Biomass of a trophic level increases with maximum body size, but less than proportionally

A recent paper by Enquist and colleagues1 took a very important step in predicting the ecosystemic effects of species losses on a global scale. Using Metabolic Scaling Theory (MST), they concluded that large-sized species contribute disproportionately to several ecosystem functions. One of their key predictions is that total biomass of animals in a trophic level (MTot, using their notation) should increase more than proportionally with its maximum body size (mmax), following the relationship MTot ∝ mmax5/4. Here I argue that this superlinear scaling results from an incorrect representation of the individual size distribution and that the exponent should be 1/4, implying a sublinear scaling. The same reasoning applies to total energy flux or metabolism BTot, which should be invariant to maximum size according to the energetic equivalence and perfect compensatory responses entailed by MST.

Patterns of mammalian jaw ecomorphological disparity during the Mesozoic/Cenozoic transition

The radiation of mammals after the Cretaceous/Palaeogene (K/Pg) boundary was a major event in the evolution of terrestrial ecosystems. Multiple studies point to increases in maximum body size and body size disparity, but patterns of disparity for other traits are less clear owing to a focus on different indices and subclades. We conducted an inclusive comparison of jaw functional disparity from the Early Jurassic–latest Eocene, using six mechanically relevant mandibular ratios for 256 species representing all major groups. Jaw functional disparity across all mammals was low throughout much of the Mesozoic and remained low across the K/Pg boundary. Nevertheless, the K/Pg boundary was characterized by a pronounced pattern of turnover and replacement, entailing a substantial reduction of non-therian and stem-therian disparity, alongside a marked increase in that of therians. Total mammal disparity exceeded its Mesozoic maximum for the first time during the Eocene, when therian mammals began exploring previously unoccupied regions of function space. This delay in the rise of jaw functional disparity until the Eocene probably reflects the duration of evolutionary recovery after the K/Pg mass extinction event. This contrasts with the more rapid expansion of maximum body size, which occurred in the Palaeocene.

Reproductive aspects of Galaxias platei (Pisces, Galaxiidae) in a deep lake in North Patagonia

Reproductive characteristics of the native fish Galaxias platei were studied in Lake Moreno, an ultra-oligotrophic deep lake in North Patagonia. According to histological analysis of ovaries, G. platei presents synchronous oocyte development typical of a group-synchronous spawner. Mature oocyte diameter ranged from 1031 to 1419μm. Based on the gonadosomatic index, annual spawning occurs between April and June (austral autumn) and is directly related to the water temperature of deeper strata (below 30m) where this species lives, but not with photoperiod. Female G. platei acquire sexual maturity at a length of 105mm, whereas males acquire sexual maturity at a length of 177mm. Delaying maturity to obtain higher fecundity, as well as maximum body size and longevity, indicates that G. platei is more specialised than the other South American Galaxias, G. maculatus, in terms of lifestyle. These specialised features are related to the stable environment G. platei lives in and indicate that it could eventually become a vulnerable species in unstable environments, such as the Patagonian lakes dominated by salmonids.

Perisesarma tuerkayi, a new species of mangrove crab from Vietnam (Decapoda, Brachyura, Sesarmidae), with an assessment of its phylogenetic relationships

A new species ofPerisesarma,P. tuerkayi, is described from mangroves of Tan Thoi Island, southern Vietnam. Morphologically, the new species differs most significantly from congeners by the tuberculation pattern of the chelar dactylus, its unique G1 morphology, an unusually large maximum body size, and relatively short and broad ambulatory legs. Genetically,P. tuerkayin. sp. is markedly divergent from other congeneric species, both in mitochondrial and nuclear DNA. It is the fifth species ofPerisesarmareported from Vietnam.

The rise of ocean giants: maximum body size in Cenozoic marine mammals as an indicator for productivity in the Pacific and Atlantic Oceans

Large consumers have ecological influence disproportionate to their abundance, although this influence in food webs depends directly on productivity. Evolutionary patterns at geologic timescales inform expectations about the relationship between consumers and productivity, but it is very difficult to track productivity through time with direct, quantitative measures. Based on previous work that used the maximum body size of Cenozoic marine invertebrate assemblages as a proxy for benthic productivity, we investigated how the maximum body size of Cenozoic marine mammals, in two feeding guilds, evolved over comparable temporal and geographical scales. First, maximal size in marine herbivores remains mostly stable and occupied by two different groups (desmostylians and sirenians) over separate timeframes in the North Pacific Ocean, while sirenians exclusively dominated this ecological mode in the North Atlantic. Second, mysticete whales, which are the largest Cenozoic consumers in the filter-feeding guild, remained in the same size range until a Mio-Pliocene onset of cetacean gigantism. Both vertebrate guilds achieved very large size only recently, suggesting that different trophic mechanisms promoting gigantism in the oceans have operated in the Cenozoic than in previous eras.