Relative importance of temperature and other factors in determining geographic boundaries of seaweeds: Experimental and phenological evidence

Experimentally determined ranges of thermal tolerance and requirements for completion of the life history of some 60 seaweed species from the North Atlantic Ocean were compared with annual temperature regimes at their geographic boundaries. In all but a few species, thermal responses accounted for the location of boundaries. Distribution was restricted by: (a) lethal effects of high or low temperatures preventing survival of the hardiest life history stage (often microthalli), (b) temperature requirements for completion of the life history operating on any one process (i.e. [sexual] reproduction, formation of macrothalli or blades), (c) temperature requirements for the increase of population size (through growth or the formation of asexual propagules). Optimum growth/reproduction temperatures or lethal limits of the non-hardiest stage (often macrothalli) were irrelevant in explaining distribution. In some species, ecotypic differentiation in thermal responses over the distribution range influenced the location of geographic boundaries, but in many other species no such ecotypic differences were evident. Specific daylength requirements affected the location of boundaries only when interacting with temperature. The following types of thermal responses could be recognised, resulting in characteristic distribution patterns: (A) Species endemic to the (warm) temperate eastern Atlantic had narrow survival ranges (between ca 5 and ca 25°C) preventing occurrence in NE America. In species with isomorphic life histories without very specific temperature requirements for reproduction, northern and southern boundaries in Eur/Africa are set by lethal limits. Species with heteromorphic life histories often required high and/or low temperatures to induce reproduction in one or both life history phases which further restricted distribution. (B) Species endemic to the tropical western Atlantic also had narrow survival ranges (between ca 10 and ca 35°C). Northern boundaries are set by low, lethal winter temperatures. Thermal properties would potentially allow occurrence in the (sub) tropical eastern Atlantic, but the ocean must have formed a barrier to dispersal. No experimental evidence is so far available for tropical species with an amphi-Atlantic distribution. (C) Tropical to temperate species endemic to the western Atlantic had broad survival ranges (<0 to ca 35°C). Northern boundaries are set by low summer temperatures preventing (growth and) reproduction. Thermal properties would permit occurrence in the (sub)tropical eastern Atlantic, but along potential “stepping stones” for dispersal in the northern Atlantic (Greenland, Iceland, NW Europe) summer temperatures would be too low for growth. (D) In most amphi-Atlantic (tropical-) temperate species, northern boundaries are set by low summer temperatures preventing reproduction or the increase of population size. On European shores, species generally extended into regions with slightly lower summer temperatures than in America, probably because milder winters allow survival of a larger part of the population. (E) Amphi-Atlantic (Arctic-) temperate species survived at subzero temperatures. In species with isomorphic life histories not specifically requiring low temperatures for reproduction, southern boundaries are set by lethally high summer temperatures on both sides of the Atlantic. None of the species survived temperatures over 30°C which prevents tropical occurrence. Species with these thermal responses are characterized by distribution patterns in which southern boundaries in Eur/Africa lie further south than those in eastern N America because of cooler summers. In most species with heteromorphic life histories (or crustose and erect growth forms), low temperatures were required for formation of the macrothalli (either directly or through the induction of sexual reproduction). These species have composite southern boundaries in the north Atlantic Ocean. On American coasts, boundaries are set by lethally high summer temperatures, on European coasts by winter temperatures too high for the induction of macrothalli. Species with this type of thermal responses are characterized by distribution patterns in which the boundaries in Eur/Africa lie further north than those in eastern N America because of warmer winters. Paper presented at the XIV International Botanical Congress (Berlin, 24 July–1 August, 1987), Symposium 6-15, “Biogeography of marine benthic algae”.     

Variation in songbird migratory behavior offers clues about adaptability to environmental change

For seasonally migrating birds, aspects of migratory behavior, such as the use of temperate versus tropical wintering areas, may influence their ability to respond to environmental change. Here, we infer potential flexibility in songbird migration from variation in two alternative stopover behaviors. Hierarchical Bayesian mark–recapture modeling was used to quantify stopover decisions over 19 years for four temperate and four tropical migratory species at a stopover site in southern Canada. Short-distance temperate migrants exhibited higher variability in behavior and greater responses to local weather than longer-distance tropical migrants, as measured by transience (the proportion of birds stopping <24 h, i.e. seeking brief sanctuary or subsequently relocating) and departure (re-initiation of migration by birds that stopped over for >24 h). In contrast to many previous works on climate–migration associations, annual variation in stopover behavior did not show strong links to broad-scale climatic fluctuations for either temperate or tropical migrants, nor was there any indication of directional changes in stopover behavior over the past two decades. In addition to suggesting that migratory songbirds—particularly tropical-wintering species—may face increasing threats with future climatic variability, our study highlights the potential importance of flexibility in en-route behavior for resilience to environmental change.     

Trophic niche differentiation in millipede communities of forests of the temperate and tropical belts

The degree of trophic differentiation of millipedes in taxocenes of temperate and tropical forests was estimated by isotopic analysis. The isotope ratio variation among species was notably wider in a tropical forest (23 millipede species, δ¹⁵N ranges within 10‰) than in a temperate broad-leaved forest (9 species, δ¹⁵N range less than 3‰). It is suggested that partitioning of food resources among species contributes significantly to the maintenance of high diversity of soil saprotrophic animals in tropical ecosystems.     

Constraint on Reproductive Output in Brachyuran Crabs: Pinnotherids Test the Rule

Brood weight and number of eggs per brood are primarily determinedby female body size in brachyuran crabs. Brood weight exhibitsan isometric relationship spanning more than four orders ofmagnitude in body weight among 33 non-pinnotherid species, withbrood size being constrained to about 10% of female body weightby the space available for yolk accumulation within the cephalothorax.In contrast, two pinnotherids (Pinnotheres ostreum, Fabiasubquadrata)have relative brood sizes which are 66% and 97%, respectively,of body weight. The allometric constraint is circumvented inthese extraordinarily large brood sizes by two pinnotherid featureswhich allow more space for yolk accumulation. Unlike other brachyurans,their ovaries extend out of the cephalothorax into the abdomen,and calcification of their exoskeleton is greatly reduced, potentiallyallowing distension of the body. As in crabs, pinnotherid eggsize is highly variable among species, which tends to increasethe variance among species in fecundity per brood, making pinnotheridfecundities not extraordinary. Thenumber of broods producedper year in these two species is limited by short reproductiveseasons, which tends to bring their annual reproductive outputin line with other brachyurans. The trade-offs among reproductivevariables in pinnotherids is adaptive for the small body sizeand parasitic niche of these species.     

Ants on plants: a meta-analysis of the role of ants as plant biotic defenses

We reviewed the evidence on the role of ants as plant biotic defenses, by conducting meta-analyses for the effects of experimental removal of ants on plant herbivory and fitness with data pooled from 81 studies. Effects reviewed were plant herbivory, herbivore abundance, hemipteran abundance, predator abundance, plant biomass and reproduction in studies where ants were experimentally removed (n = 273 independent comparisons). Ant removal exhibited strong effects on herbivory rates, as plants without ants suffered almost twice as much damage and exhibited 50% more herbivores than plants with ants. Ants also influenced several parameters of plant fitness, as plants without ants suffered a reduction in biomass (−23.7%), leaf production (−51.8%), and reproduction (−24.3%). Effects were much stronger in tropical regions compared to temperate ones. Tropical plants suffered almost threefold higher herbivore damage than plants from temperate regions and exhibited three times more herbivores. Ant removal in tropical plants resulted in a decrease in plant fitness of about 59%, whereas in temperate plants this reduction was not statistically significant. Ant removal effects were also more important in obligate ant–plants (=myrmecophytes) compared to plants exhibiting facultative relationships with hemiptera or those plants with extrafloral nectaries and food bodies. When only tropical plants were considered and the strength of the association between ants and plants taken into account, plants with obligate association with ants exhibited almost four times higher herbivory compared to plants with facultative associations with ants, but similar reductions in plant reproduction. The removal of a single ant species increased plant herbivory by almost three times compared to the removal of several ant species. Altogether, these results suggest that ants do act as plant biotic defenses, but the effects of their presence are more pronounced in tropical systems, especially in myrmecophytic plants. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. N. P. de U. Barbosa, L. Diniz, Y. Oki and F. Pezzini contributed equally to this work and are listed in alphabetical order.     

Reproduction and larval development of Polydora robi (Polychaeta: Spionidae), an obligate commensal of hermit crabs from the Philippines

Abstract. The reproduction of a recently described spionid polychaete, Polydora robi , is examined from the Philippines. Adults inhabit a burrow in the apex of gastropod shells occupied by hermit crabs. Females were found to deposit broods of 18–94 egg capsules in the summer (June–August) and winter months (January–March) sampled. Paired or single egg capsules are attached by stalks to the inside wall of the burrow and contain 40–106 eggs which average 97 μm in diameter. The total number of eggs per brood ranges from 941–8761 eggs and is positively correlated with the total number of segments and length of female worms. Adults of P. robi are polytelic, producing ≤9 successive broods over a 3-month period; a mean of 6.7 d was exhibited between broods in the laboratory. Females utilize sperm stored in the seminal receptacles during successive spawnings. Development occurs within egg capsules until the 3-segment stage, at which time the planktotrophic larvae are released. Juveniles of ∼20 segments are competent to settle on gastropod shells inhabited by hermit crabs. Members of P. robi are relatively fecund, semicontinuous breeders; the life-cycle in this species is similar to the only other known obligate polydorid commensal of hermit crabs.     

Distinctive Phyllosphere Bacterial Communities in Tropical Trees

Recent work has suggested that in temperate and subtropical trees, leaf surface bacterial communities are distinctive to each individual tree species and dominated by Alpha- and Gammaproteobacteria. In order to understand how general this pattern is, we studied the phyllosphere bacterial community on leaves of six species of tropical trees at a rainforest arboretum in Malaysia. This represents the first detailed study of ‘true’ tropical lowland tree phyllosphere communities. Leaf surface DNA was extracted and pyrosequenced targeting the V1–V3 region of 16S rRNA gene. As was previously found in temperate and subtropical trees, each tree species had a distinctive bacterial community on its leaves, clustering separately from other tree species in an ordination analysis. Bacterial communities in the phyllosphere were unique to plant leaves in that very few operational taxonomic units (0.5%) co-occurred in the surrounding soil environment. A novel and distinctive aspect of tropical phyllosphere communities is that Acidobacteria were one of the most abundant phyla across all samples (on average, 17%), a pattern not previously recognized. Sequences belonging to Acidobacteria were classified into subgroups 1–6 among known 24 subdivisions, and subgroup 1 (84%) was the most abundant group, followed by subgroup 3 (15%). The high abundance of Acidobacteria on leaves of tropical trees indicates that there is a strong relationship between host plants and Acidobacteria in tropical rain forest, which needs to be investigated further. The similarity of phyllosphere bacterial communities amongst the tree species sampled shows a significant tendency to follow host plant phylogeny, with more similar communities on more closely related hosts.     

Invasive Temperate Species are a Threat to Tropical Island Biodiversity

To protect the remaining biodiversity on tropical islands it is important to predict the elevational ranges of non-native species. We evaluated two hypotheses by examining land snail faunas on the eastern (windward) side of the island of Hawaii: (1) the latitude of a species' native region can be used to predict its potential elevational range and (2) non-native temperate species, which experience greater climatic fluctuations in their native range, are more likely to become established at higher elevations and to extend over larger elevational ranges than non-native tropical species. All non-native tropical species were distributed patchily among sites ≤500 m and occupied small elevational ranges, whereas species introduced from temperate regions occupied wide elevational ranges and formed a distinct fauna spanning elevations 500–2000 m. Most native land snail species and ecosystems occur >500 m in areas dominated by temperate non-native snail and slug species. Therefore, knowing the native latitudinal region of a non-native species is important for conservation of tropical island ecosystems because it can be translated into potential elevational range if those species are introduced. Because temperate species will survive in tropical locales particularly at high elevation, on many tropical islands the last refuges of the native species, preventing introduction of temperate species should be a conservation priority.     

Physiological costs and carry-over effects of avian interspecific brood parasitism influence reproductive tradeoffs

Although models of co-evolution between brood parasites and their hosts primarily focus upon the cost to hosts in the current reproductive bout, the impact of brood parasitism may carry over to future reproductive attempts by altering resource allocation. Glucocorticoid stress hormones help mediate resource allocation to reproduction, yet they have rarely been examined in brood parasitic systems. Here we determined if shifts in parental care and corticosterone had carry-over effects on future reproductive effort in the rufous-and-white wren (Thryophilus rufalbus), a host of the Central American striped cuckoo (Tapera naevia). We found that parasitized parents had significantly higher stress-induced, but not baseline, corticosterone than natural parents during the fledgling stage, which was associated with changes in parental care. The high investment in current reproduction while parasitized may be due to the value of fledged chicks in tropical systems. This maladaptive response by parasitized parents was associated with delayed re-nesting and a reduced likelihood of nesting in the subsequent breeding season. Although a reduction in future reproductive effort can result from a combination of factors, this work suggests that fitness costs of brood parasitism are mediated by changes in corticosterone and parental care behavior that carry over into subsequent breeding seasons.     

A seasonal natural history of the ant, Odontomachus brunneus

A north Florida population of Odontomachus brunneus, a species of ponerine ants, was studied for a one-year period to determine the annual cycle of reproduction and colony growth, including the foraging biology and seasonal changes in nest architecture. The life cycle of O. brunneus is strongly seasonal. Colonies produce brood for 6 months and are broodless for 6 months. Alates are produced in mixed broods at the beginning of each season, consuming much of the colony’s energy reserves. These reserves recover slowly through foraging during the summer’s worker production, and rapidly after brood production ceases in October. The foraging population was estimated to average 77% (SD 22) of the workforce. This proportion was not related to colony size and female alates were also found to forage. Nest architecture was found to change seasonally, with winter nests being more than twice as deep as the average summer nest.     

Epibionts of the red king crab Paralithodes camtschaticus (Tilesius, 1815) in Sayda Inlet of Kola Bay

The species composition of organisms associated with the red king crab Paralithodes camtschaticus (Tilesius, 1815) was investigated in Sayda Inlet of Kola Bay in 2004–2005. Nine fouler species and three symbiotic species were found on the carapaces of the red king crab. Balanus crenatus Bruigere 1789 barnacles were the most abundant fouler species and were found on 14.8% of the crabs. Symbiotic amphipods Ischyrocerus commensalis Chevreux, 1900 were found for one-tenth of all the crabs studied. The mean intensity of the amphipods was significantly greater for September, when the reproduction period of this species occurred. Male and female crabs were hosted with the same intensity. The number of host crabs increased accordingly to the crab size. The proportion of hosted crabs was three-fold less in Sayda Inlet than in the less polluted areas of the Barents Sea.     

Acclimation of Intertidal Crabs

SVXOPSIS. Intertidal crabs are subjected to marked fluctuationsin environmental factors. Temperature and salinity influencethe distribution of organisms both on a latitudinal basis andalong a subtidal to terrestrial gradient. These factors areoperative on all stages of the life history. Resistance-adaptations. Adult fiddler crabs (genus Uca) fromthe temperate zone are more resistant to low temperature thantropical species. Also, the tolerance to low temperature ofcrabs from the temperate zone is greatly influenced by thermalacclimation, i.e. cold-acclimated crabs are more resistant thanwarm-acclimated animals. In contrast, tropical species havelimited adaptive ability. At elevated temperatures no consistentdifference in the lethal limits of crabs from tropical and temperatezones is observed. In contrast with the adults, larvae of tropicalspecies are cold-resistant. However, the larvae of all speciestested are more sensitive to reduced salinities than are theadults. Capacity-adaptatioyis. Subtidal species of crabs tend to havea lower level of respiratory performance, as measured by variousindices, than crabs from the intertidal zone. The metabolicresponse of fiddler crabs from the temperate zone is more labileat low temperature than in species from the tropical zone. Atelevated temperature the reverse response is observed. On aninterspecific basis, differences in the metabolictemperaturepatterns of acclimation of latitudinally separated populationsof U. pugilator are observed when based on the hypotheticalschemes of Bullock, Precht, and Prosser.     

Tree species diversity in temperate and tropical forest gaps: The role of lottery recruitment

How canopy gaps promote tree species coexistence in temperate and tropical forests is reviewed. Given that evidence for traditional resource-based niche partitioning of canopy gaps is weak, lottery recruitment, whereby colonization of vacant living space is random with respect to species identity, may be key to maintaining diversity. Gap formation events are not highly predictable and species’ propagules tend to be patchily distributed. For these reasons the predictability of gap-phase recruitment is low and lottery principles apply. Recruitment limitation from discontinuities in species’ propagule supplies in space and time may permit lottery recruitment in temperate and tropical forests. However, the relative importance of recruitment limitation in species-rich versus species-poor communities is unclear. Although lottery models with purely random recruitment in vacant sites can be applied, relatively complex models appear to better capture the essential features of forest community dynamics. For example, models with recruitment probabilities weighted by species abundance can produce the non-random trajectories often observed in communities. Models with local competitive displacement by individuals of dominant species can also produce non-random trajectories. Models with spatial structure, localized competition, and dispersal limitations may provide further insight into the effects of biotic interactions and recruitment limitation on forest dynamics.     

Experimental evaluation of the potential of tropical germplasm for temperate maize improvement

 Commercial maize (Zea mays L.) in the USA has a restricted genetic base as newer hybrids are largely produced from crosses among elite inbred lines representing a small sample (predominantly about 6- to 8-base inbreds) of the Stiff stalk and Lancaster genetic backgrounds. Thus, expansion of genetic diversity in maize has been a continuous challenge to breeders. Tropical germplasm has been viewed as a useable source of diversity, although the integration of tropical germplasm into existing inbred line and hybrid development is laborious. The present study is an evaluation of the potential of tropical germplasm for temperate maize improvement. All possible single-, three-way-, and double-cross hybrids among three largely temperate and three temperate-adapted, all-tropical inbred lines were evaluated in yield-trial tests. Single-cross hybrids containing as much as 50–60% tropical germplasm produced 8.0 t ha^-1 of grain yield, equivalent to the mean yield of the commercial check hybrids. On the other hand, three-way and double-cross hybrids with the highest mean yield contained lower amounts of tropical germplasm, 10–19% and 34–44%, respectively. Overall, hybrids containing 10–60% tropical germplasm yielded within the range of the commercial hybrid checks. Hybrids with more than 60% tropical germplasm had significantly lower yields, and 100% tropical hybrids yielded the least among all hybrids evaluated. The results indicate that inbred lines containing tropical germplasm are not only a useful source to expand the genetic diversity of commercial maize hybrids, but they, also are competitive in crosses with temperate materials, producing high-yielding hybrids. These experimental hybrids exhibited good standability (comparable to the commercial check hybrids) but contained 1–2% higher grain moisture, leading to delayed maturity. Recurrent selection procedures are being conducted on derivatives of these materials to extract lines with superior yield, good standability, and reduced grain moisture which can be used for commercial exploitation. Received: 26 January 1998 / Accepted: 14 July 1998     

Tree specific traits affect flowering time in Indian dry tropical forest

Dry tropical forest tree species show variations in leafless duration (i.e. deciduousness), stem wood density (SWD), leaf mass area (LMA) and leaf strategy index (LSI, reflecting resource use rate) to overcome water limitations. We investigated the role of these tree traits in the seasonal timing of flowering and subsequent fruiting. Flowering and fruiting time of 24 tree species was recorded over two consecutive annual cycles and their relationships with the abovementioned tree specific traits were examined across the species. In leaf-exchanging species having higher SWD and LMA, low LSI and short deciduousness, flowering coincides with leaf transitional state when vegetative growth is at its minimum, and fruit formation and leaf flushing are both supported at the same time. However, >4-months-deciduous species with lowest SWD and LMA, higher LSI and longer deciduousness showed predominantly dry season flowering, subsequent fruiting on leafless shoots and distinct separation of vegetative and flowering phenophases. In contrast, intermediate species (<2 months-deciduous, 2–4-months-deciduous) showed wider flowering range through summer, rainy, autumn or winter seasons. Fruiting duration varies considerably with variation in the flowering time; ca. 5–14 months in summer flowering species; 7–12 months in rainy flowering species; 6–10 months in autumn flowering species, 4–9 months in dry season flowering and 3–7 months in winter flowering species. In most species, fruit maturation occurred just prior to the onset of rains, ensuring seedling survival. The ability of tree species to withstand (leaf-exchange) or avoid (deciduousness) drought stress and varying seasonal flowering timings appear to be the principal mechanisms for successful survival and reproduction under extremely dry and seasonal climate. Since environmental characteristics affect flowering and fruiting either directly (e.g. through conditions in the habitat) or indirectly (e.g. through deciduousness, LMA, SWD and LSI), the impact of probable global climatic change will have long implications on reproduction of dry tropical trees.     

Energetic composition,reproductive output,and resource allocation of Antarctic asteroids

Summary Thirteen species of antarctic asteroids were collected in McMurdo Sound during the austral spring and summer of 1984–1985 and 1985–1986. Variability in the energetic composition of the body wall, pyloric cecum, and gonad was directly related to differences in levels of protein, carbohydrate, lipid and ash in these tissue types. Reproductive output was generally similar between males and females when expressed in gravimetric units. When considered in energy units, females generally had greater reproductive output than males. Reproductive output values of antarctic asteroids were similar to published values for temperate, tropical, and subpolar species. In a given year, the majority of antarctic asteroids have the greatest energy resources in the body wall, a tissue representing a long-term energy investment. Lesser amounts of energy are devoted to annual nutrient storage (pyloric ceca) and reproduction (gonads).     

Aseasonality in the abundance and life history of an ecologically dominant freshwater crab in the Rift Valley, Kenya

1. Freshwater crabs appear to show at least two alternative life history patterns, which differ in the timing of seasonal reproduction. Reproduction occurs during low flow among temperate lotic species, but during high water levels among wetland species. Crab biomass is often very high and both strategies would lead to spatial and temporal pulses in density and biomass. The life history and reproductive strategy adopted by tropical lotic species is poorly known, however, despite their importance in community and ecosystem dynamics. 2. In this study, we determined annual patterns of life history, density and biomass of a lotic freshwater crab in a small headwater stream in the East African highlands where it maintains high biomass. This crab is an as yet undescribed species of Potamonautes, here referred to as the Chinga crab. 3. Crabs were sampled non‐destructively for 15 months using baited traps and benthic sampling with a Surber sampler. At the end of the study, an intensive hand search was carried out. Each method was biased towards different size classes of crabs and the efficiency of both long‐term methods varied according to water levels in the stream. The intensive search was more effective than benthic sampling, but failed to record the large individuals caught by baited traps. 4. Population density and biomass remained constantly high throughout the study period. Reproduction, as evidenced by the presence of ovigerous females and small free‐living juveniles, also showed no seasonality. As a consequence, the population size structure (size‐frequency distribution) of crabs remained constant throughout the year. 5. The Chinga crab illustrates a third life history pattern, with no clear breeding season, and this may be common among tropical species. This is probably a consequence of the non‐seasonal nature of its habitat: temperature varied little throughout the year and rainfall fluctuations were relatively small. This strategy allows the species to maintain high biomass without seasonal pulses and, perhaps, to dominate community and ecosystem processes.     

Exclusive core areas and intrasexual territoriality in Eurasian red squirrels (<Emphasis Type="Italic">Sciurus vulgaris</Emphasis>) revealed by incremental cluster polygon analysis

When animal home ranges overlap extensively in species lacking overt territorial behaviours, identifying exclusive core areas within individual ranges can be difficult. By analysing the size and overlap of successively smaller core areas among individual Eurasian red squirrels (Sciurus vulgaris), we determined exclusive areas within the home ranges of resident males and females. Possible effects of habitat composition and food supplies were explored by monitoring squirrels in different conifer forests and during years with low and high tree seed production. Using outlier-exclusive cores (OEC) revealed that the total ranges consisted of large sally zones (on average, 35% of the total minimum convex polygon [MCP] range) around home ranges with multi-nucleate cores. The mean OEC home range size did not differ between the sexes but was larger with poor food availability. Home ranges (99% incremental cluster polygons [ICP]) overlapped extensively between sexes (average overlap high food–low food: males by females 21–40%, females by males 43–45%) and among males (males by males 26–44%), while intrasexual overlap among females was low (9–10%). The overlap of inner cores among females rapidly approached zero, suggesting the intrasexual territoriality of 75% core areas. This was not the case among male squirrels, for which intrasexual overlap averaged only 4% at 50% but 18% at 75% core areas. Even the smallest inner cores had some degree of intersexual overlap, indicating that complete territoriality did not occur in this species. Female home ranges were more strongly affected by annual fluctuations in food supplies than male ranges. Females reduced the size of their food-based intrasexual territories when food availability increases. Males probably benefit from using larger home ranges and core areas, which overlap with the ranges of several females, by increasing their probability of successful mating.     

Tropical wetlands: seasonal hydrologic pulsing,carbon sequestration,and methane emissions

This paper summarizes the importance of climate on tropical wetlands. Regional hydrology and carbon dynamics in many of these wetlands could shift with dramatic changes in these major carbon storages if the inter-tropical convergence zone (ITCZ) were to change in its annual patterns. The importance of seasonal pulsing hydrology on many tropical wetlands, which can be caused by watershed activities, orographic features, or monsoonal pulses from the ITCZ, is illustrated by both annual and 30-year patterns of hydrology in the Okavango Delta in southern Africa. Current studies on carbon biogeochemistry in Central America are attempting to determine the rates of carbon sequestration in tropical wetlands compared to temperate wetlands and the effects of hydrologic conditions on methane generation in these wetlands. Using the same field and lab techniques, we estimated that a humid tropical wetland in Costa Rica accumulated 255 g C m⁻² year⁻¹ in the past 42 years, 80% more than a similar temperate wetland in Ohio that accumulated 142 g C m⁻² year⁻¹ over the same period. Methane emissions averaged 1,080 mg-C m⁻² day⁻¹ in a seasonally pulsed wetland in western Costa Rica, a rate higher than methane emission rates measured over the same period from humid tropic wetlands in eastern Costa Rica (120–278 mg-C m⁻² day⁻¹). Tropical wetlands are often tuned to seasonal pulses of water caused by the seasonal movement of the ITCZ and are the most likely to be have higher fire frequency and changed methane emissions and carbon oxidation if the ITCZ were to change even slightly.     

Maternal investment in a bee species with facultative nest guarding and males heavier than females

1. Maternal investment can be influenced by several factors, especially maternal quality and possibilities for future reproduction. Mass provisioning Hymenoptera are an excellent group for measuring maternal investment because mothers distribute food sources to each brood cell for each offspring separately. Generally in aculeate Hymenoptera, larger females produce larger offspring and invest more in female offspring than in male offspring. 2. This study investigated patterns of maternal investment in Ceratina chalcites, which has an uncommon type of sexual size dimorphism in Hymenoptera: on average, males are heavier than females. It was found that larger females produce a significantly higher proportion of male offspring, as males are the costlier sex in this species. 3. Facultative nest guarding by females was observed. Females can guard offspring until adulthood, as is typical for bees of genus Ceratina (34.43% of nests); however, in the majority of cases (65.56% of nests), females plug and abandon the nest. Significant differences were found in the amount of investment between guarded and unguarded nests. Guarded nests had a greater number of provisioned brood cells and a higher proportion of male offspring. It is suggested that mothers have two facultative strategies – either she makes a large investment in the offspring of one nest or she abandons the first nest and carries out a second nesting elsewhere.