Six years of fruit production by mahogany trees (Swietenia macrophylla King): patterns of variation and implications for sustainability

Although mahogany, the most commercially important timber tree in Neotropical forests, is widely acknowledged to be threatened by unsustainable logging which does not provide for its regeneration, its fruiting dynamics are poorly understood. During each of six successive years, the authors measured tree diameters and counted woody fruit capsule segments that fell below the crowns of 82 mahogany trees in natural forest in central Quintana Roo, Mexico. Sample trees ranged from <20 cm to more than 100 cm DBH. Fruit production increased with diameter, and trees 75 cm produced significantly more fruits each year than did trees of smaller diameters. Large trees could produce more than 700 fruits/year. Trees 75 cm DBH were also more consistent producers: while up to 27% of trees <75 cm DBH produced <1 fruit/year in any year, at least 93% of larger trees produced fruit every year. Over the 6 years, individual trees 75 cm produced a total of 367 34 fruits, as compared to 91 8 fruits among trees <75 cm (an average of 61 7 and 15 2 fruits/year, respectively). However, the number of fruit produced per unit crown volume was not significantly different between the two size categories. Fruit production varied among years, with the highest production in 1998 and the lowest in 1999 and 2000. The population of sampled mahogany trees produced approximately three times more fruit, and individual trees produced up to five times more fruit, in the year of highest production, as compared to the lowest. Mahogany does not exhibit the fruit production patterns found in mast fruiting species. Inter-annual variability in size of fruit crops at both the population and individual-tree levels are lower than in masting species, and the synchronocity among trees was low. Basal area growth averaged 76.5 18.6 cm2/year for trees 75 cm and 29.9 1.7 cm2/year for trees <75 cm DBH, and varied significantly among years. Years of high fruit production were also years of good growth, implying ‘‘resource matching’’ rather than the ‘‘resource switching’’ associated with masting. To ensure seed production for the regeneration of mahogany it is important to retain mahogany trees 75 cm DBH as seed sources. This presents a challenge, since currently mahogany trees in this region are harvested down to a minimum diameter as low as 55 cm

Estimating the adaptive potential of critical thermal limits: Methodological problems and evolutionary implications

1.Current studies indicate that estimates of thermal tolerance limits in ectotherms depend on the experimental protocol used, with slower and presumably more ecologically relevant rates of warming negatively affecting the upper thermal limits (CTmax). Recent empirical evidence also gives credence to earlier speculations suggesting that estimates of heritability could drop with slower heating rates. 2.Using published data from the fruit fly Drosophila melanogaster, we show that empirical patterns can be explained if flies' physical condition decreases with experimental time in thermal tolerance assays. This problem could even overshadow potential benefits of thermal acclimation, also suggesting that a drop in CTmax with slower heating rates does not necessarily rule out beneficial acclimatory responses. 3.Numerical results from a simple illustrative model show that no clear conclusions can be obtained on how the phenotypic variance in CTmax will be affected with different rates of thermal change. Conversely, the genetic variance and estimated heritabilities are expected to drop with slower heating rates, hence ramping rates in experiments aiming to study the evolutionary potential of thermal tolerance to respond to global warming should be as fast as possible (within the range in which measurement accuracy and physical condition are not affected). 4.Measurements under ecologically realistic warming rates should also consider the impact of other physiological and behavioural strategies that might partly compensate the negative effects of slow heating rates. However, there are situations in which slow heating rates closely mimic natural conditions, as those encountered by some aquatic ectotherms. These heating rates may be an issue of major concern in these species, given its negative impact on CTmax and its adaptive potential. © 2010 The Authors. Functional Ecology © 2010 British Ecological Society.Peer Reviewe

ANTHROPOLOGY OF/IN CIRCULATION: The Future of Open Access and Scholarly Societies

In a conversation format, seven anthropologists with extensive expertise in new digital technologies, intellectual property, and journal publishing discuss issues related to open access, the anthropology of information circulation, and the future of scholarly societies. Among the topics discussed are current anthropological research on open source and open access; the effects of open access on traditional anthropological topics; the creation of community archives and new networking tools; potentially transformative uses of field notes and materials in new digital ecologies; the American Anthropological Association's recent history with these issues, from the development of AnthroSource to its new publishing arrangement with Wiley-Blackwell; and the political economies of knowledge circulation more generally

The effect of acclimation temperature on thermal activity thresholds in polar terrestrial invertebrates

In the Maritime Antarctic and High Arctic, soil microhabitat temperatures throughout the year typically range between -10 and +5°C. However, on occasion, they can exceed 20°C, and these instances are likely to increase and intensify as a result of climate warming. Remaining active under both cool and warm conditions is therefore important for polar terrestrial invertebrates if they are to forage, reproduce and maximise their fitness. In the current study, lower and upper thermal activity thresholds were investigated in the polar Collembola, Megaphorura arctica and Cryptopygus antarcticus, and the mite, Alaskozetes antarcticus. Specifically, the effect of acclimation on these traits was explored. Sub-zero activity was exhibited in all three species, at temperatures as low as -4.6°C in A. antarcticus. At high temperatures, all three species had capacity for activity above 30°C and were most active at 25°C. This indicates a comparable spread of temperatures across which activity can occur to that seen in temperate and tropical species, but with the activity window shifted towards lower temperatures. In all three species following one month acclimation at -2°C, the chill coma (= the temperature at which movement and activity cease) and critical thermal minimum (= low temperature at which coordination is no longer shown) occurred at lower temperatures than for individuals maintained at +4°C (except for the CTmin of M. arctica). Individuals acclimated at +10°C conversely showed little change in their chill coma or CTmin. A similar trend was demonstrated for the heat coma and critical thermal maximum (CTmax) of all species. Following one month at -2°C, the heat coma and CTmax were reduced as compared with +4°C reared individuals, whereas the heat coma and CTmax of individuals acclimated at +10°C showed little adjustment. The data obtained suggest these invertebrates are able to take maximum advantage of the short growing season and have some capacity, in spite of limited plasticity at high temperatures, to cope with climate change

Pre-adapted to the maritime Antarctic? - Rapid cold hardening of the midge, Eretmoptera murphyi

During the 1960s, the midge, Eretmoptera murphyi, was transferred from sub-Antarctic South Georgia (55oS 37oW) where it is endemic to a single location on maritime Antarctic Signy Island (60oS 45oW). Its distribution has since expanded considerably, suggesting that it is pre-adapted to the more severe conditions further south. To test one aspect of the level of its pre-adaptation, the rapid cold hardening (RCH) response in this species was investigated. When juvenile (L1–L2) and mature (L3–L4) larvae of E. murphyi were directly exposed to progressively lower temperatures for 8 h, they exhibited Discriminating Temperatures (DTemp, temperature at which there is 10–20% survival of exposed individuals) of −11.5 and −12.5 °C, respectively. The mean SCP was above −7.5 °C in both larval groups, confirming the finding of previous studies that this species is freeze-tolerant. Following gradual cooling (0.2 °C min−1), survival was significantly greater at the DTemp in both larval groups. The response was strong, lowering the lower lethal temperature (LLT) by up to 6.5 °C and maintaining survival above 80% for at least 22 h at the DTemp. RCH was also exhibited during the cooling phase of an ecologically relevant thermoperiodic cycle (+4 °C to −3 °C). Mechanistically, the response did not affect freezing, with no alteration in the supercooling point (SCP) found following gradual cooling, and was not induced while the organism was in a frozen state. These results are discussed in light of E. murphyi’s pre-adaptation to conditions on Signy Island and its potential to colonize regions further south in the maritime Antarctic