend. In contrast, process rates increased with decreasing species richness in both grazers and predators.
Comparisons of expected with observed process rates in two‐ and three‐species treatments indicated underlying mechanisms. In grazers resource dominance by one species seemed to negatively affect the other species so that grazing rates decreased when species were combined. In predators interference by two of the species on a smaller predator species seemed to affect predation rates negatively.
Our results show that the effects of species loss greatly depend on what type of interactions the lost species participated in and that species identity may be the most important factor generating effects of species loss in cases when the interaction affects species differently.
Spatial dynamics and cross‐correlation in a transient predator–prey system
Authors: Tobin Patrick C. , Bjørnstad Ottar N. 
Published: May 2003

Summary

We examined spatiotemporal data in a transient, seasonal system involving a specialist predatory beetle, Carcinops pumilio (Erichson), and its prey, larval Musca domestica L.
Prior to beetle colonization, larval fly populations were highly spatially structured, but as adult predatory beetles immigrated and colonized the field, the beetles became increasingly clustered at local spatial scales, causing spatial decorrelation in the dynamics of their prey. Larval flies appeared to regain local clustering as beetle abundance approached a carrying capacity with the prey population.
During exponential population growth, beetles were generally strongly negatively cross‐correlated with their prey at local spatial scales.
We were able to simulate these spatially–extended interactions in a predator‐prey coupled map lattice model. We used this model to investigate the effects of global and local prey reproduction, in the presence and absence of global stochasticity, on predator and prey spatial structuring and cross‐correlation.
The work shows in a uniquely detailed fashion how the transition from eruptive pest abundance to regulation by a specialist predator is associated with a transition in spatial structure.
Predicting abundance from occupancy: a test for an aggregated insect assemblage
Authors: Warren M. , Mcgeoch M. A. , Chown S. L. 
Published: May 2003

Summary

The ubiquitous, positive abundance‐occupancy relationship is of potential value to conservation and pest management because of the possibility of using it to predict species abundance from occupancy measures.
He & Gaston (2000a) developed a model, and a parameterization method, for the prediction of abundance from occupancy based on the negative binomial distribution. There are to date few empirical tests of either the estimation method or model. Here we conduct such a test in a field‐based mesocosm experiment using a Drosophilidae assemblage associated with decaying fruit.
With individual (and groups of) fruit as minimum mapping units, abundance estimates derived using the parameterization method of the He‐Gaston model differed significantly from measured values, and were least accurate for the most abundant species.
Substitution of k‐values corrected for species density in the model did not improve abundance predictions significantly. However, substitution of k‐values calculated directly from the negative binomial distribution yielded highly accurate abundance predictions.
Although the distribution of fly species did not deviate significantly from the negative binomial distribution, and the finest possible minimum mapping units were used (individual fruit), the parameterization method in the He‐Gaston model consistently underestimated the abundance of species in the assemblage because individuals were very highly aggregated within fruit.
Because of its potential importance, this model and parameterization method require further exploration at fine scales, commonly represented by individual habitat units, for highly aggregated species. The incorporation of spatially explicit information may provide a means of improving abundance predictions in this regard.
Effects of floristics, physiognomy and non‐native vegetation on riparian bird communities in a Mojave Desert watershed
Authors: Fleishman Erica , Mcdonal Neil , Nally Ralph Mac , Murphy Dennis D. , Walters Jack , Floyd Ted 
Published: May 2003

SummaryIn the deserts of the south‐western United States of America, as in many ecoregions around the world, invasion of non‐native plants is modifying the structure and composition of riparian vegetation.Restoration of native plant species frequently proves to be ecologically and economically difficult. In the Muddy River drainage in the Mojave Desert (Nevada, USA), eradication of one the most aggressive invasive plants,Tamarix ramosissima(salt‐cedar), often reduces the structural and compositional diversity of the remaining vegetation. This can have negative effects on native animals, including birds.The objectives of our work were (i) to examine relationships between avian diversity and measures of vegetational diversity (species richness, dominance of non‐native plants and vegetation structure [total vegetation volume]), (ii) to explore the extent to which avian community composition was associated with vegetation composition (floristics) or vegetation structure (physiognomy), and (iii) to consider the potential effects of alternative land management and ecological restoration strategies on the biodiversity of birds and other native fauna in watersheds in the arid south‐western USA.Species richness of all birds and of breeding birds was best modelled by total vegetation volume alone. Neither species richness of plants nor dominance of non‐native plants had a statistically significant effect on species richness, abundance or evenness of birds.Species composition of birds between sites was more similar when floristics was more similar, and vice versa. Species composition of birds was not correlated with physiognomy.Species richness of native birds in the Muddy River drainage appears not to suffer from invasion of non‐native plants, provided that the vegetational community retains sufficient structural diversity.The composition of the bird community is closely related to floristics, and other taxonomic groups may exhibit different responses to vegetation structure and composition. Therefore, explicit strategies for landscape‐scale management, restoration and maximization of native faunal diversity should consider how removal of invasive plants may affect physiognomy and floristics of the vegetational community as a whole.
The effect of helping behaviour on the survival of juvenile and adult long‐tailed tits Aegithalos caudatus
Authors: McGowan Andrew , Hatchwell Ben J. , Woodburn Richard J. W. 
Published: May 2003

Summary

In the cooperative breeding system of the long‐tailed tit Aegithalos caudatus failed breeders may become helpers at the nest of another pair to whom they are usually related. The aim of this study was to determine the effect of helping behaviour on the survival of helpers and the recipients of their help.
We used capture–mark–recapture data and the MARK program to analyse survival of 482 birds ringed as fledglings and 155 birds ringed as adults.
Juvenile males had a higher survival probability than juvenile females across all years whilst their subsequent adult survival was constant. Within sex, the survival probability of juveniles that fledged from nests with helpers was higher than those that did not receive help as nestlings.
Failed breeders that became helpers had a higher survival probability (56%) than those failed breeders that did not become helpers (46%). Successful breeders had a survival probability of 56% regardless of whether they received help or not.
Failed breeders that became helpers had a lower probability of successfully breeding in a subsequent year (27%) when compared to those failed breeders that did not become helpers (38%).
6. We conclude that helpers gain kin‐selected fitness benefits through the increased survival of related offspring but not through the increased survival of related breeders. Furthermore, helpers gain direct fitness benefits through increased personal survival, but at a cost of reduced probability of successful future personal reproduction.
Interactions over four trophic levels: foodplant quality affects development of a hyperparasitoid as mediated through a herbivore and its primary parasitoid
Authors: Harvey Jeffrey A. , Van Dam Nicole M. , Gols Rieta 
Published: May 2003

SummaryRelated plant species with different spatial and/or temporal life‐history characteristics often possess differences in secondary chemistry and thus direct defensive capability. These differences are often attributed to a range of divergent selection pressures from herbivores and pathogens. Most studies of insect–plant interactions have examined the effects of plant defence on herbivore performance, with less attention being paid to higher trophic levels, such as parasitoid wasps. Moreover, to date it is not known whether secondary plant compounds may affect organisms in the fourth trophic level.Here, we study interactions in a four‐trophic‐level system. The development of a solitary secondary hyperparasitoid,Lysibia nana, and its primary endoparasitoid host,Cotesia glomerata, are compared when reared from a primary herbivore host,Pieris brassicae, which was itself reared on two cruciferous plants with contrasting life histories. WhereasL. nanais known to attack the pupae of a number of primary parasitoids in the genusCotesia, bothC. glomerataandP. brassicaeare intimately associated with plants in the family Brassicaceae.Insects were reared from a feral population of the spring perennial,Brassica oleracea, and a naturally occurring population of a summer annual,B. nigra. Like other cruciferous plants, both species are known to produce glycoside toxins (= glucosinolates) after they are attacked by foliar herbivores. However, concentrations of glucosinolates were more than 3·5 times higher in young shoots ofB. nigrathan in corresponding shoots ofB. oleracea.Cocoon weight inC. glomeratawas unaffected by the foodplant on whichP. brassicaewas reared, whereas in 24‐h‐old host cocoons emerging adult hyperparasitoid body mass increased significantly with cocoon size and wasps were significantly larger, and survived better onB. oleraceathan onB. nigra. Moreover, body mass inL. nanawas typically larger in young (c.24 h), than in older (c.72 h) cocoons ofC. glomerata. Egg‐to‐adult development time inL. nanagenerally increased with host size and age, and wasps on younger hosts completed their development more rapidly onB. nigra.Our results clearly demonstrate that qualitative differences in herbivore diet can differently affect the performance of interacting organisms across several trophic levels, and suggest that bottom‐up forces may also play a role in mediating interactions involving plants–herbivores–parasitoids and hyperparasitoids.
Morphometric characterization of thalassohaline Artemia franciscana populations from the Colombian Caribbean
Authors: Camargo W. N. , Ely J. S. , Sorgeloos P. 
Published: May 2003

AbstractAim To establish possible interpopulation relationships among Colombian Artemia franciscana (Crustacea, Anostraca) populations.Location Colombian Caribbean coast (Manaure, Galerazamba, Salina Cero and Tayrona) and a similar thalassohaline reference population from San Francisco Bay (SFB‐USA).Methods Morphometric characters of male and female cultured individuals of A. franciscana were measured. The populations were grouped according to: (1) population type (populations grouped according to two broad regions of origin: North America and the Caribbean coast), and (2) specific geographical origin (populations selected according to five specific local origins: Manaure, Galerazamba, Salina Cero, Tayrona and SFB) and evaluated using forward stepwise discriminant analysis (SPSS, Ver. 10).Results Optimal discriminant variables for males grouped by the type of population were left setae and antenna length, and for females they were abdominal length and antenna length. However, for males grouped by their specific geographical origin, the optimal variables were furca length, left setae, antenna length, eye separation, abdominal width and abdominal length, and for the females, they were furca length, abdominal length, left setae and eye separation. Male and female Colombian Caribbean populations were separated from the North American populations. However, our results show that the classification based on male characters provides better group membership than females.Main conclusions Male morphometric characters separated the type of population groups more clearly than the female characters, because all Colombian populations were correctly positioned in the Caribbean coast region and the SFB population in the North American region, with no overlapping between the two types, as was the case for the female individuals. Likewise, male individuals correctly position the Salina Cero population to its neighbouring Galerazamba population and to the other Colombian populations. In contrast, female individuals from Salina Cero did not cluster with the other Colombian coast populations (Galerazamba, Tayrona and Manaure) or with the SFB population.
Variation in invertebrate–bryophyte community structure at different spatial scales along altitudinal gradients
Authors: Andrew N. R. , Rodgerson L. , Dunlop M. 
Published: May 2003

AbstractAim  This study assessed changes in diversity and assemblage composition in bryophytes and their associated invertebrates along altitudinal gradients in Australia and New Zealand. The importance of altitude in shaping these communities and for the diversity of both invertebrates and bryophytes was examined at different spatial scales, including local, altitudinal, regional and biogeographical.Location  Samples were taken from four Australasian mountain ranges between 42° and 43°S: Mt Field and Mt Rufus, Tasmania, Australia, and Otira Valley and Seaward Kaikoura Mountains, South Island, New Zealand.Methods  On both Tasmanian mountains, five altitudes were assessed (250, 500, 750, 1000 and 1250 m). At each location (mountain/altitude combination) two sites were chosen and six samples were taken. Six altitudes were assessed on New Zealand mountains (Otira: 250, 500, 750, 1000, 1250 and 1500 m; Kaikoura: 1130, 1225, 1325, 1425, 1525 and 2000 m). Bryophyte substrate was collected, and all samples were stored in 70% ethanol. Invertebrates were extracted from bryophytes using kerosene‐phase separation and all invertebrates were identified to family. At each location in Tasmania, all bryophyte species within six 25‐cm2 grids per site were collected and identified to species. Bryophytes from New Zealand were identified to species from the invertebrate sample substrate because of sampling constraints.Results  Altitude did have a significant effect on diversity, however, no general trend was found along the altitudinal gradient on the four mountains. There were distinct differences in diversity between biogeographical regions, mountains, altitudes and sites. In Tasmania, Mt Field had the highest diversity in invertebrates and bryophytes at 750 m. In contrast, Mt Rufus had consistent low invertebrate and bryophyte diversity along the entire altitudinal gradient. There were also distinctive differences between locations in the composition of invertebrate and bryophyte communities in Tasmania. Along the two altitudinal gradients in New Zealand, Otira had highest diversity for both invertebrates and bryophytes at low altitudes, whereas Kaikoura had highest invertebrate and lowest bryophyte diversity at the highest altitude.Main conclusions  There was an effect of altitude, however, there were no consistent changes in diversity or composition on the four different mountains. There was considerable local and regional variation, and, despite a strong sampling design, no underlying altitudinal trends were detectable. This study demonstrates the importance of examining a range of spatial scales if patterns in community structure along altitudinal gradients are to be studied. The implications of this study are discussed with reference to survey design, taxonomic resolution, climate change and conservation of habitat.