Rain,rats and pythons: Climate‐driven population dynamics of predators and prey in tropical Australia

Abstract: All natural populations fluctuate in abundance and age structure through time; understanding why they do so is a critical step towards their effective management and conservation. However, the long‐term data sets needed for such an understanding are rarely available, especially for tropical organisms. A 17‐year capture‐mark–recapture study yielded detailed information on the demography of water pythons (Liasis fuscus) and their main prey, the dusky rat (Rattus colletti), on the Adelaide River flood plain in tropical Australia. The link between annual rainfall patterns and rat demography was highly non‐linear. Rat numbers were low during years with low and high rainfall at the end of the wet season (April). Numbers of both predators and prey fluctuated considerably among years. Annual fluctuations in rat numbers generated a corresponding variation in rates of female python reproduction, python body condition and survival. Although variation in recruitment, survival and prey abundance all had a significant impact on annual fluctuations in python numbers, our analyses suggest that recruitment constituted the main determinant in driving the population dynamics of these large tropical predators. In combination with our other studies on this system, the data show that population dynamics of the water python population is ultimately driven by annual variation in rainfall, mediated via shifts in prey availability. The water pythons and the dusky rats of the Adelaide River flood plain thus demonstrate an unusually clear and direct link between an abiotic factor (rainfall) and predator–prey population dynamics.     

Genetic, morphological, and feather isotope variation of migratory willow warblers show gradual divergence in a ring

The circular distribution of the willow warbler Phylloscopus trochilus around the Baltic Sea shares many features with the classic examples of ring species; however, the system is much younger. It has previously been shown that a secondary contact zone is located in central Scandinavia, where there are narrow clines for several morphological traits coincident with a migratory divide. Here we analyse multiple traits and genes from > 1700 males captured on breeding territories at 77 sites spread around the Baltic Sea to test the following hypothesis. If the secondary contact zone in Scandinavia is a result of divergence in two allopatric refuge populations during the last glaciation, we expect to find a similar secondary contact zone somewhere else around the circular distribution. Our results show that the trait clines were wider and displaced from each other along the eastern side of the Baltic Sea. Analyses of 12 microsatellite loci confirmed that the genome is very similar between the terminal forms ( F _ST = 0). Two AFLP-derived markers filtered out from a genomic scan instead appear to be maintained by selection. These markers exhibited steep clines at the secondary contact zone in Scandinavia, but as for the phenotypic traits, had vastly different cline centres east of the Baltic Sea. The trait clines along the ring distribution outside the Scandinavian secondary contact zone thus seem to have been shaped by independent action of selection or drift during the process of postglacial colonization.     

Phylogeny of the vipers of the Caucasus (Reptilia, Viperidae)

Phylogenetic relationships for five taxa of Palearctic vipers (genus Vipera ) from the Caucasian region were revealed by cladistic analyses of separate and combined morphological and biochemical characters. The different data sets yielded largely congruent cladograms. Vipera berus from Sweden was included as an ingroup and V. aspis was used for outgroup comparison. For V. kaznakovi and V. dinniki , three and four different sub-populations, respectively, were treated as independent terminal taxa in the analyses. The most parsimonious cladograms confirmed the systematic positions of these populations, discussed in a recent study, and support the hypothesis that the montane populations of the western main Caucasus comprise one polymorphie species: V. dinniki.
Analyses of combined biochemical and morphological data generated two equally parsimonious cladograms (for all ingroups compared), but yielded only one fully resolved topology when ingroups were condensed to the species level: ( berus ((renardi ('ursinii'-eriwanensis )))( dinnikikaznakovi )).     

The Distribution of 14C-labelled Assimilates in Young Apple Trees as Influenced by Doses of Supplementary Nitrogen: II. Soluble Carbohydrates and Amino Acids

Methanol extracts of young MM.104 apple trees fed ¹⁴CO₂ viaa single leaf were fractionated to compare ¹⁴C activity in totalsoluble sugar and amino acid components. ¹⁴C activity in aminoacids increased after the supply of ammonium nitrate to thesoil in plants where ¹⁴C labelled carbohydrates were presentin the roots. Estimates of specific carbon activity gave lowervalues for the amino acid carbon than the general value fortotal soluble carbohydrates. The fractionation of subsequentmethanol extracts of MM.104 roots has shown that sucrose hadlower specific activity than other components. Although thelevels of activity would accord with sucrose being a substratefor amino acid synthesis, an alternative explanation for theobserved results involving a cyclical system for transferringnitrogen is postulated.     

The Distribution of 14C-Labelled Assimilates in Young Apple Trees as Influenced by Doses of Supplementary Nitrogen: I. Total 14C Radioactivity in Extracts

Rooted shoots of apple rootstock MM.104 were grown in soil andsupplied with doses of ammonium nitrate at different stagesof shoot extension growth. ¹⁴CO₂ was supplied in associationwith the supplementary nitrogen via the largest healthy leafnear the base of the current season's shoot. Samples from thevarious regions of the plants were extracted, giving methanolicsolutions (containing principally sugars and soluble resources)and T.C.A. extracts (containing principally hydrolysis productsof available polysaccharides). These were counted for total¹⁴C activity using liquid scintillation spectrometry. Around90 per cent of the activity was present in the methanolic extracts.Virtually no ¹⁴C activity was transferred to the root regionbefore shoot extension was under way whereas up to 45 per centof the translocated activity occurred in the roots during andafter the main period of shoot extension. Nitrogen uptake hadbeen confined to these later stages but no influence of nitrogensupply on the gross distribution of ¹⁴C outside the source leafwas detected.     

Size matters: extraordinary rodent abundance on an Australian tropical flood plain

Abstract: Published estimates of the total biomass of natural populations of mammalian herbivores generally have ignored small‐bodied taxa (especially, rodents). Including such taxa may dramatically change our understanding of total biomass and energy flow in such systems. Dusky rats (Rattus colletti) are small (up to 210 g) native Australian mammals, and our 5‐year mark‐recapture study on a tropical flood plain (Adelaide River, Northern Territory) revealed that rat biomass can reach extraordinary levels (up to 4.7 t km^?2). Because their small body size results in high mass‐specific metabolic rates, a given biomass of rodents has a several‐fold higher total energy requirement than the same mass of large‐bodied herbivores. Accordingly, during some years dusky rat biomass can be double that estimated for large herbivores on the world's most productive savannas in eastern and southern Africa. The huge rodent biomass strongly suggests that the Adelaide River flood plain must be an incredibly productive habitat. Considering the immense biological importance of these productive ecosystems, flood plain conservation must be placed high on the priority list of habitats that require immediate protection.