Evaluation of indicators of nitrogen limitation in deep prairie lakes with laboratory bioassays and limnocorrals

A comparison of Kenyan reefs of different historical and observed levels of fishing exploitation showed that more exploited reef lagoons had greater sea urchin densities and sizes, fewer and smaller fish and less coral cover. In the most exploited lagoon the biomass of the burrowing sea urchin Echinometra mathaei increased five fold during the previous 15 years. An ecological study of the three most common omnivorous sea urchin species inhabiting hard substrate within these reef lagoons (E. mathaei, Diadema savignyi and D. setosum) suggests that they are ecologically separated by predation and avoid predators and competitors by occupying different size burrows or crevices within the lagoon. Predator removal through fishing activities may result in ecological release of the sea urchins and result in competitive exclusion of weaker competitors. The most exploited reef had a nearly monospecific barren of E. mathaei living outside burrows suggesting that E. mathaei may be the top competitor. Its ecological release appears to lead to a decrease in live coral cover, increased substrate bioerosion and eventually a loss of topographic complexity, species diversity, fish biomass and utilizable fisheries productivity. Data from the outer reef edge were more difficult to interpret but may indicate similar patterns. Within this area, physical stresses such as waves and currents may be a greater controlling force in regulating fishing activities and coral reef community structure.     

On the Fourth Diadema Species (Diadema-sp) from Japan

Four long-spined sea urchin species in the genus Diadema are known to occur around the Japanese Archipelago. Three species (D. savignyi, D. setosum, and D. paucispinum) are widely distributed in the Indo-Pacific Ocean. The fourth species was detected by DNA analysis among samples originally collected as D. savignyi or D. setosum in Japan and the Marshall Islands and tentatively designated as Diadema -sp, remaining an undescribed species. We analyzed nucleotide sequences of the cytochrome oxidase I (COI) gene in the “D. savignyi-like” samples, and found all 17 individuals collected in the mainland of Japan (Sagami Bay and Kyushu) to be Diadema-sp, but all nine in the Ryukyu Archipelago (Okinawa and Ishigaki Islands) to be D. savignyi, with large nucleotide sequence difference between them (11.0%±1.7 SE). Diadema-sp and D. savignyi shared Y-shaped blue lines of iridophores along the interambulacrals, but individuals of Diadema-sp typically exhibited a conspicuous white streak at the fork of the Y-shaped blue iridophore lines, while this feature was absent in D. savignyi. Also, the central axis of the Y-shaped blue lines of iridophores was approximately twice as long as the V-component in D. savignyi whereas it was of similar length in Diadema-sp. Two parallel lines were observed to constitute the central axis of the Y-shaped blue lines in both species, but these were considerably narrower in Diadema-sp. Despite marked morphological and genetic differences, it appears that Diadema-sp has been mis-identified as D. savignyi for more than half a century.     

Lunar periodicities of diadematid echinoids breeding in Fiji

Gonad indices for two species of Diadema and two species of Echinothrix, including two color morphs of Echinothrix calamaris, are described for a 12-month period on Sosoikula Reef and Nukubuco Reef, Viti Levu, Fiji. Seasonal fluctuations in salinity (36.11±0.88 ppt) and water temperature (26.35±0.91°C) occurred. Gonad index data showed monthly reproductive rhythms, closely attuned to the lunar cycle. Diadema savignyi and Echinothrix diadema spawned on the full moon, and Diadema setosum and E. calamaris (white and brown color morphs) spawned on the new moon. Breeding periodicities coincided with the spring tides, thus maximizing chances of fertilization and dispersal. Such breeding cycles indicate how closely related species can co-exist with minimum risk of hybridization. Unusual sex ratios were found for all species, with an exceptionally low incidence of males. Reasons for this deviation from the typically reported 1:1 sex ratio may relate to the exceptionally high levels of tributyltin (TBT) recorded in Suva Harbor.     

POPULATION STRUCTURE AND SPECIATION IN TROPICAL SEAS: GLOBAL PHYLOGEOGRAPHY OF THE SEA URCHIN DIADEMA

Abstract.— The causes of speciation in the sea are rarely obvious, because geographical barriers are not conspicuous and dispersal abilities or marine organisms, particularly those of species with planktonic larvae, are hard to determine. The phylogenetic relations of species in cosmopolitan genera can provide information on the likely mode of their formation. We reconstructed the phylogeny of the pantropical and subtropical sea urchin genus Diadema, using sequences of mitochondrial DNA from 482 individuals collected around the world, to determine the efficacy of barriers to gene flow and to ascertain the history of possible dispersal and vicariance events that led to speciation. We also compared 22 isozyme loci between all described species except D. palmeri. The mitochondrial DNA data show that the two deepest lineages are found in the Indian and West Pacific Oceans. (Indo‐Pacific) Diadema setosum diverged first from all other extant Diadema, probably during the initiation of wide fluctuations in global sea levels in the Miocene. The D. setosum clade then split 3‐5 million years ago into two clades, one found around the Arabian Peninsula and the other in the Indo‐West Pacific. On the lineage leading to the other species of Diadema, the deepest branch is composed of D. palmeri, apparently separated when the climate of New Zealand became colder and other tropical echinoids at these islands went extinct. The next lineage to separate is composed of a currently unrecognized species of Diadema that is found at Japan and the Marshall Islands. Diadema mexicanum in the eastern Pacific separated next, whereas D. paucispinum, D. savignyi, and D. antillarum from the western and central Atlantic, and (as a separate clade) D. antillarum from the eastern Atlantic form a shallow polytomy. Apparently, Indo‐Pacific populations of Diadema maintained genetic contact with Atlantic ones around the southern tip of Africa for some time after the Isthmus of Panama was complete. Diadema paucispinum contains two lineages: D. paucispinum sensu stricto is not limited to Hawaii as previously thought, but extends to Easter Island, Pitcairn, and Okinawa; A second mitochondrial clade of D. paucispinum extends from East Africa and Arabia to the Philippines and New Guinea. A more recent separation between West Indian Ocean and West Pacific populations was detected in D. setosum. Presumably, these genetic discontinuities are the result of water flow restrictions in the straits between northern Australia and Southeast Asia during Pleistocene episodes of low sea level. Diadema savignyi is characterized by high rates of gene flow from Kiribati in the central Pacific all the way to the East African Coast. In the Atlantic, there is a biogeographic barrier between the Caribbean and Brazil, possibly caused by fresh water outflow from the Amazon and the Orinoco Rivers. Diadema antillarum populations of the central Atlantic islands of Ascension and St. Helena are genetically isolated and phylogenetically derived from Brazil. Except for its genetic separation by the mid‐Atlantic barrier, Diadema seems to have maintained connections through potential barriers to dispersal (including the Isthmus of Panama) more recently than did Eucidaris or Echinometra, two other genera of sea urchins in which phylogeography has been studied. Nevertheless, the mtDNA phylogeography of Diadema includes all stages expected from models of allopatric differentiation. There are anciently separated clades that now overlap in their geographic distribution, clades isolated in the periphery of the genus range that have remained in the periphery, clades that may have been isolated in the periphery but have since spread towards the center, closely related clades on either side of an existing barrier, and closely related monophyletic entities on either side of an historical barrier that have crossed the former barrier line, but have not attained genetic equilibrium. Except for D. paucispinum and D. savignyi, in which known hybridization may have lodged mtDNA from one species into the genome of the other, closely related clades are always allopatric, and only distantly related ones overlap geographically. Thus, the phylogenetic history and distribution of extant species of Diadema is by and large consistent with allopatric speciation.     

Taxonomic significance of spine morphology in the echinoid genera Diadema and Echinothrix

Abstract. The spine morphology of all established species of Diadema and Echinothrix, including 2 color morphs of E. calamaris, were examined externally and internally via transverse sectioning to identify diagnostic species features and to assess the morphological relationship between species. Forty‐nine different morphological characters were measured and analysed using ordination by multi‐dimensional scaling (MDS) and cluster analysis. Specimens of Diadema paucispinum and D. setosum had very distinct spine structures. In D. paucispinum, the spines were more robust than those of other species of Diadema. This was evident in the spine's internal structure, with large, closely packed solid wedges, a small axial cavity, and rings of trabeculae throughout the spine's length. The spines in D. setosum were distinctive because of their length in relation to test size and the reduced flaring of their verticillations. The spines of other members of this genus were very similar to each other. Without careful sectioning, the spines from specimens of D. antillarum, D. ascensionis, D. mexicanum and D. savignyi were difficult to differentiate. The internal structures of spines for each species did, however, possess a combination of features that differentiated the species. Such features included the shape, orientation, and number of solid wedges, the presence or absence of spokes and rings of trabeculae between the solid wedges, and the presence or absence of tissue within the axial cavity. Individuals of Diadema palmeri also had spines morphologically similar to other species, however, the red pigmentation of these spines (in life and when preserved) made them easily distinguishable. The spine structures of the 2 species of Echinothrix were starkly different, while the white and brown color morphs of E. calamaris had morphologically distinctive ambulacral and interambulacral spines. The blunt, open‐tipped interambulacral spines, with reticular tissue present in the axial cavity of the white color morph, were easily distinguished from the pointed, closed‐tipped spines, with a hollow axial cavity found in the brown color morph. Such differences indicate that the brown color morph is either a subspecies or a separate species. Taken together the data show that each species has significant morphological differences in the structure of the spines. It is evident from our data that spine morphology is a useful tool to differentiate these commonly confused species.     

Environmental factors influencing urchin spatial distributions on disturbed coral reefs (New Caledonia, South Pacific)

Few works have examined the relative contributions of habitat variables to the distribution of coral reef urchins. In the present study, the spatial distribution of two common urchin species (Diadema setosum and Echinometra mathaei) was studied in the fringing reefs of two urban bays in New Caledonia (South Pacific). Urchins were surveyed at 105 stations with contrasted habitat structure/anthropic disturbance levels; 32 environmental variables (water/sediment characteristics, reef structuring species) were considered. Moderate densities were generally observed at station scale (mean 0.5 individuals m^− 2). The combination of univariate and multivariate techniques highlighted patchy distributions for Diadema as well as Echinometra, with distinct species/habitat associations; environmental gradients occurring within the bays did not seem to influence the species patterns. For Diadema, the spatial variability was better explained by sediment type than by biotic cover; increasing densities occurred across habitats with larger sediment sizes and decreasing coral complexity/macrophytes cover. In contrast, the distribution of E. mathaei exhibited weak relationships with habitat variables. In coral reefs, small-scale heterogeneity may thus be responsible for most of urchins spatial variability.     

Grazing preferences of diadematid echinoids in Fiji

Grazing preferences of two species of Diadema and two species of Echinothrix, including two colour morphs of Echinothrix calamaris, were investigated by gut contents analysis, in situ feeding observations, and grazing preferences trials in aquaria. Grazing preferences were compared to the distribution and abundance of diadematid sea urchins and the percentage cover of algal and seagrass species throughout Sosoikula Reef and Nukubuco Reef, Fiji. Results showed that grazing was selective, with distinct preferences between sea urchin genera, species, and colour morphs of E. calamaris. Preferred species of algae were non-calcareous, with reportedly low concentrations of tannins, phenols and bioactive compounds. Both Diadema savignyi and D. setosum selected Codium geppiorum as their most preferred species, followed by Hydroclathrus clathratus. All Echinothrix favoured Hy. clathratus, with both colour morphs of E. calamaris next selecting Padina pavonica and E. diadema selecting green filamentous algae. The seagrass species Syringodium isoetifolium was only grazed in significant quantities by E. calamaris (b) and E. diadema. This reflected species distributions in the seagrass bed. Peak abundances of diadematid sea urchins coincided with many of their grazing preferences at their maximum percentage cover. However, only E. diadema and D. savignyi had significant correlations with preferred algal/seagrass species (E. diadema with Co. geppiorum, and D. savignyi with G. marginata) throughout the subhabitats identified on the reefs.     

Systematic significance of tridentate pedicellariae in the echinoid genera Diadema and Echinothrix

Abstract. The tridentate pedicellariae in all species of Diadema and Echinothrix recognized by Mortensen, plus species described later (to include D. palmeri and two color morphs of E. calamaris) were examined to identify diagnostic species characters, and to determine whether such characters are useful in inferring phylogenetic relationships between species. Nineteen morphological characters were measured and analyzed, and species‐specific characters were identified. The morphometric data were then transformed using gap coding and a parsimony analysis was undertaken. The resulting cladogram for the tridentate pedicellariae present in species of Diadema was compared with the mitochondrial DNA phylogeny of Lessios et al., with a good level of congruence observed. Very narrow forceps‐like tridentate pedicellariae were found to be basal among Recent species, present only in D. setosum and D. palmeri. Members of D. palmeri were found to be unique within the genus, having both the forceps‐like form and a broad form of tridentate pedicellaria. The very narrow forceps‐like form is absent in all subsequent divergent species, while the broad form of tridentate pedicellaria in D. palmeri is basal to the broad forms in D. antillarum, D. mexicanum, D. paucispinum, and both the broad and narrow forms of tridentate pedicellaria of D. savignyi. The greatest similarity was found between the broad forms of tridentate pedicellaria in D. antillarum and D. mexicanum. These species were also found to have narrow forms of tridentate pedicellaria that showed a reasonable level of association to one another and to the rostrate form in D. ascensionis. Since the work of Mortensen, D. ascensionis has been shown, using mitochondrial DNA, to be nested within D. antillarum. The results of this study show that the tridentate pedicellaria in D. ascensionis are distinctly different from all other forms within the genus, to the extent that they belong to a rostrate subclass. This indicates that, among Diadema species, the tridentate pedicellariae are one of the first morphological characters to diverge in genetically isolated populations. Unlike the tridentate pedicellariae in Diadema, the different forms of tridentate pedicellariae in E. calamaris and E. diadema showed a stronger association intraspecifically than between forms interspecifically. The small forms of tridentate pedicellaria of the white and brown color morphs in E. calamaris showed a high level of association, while the large forms showed only a moderate association, far lower than would be expected between color morphs of the same species. This suggests that they are either subspecies or recently diverged separate species. This study demonstrates the taxonomic value contained within the characters of the tridentate pedicellariae for both differentiating species (even subspecies) and inferring phylogenetic relationships between species.     

Intertidal estimates of sea urchin abundance reveal congruence in spatial structure for a guild of consumers

We hypothesized congruence in the spatial structure of abundance data sampled across multiple scales for an ecological guild of consumers that exploit similar nutritional and habitat resources. We tested this hypothesis on the spatial organization of abundance of an herbivorous guild of sea urchins. We also examined whether the amount of local along‐shore rocky habitat can explain the observed spatial patterns of abundance. Standardized estimates of abundance of four intertidal sea urchins—Diadema cf. savignyi, Echinometra mathaei, Parechinus angulosus, and Stomopneustes variolaris—were determined by six observers at 105 sites across 2,850 km of coast of South Africa. For each species and observer, wavelet analysis was used on abundance estimates, after controlling for potential biases, to examine their spatial structure. The relationship between local sea urchin abundance and the amount of upstream and downstream rocky habitat, as defined by the prevailing ocean current, was also investigated. All species exhibited robust structure at scales of 75–220 km, despite variability among observers. Less robust structure in the abundances of three species was detected at larger scales of 430–898 km. Abundance estimates of sympatric populations of two species (D. cf. savignyi and E. mathaei) were positively correlated with the amount of rocky habitat upstream of the site, suggesting that upstream populations act as larval sources across a wide range of scales. No relationship between abundance and habitat size was found for P. angulosus or S. variolaris. Within the range of scales examined, we found robust congruence in spatial structure in abundance at the lower, but not the larger, range of scales for all four species. The relationship between abundance and upstream habitat availability in two species suggests that larval supply from upstream populations was probably the mechanism linking habitat size and abundance.     

Diel patterns in sea urchin activity and predation on sea urchins on the Great Barrier Reef

Understanding diel patterns in sea urchin activity is important when assessing sea urchin populations and when interpreting their interactions with predators. Here we employ a combination of surveys and a non-invasive tethering technique to examine these patterns in an intact coral reef system on the Great Barrier Reef (GBR). We also assess local scale variation in relative diurnal predation pressure. Surveys revealed that sea urchins were active and exposed at night. Echinometra mathaei and Echinothrix calamaris were the most abundant species with significantly higher night densities (0.21 and 0.03 ind. m⁻², respectively), than daytime densities (0.05 and 0.001, respectively). Bioassays revealed that exposed adult E. mathaei (the most abundant sea urchin species) were 30.8 times more likely to be eaten during the day than at night when controlling for sites. This observation concurs with widely held assumptions that nocturnal activity is a risk-related adaptive response to diurnal predation pressure. Despite relatively intact predator communities on the GBR, potential predation pressure on diurnally exposed E. mathaei assays was variable at a local scale and the biomass of potential fish predators at each site was a poor predictive measure of this variation. Patterns in predation appear to be more complex and variable than we may have assumed.     

Contrasting patterns of body size for Daphnia species that segregate by habitat

Summary We investigate how body size of two coexisting Daphnia species varies among 7 lakes that represent a gradient of predation risk. The two species segregate vertically in stratified lakes; D. galeata mendotae is typically smaller and more eplimnetic than D. pulicaria. The extent of vertical habitat partitioning, however, varies seasonally within and among lakes in apparent response to predation intensity by epilimnetic planktivorous fishes. Daphnia pulicaria uses the epilimnion at low levels of fish predation but is restricted to the hypolimnion under high fish predation, whereas D. galaeta mendotae always utilizes the epilimnion. The species display contrasting patterns of genetic variation in neonate size and size at maturity. D. pulicaria is larger in lakes with higher fish and Chaoborus densities whereas D. galeata mendotae is smaller. This contrast in body size in lakes with high predation is associated with greater habitat segregation in those lakes. In lakes with low predation risk, the two species are similar in body size at birth and maturity.Authorship order alphabetical     

Fish predation on sea urchins on the Great Barrier Reef

Predators are important for regulating adult sea urchin densities. Here, we employ remote underwater video cameras to record diurnal predation on tethered sea urchins at Lizard Island on the Great Barrier Reef (GBR). We identified four fish predators of adult sea urchins (Balistoides viridescens, Balistapus undulatus, Lethrinus atkinsoni and Choerodon schoenleinii). Predator activity appeared to be site-specific. Balistoides viridescens and B. undulatus (f: Balistidae) were the two most important predators of Echinometra mathaei with the former handling E. mathaei significantly faster (mean 0.7?min) than B. undulatus (5.2?min). Balistoides viridescens also successfully preyed on 70?% of detections, while C. schoenleinii, B. undulatus and L. atkinsoni preyed on just 33, 17 and <1?%, respectively. Additionally, B. viridescens were behaviourally dominant among predator species and were observed as aggressors in 30 encounters with B. undulatus and 8 encounters with L. atkinsoni. In only one encounter was B. viridescens the recipient of any aggression (from B. undulatus). In terms of relative vulnerability, of the three sea urchin species examined, E. mathaei were more vulnerable to predation than Diadema setosum or Echinothrix calamaris, with mean handling times of 1.2, 4.8 and 10.3?min, respectively. Balistoides viridescens and B. undulatus both appear to be able to play an important role as predators of sea urchins on the relatively intact coral reefs of Lizard Island. However, B. viridescens emerge as the most efficient predator in terms of handling speed and the proportion of detections preyed upon. They were also the behaviourally dominant predator. This preliminary study of the predators of sea urchins on the GBR highlights the potential significance of relatively scarce but functionally important species.     

Consistent social structure within aggregations of the Australian lizard, <Emphasis Type="Italic">Egernia stokesii</Emphasis> across seven disconnected rocky outcrops

The Australian skink lizard Egernia stokesii lives in aggregations of up to 17 individuals. Previously, at one site, these aggregations have been shown to comprise paired unrelated individuals and several cohorts of their young. To investigate whether social structuring in this species is a response to ecological conditions or is phylogenetically constrained, we sampled social aggregations of E. stokesii from seven geographically adjacent rocky outcrops (including the site previously studied) that differ in the availability of homesite crevices. Analysis of genotypes from ten microsatellite loci indicate that social structures were similar at all sites and were comparable with that of the previous study. Over all sites highly significant positive relationships were observed between the number of crevices at a site and both the number of lizards and the number of social groups. Social structure in this species seems to be phylogenetically constrained, at least in relation to the abundance of potential homesite crevices.     

Interspecific competition between two parasitoids of Helicoverpa zea: Eucelatoria bryani and E. rubentis

Multiple parasitism of Helicoverpa zea (Lepidoptera: Noctuidae) had differential effects on the gregarious endoparasitoids Eucelatoria bryani and E. rubentis (Diptera: Tachinidae). Both species were able to survive in multiparasitized hosts. However while the survival of E. bryani was not affected by the presence of E. rubentis, E. rubentis survival was reduced when competing with 24-h older E. bryani. The presence of E. rubentis did not result in a decrease in the size of E. bryani except when E. rubentis was 24-h older than E. bryani. The presence of E. bryani tended to result in smaller E. rubentis. The presence of similarly aged heterospecific competitors often resulted in prolonged development time for both species. Naïve females did not alter oviposition between unparasitized and heterospecifically parasitized fifth-instar larvae of H. zea, either by ovipositing less frequently in parasitized hosts than unparasitized ones, or by reducing clutch size in parasitized hosts. These results indicate that in H. zea, E. bryani is a superior competitor compared with E. rubentis. These factors should be considered in evaluating the potential of E. bryani and E. rubentis as biological control agents of H. zea.     

Density-dependent size regulation and negative growth in the sea urchin Diadema antillarum Philippi

Summary This study documents size- and density-dependent growth (positive and negative), in the sea urchin Diadema antillarum. In the summer of 1983, an inverse relationship was found between Diadema test diameter and population density at seven sites in Lameshur Bay, St. John, United States Virgin Islands. The regression of this relationship improved when test diameter was plotted against density per unit grazing area. A field experiment demonstrated that 1) Diadema has the ability to reduce skeletal body size, and 2) direction (growth or shrinkage) and rate of growth can be predicted accurately based on the urchin's body size and population density. The ability to adjust body size as density fluctuates may allow Diadema to persist when density increases, by shrinking and reducing metabolic costs, and to take advantage of decreases in density, by increasing in size and fecundity.     

Mast-seeding in the cycad genus Encephalartos: a test of the predator satiation hypothesis

Mast-seeding behaviour was monitored in 18 populations of eight species of the African cycad genus Encephalartos between 1988 and 1991. The coefficient of variation (V) in annual cone production for each population ranged between 88 and 200, indicating large fluctuations in reproductive effort between years. Data were collected to determine whether mast-seeding reduced levels of predispersal seed predation by satiating seed predators in mast years and whether it resulted in a reproductive advantage over plants which reproduced more frequently. Masting intensity was greatest in those populations in which individual plants suffered the highest levels of predispersal seed predation in years when only a few plants produced seeds. The principal seed predators were two congeneric weevil species, Antliarhinus zamiae and A. signatus, which develop exclusively on cycad seeds. The lowest intensity of mast-seeding was recorded for cycad populations with low levels of seed predation and in which A. zamiae and A. signatus occurred only in low numbers or were entirely absent. Larger seed crops appeared to result in lower levels of seed predation by A. zamiae and A. signatus in four populations of E. altensteinii, and differences in seed crop size accounted for 48–66% of variation in levels of seed predation in populations of five cycad species. In one population of E. altensteinii, lower levels of seed predation in plants reproducing periodically resulted in a reproductive advantage over plants reproducing more frequently. These results are consistent with the predator satiation hypothesis. However, in most cycad populations, numbers of seed predators did not appear to decrease significantly after a period of 2–8 years between reproductive episodes and, in two of three populations examined, periodic reproduction did not increase the number of seeds surviving to dispersal over a 4-year period. These results are interpreted to mean that periodic reproduction has not evolved in response to selection imposed by seed predators, but that selection may favour those plants which experience lower levels of seed predation by coning in synchrony with the majority of plants in the population.     

Temperature and kairomone induced life history plasticity in coexisting Daphnia

We investigated the life history alterations of coexisting Daphnia species responding to environmental temperature and predator cues. In a laboratory experiment, we measured Daphnia life history plasticity under different predation risk and temperature treatments that simulate changing environmental conditions. Daphnia pulicaria abundance and size at first reproduction (SFR) declined, while ephippia (resting egg) formation increased at high temperatures. Daphnia mendotae abundance and clutch size increased with predation risk at high temperatures, but produced few ephippia. Thus, each species exhibited phenotypic plasticity, but responded in sharply different ways to the same environmental cues. In Glen Elder reservoir, Kansas USA, D. pulicaria dominance shifted to D. mendotae dominance as temperature and predation risk increased from March to June in both 1999 and 2000. Field estimates of life history shifts mirrored the laboratory experiment results, suggesting that similar phenotypic responses to seasonal cues contribute to seasonal Daphnia population trends. These results illustrate species-specific differences in life history plasticity among coexisting zooplankton taxa.     

Belly up: Reduced crevice accessibility as a cost of reproduction caused by increased girth in a rock‐using lizard

Costs of reproduction are any aspect of current reproduction that has the potential to reduce survivorship or reproductive output, and may include physiological costs or increased risks. Females of many species experience increased body mass, and increased girth, when gravid. Increased body mass reduces running speed and increases the cost of locomotion during pregnancy, but few studies have examined the cost of increased girth. If increased girth of gravid females reduces access to shelter from predators or the elements, increased girth could constitute a cost of reproduction. In the laboratory, we experimentally tested whether access to crevices was limited in viviparous, saxicolous female lizards (Eulamprus brachysoma), which use crevices for shelter, by measuring access to artificial crevices of known widths, and body height during and after pregnancy. Gravid E. brachysoma had significantly greater body height (11.2% on average), and as a result were forced to use significantly wider crevices (18.4% wider on average) than post‐parturition. Females with larger clutch sizes had wider mid‐bodies and required larger crevices. Control females, which were not gravid at either time of testing, showed no significant change in the size of crevice they could enter over time. If access to narrow crevices provides advantages such as protection from predators, or is important for thermoregulation, then gravid females may suffer a cost of reproduction because their access to narrower crevices is limited.     

Germination as a determinant of seedling distributions among natural substrates in Picea engelmannii (Pinaceae) and Abies lasiocarpa (Pinaceae)

In Rocky Mountain (USA) subalpine forests, seedlings of Picea engelmannii (Engelmann spruce) colonize logs more frequently than seedlings of its codominant associate Abies lasiocarpa (subalpine fir). We hypothesized that spruce germinates more readily on logs than fir, perhaps because small spruce seeds are more likely to lodge in log crevices than larger fir seeds. Our objectives were to test this hypothesis and compare both species' germination among several substrates to assess germination influences on natural seedling distributions. Spruce and fir seeds were sown on field-collected logs, litter, and soil in the greenhouse and monitored for 36 d. To test the crevice hypothesis, seeds were either scattered on logs or wedged into crevices, assuming that if both species were placed in crevices, interspecific germination differences on logs would decrease. Spruce mean germination percentages were significantly greater than fir's in all substrate treatments except when seeds were wedged in log crevices. The difference in means between the two log treatments was greater for fir (68%) than spruce (21%). Spruce germinated more rapidly than fir on all substrates. We suggest that large seed size reduces fir's success in colonizing logs, and that germination and establishment factors interact to determine natural seedling distributions for these subalpine conifers.     

Effects of predator-mediated apparent competition on the population dynamics of Tetranychus urticae on apples

The two spotted spider mite, Tetranychus urticae Koch, is an important herbivore pest of apple trees in Northwest China. This spider mite and another less damaging spider mite, Eotetranychus pruni Oudemans, are attacked by a common and often effective phytoseiid predator, Euseius finlandicus (Oudemans). Functional relationships were studied in the field to evaluate the impact of E. pruni and E. finlandicus on T. urticae. The results from this study showed that the predator-mediated apparent competition strongly affected the population dynamics of T. urticae. The addition of the apparent competitor E. pruni alone had little impact on T. urticae densities. Although the release of the predator E. finlandicus alone could result in reduction in T. urticae densities, the greatest reduction in T. urticae densities occurred in plots where both the predator E. finlandicus and apparent competitor E. pruni were released. In apple orchards, the early introduction of both the apparent competitor E. pruni and predator E. finlandicus would evidently increase the population size of the predator E. finlandicus and consequently significantly enhance the control of T. urticae populations. It is concluded from the study that the predator and apparent competitor release might be an appropriate control for the target species.