Thermal tolerance,evaporative water loss,air-water oxygen consumption and zonation of intertidal prosobranchs: a new synthesis

Duration of emergence increases with tidal height on rocky shores therefore, emergence adaptations in intertidal species such as littorine and other prosobranch gastropods have been considered correlated with zonation patterns; temperature tolerance, desiccation resistance and aerial respiration rate all commonly assumed to increase progressively with increasing zonation level. Such direct correlations are rarely observed in nature. Maximal aerial gas exchange occurs in mid-shore, not high shore species. Temperature tolerance and desiccation resistance do not increase directly with shore height. Thus, hypotheses regarding physiological correlates of zonation require revaluation. A new hypothesis is presented that the high tide mark presents a single major physiological barrier on rocky shores. Above it, snails experience prolonged emergence and extensive desiccation; below it, predictable submergence and rehydration with each tidal cycle. Thus, desiccation stress is minimal below the high tide mark and maximal above it. Therefore, species restricted below high tide (the eulittoral zone) should display markedly different adaptive strategies to emergence than those above it (the eulittoral fringe). A review of the literature indicated that adaptations in eulittoral species are dominated by those allowing maintenance of activity and foraging in air including: evaporative cooling; low thermal tolerance; elevated aerial O₂ uptake rates; and high capacity for radiant heat absorption. Such adaptations exacerbate evaporative water loss. In contrast, species restricted to the eulittoral fringe display adaptive strategies that minimize desiccation and prolong survival of emergence including: foot withdrawal, preventing heat conduction from the substratum; aestivation in air; elevated thermal tolerance reducing necessity for evaporative cooling; position maintenance by cementation to the substratum and increased capacity for heat dissipation. In order to test of this hypothesis the upper thermal limits, tissue and substratum temperatures on emergence in direct sunlight and evaporative water loss and tissue temperatures on emergence in 40 °C were evaluated for specimens of six species of eulittoral and eulittoral fringe gastropods from a granite shore on Princess Royal Harbour near Albany, Western Australia. The results were consistant with adaptation to the proposed desiccation barrier at high tide. The eulittoral species, Austrocochlea constricta, Austrocochlea concamerata, Nerita atramentosa and Lepsiella vinosa, displayed adaptations dominated by maintenance of activity and foraging during emergence while the eulittoral fringe littorine species, Bembicium vittatum and Nodilittorina unifasciata displayed adaptations dominated by minization of activity and evaporative water loss during emergence. The evolution of adaptations allowing tolerance of prolonged desiccation have allowed littorine species to dominate high intertidal rocky shore gastropod faunas throughout the world's oceans.     

A comparative analysis of the upper thermal tolerance limits of eastern Pacific porcelain crabs, genus Petrolisthes: influences of latitude, vertical zonation, acclimation, and phylogeny

Marine intertidal organisms are subjected to a variety of abiotic stresses, including aerial exposure and wide ranges of temperature. Intertidal species generally have higher thermal tolerance limits than do subtidal species, and tropical species have higher thermal tolerance limits than do temperate species. The adaptive significance of upper thermal tolerance limits of intertidal organisms, however, has not been examined within a comparative context. Here, we present a comparative analysis of the adaptive significance of upper thermal tolerance limits in 20 congeneric species of porcelain crabs, genus Petrolisthes, from intertidal and subtidal habitats throughout the eastern Pacific. Upper thermal tolerance limits are positively correlated with surface water temperatures and with maximal microhabitat temperatures. Analysis of phylogenetically independent contrasts (from a phylogenetic tree on the basis of the 16s rDNA gene sequence) suggests that upper thermal tolerance limits have evolved in response to maximal microhabitat temperatures. Upper thermal tolerance limits increased during thermal acclimation at elevated temperatures, the amount of increase being greater for subtidal than for intertidal species. This result suggests that the upper thermal tolerance limits of some intertidal species may be near current habitat temperature maxima, and global warming thus may affect the distribution limits of intertidal species to a greater extent than for subtidal species.     

The spatial and vertical distribution of living (stained) benthic foraminifera from a tropical,intertidal environment,north Queensland,Australia

We investigated the distribution of living (stained) benthic foraminifera across a tropical, intertidal shoreline adjacent to Cocoa Creek, Queensland, Australia for the purpose of better understanding the nature of test production and ultimately fossil assemblage development within such environments. Short cores (up to 1 m) were collected during the wet and dry season, along an elevational gradient comprising non-vegetated intertidal mudflat and higher-intertidal mangrove forest environments. The distribution of stained specimens can be broadly delineated into assemblages characterising ‘upper mangrove’ (2.64–2.91 m above Lowest Astronomical Tide (LAT)) and ‘low mangrove-mudflat’ (1.62–2.18 m above LAT) environments. Agglutinated species were generally limited to upper mangrove stations. Calcareous species occurred within all of the intertidal environments examined but differ in their composition between upper and lower intertidal settings. Upper mangrove faunas were characterised by the agglutinated species Arenoparrella mexicana, Haplophragmoides wilberti, Miliammina fusca, Miliammina obliqua and Trochammina inflata and the calcareous species Helenina anderseni. Live (stained) assemblages at lower intertidal elevations were dominated by the calcareous species Ammonia aoteana, as well as Rosalina spp., Elphidium oceanicum, Triloculina oblonga, Ammonia pustulosa and Shackoinella globosa.     

Molluscan grazing and macroalgal zonation on a rocky intertidal platform at Perth,Western Australia

Abstract Intertidal limestone platforms off Perth show a characteristic pattern of algal zonation, with dense macroalgal beds nearshore bounded by a ‘barren zone’ along the seaward edge. Abalone (Haliotis roei) and several species of limpets and chitons are abundant in the barren zone, which is generally devoid of non-coralline macroalgae. The relative importance of abalone versus limpets and chitons in limiting macroalgal abundance in the barren zone was evaluated by manipulating the presence of each group in a factorial experiment. Percentage algal cover was measured photographically in 0.25m² plots at 1–2 month intervals for 9 months. Mean algal cover (mainly the foliose green alga, Ulva rigida) was highest in plots where all grazers were excluded (77–99%), intermediate where only limpets and chitons were excluded (37–85%), and lowest where only abalone were excluded (4–30%) or where no grazers were excluded (2–19%). The effect of limpets and chitons accounted for 55–89% of the variance in total algal cover, whereas the effect of abalone generally accounted for <10% of the variance. Similar results were obtained in terms of the biomass of Ulva rigida at the end of the experiment. Haliotis roei are relatively large and sedentary herbivores, feeding mainly on drift algae. Their effect on algal abundance was mediated both through pre-emption of space, which might otherwise be colonized by algae, and by grazing around their home scar. Limpets and chitons are smaller than abalone, but were much more abundant. Intensive grazing of the reef surface by limpets and chitons precluded the establishment of non-coralline macroalgae, even where abalone were absent.     

Miocene intertidal zonation on a volcanically active shoreline: Porto Santo in the Madeira Archipelago,Portugal

Santos, A., Mayoral, E.J., da Silva, C.M., Cachão, M., Johnson, M.E. & Baarli, B.G. Miocene intertidal zonation on a volcanically active shoreline: Porto Santo in the Madeira Archipelago, Portugal. Lethaia, Vol. 44, pp. 26–32. Short‐term biological colonization of rockgrounds on the basaltic shorelines of oceanic islands has, as yet, been poorly explored. A Miocene sea cliff on Ilhéu de Cima off Porto Santo in the Madeira Archipelago of Portugal provides a case study showing intertidal zonation with two types of barnacles, serpulid worm tubes, two coral species, epifaunal bivalves and the trace fossils of endolithic bivalves. Large barnacles (Balanus sp.) and serpulids are limited to the upper 400 mm of a basalt cliff of 1.6 m in height. Small barnacles, possibly of the same species, extend to the base. The upper half includes the corals Isophyllastrea orbignyana and Tarbellastraea reussiana, to which many small, coral‐inhabiting, barnacles (Ceratoconcha costata) are fixed. Borings identified as Gastrochaenolites torpedo appear through the bottom two‐thirds of the cliff face. Rarely, Gastrochaenolites lapidicus is exposed in longitudinal section with borings up to 45 mm deep in solid basalt. Epifaunal bivalves, such as Spondylus sp., are limited to a middle zone. Associated with the sea cliff is an outer platform on which a multitude of T. reussiana colonies occur in growth position. The corals exhibit planar erosion over180 m². The shelf was faulted and cut by a basalt dike prior to the brief recolonization of I. orbignyana, found attached to low fault scarps. Habitation of the sea cliff was facilitated by rising sea level, but abruptly terminated by burial under volcanoclastic ejecta. □Basalt bioerosion, coastal dynamics, Ilhéu de Cima (Porto Santo), Miocene intertidal zonation, volcanogenic perturbations.     

Evolutionary and acclimation-induced variation in the thermal limits of heart function in congeneric marine snails (genus Tegula): implications for vertical zonation

We analyzed the thermal limits of heart function for congeneric species of the marine snail Tegula that have different patterns of vertical zonation. T. funebralis is found in the low to mid-intertidal zone, and T. brunnea and T. montereyi live in the low-intertidal or subtidally. As indices of thermal limits of heart function, we used the temperature at which heart rate initially decreased rapidly during heating (the Arrhenius break temperature, or ABT) and the temperature at which heart ceased to beat with either heating or cooling (the flatline temperature, or FLT(hot) or FLT(cold), respectively). These three indices provide an estimate of the thermal range within which Tegula heart function is maintained. For field-acclimatized specimens, the thermal range of the high-intertidal T. funebralis was greater than those of its two lower-occurring congeners (higher ABT, higher FLT(hot), lower FLT(cold)). We also demonstrated the effects of constant thermal acclimation on the heart rate response to heat stress. Acclimation to 14 degrees C and 22 degrees C resulted in increases in ABT and FLT(hot), with the largest changes in T. brunnea and T. montereyi. Although T. funebralis is more heat tolerant and eurythermal than its two lower-occurring congeners, it can encounter field body temperatures that exceed ABT, indicating that T. funebralis faces a larger threat from heat stress, in situ. These findings are consistent with recent studies on other taxa of marine invertebrates that have shown, somewhat paradoxically, that warm-adapted, eurythermal intertidal species may be more impacted by global warming than congeneric subtidal species that are less heat tolerant.     

Speciation and the establishment of zonation in an intertidal barnacle: specific settlement vs. selection

The tropical barnacle Tetraclita forms a belt on hard substrates in the intertidal zone of the Red Sea. Based on morphological data, three distinct species were suggested to exist, occupying different vertical levels - T. barnesorum, T. rufotincta and T. achituvi. In this study we used molecular (12S mitochondrial ribosomal DNA) and ecological data to examine whether this morphological variability reflects genetic differences, or is a result of environmental factors. Adults and spats, collected from settlement plates, were censused and screened genotypically using single strand conformation polymorphism (SSCP) analysis, and settlement dynamics was recorded. We provide evidence for the existence of only two distinct species, and point out both phenotypic plasticity and convergence within and between the proposed species. Cyprids of T. achituvi settle specifically at the lower part of the Tetraclita belt, and feature one phenotype. In contrast, T. rufotincta, occupying the upper and middle portions of the Tetraclita belt, settles throughout the range, shows phenotypic plasticity (three variants), and presumably undergoes selection at the lower part. Thus, the vertical zonation of Tetraclita is produced by the combination of pre-settlement and post-settlement factors, in T. achituvi and T. rufotincta, respectively. The examined system may offer a model in which to study the mechanisms underlying sympatric speciation.     

Deer,wolves, and people: costs,benefits and challenges of living together

Human‐driven species annihilations loom as a major crisis. However the recovery of deer and wolf populations in many parts of the northern hemisphere has resulted in conflicts and controversies rather than in relief. Both species interact in complex ways with their environment, each other, and humans. We review these interactions in the context of the ecological and human costs and benefits associated with these species. We integrate scattered information to widen our perspective on the nature and perception of these costs and benefits and how they link to each other and ongoing controversies regarding how we manage deer and wolf populations. After revisiting the ecological roles deer and wolves play in contemporary ecosystems, we explore how they interact, directly and indirectly, with human groups including farmers, foresters, shepherds, and hunters. Interactions with deer and wolves generate various axes of tension, posing both ecological and sociological challenges. Resolving these tensions and conflicts requires that we address key questions using integrative approaches: what are the ecological consequences of deer and wolf recovery? How do they influence each other? What are the social and socio‐ecological consequences of large deer populations and wolf presence? Finally, what key obstacles must be overcome to allow deer, wolves and people to coexist? Reviewing contemporary ecological and sociological results suggests insights and ways to improve our understanding and resolve long‐standing challenges to coexistence. We should begin by agreeing to enhance aggregate benefits while minimizing the collective costs we incur by interacting with deer and wolves. We should also view these species, and ourselves, as parts of integrated ecosystems subject to long‐term dynamics. If co‐existence is our goal, we need deer and wolves to persevere in ways that are compatible with human interests. Our human interests, however, should be inclusive and fairly value all the costs and benefits deer and wolves entail including their intrinsic value. Shifts in human attitudes and cultural learning that are already occurring will reshape our ecological interactions with deer and wolves.     

西藏色季拉山土壤物理性质垂直地带性

以色季拉山为代表的藏东南高原山地的水土流失已成为区域生态环境的重要问题。对色季拉山不同海拔梯度土壤物理性质进行分析,结果表明:(1)除海拔3600、4200m外,土壤容重随土层深度增加而增大;总孔隙度、毛管孔隙度随土层深度增加而减小;非毛管孔隙度随土层变化无明显规律;饱和含水率、毛管含水率、田间持水率均随土层深度增加而减小。(2)不同海拔梯度,土壤容重总均值、总孔隙度、毛管孔隙度和非毛管孔隙度变化范围分别为:0.58—1.10g/cm~3、57.00%—72.47%、53.33%—67.59%和3.20%—4.87%。饱和含水率、毛管含水率、渗透性具有相同规律,均为3800、3400m处最大,3200m和3600m处最小,4000—4600m居中,田间持水率随海拔梯度变化呈M型波动性趋势。(3)土壤物理性质具有较强的空间异质性,各指标间有明显的空间自相关现象。土壤物理性质各指标在不同土层和海拔间有较明显的差异性,人为干扰也是导致土壤物理性质空间异质性的重要原因。(4)总体上,色季拉山表层土壤(0—10cm)物理结构优于深层次(10—30cm)土壤;3200m和3600m处最差,4000—4600m居中,3400—3800m最佳。研究结果提示,以色季拉山为代表的藏东南原始森林地带,土壤结构脆弱,为保持水土,应防止旅游和森林生产经营的过度开发。     

Coastal residents,stingray style: Selecting the best intertidal creeks for seasonal living

Graphing and calculating percentages are integral skills in a STEM curriculum. Teaching students how to create graphs allows them to identify numerical trends and to express results in a clear and concise manner. In this activity, students will remain engaged in the lesson by moving around the room and then work together to generate their own data. Students will act like stingrays and determine the costs and benefits of selecting different habitats. The skills honed in the activity will enable students to compare actual stingray data with in-class data and to express the results graphically. This activity aligns with Ocean Literacy Principles, Common Core Standards, and National Science Education Standards. The Next Generation Science Standard of including the analysis and interpretation of data to provide evidence for the effects of resource availability on organisms in an ecosystem is also incorporated.     

Temporal comparison of the composition and zonation of rocky intertidal organisms at Cocos Island National Park, Pacific, Costa Rica

Several biological and physical factors change the rocky shore communities. The desiccation time and the tolerance of the intertidal species produce the vertical zonation. In many studies around the world, a temporal change in this zonation is presented.In Costa Rica, only studies that include temporal trends were carried out in Punta Mala and Montezuma, Pacific coast in 80's. The rocky intertidal of the Cocos Island National Park, Costa Rica were surveyed photographically. The Chatham bay was sampled in three expeditions (January 2007, October 2007 and April 2008). Photos corresponding to 25x25cm quadrats were taken with the goal to determine diversity and composition differences in rocky shore organisms between sampling dates. The Wafer bay was sampled in January and October 2007. The intertidal of Chatham consists of basaltic rock, while Wafer has basaltic and ignimbrite boulders. The main difference between sites were the higher algae cover (erect-frondose forms) and number of organism bands at Chatham bay. Temporal change was not found in the total cover of sessile fauna and autotrophs. The barnacle Tetraclita stalactifera, that occurs above the algal fringe (lower intertidal), was the invertebrate with the highest coverage. The mobile fauna biodiversity presented no significant trend between sampled months. However, the identity of species, their cover and their abundance showed a moderate temporal change. In October 2007, when the sea surface temperature was 23 degrees C the infralittoral zone had an increase in green algae cover. The red algae (crust and erect-frondose forms) were dominant in January and April. The pulmonate limpet, Siphonaria gigas and a bacterial biofilm at mid littoral showed a negative association. The snails of the high littoral and the supralittoral zone showed a temporal change in their abundance, but with contrasting patterns between sites. The temporal variation in the assemblages increased from the supralittoral to the infralittoral possibly due to changes in the water temperature and climatic conditions, that could influence the intertidal zone during the high and low tide, respectively.     

Causes and consequences of thermal tolerance limits in rocky intertidal porcelain crabs, genus petrolisthes

Vertical zonation of intertidal organisms, from the shallowsubtidal to the supralittoral zones, is a ubiquitous featureof temperate and tropical rocky shores. Organisms that livehigher on the shore experience larger daily and seasonal fluctuationsin microhabitat conditions, due to their greater exposure toterrestrial conditions during emersion. Comparative analysesof the adaptive linkage between physiological tolerance limitsand vertical distribution are the most powerful when the studyspecies are closely related and occur in discrete vertical zonesthroughout the intertidal range. Here, I summarize work on thephysiological tolerance limits of rocky intertidal zone porcelaincrab species of the genus Petrolisthes to emersion-related heatstress. In the eastern Pacific, Petrolisthes species live throughouttemperate and tropical regions, and are found in discrete verticalintertidal zones in each region. Whole organism thermal tolerancelimits of Petrolisthes species, and thermal limits of heartand nerve function reflect microhabitat conditions. Speciesliving higher in the intertidal zone are more eurythermal thanlow-intertidal congeners, tropical species have the highestthermal limits, and the differences in thermal tolerance betweenlow- and high-intertidal species is greatest for temperate crabs.Acclimation of thermal limits of high-intertidal species isrestricted as compared to low-intertidal species. Thus, becausethermal limits of high-intertidal species are near current habitattemperature maxima, global warming could most strongly impactintertidal species.     

The costs and benefits of fast living

Growth rates play a fundamental role in many areas of biology (Q. Rev. Biol., 67, 1992, 283; Life History Invariants. Some Explorations of Symmetry in Evolutionary Biology, 1993; Philos. Trans. R. Soc. Lond. B Biol. Sci., 351, 1996, 1341; Plant Strategies, Vegetation Processes, and Ecosystem Properties, 2002; Trends Ecol. Evol., 18, 2003, 471; Q. Rev. Biol., 78, 2003, 23; J. Ecol., 95, 2007, 926.) but the cost and benefits of different growth rates are notoriously difficult to quantify (Q. Rev. Biol., 72, 1997, 149; Funct. Ecol., 17, 2003, 328). This is because (1) growth rate typically declines with size and yet the most widely used growth measure – relative growth rate or RGR (conventionally measured as the log of the ratio of successive sizes divided by the time interval) – is not size-corrected and so confounds growth and size, (2) organisms have access to different amounts of resource and (3) it is essential to allow for the long-term benefits of larger size. Here we experimentally demonstrate delayed costs and benefits of rapid growth in seven plant species using a novel method to calculate size-corrected RGR. In control treatments, fast-growing plants benefited from increased reproduction the following year; however, fast-growing plants subjected to an experimental stress treatment (defoliation) showed strongly reduced survival and reproduction the following year. Importantly, when growth was estimated using the classical RGR measure, no costs or benefits were found. These results support the idea that life-history trade-offs have a dominant role in life-history and ecological theory and that the widespread failure to detect them is partly due to methodological shortcomings.     

Stench and sensibilities: On living with waste,animals and microbes in India

Stench is often the most immediate mark of something dirty, decaying and diseased. In India, stench and the smell of acrid smoke commonly indicate the proximity of an open dump or landfill. Frequently a slum is located in the vicinity too, housing waste‐pickers who forage in these sprawling dumps for salvageable waste. These spaces are also host to vermin, birds, stray dogs, pigs, cows and, more recently, dangerous bacteria resistant to even top‐end antibiotics, popularly known as ‘superbugs’. In this paper I examine the socio‐ecological context of neighbourhood, community open garbage dumps and larger landfills in an effort to understand these as part of a dynamic ecosystem of ‘more‐than‐human’ relations. Perceptual variations of smell as experienced in and around waste (in its solid, liquid and gas states) are intrinsically linked to symbolic and material practices across species. Additionally, I suggest that one productive way to think about the emergence of disease and pathogenicity is by considering the information stimulated by smell, which is mediated by cultural interpretations, biological capacities and wider political economies.     

Thermal physiology of laboratory mice: Defining thermoneutrality

In terms of total number of publications, the laboratory mouse (Mus musculus) has emerged as the most popular test subject in biomedical research. Mice are used as models to study obesity, diabetes, CNS diseases and variety of other pathologies. Mice are classified as homeotherms and regulate their core temperature over a relatively wide range of ambient temperatures. However, researchers find that the thermoregulatory system of mice is easily affected by drugs, chemicals, and a variety of pathological conditions, effects that can be exacerbated by changes in ambient temperature. To this end, a thorough review of the thermal physiology of mice, including their sensitivity and regulatory limits to changes in ambient temperature is the primary focus of this review. Specifically, the zone of thermoneutrality for metabolic rate and how it corresponds to that for growth, reproduction, development, thermal comfort, and many other variables is covered. A key point of the review is to show that behavioral thermoregulation of mice is geared to minimize energy expenditure. Their zone of thermal comfort is essentially wedged between the thresholds to increase heat production and heat loss; however, this zone is above the recommended guidelines for animal vivariums. Future work is needed to better understand the behavioral and autonomic thermoregulatory responses of this most popular test species.     

Taconic Foreland Basin graptolites: age zonation, depth zonation, and use in ecostratigraphic correlation

Late Middle Ordovician graptoloids are stratigraphically zoned by depth of deposition as well as by age along an 83 km long downslope transect through a roughly four million year long continental-shelf and outer-trench slope sequence in the Mohawk Valley, New York. The distribution of graptoloid assemblages parallels the distribution of sediment types and benthic macroinvertebratc assemblages in showing the general, convergence-related marine transgression, secondary transgressive and regressive pulses, and topographic irregularities related to syndepositional block faulting. The relationship of ordination scores for graptoloid assemblages (which arc based on relative abundances of genera) to the samples' positions on downslope transects along bentonite beds, and to depth-related ordination scores for benthic macroin-vertebrate assemblages in the same samples throughout the sequence, quantitatively demonstrates zonation by depth of deposition. Rather like modern pelagic colonial tunicates, graptoloids were evidently zoned by depth in the water column, with Orthograptus spp. predominating in offshore waters above the oxygen minimum zone, Climacograptus spp. near the top of the minimum zone at 300 to 500 m depths, and Corynoides spp. well within the minimum zone. Destruction of sinking rhabdosomes by decomposers evidently accentuated zonation by depth of deposition, and may have contributed to the strong, broad oxygen minimum zone thought to have been characteristic of graptolitic shale basins. Stratigraphic sections' approximate relative sea level curves, calibrated in terms of graptoloid assemblage ordination score, give ecostratigraphic correlations of 2–3 × 10⁵ year average accuracy when statistically cross-correlated between sections, and when cross-correlated with similar curves based on benthic macroinvertebratc assemblage ordination score. □Graptolithina, age zonation, depth zonation, paleoeco-logy, Middle Ordovician, ecostratigraphy, coenocorrelation.     

Range limits and geographic patterns of abundance of the rocky intertidal owl limpet,Lottia gigantea

Aim We evaluate the stability of the range limits of the rocky intertidal limpet, Lottia gigantea, over the last c. 140 years, test the validity of the abundant centre hypothesis, and test indirectly the roles played by recruitment limitation and habitat availability in controlling the range limits. Because this species is size‐selectively harvested, our results also allow us to assess conservation implications. Location The Pacific coast of North America, from northern California to southern Baja California (41.74° N–23.37° N), encompassing the entire range of L. gigantea. Methods The historical and modern distributions of L. gigantea were established using museum data and field observations. Overall and juvenile abundances of local populations were estimated at 25 field sites. The spatial distribution of abundance was evaluated statistically against the predictions of five hypothetical models. The availability of habitat was estimated by measuring the percentage of unavailable sandy beach within cumulative bins of coast across the range of L. gigantea. Results The northern limit of L. gigantea has contracted by c. 2.4° of latitude over recent decades (after 1963), while the southern limit has remained stable. The highest abundances of L. gigantea occur in the centre of its geographic range. Habitat availability is ample in the centre and northern portions of its range, but is generally lacking in the southern range. The northern range is only sparsely populated by adults, with sharp declines occurring north of Monterey Bay (36.80° N). In the southern range, abundance drops precipitously south of Punta Eugenia (27.82° N), coinciding with the region where suitable habitat becomes sparse. Main conclusions Support for the abundant centre hypothesis was found for L. gigantea. Northern populations are characterized as being recruitment‐limited, demographically unstable and prone to local extinctions, while southern populations are suggested to be habitat‐limited. The abundant centre is suggested to result partly from a combination of the indirect effects of human harvesting, generating denser populations of smaller individuals, and larval recruitment from well‐protected offshore rocky islands primarily found in the range centre.     

The natural history, thermal physiology, and ecological impacts of intertidal mesopredators, Oedoparena spp. (Diptera: Dryomyzidae)

Abstract. The ecological roles of small (1–1000 mg) predators in benthic marine systems are poorly understood. We investigated the natural history and predatory impact of one group of such mesopredators—larvae of dipteran flies in the genus Oedoparena —which prey on intertidal barnacles. We 1) quantified patterns of larval Oedoparena distribution and abundance in the Northwest Straits of Washington State, USA, 2) determined larval physiological tolerance limits in the laboratory, and 3) conducted a manipulative field experiment to assess the role of microhabitat temperature on predation rates in Oedoparena . Members of Oedoparena in Washington are univoltine, with peak larval abundance in late spring and early summer. Infestation frequencies in the barnacles Balanus glandula and Chthamalus dalli were as high as 22% and 35%, respectively. In laboratory studies, larvae of O . glauca were able to tolerate temperatures up to 37°C; however, this temperature is often exceeded in high intertidal habitats. In a field manipulation using experimental shades, we demonstrate that the alleviation of physiological stress greatly increased the abundance of larvae of Oedoparena spp. As a result of increased larval densities under shades, adult B. glandula mortality increased from 5% to nearly 30%, and C. dalli mortality increased from less than 20% to over 60%. Because high intertidal barnacles serve as food and habitat for a diverse array of species, Oedoparena spp. have the potential to play a major role in structuring high intertidal communities, particularly in cooler microhabitats.     

Female polymorphisms, sexual conflict and limits to speciation processes in animals

Heritable and visually detectable polymorphisms, such as trophic polymorphisms, ecotypes, or colour morphs, have become classical model systems among ecological geneticists and evolutionary biologists. The relatively simple genetic basis of many polymorphisms (one or a few loci) makes such species well-suited to study evolutionary processes in natural settings. More recently, polymorphic systems have become popular when studying the early stages of the speciation process and mechanisms facilitating or constraining the evolution of reproductive isolation. Although colour polymorphisms have been studied extensively in the past, we argue that they have been underutilized as model systems of constraints on speciation processes. Colouration traits may function as signalling characters in sexual selection contexts, and the maintenance of colour polymorphisms is often due to frequency-dependent selection. One important issue is why there are so few described cases of female polymorphisms. Here we present a synthetic overview of female sexual polymorphisms, drawing from our previous work on female colour polymorphisms in lizards and damselflies. We argue that female sexual polymorphisms have probably been overlooked in the past, since workers have mainly focused on male-male competition over mates and have not realized the ecological sources of genetic variation in female fitness. Recent experimental evolution studies on fruit flies (Drosophila melanogaster) have demonstrated significant heritable variation among female genotypes in the fitness costs of resistance or tolerance to male mating harassment. In addition, female-female competition over resources could also generate genetic variation in female fitness and promote the maintenance of female sexual polymorphisms. Female sexual polymorphisms could subsequently either be maintained as intrapopulational polymorphisms or provide the raw material for the formation of new species.