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Interspecific Differences (interspecific + difference)
Selected AbstractsInterspecific Differences in Responses to Predation Risk May Confer Competitive Advantages to Invasive Freshwater Turtle SpeciesETHOLOGY, Issue 2 2008Nuria Polo-Cavia The nature of competitive interactions between native and introduced invasive species is unclear. In the Iberian Peninsula, the introduced red-eared slider (Trachemys scripta elegans) is an invasive species that is competing and displacing the endangered native Spanish terrapin (Mauremys leprosa). We hypothesized that interspecific differences in antipredatory behavior might confer competitive advantages to introduced T. scripta. We examined whether interspecific differences in responses to predation risk affect the time that turtles remained hidden in the shell before using an active escape to water. Both turtle species adjusted hiding times by balancing predation threat, microhabitat conditions and the costs of remaining hidden. However, introduced T. scripta showed longer hiding times before escaping than native M. Leprosa, which, in contrast, switched from waiting hidden in the shell to escape to deep water as soon as possible. These interspecific differences might result from the risk of facing different types of predators in different microhabitats (land vs. water) in their original habitats. However, in anthropogenically altered habitats where predators have been greatly reduced, T. scripta may avoid potential costs of unnecessary repeated escape responses to water (e.g. interruption of basking). These behavioral asymmetries could contribute to the greater competitive ability of introduced T. scripta within anthropogenically disturbed environments. [source] Effects of experimental canopy gaps on mangrove recruitment: lack of habitat partitioning may explain stand dominanceJOURNAL OF ECOLOGY, Issue 2 2004Peter J. Clarke Summary 1Few species of Indo-pacific mangroves co-occur at spatial scales of canopy gaps despite environmental heterogeneity and a flora that has varied physiological and morphological traits, but experiments on why such communities are species poor are uncommon. 2Lack of habitat partitioning, in concert with competitive exclusion, may explain low species richness at canopy gap scales. This study examined whether mangrove recruitment differs among species with respect to the effect of forest gap size, ground disturbance, position along an intertidal gradient and canopy membership. 3The canopy of a tropical mangrove forest in northern Australia was experimentally manipulated to create two gap sizes (50 m2 and 225 m2) in low and high intertidal forests with or without sediment disturbance. Propagules of six species, from three mangrove families, were sown into treatments and their predation, establishment, growth and survival measured for 5 years. 4All species established, and five survived, in canopy gaps in both high and low intertidal positions. Interspecific difference in establishment, growth and survival of seedlings in two intertidal positions were not closely matched to canopy membership and hence this does not explain zonation. 5No seedlings survived under the canopy and there was little evidence for shade-tolerant species. The interactions between canopy treatments and sediment disturbance that would have indicated gap partitioning were not detected. Seedling growth and survival was enhanced in large canopy gaps but there were no growth differences among species that matched canopy membership of plots. 6Most species appear to be able to recruit in canopy gaps if there is no dispersal limitation. Rather, the range of species available to fill gaps is limited because predation of propagules advantages species that are from the adjacent canopy. Lack of partitioning of resources within gaps by species may result in the exclusion of competitors that are not canopy members, further reducing coexistence. [source] Spatial distribution and environmental correlates of Australian snubfin and Indo-Pacific humpback dolphinsECOGRAPHY, Issue 3 2006Guido J. Parra We present data on the spatial distribution of Australian snubfin and humpback dolphins using boat-based line transect surveys in three adjacent bays located in the Far Northern Section of the Great Barrier Reef Marine Park, northeast Queensland. We used Geographic Information Systems (GIS), and both randomization and Mantel tests to examine the relationship between the spatial distribution of the dolphins and three simple, readily quantified, environmental variables: distance to land, distance to river mouth, and water depth. Mantel tests allowed us to make clear inferences about the correlation of the species' distributions with environmental variables, while taking into account spatial autocorrelation and intercorrelation among variables. Randomization tests indicated snubfin and humpback dolphins occur closer to land than would be expected at random. Two-sample randomization tests indicated snubfin dolphins were found closer to river mouths than were humpback dolphins. Taking spatial autocorrelation into account, Mantel tests indicated all environmental variables were correlated with the spatial distribution of snubfin and humpback dolphins. Interspecific differences in spatial distribution appeared to be related to proximity to river mouths. Preference by snubfin and humpback dolphins for nearshore, estuarine waters is likely related to the productivity of these tropical coastal areas. This spatial analysis suggests that existing protected areas in this region may not include the most critical habitats for snubfin and humpback dolphins. The techniques used here shown relationships between the spatial distribution of the dolphins and environmental features that should facilitate their management and conservation. [source] Interspecific differences in population trends of Spanish birds are related to habitat and climatic preferencesGLOBAL ECOLOGY, Issue 1 2008Javier Seoane ABSTRACT Aim, Animal monitoring programmes have allowed analyses of population trends, most of which now comment on the possible effect of global climate change. However, the relationship between the interspecific variation in population trends and species traits, such as habitat preferences, niche breadth or distribution patterns, has received little attention, in spite of its usefulness in the construction of ecological generalizations. The objectives of this study were: (1) to determine whether there are characteristics shared among species with upwards or downwards trends, and (2) to assess whether population changes agree with what could be expected under global warming (a decrease in species typical of cooler environments). Location, The Spanish part of the Iberian Peninsula (c. 500,000 km2) in the south-western part of the Mediterranean Basin. Methods, We modelled recent breeding population changes (1996,2004), in areas without apparent land use changes, for 57 common passerine birds with species-specific ecological and distributional patterns as explanatory variables. Results, One-half of these species have shown a generalized pattern towards the increase of their populations, while only one-tenth showed a significant decrease. One half (54%) of the interspecific variability in yearly population trends is explained considering species-specific traits. Species showing more marked increases preferred wooded habitats, were habitat generalists and occupied warmer and wetter areas, while moderate decreases were found for open country habitats in drier areas. Main conclusions, The coherent pattern in population trends we found disagrees with the proposed detrimental effect of global warming on bird populations of western Europe, which is expected to be more intense in bird species inhabiting cooler areas and habitats. Such a pattern suggests that factors other than the increase in temperature may be brought to discussions on global change as relevant components to explain recent changes in biodiversity. [source] Influence of selected factors on the dietary compositions of three targeted and co-occurring temperate species of reef fishes: implications for food partitioningJOURNAL OF FISH BIOLOGY, Issue 6 2010M. E. Platell The dietary compositions of three medium to large targeted fish species, which co-occur over reefs in temperate waters of south-western Australia, were determined. These data were then used to ascertain statistically the extent to which body size, season and habitat influence the diets of these species and the degree to which food resources were partitioned among and within those species, and thus reduced the potential of interspecific and intraspecific competition. On the west coast, Bodianus frenchii (Labridae) and Epinephelides armatus (Serranidae) spent their whole life over prominent limestone reefs, as did Glaucosoma hebraicum (Glaucosomatidae) in all but juvenile life, when it lived over low-relief, limestone substrata. The dietary composition of each species changed with increasing body size, which, in G. hebraicum, was particularly pronounced at c. 300 mm total length (LT) and therefore at the size when this species shifts habitat. When the three species co-occurred over the same reefs, their dietary compositions were significantly different, with that of B. frenchii being by far the most discrete, reflecting a far greater contribution by sedentary taxa. Thus, the diet of B. frenchii was distinguished from those of the other two species in containing substantial volumes of bivalve and gastropod molluscs and echinoid echinoderms and essentially no teleosts. Although the diets of G. hebraicum and particularly E. armatus were dominated by teleosts, and especially for larger individuals, the former species ingested greater volumes of cephalopods and small crustaceans. The pointed jaws of B. frenchii, with their forwardly directed and interlocking anterior incisors, are ideally adapted for biting and retaining their invertebrate prey, which are attached to or reside within reef crevices. In contrast, the mouths of G. hebraicum and E. armatus are broader and rounder and contain numerous small, slender and inward-pointing teeth. These teeth, in conjunction with prominent backward-curved canines in E. armatus, facilitate the capture and retention of fish prey. Observations in situ indicate that G. hebraicum is a suction feeder, while E. armatus is predominantly a ram feeder. Although reef environments on the west and south coasts differ, the diet of B. frenchii on these coasts differed only slightly. Interspecific differences in diet, combined with size-related changes in dietary compositions and the occupation of different habitats by juvenile and adult G. hebraicum, reduce the potential for competition for food resources among and within B. frenchii, G. hebraicum and E. armatus and thus helps facilitate the coexistence of these species which historically have been abundant over reefs in south-western Australia. [source] COALESCENCE VERSUS COMPETITION: FIELD AND LABORATORY STUDIES OF INTRA- AND INTERSPECIFIC ENCOUNTERS AMONG COALESCING SEAWEEDSJOURNAL OF PHYCOLOGY, Issue 2000B. Santelices Classical ecological theory predicts that whenever growing individuals share a common and limiting resource, such as substratum in mid-intertidal and shallow subtidal habitats, preemptive competition will occur determining species abundance and distribution patterns. However, conspecificity of several ecologically dominant Rhodophyta may coalesce when grown in laboratory cultures. The extent at which intraspecific coalescence occurs in the field and whether the process may also happens during interspecific encounters remain to be determined. If intra- and interspecific coalescence effectively occurs, then coexistence through coalescence rises as an alternative to competition among red-algal dominated intertidal and shallow subtidal communities. Populations of Mazzaella laminarioides and Nothogenia fastigiata living in mid-intertidal, semi-exposed rocky habitats in Central Chile are being used to test the above ideas. Intra- and interspecific encounters occur in the field throughout the year. Coalescence does occur among conspecific partners but it has not been detected in interspecific encounters. Rather, a thick interface of compressed cells, necrotic tissues and cyanobacterial nodules is formed between the two contacting partners. In addition, observations of laboratory cultures indicate that spore germination, germling survival and differentiation of erect axes in bispecific cultures may be reduced when compared to single-species controls. Interspecific differences in growth and differentiation rates appear as the mechanisms explaining a lack of coalescence and negative effects during interspecific contacts. On the other hand, the existence of conspecific coalescence in the field suggests this process should be considered as a real alternative to intraspecific competition among coalescing Rhodophyta. [source] Interspecific differences in foraging preferences, breeding performance and demography in herring (Larus argentatus) and lesser black-backed gulls (Larus fuscus) at a mixed colonyJOURNAL OF ZOOLOGY, Issue 4 2006S.-Y. Kim Abstract Herring gulls Larus argentatus and lesser black-backed gulls Larus fuscus breeding at Walney Island, Cumbria, the largest breeding colony of the two species in the UK, have recently shown very different population trends. The former has declined sharply, whereas numbers of the latter have been maintained for several years. Here we compare aspects of the feeding and breeding ecology of the two species in order to examine whether or not this suggests explanations for their different population trends. Comparison of the ratio of the two species in flight lines leading to different feeding sites and their diet composition showed that the lesser black-backed gulls fed more at sea and the herring gulls fed more in the intertidal zone. Urban resources were used by both these species. These differences have been consistent over the last three decades. Susceptibility to death from botulism at the breeding colony was the same for the two species. The availability of the intertidal zone for foraging appears to have declined in recent years, and this may have had a more negative impact on the herring gull. However, the breeding success of the two species remains relatively high. This study suggests that differences in foraging behaviour and food availability during the breeding season are unlikely to be responsible for the marked differences in demographic trends in the two species. Changes in local food availability during the winter would be expected to have more effect on the resident herring gull. This work highlights the need for more detailed studies of the ecology of both species during the breeding season and in winter in regions showing differing patterns of population change. [source] Increased N affects P uptake of eight grassland species: the role of root surface phosphatase activityOIKOS, Issue 10 2010Yuki Fujita Increased N deposition may change species composition in grassland communities by shifting them to P limitation. Interspecific differences in P uptake traits might be a crucial yet poorly understood factor in determining the N effects. To test the effects of increased N supply (relative to P), we conducted two greenhouse fertilization experiments with eight species from two functional groups (grasses, herbs), including those common in P and N limited grasslands. We investigated plant growth and P uptake from two P sources, orthophosphate and not-readily available P (bound-P), under different N supply levels. Furthermore, to test if the N effects on P uptake was due to N availability alone or altered N:P ratio, we examined several uptake traits (root-surface phosphatase activity, specific root length (SRL), root mass ratio (RMR)) under varying N:P supply ratios. Only a few species (M. caerulea, A. capillaris, S. pratensis) could take up a similar amount of P from bound-P to that from orthophosphate. These species had neither higher SRL, RMR, phosphatase activity per unit root (Paseroot), nor higher total phosphatase activity (Pasetot: Paseroot times root mass), but higher relative phosphatase activity (Paserel: Pasetot divided by biomass) than other species. The species common from P-limited grasslands had high Paserel. P uptake from bound-P was positively correlated with Pasetot for grasses. High N supply stimulated phosphatase activity but decreased RMR and SRL, resulting in no increase in P uptake from bound-P. Paseroot was influenced by N:P supply ratio, rather than by only N or P level, whereas SRL and RMR was not dominantly influenced by N:P ratio. We conclude that increased N stimulates phosphatase activity via N:P stoichiometry effects, which potentially increases plant P uptake in a species-specific way. N deposition, therefore, may alter plant community structure not only by enhancing productivity, but also by favouring species with traits that enable them to persist better under P limited conditions. [source] Interspecific variation in the response to low temperature storage in different aphid parasitoidsANNALS OF APPLIED BIOLOGY, Issue 1 2010H. Colinet Cold storage of natural enemies usually involves placing insects under constant subambient temperatures. Even at non-freezing temperatures, a reduction in survival is the norm. Using fluctuating thermal regimes (FTR) instead of constant low temperature (CLT) has shown that mortality due to accumulation of chilling injuries was significantly reduced in Aphidius colemani. Whether this phenomenon can be generalised to other parasitoid species is not known. The aim of this study was to analyse interspecific variation in the ability to tolerate cold storage under CLT (continuous 2°C) versus FTR (daily cycle: 2°C for 22 h and 20°C for 2 h) for various durations (0,20 days). Survival, sex ratio and development of five different Aphidiine parasitoids were analysed: A. colemani, Aphidius ervi, Aphidius matricariae, Ephedrus cerasicola and Praon volucre. A marked interspecific variation in the ability to tolerate cold storage was observed: A. matricariae and A. ervi were most chill tolerant, P. volucre and E. cerasicola had an intermediate chill sensitivity and A. colemani was most chill sensitive. In all species tested, FTR significantly reduced cold-induced mortality. This phenomenon was manifested more in chill-sensitive species as they probably accumulate chilling injuries more rapidly. The sex ratio remained unaffected in all the species. Interspecific variation was also observed in developmental responses to cold storage. Under CLT, time to adult emergence of A. matricariae, A. colemani, A. ervi and P. volucre was temporarily stopped and in E. cerasicola it increased. Under FTR, the short daily intervals at 20°C for 2 h allowed parasitoids to continue development in all the species. Interspecific differences are discussed. This study suggests that positive impact of FTR may apply to a wide range of species. [source] Hurricane Impacts on a Mangrove Forest in the Dominican Republic: Damage Patterns and Early Recovery,BIOTROPICA, Issue 3 2001Ruth E. Sherman ABSTRACT On 22 September 1998, Hurricane Georges passed over the Dominican Republic causing extensive damage to a 4700 ha mangrove forest that has been the site of a detailed study of vegetation and ecosystem dynamics since 1994. We resurveyed the vegetation in permanent plots at 7 and 18 months after the hurricane to document structural damage of the forest and evaluate early recovery patterns. The intensity of damage was patchy across the landscape. Mortality (>5 cm DBH) ranged from 14 to 100 percent (by density) among the 23 different plots and averaged 47.7 percent across all plots. Reductions in total basal area ranged from 9 to 100 percent, averaging 42.4 percent. Mortality increased by 9 percent between surveys at 7 and 18 months post-hurricane. Interspecific differences in susceptibility to wind damage appeared to be a primary factor contributing to spatial patterns in mortality. Laguncularia racemosa experienced much less mortality (26%) than either Rhizophora mangle (50%) or Avicennia germinans (64%), and plot-level mortality was strongly associated with differences in species composition. There were no clear relationships between canopy height and tree damage at this site. Over 80 percent of the of the surviving R. mangle trees exhibited less than 50 percent crown damage, whereas ca 60 percent of the L. racemosa survivors suffered almost complete (75,100%) crown loss. By 18 months after the hurricane, the percentage of L. racemosa trees in the 75 to 100 percent damage class was reduced to 20 percent; in contrast, the health of many R. mangle individuals appeared to be declining, as the percentage of trees in the 50 to 100 percent damage class increased from 16 to 36 percent. Understory light levels, as measured by the gap light index, increased from an average value of 3 percent in the pre-hurricane forest to 51 percent at 7 months after the hurricane and decreased slightly to 47 percent at 18 months. Few saplings (>1 m tall and <5 cm DBH) survived the hurricane; 72 percent of the tagged individuals in transect-based plots and 66 percent of saplings in pre-hurricane canopy gaps were killed. Seedling and sapling populations of all three species appear to be recovering rapidly although their densities still are lower than in the pre-hurricane forest. It is too early to predict the trajectory of forest recovery, and continued monitoring of the spatial and temporal patterns of forest development is needed to improve our understanding of the role that large-scale disturbance events play on the dynamics of mangrove forest ecosystems. RESUMES El 22 de septiembre de 1998, el huracán Georges pasó sobre la República Dominicana causando daños extensos a 47 km2 de manglar que ha sido objeto un estudio detallado de vegetacion y dinámica de la communidad desde 1994. Se tomarón muestras de la vegetación en parcelas permanentes 7 y 18 meses después de paso del huracán para documentar los daños estructurales del bosque y evaluar los modelos de recuperacion temprana que siguieron posteriormente. La intensidad del daño fue irregular a través del paisaje. La mortalidad (>5 cm de dap) fue de 14 a 100 por ciento (para la densidad) en las 23 parcelas con un promedio de 47.7 por ciento. La reducción en área basal total fue de 9 a 100 por ciento con un promedio de 42.4 por ciento. La mortalidad aumentó 9 por ciento a los 7 y 18 meses después del huracán. Las diferencias interspecificas en la susceptibilidad a los daños causados por el viento fueron un factor contribuyente importante en los patrones espacios de mortalidad. Laguncularia racemosa sufrió menor mortalidad (26%) que Rhizophora mangle (50%) o Avicennia germinans (64%), la mortalidad en las parcelas estuvo asociada fuertemente con la diferencia en composición de especies. No hubo ningún patron definido entre la altura del dosel y el daño del árbol. Más del 80 por ciento de los árboles sobrevivientes de R. mangle exhibieron daoñres menores de 50 por ciento en sus copas, mientras que ca 60 por ciento de los L. racemosa sobrevivientes sufrió una perdida casi total (75-100%). Dieciocho meses despues del huracan, el porcentaje de arboles de L. racemosa con daños del 75-100 por ciento se redujó a 20 por ciento; en contraste, la salud de muchos individuos de R. mangle disminuyó conforme el porcentaje de árboles con daños del 50-100 por ciento aumentó de 16 a 36 por ciento. Los niveles de penetración de luz en el sotobosque, medidos como el indice de iluminacion en los claros, aumentó de un promedio de 3 por ciento antes del huracán. a 51 por ciento 7 meses después del huracán, y disminuyo ligeramente a 47 por [source] Feeding methods, visual fields and vigilance in dabbling ducks (Anatidae)FUNCTIONAL ECOLOGY, Issue 4 2002M. Guillemain Summary 1.,Visual fields were determined in two species of dabbling ducks (Anatini): Shoveler Anas clypeata L. (planktivore whose foraging is guided mainly by tactile cues) and Wigeon A. penelope L. (herbivore whose foraging is guided mainly by visual cues). 2.,The binocular fields of Shoveler and Wigeon are of similar maximum width (20°), but they differ in their position and vertical extent. The bill of the Shoveler lies in the very periphery of its frontal binocular field, which extends through 220° thus providing comprehensive visual coverage about the head. In Wigeon the bill is positioned more centrally in the frontal binocular field, which extends through 150° and results in the birds having a narrow blind area behind the head. 3.,The vigilance behaviour of Shoveler and Wigeon when foraging simultaneously was studied using a focal observation procedure at sites where the two species winter in sympatry. Focal Wigeon almost only fed by grazing. Only Shoveler feeding by dabbling (filtering the first centimetres of water) were used in the analyses. Wigeon spent significantly more time in head-up vigilance than Shoveler (F1,75 = 14·70, P = 0·0003). 4.,It is proposed that this interspecific difference in the proportion of time spent in vigilance behaviour may be an adaptive response to differences in the visual field topography of these species, particularly with respect to the presence/absence of a blind area to the rear of the head. 5.,The ability of foragers to combine part of their vigilance behaviour with head-down feeding has recently been recognized as influencing the trade-offs related to vigilance while foraging. This study shows that this ability may vary significantly between species, even within the same genus, and that these variations are likely to be due to contrasted visual fields, themselves related to the type of feeding techniques employed by the different duck species. [source] Photoperiodic and temperature control of nymphal development and induction of reproductive diapause in two predatory Orius bugs: interspecific and geographic differencesPHYSIOLOGICAL ENTOMOLOGY, Issue 4 2008DMITRY L. MUSOLIN Abstract The effects of day-length and temperature on pre-adult growth and induction of reproductive diapause are studied in Orius sauteri and Orius minutus (Heteroptera: Anthocoridae) from northern (43.0°N, 141.4°E) and central (36.1°N, 140.1°E) Japan. In the north, at 20 °C, pre-adult growth is slower under an LD 14 : 10 h photoperiod than under shorter or longer photophases. At 24 and 28 °C, the longer photophases result in shorter pre-adult periods. Acceleration of nymphal growth by short days in autumn appears to be adaptive. In the central region, this response is less pronounced, suggesting that timing of adult emergence is less critical than in the north. Day length also influences the thermal requirements for pre-adult development. The slope of the regression line representing temperature dependence of pre-adult development is significantly smaller and the lower development threshold (LDT) is significantly lower under an LD 12 : 12 h photoperiod than under long-day conditions. The weaker dependence of nymphal growth on temperature and the lower LDT in autumn might be adaptive. In the north, increased temperature shifts the critical day length of diapause induction and suppresses the photoperiodic response in O. sauteri but not in O. minutus. Further south, the incidence of diapause in both species is low even under short-day conditions but the same interspecific difference is observed (i.e. increase of temperature affects the response in O. sauteri but not in O. minutus). This suggests seasonally earlier diapause induction with weaker temperature dependence in O. minutus than in O. sauteri. [source] Carbon isotope discrimination and wood anatomy variations in mixed stands of Quercus robur and Quercus petraeaPLANT CELL & ENVIRONMENT, Issue 8 2001S. Ponton Abstract The two most common oak species in western Europe, Quercus robur and Quercus petraea, display different ecological behaviours, particularly with respect to their responses to drought. The ecophysiological basis of this niche difference is not understood well. Here we test the hypothesis that these two species present distinct water use efficiencies (WUEs), using the carbon isotope discrimination approach. Leaves and 13 dated ring sequences were sampled in 10 pairs of adult trees growing side by side. Carbon isotope composition was measured on cellulose extracts. In addition, relationships between carbon isotope discrimination and wood anatomy were assessed at the tree level. Quercus robur displayed a 1·0, larger isotopic discrimination than Q. petraea, and therefore a lower intrinsic WUE (,13%). This interspecific difference of isotopic discrimination was quite stable with time and independent of tree radial growth and climate fluctuations. A strong positive correlation was observed between average tree values of earlywood vessel surface area and 13C isotopic discrimination. This correlation was even higher with 13C of the 1976 dry year (r = 0·86). These observations led to the hypothesis that hydraulic properties of xylem could exert a constraint on leaf gas exchange, resulting in a larger WUE for individuals with smaller vessel cross-section area. [source] Growth and food availability of silver and bighead carps: evidence from stable isotope and gut content analysisAQUACULTURE RESEARCH, Issue 14 2009Qiong Zhou Abstract A 2-year investigation of growth and food availability of silver carp and bighead was carried out using stable isotope and gut content analysis in a large pen in Meiliang Bay of Lake Taihu, China. Both silver carp and bighead exhibited significantly higher ,13C in 2005 than in 2004, which can probably be attributed to two factors: (i) the difference between isotopic compositions at the base of the pelagic food web and (ii) the difference between the compositions of prey items and stable isotopes. The significantly positive correlations between body length, body weight and stable isotope ratios indicated that isotopic changes in silver carp and bighead resulted from the accumulation of biomass concomitant with rapid growth. Because of the drastic decrease in zooplankton in the diet in 2005, silver carp and bighead grew faster in 2004 than in 2005. Bighead carp showed a lower trophic level than silver carp in 2005 as indicated by stable nitrogen isotope ratios, which was possibly explained by the interspecific difference between the prey species and the food quality of silver carp and bighead. [source] Difference in Intensity of Ant Defense among Three Species of Macaranga Myrmecophytes in a Southeast Asian Dipterocarp Forest,BIOTROPICA, Issue 2 2000Takao Itioka ABSTRACT To examine interspecific variation in the intensity of ant defense among three sympatric species of obligate myrme-cophytes of Macaranga (Euphorbiaceae), we measured the ratio of ant biomass to plant biomass, ant aggressiveness to artificial damage on host plants, and increase in herbivore damage on host plants when symbiont ants were removed. Increase in herbivore damage from two- and four-week ant exclusion varied significantly among the three species. The decreasing order of vulnerability to herbivory was M. winkleri, M. trachyphylla, and M. beccariana. The antip/ant biomass ratio (= rate of the dry weight of whole ant colonies to the dry weight of whole aboveground plant parts) and ant agressiveness also varied significantly among the three species; the orders of both the ant/plant biomass ratio and ant aggressiveness were the same as in the herbivory increase. These results indicated that the intensity of ant defense differs predictably among sympatric species of obligate myrmecophytes on Macaranga. In addition to the interspecific difference in the total intensity of ant defense, when symbiont ants were excluded, both patterns of within-plant variation in the amount of herbivore damage and compositions of herbivore species that caused the damage differed among species. This suggests that the three Macaranga species have different systems of ant defense with reference to what parts of plant tissue are protected and what herbivorous species are avoided by ant defense. Thus, it is important to consider the interspecific variation in ant defense among Macaranga species to understand the herbivore community on Macaranga plants and the mechanisms that promote the coexistence of multiple Macaranga myrmecophytes. [source] Dispersal characteristics of three odonate species in a patchy habitatECOGRAPHY, Issue 1 2003S. Angelibert Dispersal has a potentially profound effect on the dynamics of populations especially when a population occupies a patchy habitat. Ponds surrounded by terrestrial landscape are an example of patchy distribution of physical conditions and constitute "islands" for odonates. Few studies have focussed on dispersal in odonates. We have used the direct method of dispersal observing (capture-mark-recapture technique) in order to estimate the degree of linkage in three patchy populations of odonate localised on three ponds. We also examined the differences in dispersal ability within and among three species (Coenagrion puella, Coenagrion scitulum and Libellula depressa). The ponds were situated in southwest France on a limestone plateau. In this arid area, these ponds constitute the only surface water available and are relatively sparsely distributed. The size of the ponds ranged from 48 to 79 m2 and they were 200 and 775 m apart. We demonstrated that three factors influence the dispersal ability of these odonates. The first is represented by the abiotic factors and especially weather conditions. This determines the number of days that dispersal is possible. The second is interspecific differences. We showed that sensitivity to weather conditions, species size and species behaviour influence dispersal ability. The third factor is the intraspecific characteristics. We demonstrated that there are differences in dispersal ability according to sex and age. To conclude, we discuss the importance of pond management to maintain the existing odonate populations and to facilitate introduction of new populations in this region where little exchange occurs between ponds. [source] Variation in mistletoe seed deposition: effects of intra- and interspecific host characteristicsECOGRAPHY, Issue 2 2002Juliann Eve Aukema We investigated differences in host infection by a desert mistletoe, Phoradendron californicum, and examined one of the processes that contributes to these differences: variation in seed deposition among host individuals and species. In the Sonoran Desert, P. californicum parasitizes the sympatric leguminous trees Olneya tesota, Cercidium microphyllum, Prosopis velutina, Acacia constricta, and Acacia greggii. We hypothesized that seed deposition depends on host height and crown architecture. At a site in Arizona, frequency of infection did not reflect host relative abundance. Olneya tesota was parasitized at a higher frequency than expected from its abundance and maintained the highest mistletoe loads per individual host. In contrast, P. velutina was infected less frequently than expected. Infection frequency increased with host tree height for all hosts. Mistletoe seed deposition by avian dispersers differed among host species and was disproportionately high in O. tesota and P. velutina. Seed deposition was higher in infected than in non-infected host trees, and increased with tree height in O. tesota but not in C. microphyllum. We suspect that increased seed deposition with height in O. tesota may be due to the preference of seed-dispersing birds for higher perches. Some host tree species, such as C. microphyllum and A. constricta, probably received fewer mistletoe seeds because birds avoid hosts with dense and spiny crowns. Mistletoe populations are plant metapopulations in which host trees are patches and the frequency of infection in each host species/patch type is the result of interspecific differences in the balance between mistletoe colonization and extinction. From this perspective, our study of host use and seed dispersal is a metapopulation study of patch occupancy and propagule distribution among available patch types. Our seed-dispersal study demonstrates that the mechanisms that create pattern in patchy plant populations can be investigated in mistletoe systems. [source] Modelling rainfall interception loss in forest restoration trials in PanamaECOHYDROLOGY, Issue 3 2010Darryl E. Carlyle-Moses Abstract A modified Liu analytical model of rainfall interception (Ic) by tree canopies was evaluated using rainfall, throughfall and stemflow data collected from forest restoration trials in the Republic of Panama. The model uses an introduced approach to estimating the water storage capacities of tree boles, which has a more realistic physical basis than earlier iterations of the Liu model. Study species (Acacia mangium, Gliricidia sepium, Guazuma ulmifolia, Ochroma pyramidale, and Pachira quinata) were selected on the basis of differing leaf size and crown characteristics. Significant interspecific differences in both observed and simulated cumulative interception loss were found, with A. mangium intercepting more rainfall than other species. Errors between calculated and modelled cumulative Ic ranged from + 6·3% to + 30·5%, with modelled Ic always being the larger term. During-event evaporation rates from the study trees were positively related to tree height, crown area, and basal diameter. Crown area and the storage capacity of tree boles were negatively correlated. The results of a sensitivity analysis suggested that the modified model was most sensitive to variations in during-event evaporation rate. The implications of the model's sensitivity to during-event evaporation and the importance of this mechanism of interception loss are discussed, while suggestions are provided that may lead to further improvements to the analytical model. Copyright © 2010 John Wiley & Sons, Ltd. [source] Non-random distribution among a guild of parasitoids: implications for community structure and host survivalECOLOGICAL ENTOMOLOGY, Issue 6 2006ANTHONY M. ROSSI Abstract 1.,Immature stages of the gall midge, Asphondylia borrichiae, are attacked by four species of parasitoids, which vary in size and relative abundance within patches of the gall midge's primary host plant, sea oxeye daisy (Borrichia frutescens). 2.,In the current study, a bagging experiment found that the smallest wasp, Galeopsomyia haemon, was most abundant in galls exposed to natural enemies early in the experiment, when gall diameter is smallest, while the wasp with the longest ovipositor, Torymus umbilicatus, dominated the parasitoid community in galls that were not exposed until the 5th and 6th weeks when gall diameter is maximal. 3.,Moreover, the mean number of parasitoids captured using large artificial galls were 70% and 150% higher compared with medium and small galls respectively, while stem height of artificial galls significantly affected parasitoid distribution. Galls that were level with the top of the sea oxeye canopy captured 60% more parasitoids compared with those below the canopy and 50% more than galls higher than the plant canopy. 4.,These non-random patterns were driven primarily by the differential distribution of the largest parasitoid, T. umbilicatus, which was found significantly more often than expected on large galls and the smallest parasitoid of the guild, G. haemon, which tended to be more common on stems level with the top of the plant canopy. 5.,Large Asphondylia galls, especially those located near the top of the Borrichia canopy, were more likely to be discovered by searching parasitoids. Results using artificial galls were consistent with rates of parasitism of Asphondylia galls in native patches of sea oxeye daisy. Gall diameter was 19% greater and the rate of parasitism was reduced by almost 50% on short stems; as a result, gall abundance was 24% higher on short stems compared with ones located near the top of the plant canopy. 6.,These results suggest that parasitoid community composition within galls is regulated by both interspecific differences in ovipositor length and preferences for specific gall size and/or stem length classes. [source] Insect colonisation sequences in bracts of Heliconia caribaea in Puerto RicoECOLOGICAL ENTOMOLOGY, Issue 4 2000Barbara A. Richardson Summary 1. It was predicted that insects colonising Heliconia phytotelmata would exploit the different bract conditions along inflorescences, which result from sequential ageing. 2. Flowering of H. caribaea is asynchronous over a 6-month period. A method of identifying bracts of the same age, regardless of position on the inflorescence or inflorescence age, and from different plants over 2 years, was developed using comparative flowering phenology. 3. Heliconia insect larval communities were remarkably consistent from year to year in species composition and relative abundance. Occurrence within the plant population was also similar from year to year, and most species were Heliconia specific. 4. Significant interspecific differences were found in bract utilisation, with populations peaking at different stages of bract development. Ceratopogonid larvae were the earliest colonisers, followed by psychodids, syrphids, and culicids. Tipulids occurred much later in the cycle of bract development and ageing. These patterns were consistent in both years. 5. Patterns of bract utilisation provide strong support for temporal niche partitioning by variation in oviposition and development time. Communities were not considered to be structured by predation or pH changes along the bract sequence. [source] Is selection of host plants by Plagiodera versicolora based on plant-related performance?ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 2 2008Sawako Egusa Abstract Plant-related performance may be one of the most important factors in the selection of host plants by insect herbivores. We investigated the importance of plant-related performance in host selection by the willow leaf beetle, Plagiodera versicolora (Laicharting) (Coleoptera: Chrysomelidae), on four willow species: Salix chaenomeloides Kimura, Salix eriocarpa Fr. et Sav., Salix integra Thunb., and Salix serissaefolia Kimura (Salicaceae). Bagging experiments in the field revealed that the performance of P. versicolora adults and larvae differed significantly among willow species under enemy-free conditions and at constant densities. Egg clutch and larval abundance were positively related to adult abundance. Plagiodera versicolora adults did not discriminate strongly among willow species for feeding and oviposition. Larval performance did not differ among willow species in the presence of natural enemies, suggesting that interspecific differences in host quality were overridden by mortality from natural enemies. Adult and egg clutch abundance of P. versicolora changed seasonally despite the temporal stability of adult and larval performance under enemy-free field conditions. Thus, plant-related performance of P. versicolora adults and larvae may contribute little to population growth and temporal dynamics of host use in P. versicolora. Potential factors that reduce discrimination of P. versicolora among host willow species are discussed. [source] Nonnutrient anthropogenic chemicals in seagrass ecosystems: Fate and effectsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2009Michael A. Lewis Abstract Impacts of human-related chemicals, either alone or in combination with other stressors, are important to understand to prevent and reverse continuing worldwide seagrass declines. This review summarizes reported concentrations of anthropogenic chemicals in grass bed,associated surface waters, sediments, and plant tissues and phytotoxic concentrations. Fate information in seagrass-rooted sediments and overlying water is most available for trace metals. Toxicity results in aqueous exposures are available for at least 13 species and a variety of trace metals, pesticides, and petrochemicals. In contrast, results for chemical mixtures and chemicals in sediment matrices are uncommon. Contaminant bioaccumulation information is available for at least 23 species. The effects of plant age, tissue type, and time of collection have been commonly reported but not biological significance of the chemical residues. Experimental conditions have varied considerably in seagrass contaminant research and interspecific differences in chemical residues and chemical tolerances are common, which limits generalizations and extrapolations among species and chemicals. The few reported risk assessments have been usually local and limited to a few single chemicals and species representative of the south Australian and Mediterranean floras. Media-specific information describing exposure concentrations, toxic effect levels, and critical body burdens of common near-shore contaminants is needed for most species to support integrated risk assessments at multiple geographical scales and to evaluate the ability of numerical effects-based criteria to protect these marine angiosperms at risk. [source] Linking metal bioaccumulation of aquatic insects to their distribution patterns in a mining-impacted riverENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2004Daniel J. Cain Abstract Although the differential responses of stream taxa to metal exposure have been exploited for bioassessment and monitoring, the mechanisms affecting these responses are not well understood. In this study, the subcellular partitioning of metals in operationally defined metal-sensitive and detoxified fractions were analyzed in five insect taxa. Samples were collected in two separate years along an extensive metal contamination gradient in the Clark Fork River (MT, USA) to determine if interspecific differences in the metal concentrations of metal-sensitive fractions and detoxified fractions were linked to the differences in distributions of taxa relative to the gradient. Most of the Cd, Cu, and Zn body burdens were internalized and potentially biologically active in all taxa, although all taxa appeared to detoxify metals (e.g., metal bound to cytosolic metal-binding proteins). Metal concentrations associated with metal-sensitive fractions were highest in the mayflies Epeorus albertae and Serratella tibialis, which were rare or absent from the most contaminated sites but occurred at less contaminated sites. Relatively low concentrations of Cu were common to the tolerant taxa Hydropsyche spp. and Baetis spp., which were widely distributed and dominant in the most contaminated sections of the river. This suggested that distributions of taxa along the contamination gradient were more closely related to the bioaccumulation of Cu than of other metals. Metal bioaccumulation did not appear to explain the spatial distribution of the caddisfly Arctopsyche grandis, considered to be a bioindicator of metal effects in the river. Thus, in this system the presence/absence of most of these taxa from sites where metal exposure was elevated could be differentiated on the basis of differences in metal bioaccumulation. [source] Interspecific Differences in Responses to Predation Risk May Confer Competitive Advantages to Invasive Freshwater Turtle SpeciesETHOLOGY, Issue 2 2008Nuria Polo-Cavia The nature of competitive interactions between native and introduced invasive species is unclear. In the Iberian Peninsula, the introduced red-eared slider (Trachemys scripta elegans) is an invasive species that is competing and displacing the endangered native Spanish terrapin (Mauremys leprosa). We hypothesized that interspecific differences in antipredatory behavior might confer competitive advantages to introduced T. scripta. We examined whether interspecific differences in responses to predation risk affect the time that turtles remained hidden in the shell before using an active escape to water. Both turtle species adjusted hiding times by balancing predation threat, microhabitat conditions and the costs of remaining hidden. However, introduced T. scripta showed longer hiding times before escaping than native M. Leprosa, which, in contrast, switched from waiting hidden in the shell to escape to deep water as soon as possible. These interspecific differences might result from the risk of facing different types of predators in different microhabitats (land vs. water) in their original habitats. However, in anthropogenically altered habitats where predators have been greatly reduced, T. scripta may avoid potential costs of unnecessary repeated escape responses to water (e.g. interruption of basking). These behavioral asymmetries could contribute to the greater competitive ability of introduced T. scripta within anthropogenically disturbed environments. [source] Evolution of Courtship Behaviour Patterns and Reproductive Isolation in the Desmognathus ochrophaeus ComplexETHOLOGY, Issue 5 2002Louise S. Mead The extent to which differences in courtship behaviour patterns act as mechanisms of reproductive isolation is critical to understanding both speciation and the evolution of these behaviour patterns. While numerous studies have investigated intraspecific and interspecific differences in courtship, fewer interpret results in a phylogenetic framework. We describe and analyse geographic variation in the courtship behaviour patterns of the Allegheny Dusky salamander (Desmognathus ochrophaeus). We then examine courtship among closely related species in the D. ochrophaeus complex in a phylogenetic context. We found that populations of D. ochrophaeus separated by extensive geographic distances show little variation in courtship behaviour patterns and are sexually compatible. This contrasts with significant levels of sexual isolation between D. ochrophaeus and other species in the complex. Mapping behaviour patterns onto a phylogeny that we generated from cytochrome b sequences indicates that two behaviour patterns present in the courtship sequence of other members in the complex have either been lost in D. ochrophaeus or gained independently in other species in the complex. Loss of these behaviour patterns may result in reproductive isolation between D. ochrophaeus and its sister taxon, D. orestes. [source] PERSPECTIVE: FEMALE REMATING, OPERATIONAL SEX RATIO, AND THE ARENA OF SEXUAL SELECTION IN DROSOPHILA SPECIESEVOLUTION, Issue 9 2002Therese Ann Markow Abstract., As commonly observed among closely related species within a variety of taxa, Drosophila species differ considerably in whether they exhibit sexual dimorphism in coloration or morphology. Those Drosophila species in which male external sexual characters are minimal or absent tend, instead, to have exaggerated ejaculate traits such as sperm gigantism or seminal nutrient donations. Underlying explanations for the interspecific differences in the presence of external morphological sexual dimorphism versus exaggerated ejaculate traits are addressed here by examining the opportunity for sexual selection on males to occur before versus after mating in 21 species of Drosophila. Female remating frequency, an important component of the operational sex ratio, differs widely among Drosophila species and appears to dictate whether the arena of sexual selection is prior to, as opposed to after, copulation. Infrequent female mating results in fewer mating opportunities for males and thus stronger competition for receptive females that favors the evolution of male characters that maximize mating success. On the other hand, rapid female remating results in overlapping ejaculates in the female reproductive tract, such that ejaculate traits which enhance fertilization success are favored. The strong association between female remating frequency in a given species and the presence of sexually selected external versus internal male characters indicates that the relationship be examined in other taxa as well. [source] Temperature-dependent plasticity of segment number in an arthropod species: the centipede Strigamia maritimaEVOLUTION AND DEVELOPMENT, Issue 4 2008Vincent Vedel SUMMARY The evolution of arthropod segment number provides us with a paradox, because, whereas there is more than 20-fold variation in this character overall, most classes and orders of arthropods are composed of species that lack any variation in the number of segments. So, what is the origin of the higher-level variation? The centipede order Geophilomorpha is unusual because, with the exception of one of its families, all species exhibit intraspecific variation in segment number. Hence it provides an opportunity to investigate how segment number may change in a microevolutionary context. Here, we show that segment number can be directly altered by an environmental factor (temperature),this is the first such demonstration for any arthropod. The direction of the effect is such that higher temperature during embryogenesis produces more segments. This potentially explains an intraspecific cline in the species concerned, Strigamia maritima, but it does not explain how such a cline is translated into the parallel interspecific pattern of lower-latitude species having more segments. Given the plastic nature of the intraspecific variation, its link with interspecific differences may lie in selection acting on developmental reaction norms. [source] Genetic variation for dorsal,ventral patterning of the Drosophila melanogaster eggshellEVOLUTION AND DEVELOPMENT, Issue 2 2005Lisa M. Goering Summary Patterning of the insect eggshell is an excellent system for exploring the molecular basis of phenotypic variation. In Drosophila melanogaster, two dorsal,anterior respiratory appendages are produced in response to signaling through the Epidermal growth factor receptor (Egfr). Previous work implicates Egfr pathway function in both intraspecific variation for dorsal appendage spacing (DAS) on the eggshell, as well as interspecific differences in dorsal appendage number and location. To test the hypothesis that genetic variation in Egfr contributes to variation in eggshell patterning, we have made use of naturally occurring intraspecific variation for DAS as a model quantitative trait. We found that there is substantial segregating genetic variation for DAS in D. melanogaster, and have tested for associations with 289 common polymorphisms in the Egfr locus. A marginal association was seen with two polymorphic sites in Egfr; however, we failed to replicate these findings in a second population, or in a modified quantitative complementation test designed to specifically test the effects of the putative polymorphisms. Therefore, we conclude that the polymorphisms we have identified in Egfr do not contribute to variation in DAS, and further work is required to understand the genetic architecture of this trait. [source] Amphibian defenses against ultraviolet-B radiationEVOLUTION AND DEVELOPMENT, Issue 1 2003Andrew R. Blaustein SUMMARY As part of an overall decline in biodiversity, amphibian populations throughout the world are disappearing. There are a number of potential causes for these declines, including those related to environmental changes such as increasing ultraviolet-B (UV-B) radiation due to stratospheric ozone depletion. UV-B radiation can kill amphibian embryos or can cause sublethal effects that can harm amphibians in later life stages. However, amphibians have defenses against UV-B damage that can limit damage or repair it after exposure to UV-B radiation. These include behavioral, physiological, and molecular defenses. These defenses differ interspecifically, with some species more able to cope with exposure to UV-B than others. Unfortunately, the defense mechanisms of many species may not be effective against increasing persistent levels of UV-B radiation that have only been present for the past several decades due to human-induced environmental damage. Moreover, we predict that persistent UV-B,induced mortality and sublethal damage in species without adequate defenses could lead to changes in community structure. In this article we review the effects of UV-B radiation on amphibians and the defenses they use to avoid solar radiation and make some predictions regarding community structure in light of interspecific differences in UV-B tolerance. [source] Pond canopy cover: a resource gradient for anuran larvaeFRESHWATER BIOLOGY, Issue 3 2006LUIS SCHIESARI Summary 1.,The gradient in pond canopy cover strongly influences freshwater species distributions. This study tested the effects of canopy cover on the performance of two species of larval anurans, a canopy cover generalist (Rana sylvatica, the wood frog) and an open-canopy specialist (R. pipiens, the leopard frog), and tested which factors co-varying with canopy cover mediate these effects. 2.,A field transplant experiment demonstrated that canopy cover had negative performance effects on both species. However, leopard frogs, which grow faster than wood frogs in open-canopy ponds, were more strongly affected by closed-canopy pond conditions. 3.,Closed-canopy ponds had lower temperature, dissolved oxygen (DO), and food nutritional quality as indicated by carbon-to-nitrogen ratio (C : N) analysis of field-sampled food types, and of gut contents of transplanted larvae. 4.,Laboratory experiments demonstrated that higher temperature and food quality but not DO substantially increased larval growth. However, only food quality increased growth rates of leopard frogs more than wood frogs. 5.,The strong correlation of growth rates to gut content C : N in the field, and the similarity of growth curves as a function of resource quality in the field and laboratory, strongly suggest that resources are of primary importance in mediating intraspecific, and especially interspecific differences in performance across the canopy cover gradient. [source] | ||||||||||||||||||||||||||||||||||