Interspecific Correlation Research Articles

Density-dependent mortality versus spatial segregation in early life stages of Abies densa and Rhododendron hodgsonii in Central Bhutan

In order to improve the understanding on the coexistence of rhododendron species and canopy trees in old growth forests with less anthropogenic influence, we studied the role of spatial segregation versus density-dependent mortality of regeneration of Abies densa and Rhododendron hodgsonii in Central Bhutan. The spatial patterns and the microsite preferences of A. densa and R. hodgsonii were studied on 12 permanent sample plots in 1996 and 2001 in Central Bhutan. We characterized survival of the two species on different microsites and tested for deviations of random mortality. Intraspecific spatial correlations were highly positive for individuals of both species in adjacent size classes. Higher positive intraspecific as compared to interspecific correlations suggested spatial segregation of patches of different species and of plants in different size classes. For A. densa seedlings, we detected density-independent mortality as a response to environmental heterogeneity. Spatial distribution of A. densa trees was random or overdispersed showing that in later life stages competition gets stronger. Seedlings of R. hodgsonii showed higher densities than seedlings of A. densa. Density-dependent mortality started at earlier life stages, when density in clumps was high. We found seedlings of both species on all microsites; temporal changes of percentages of seedlings on different microsites showed a similar trend with increases of seedlings on bryophyte mats and decreases on all other microsites. Decreases on litter and nurse logs, however, were much stronger for A. densa than for R. hodgsonii. R. hodgsonii was more frequent on nurse logs and showed better survival on this microsite. Survival of A. densa on nurse logs was low; nurse logs do not play an important role as safe site for A. densa in stands with an understory of R. hodgsonii. Percentages of R. hodgsonii established on litter showed only small decreases and were still higher than its spatial coverage. A. densa had seedlings in a seedling and sapling bank. Survival in a storage stage allows A. densa to outweigh the limitations of narrower regeneration niches and may, in combination with spatial segregation in early life stages, contribute to the coexistence of the two species.

Morphometric Analysis of Male Genitalia in Sibling Species of Drosophila virilis Sturt.

The structure of male genital organs in sibling species of the virilis group of Drosophila was examined using methods of multivariate statistics. The differences among these species were estimated using 33 indices and 2 angle parameters. The intraspecific and interspecific correlation structure of the examined characters and the order of their divergence were established. The key characters with respect to forming interspecific differences in the virilis species group were identified. Based on these results, the relative systematic positions of the sibling species are discussed as well as similarities and differences of the pattern of relationships among the species from that generally accepted for the virilis group.

Metabolic rate and jump performance in seven species of desert fleas

We hypothesized that sexual and interspecific differences in jumping performance of fleas found in our previous study are correlated with differences in resting metabolic rate (RMR) between sexes and among species. To test this hypothesis, we measured RMR of seven flea species ( Xenopsylla conformis mycerini, Xenopsylla ramesis, Xenopsylla dipodilli, Parapulex chephrenis, Synosternus cleopatrae pyramidis, Nosopsyllus iranus theodori and Stenoponia tripectinata medialis). We compared RMR between sexes and among species and examined whether there is intra- and interspecific correlation between RMR and jumping ability. Both mass-specific and mass-independent RMR were the highest in female S. t. medialis, whereas mass-specific RMR was the lowest in male X. dipodilli and mass-independent RMR was the lowest in three Xenopsylla species and P. chephrenis. Mass-specific and mass-independent RMR were significantly higher in females than in males in all fleas except S. t. medialis. Differences in jumping ability between males and females were found to be correlated with sexual differences in mass-specific or mass-independent RMR. Interspecific comparison showed that the length of jump in both male and female fleas was strongly affected by their mass-specific and mass-independent RMR.

Colonization of fleshy-fruited plants beneath perch plant species that bear fleshy fruit

We evaluated the contribution of seed dispersal by birds to the colonization of fleshy-fruited plants beneath plants that bear fleshy fruits and were used as perches by birds. Specifically, we investigated the composition of seeds and saplings sampled beneath nine fleshy-fruited perch plant species in a Pinus thunbergii stand on a coastal sand dune in central Japan. Both the numbers and the species numbers of bird-dispersed (pulpless) seeds differed significantly among the perch plant species. Nevertheless, the quantitative compositions of bird-dispersed seeds were similar among the perch plant species because of the significant positive interspecific correlations of species rank order in numbers of bird-dispersed seeds per species. Similar relationships were also found for saplings. For each perch plant species, the numbers of fallen conspecific seeds were significantly higher than or not different from those of heterospecific seeds. Furthermore, the numbers of pulpy seeds that fell directly from the perch plant were significantly higher than those of bird-dispersed conspecific seeds for seven of nine perch plant species. However, the densities of conspecific saplings were significantly lower than those of heterospecific saplings. Most pulpy seeds, therefore, probably do not germinate beneath their mother plants, and conspecific seeds probably accumulate in seed banks or are consumed by herbivores.

Morphometrical evolution in a Drosophila clade: theDrosophila obscuragroup

Five morphometrical traits (wing and thoraxlength, ovariole number, and thoracic and female abdomen pigmentation) were investigated in laboratory stocks of 20 species belonging to the Drosophila obscura group (subgenus Sophophora). These species originated from four biogeographical regions and represent all five of the presently recognized, taxonomic subgroups. Size-related traits (wing and thorax length) were highly variable across species, and interspecific variation explained more than 90% of total variability. In both traditional and phylogenetic analyses, wing size was positively correlated with latitude of origin. These interspecific correlations were however notably weaker than those for intraspecific correlations. Wing/thoraxratio, which may be related to flight capacity, showed little variation. Ovariole number was highly variabl e (range 27–53) both within and between species, and was positively correlated with the wing/thoraxratio, suggesting that species with relatively large ovaries have relatively low wing loading. Although many species are completely dark, 11 had some regions of light coloration. A light thoraxwith a median darkening was observed in sixspecies. A variable pigmentation of abdominal tergites, in females only, was found in nine species, belonging to three subgroups only. With respect to both molecular phylogeny and morphometrical evolution, the D. obscura subgroup is probably now the best investigated clade in Drosophila.

No significant relationship exists between seedling relative growth rate under nutrient limitation and potential tissue toxicity

Summary We asked two questions in this study: (i) is there is there a negative correlation between relative growth rate (RGR) among 19 species of herbaceous Asteraceae grown under nutrient limitation and potential tissue toxicity; and (ii) is the degree of toxicity of these species different than those measured in a previous study, in which the same species were grown under non‐limiting conditions? In the present study we grew 19 of the same species as previously in hydroponic sand culture for which the growth rate was limited by nutrient supply, and compared RGR and potential tissue toxicity due to secondary compounds. Under such conditions, RGR was reduced by 25%; specific leaf area was reduced by 32%; root : shoot ratios were increased by 320%; leaf nitrogen content was reduced by 69%; and potential toxicity was decreased by 46%. Although nutrient limitation clearly decreased both RGR and potential toxicity, we found no interspecific correlation between RGR and toxicity. We conclude that there was no detectable trade‐off between RGR and potential toxicity due to secondary compounds.

Population density and geographical range size in the introduced and native passerine faunas of New Zealand

AbstractThe current avifauna of New Zealand comprises species with two distinct origins: those that evolved in New Zealand or colonized naturally from neighbouring landmasses, and those that were deliberately introduced to the islands by European settlers. Elsewhere, it has been shown that for species introduced to New Zealand from Britain there is a positive interspecific correlation between the geographical range sizes attained in both countries. Since positive relationships between abundance, measured either as population size or density, and geographical range size are a near ubiquitous feature of assemblages of closely related animal species, this suggests that species’ abundances may also be so correlated between the two countries. Here, data for 12 passerine bird species introduced to New Zealand from Britain are used to compare population densities and density–range size relationships in their native and alien ranges. In addition, the density–range size relationship for 12 passerine bird species that can be considered native to New Zealand is compared to that for the introduced species. The geographical range size and the mean and maximum densities of introduced species in New Zealand were significantly positively correlated with those values for the same species in Britain. However, in no case was the relationship between mean density and range size significant. While not statistically significant, density–range size relationships for introduced species are similar in New Zealand and Britain, but those for introduced and native species in New Zealand are quite different. Implications of these patterns are discussed.

Effects of high intensity exercise training on cardiovascular function, oxygen uptake, internal oxygen transport and osmotic balance in chinook salmon (Oncorhynchus tshawytscha) during critical speed swimming.

To examine cardiorespiratory plasticity, cardiovascular function, oxygen consumption, oxygen delivery and osmotic balance were measured at velocities up to critical swimming speed (Ucrit) in seawater-adapted chinook salmon. We used two groups of fish. The control group had swum continuously for 4 months at a low intensity (0.5 BLs(-1)) and the other was given a high-intensity training regimen (a Ucrit swim test on alternate days) over the same period of time. Compared with available data for other salmonid species, the control group had a higher maximum oxygen consumption (MO2max; 244 micromol O2 min(-1) kg(-1)), cardiac output (Qmax; 65 ml min(-1) kg(-1)) and blood oxygen content (CaO2; 15 ml O2 dl(-1)). Exercise training caused a 50% increase in MO2max without changing either Ucrit or CaO2, even though there were small but significant increases in hematocrit, hemoglobin concentration and relative ventricular mass. During swimming, however, exercise-trained fish experienced a smaller decrease in body mass and muscle moisture, a smaller increase in plasma osmolality, and reduced venous oxygen stores compared with control fish. Consequently, exercise training apparently diminished the osmo-respiratory compromise, but improved oxygen extraction at the tissues. We conclude that the training-induced increase in MO2max provided benefits to systems other than the locomotory system, such as osmoregulation, enabling trained fish to better multitask physiological functions while swimming. Furthermore, because a good interspecific correlation exists between MO2max and arterial oxygen supply (TO2max; r2=0.99) among temperate fish species, it is likely that CaO2 and Qmax are principal loci for cardiorespiratory evolutionary adaptation but not for intraspecific cardiorepiratory plasticity as revealed by high intensity exercise training.

Resistance to temperature extremes between and within life cycle stages in Drosophila serrata, D. birchii and their hybrids: intraspecific and interspecific comparisons

Intraspecific Drosophila studies suggest that resistance to heat and cold stresses are largely independent and that correlations across life cycle stages are low whereas comparisons of Drosophila species indicate correlations between heat and cold resistance as well as between resistance levels in different life cycle stages. These inconsistent results may reflect differences in associations among traits at the interspecific and intraspecific levels or interspecific correlations arising because of correlated selection pressures. These alternatives were tested using Drosophila serrata, D. birchii and hybrids derived from these species. Variation among hybrid lines and families was used to test associations at the interspecific level while intraspecific variation was examined using isofemale lines of D. serrata. There was a significant association between adult heat knockdown time at 38°C and adult cold resistance in one set of hybrid lines. An association between female knockdown resistance to heat and larval heat resistance was also evident in one set of hybrids. Resistance to heat and cold at the larval stage were not correlated at either the intraspecific or interspecific levels. At the intraspecific level, larval heat resistance and two measures of adult heat resistance were uncorrelated. Moreover, adult and larval cold resistance measures were not correlated at either the intraspecific or interspecific levels. These results suggest that there are no associations between resistance to heat and cold extremes and that extreme temperature resistance is largely independent across life cycle stages at both the intraspecific and interspecific levels. Species associations may therefore arise from correlated selection pressures rather than trait correlations.

Resistance to temperature extremes between and within life cycle stages in Drosophila serrata, D. birchii and their hybrids: intraspecific and interspecific comparisons

Intraspecific Drosophila studies suggest that resistance to heat and cold stresses are largely independent and that correlations across life cycle stages are low whereas comparisons of Drosophila species indicate correlations between heat and cold resistance as well as between resistance levels in different life cycle stages. These inconsistent results may reflect differences in associations among traits at the interspecific and intraspecific levels or interspecific correlations arising because of correlated selection pressures. These alternatives were tested using Drosophila serrata, D. birchii and hybrids derived from these species. Variation among hybrid lines and families was used to test associations at the interspecific level while intraspecific variation was examined using isofemale lines ol'D. serrata. There was a significant association between adult heat knockdown time at 38oC and adult cold resistance in one set of hybrid lines. An association between female knockdown resistance to heat and larval heat resistance was also evident in one set of hybrids. Resistance to heat and cold at the larval stage were not correlated at either the intraspecific or interspecific levels. At the intraspecific level, larval heat resistance and two measures of adult heat resistance were uncorrected. Moreover, adult and larval cold resistance measures were not correlated at either the intraspecific or interspecific levels. These results suggest that there arc no associations between resistance to heat and cold extremes and that extreme temperature resistance is largely independent across life cycle stages at both the intraspecific and interspecific levels. Species associations may therefore arise from correlated selection pressures rather than trait correlations.

Mitochondrial DNA variation in the hybridizing fire-bellied toads, Bombina bombina and B. variegata.

Using five restriction enzymes, geographical variation of mitochondrial DNA (mtDNA) in Bombina bombina and B. variegata was studied in samples from 20 locations. Each restriction enzyme produced a species-specific fragment pattern. B. bombina haplotypes A and B were closely related to each other. In contrast, haplotypes A and B of B. variegata formed two distinct lineages. A very distinctive haplotype (C) was found in the Carpathian Mountains, whereas two other haplotypes, D and E (differing by a single AvaI site), were present in western Europe and the Balkans, respectively. Populations polymorphic for haplotypes D and E occurred in the central Balkans where the haplotypes could replace each other clinally. mtDNA sequence divergence between B. bombina and B. variegata was estimated as 6.0-8.1% and 4.7-5.2% between type C and types D/E of B. variegata. The latter divergence is contrary to allozyme and morphological data that place the western and Carpathian B. v. variegata together (Nei's D = 0.07) and separate them from the Balkan subspecies B. v. scabra (Nei's D = 0.18). Broad interspecific correlation among morphology, allozymes and mtDNA types in European fire-bellied toads argues that, despite continuous hybridization (interrupted perhaps during Pleistocene glacial maxima), little or no mtDNA introgression between the species has occurred outside the narrow hybrid zones that separate these parapatric species.

Correlations between measures of thermal stress resistance within and between species

Resistance to an environmental stress such as elevated temperature can almost always be measured in several different ways. A number of recent studies in Drosophila show that lethal and non-lethal measures of resistance to heat stress are genetically independent. In contrast, data reported here suggest that there are interspecific correlations between measures of thermal stress resistance. Together, these results show that studies of intraspecific variation in stress resistance must demonstrate the ecological relevance of the measures of stress resistance chosen for study. In contrast, interspecific comparisons could be based on any of several measures of resistance. It would be interesting to determine if this pattern holds for resistance to other major environmental stresses.

Do plant species with high relative growth rates have poorer chemical defences?

1. Most theories of plant strategies assume the presence of certain ‘trade‐offs’. One such evolutionary trade‐off assumes a decrease in growth rate with increasing investment in chemical defences in species adapted to different levels of habitat fertility. 2. To test this hypothesis, we grew 31 herbaceous species of Asteraceae under controlled conditions of temperature (25 °C), humidity (80%), light (500 μmol m–2 s–1) and photoperiod (16 h day–1) in a modified Hoagland hydroponic solution. The plants grew from seed for 35 days post‐germination and were harvested at 14, 21, 28 and 35 days. Relative growth rate (RGR) was calculated as well as a general measure of potential phytochemical toxicity (LC50) using an alcohol extraction of secondary compounds followed by Brine Shrimp bioassay and an assay of total phenolics. 3. The interspecific correlation between RGR and the potential phytochemical toxicity was weak and non‐significant (rS = 0·12, P = 0·53). The correlation between RGR and total phenolics was weak, positive but significant (rS = 0·40, P = 0·03). 4. These results suggest that such an evolutionary trade‐off does not exist in this group of Asteraceae.

Changes in gut capacity with lactation and cold exposure in a species with low rates of energy use, the pine vole (Microtus pinetorum).

Interspecific differences in the adaptive capacity of the gut may contribute to interspecific differences in rate of energy use and life-history traits. We tested the hypothesis that changes in gut capacity when energy demands are elevated are similar in species with low average rates of energy use compared with a species with higher average rates of energy use. We measured changes in gut capacity in Microtus pinetorum, a species with low average rates of energy use, and compared these with published data of changes in gut capacity of other rodent species with higher average rates of energy use. We quantified food ingestion, daily metabolic rate, resting metabolic rate, and gut organ masses, lengths, and functional volumes in nonreproducing, lactating, and cold-exposed females. Cold-exposed females had significantly higher, and lactating females moderately higher, mass-independent daily metabolic rates than control females. No significant changes in the mass or length of the intestinal organs occurred with cold exposure. Length, but not mass, of the gut was significantly greater in lactating females and functional volume was greater in cold-exposed females, compared with control females, independent of body mass. These changes in gut capacity were much less extensive than those reported for other rodent species. Interspecific differences in gut capacity were not attributable to differences in rates of ingestion and energy need among species. A large adaptive capacity of the gut or maintenance of a large reserve capacity may be a requirement for high rates of energy use and may contribute to the positive interspecific correlations that exist between rates of growth and reproduction and energy use for maintenance metabolism.

Of mice and wrens: the relation between abundance and geographic range size in British mammals and birds

We examine the relation between population size and geographic range size for British breeding birds and mammals. As for most other assemblages studied, a strong positive interspecific correlation is found in both taxa. The relation is also recovered once the phylogenetic relatedness of species has been controlled for using an evolutionary comparative method. The slope of the relation is steeper for birds than for mammals, but this is due in large part to two species of mammals that have much higher population sizes than expected from their small geographic ranges. These outlying mammal species are the only ones in Britain to be found only on small offshore islands, and so may be exhibiting density compensation effects. With them excluded, the slope of the abundance–range size relation for mammals is not significantly different to that for birds. However, the elevation of the relation is higher for mammals than for birds, indicating that mammals are approximately 30 times more abundant than birds of equivalent geographic range size. An earlier study of these assemblages showed that, for a given body mass, bats had abundances more similar to birds than to non–volant mammals, suggesting that the difference in abundance between mammals and birds might be due to constraints of flight. Our analyses show that the abundance–range size relation for bats is not different for that from other mammals, and that the anomalously low abundance of bats for their body mass may result because they have smaller than expected geographic extents for their size. Other reasons why birds and mammals might have different elevations for the relation between population size and geographic range size are discussed, together with possible reasons for why the slopes of these relations might be similar.

Co-occurrence of prairie and barrens butterflies: applications to ecosystem conservation

Abundance indices from transect surveys for species restricted to prairies and barrens were correlated to test the degree to which these species of conservation concern co-occur. In 56 pair-wise tests among 15 species by subregion, 29 (52%) correlated significantly, all but one positively, and only 17 (37%) of 46 tests involving samples of >60 individuals for each species were non-significant. The species producing the most significant interspecific correlations in prairie were Speyeria idalia (five of ten tests) and Atrytone arogos (four of six tests); in barrens, Euchloe olympia (seven of eight tests) and Hesperia l. leonardus (six of eight tests). Lycaeides melissa samuelis, the butterfly receiving the most conservation attention in these habitats, produced few significant correlations. To explicate these patterns of co-occurrence, case histories were compiled for these species at sites of comparable vegetation by subregion. No management type was clearly favourable for all specialists of a given habitat, although some managements were favourable for more species than others (e.g. haying vs. burning in prairie). Analysis of variance of management at these sites produced more results with significant effects than did correlations of the species' abundance indices with habitat patch size. These results were inconsistent with prevailing ecological theory about the natural maintenance of these habitats; conversely, a single unified (alternative) theory of ecosystem management could not be inferred from these results. These patterns of butterfly co-occurrence suggest an alternative approach to ecosystem conservation that focuses on subsets of species native to a particular ecosystem. These smaller species assemblages significantly co-occur in range, habitat, and management tolerance, and may be amenable to monitoring with indicator species.

Larval niche differences between the sibling species, <i>Drosophila montana</i> and <i>D. littoralis</i> (Diptera) in northern Finland

Differences in larval substrate, or in the spatial and temporal occurrence of larvae between two closely related and ecologically similar Drosophila species were investigated. Vials containing homogenised tissue of water lily stems or birch phloem wetted with sap were exposed for oviposition in two habitats during two time periods. A logit analysis of the field emergence data suggested significant niche differences between the species. The logit model best explaining the species composition among emerging adults included an interaction between habitat and substrate, and also an interaction between habitat and exposure period. The differences between the species were, however, small and the species overlapped broadly with respect to each of the studied niche dimensions. The distribution of emerging flies among the yellow water lily vials appeared to fulfill the assumptions of a theoretical model for aggregation-mediated coexistence, i.e. the distribution of flies was aggregated among vials in both species, and there was no interspecific correlation in the numbers of flies emerging from the vials.

Allometric Patterns in the Ecology of Australian Snakes

This paper summarizes published and original data on ecological characteristics of 103 species of Australian snakes, based on dissection of > 22,000 specimens in museum collections. Principal Component Analyses suggest that much of the interspecific variance in ecology is the result of differences in mean adult body sizes. Thus, I examine the degree to which absolute body size is correlated with other ecological variables in interspecific comparisons and investigate interspecific associations between ecological traits after the confounding effect of absolute body size is removed from the analysis. Mean adult body size is significantly correlated with measures of population structure (adult sex ratio), growth trajectories (size at maturation relative to mean adult size, and sexual size dimorphism), mating systems (presence or absence of male-male combat), reproductive biology (offspring size, clutch size, reproductive mode, and reproductive frequency in females), and food habits (proportional composition of major prey types). Phylogenetically based analyses show that some of these interspecific correlations are the result of phylogenetic conservatism, whereas others reflect underlying functional relationships. When these kinds of allometric effects are taken into account, clear patterns in interspecific variation in life-history attributes are revealed. For example, a trade-off is apparent between clutch size and offspring size: species with relatively large clutches produce relatively small offspring. Offspring size is unaffected by shifts in reproductive mode (oviparity/viviparity) but is correlated with the extent of postmaturational growth by females (in species with relatively large offspring, females delay maturation until they reach a large size). The presence or absence of male-male combat in a species affects adult sex ratio in collections (probably via sex biases in catchability), growth trajectories in males, and the degree of sexual size dimorphism.

On the factors influencing juvenile flatfish abundance in the lower Severn Estuary, England

Bridgwater Bay within the Bristol Channel, Somerset, England is a nursery ground for sole, Solea solea, and dab, Limanda limanda, during the autumn and winter. Flounder, Platichthys flesus, both juveniles and adults, are common during the summer. Using a 13-year data set of fish in the bay, correlations were studied between climatic, predatory and competitive factors and juvenile flatfish abundance. The major factor was found to be seawater temperature. For sole, abundance was positively correlated with the temperature in the spawning period (April and May). For flounder, abundance was negatively correlated with average temperature during the previous year. For dab, average winter temperature over the spawning period was negatively correlated with juvenile abundance and with mean length observed during the following autumn. These climatic changes were also found to influence the abundance of a large number of other fish and crustacean species which were potential predators or competitors and which in some cases were significantly correlated with flatfish abundance. The data set was analysed using multiple correlation analysis. Multi-factorial models of population change which included interspecific and climatic factors were examined. Using first-order partial correlations it was possible to distinguish between different causal models. In every case it was found that inter-specific correlations were attributable to both species independently changing in abundance with temperature. No significant correlations between the abundance of potential predators or competitors and juvenile flatfish were detected.

Predicting the Height of Fossil Plant Remains: An Allometric Approach to an Old Problem

Interspecific correlations between plant height and basal stem diameter (the allometry of height) and between stem length distal to where diameter is measured (the allometry of stem taper) were determined for a total of 265 species with self-supporting stems and for the shoots of five conifers and 15 angiosperm vine species. The allometric equations obtained for these data are proposed as a method to predict the heights of fossil plants for which basal stem diameters are either known or inferred, and to predict the missing lengths of fragmented stems based on the most proximal stem diameters observed.