Status of the tuatara,Sphenodon punctatus,on Hongiora and Ruamahua-iti Islands,Aldermen Group,New Zealand

Abstract

Results from a survey of the tuatara populations on Hongiora and Ruamahua-iti Islands, conducted in March 1986, do not support an earlier report that the Hongiora population is declining (Crook 1973). On Hongiora, 49 captures were made of 43 tuatara over 12 man-hours, and on Ruamahua-iti, 67 captures of 60 tuatara were made over 12.5 man-hours. The mean body lengths of Hongiora tuatara (male=250.4 mm, female=220.8 mm) were significantly larger than those of Ruamahua-iti animals (male= 187.6mm, female= 179.3 mm). We question the interpretation that the smaller average size of tuatara on Ruamahua-iti Island indicates that they are younger than those on Hongiora Island.     

Growing islands and sinking solutes: processes maintaining the endorheic Okavango Delta as a freshwater system

In the Okavango Delta 98–99% of the water from inflow and rainfall is lost to the atmosphere through evapotranspiration. As a consequence 94% of inflowing solutes are retained within the Delta landscape. This process might be expected to result in an entirely saline environment, but that is not the case: the surface waters have very low salinity, supporting a typical freshwater biota. It has been deduced that the numerous islands in the Delta (about 150,000 within an area of 13,500 km²) have been formed through evapotransporative concentration in the groundwater, of infiltrating solutes, followed by precipitation and volume increase. Evidence of this is the large amount of calcrete in island soils. These islands of 3–10 m thickness with clayey soils are underlain by fine Kalahari sand to a depth of 200–300 m, which also indicates that they are formed through surface processes. The infiltration rate of surface water from floodplains and streams into islands is very high, and is predominantly a lateral process that is unidirectional. Evapotranspiration in the riparian woodland zone cause the ground-waters in the central area of islands—with halophyte grasslands—to have very high salinities. By use of chloride as a conservative element the concentration factor between central island groundwater and surface water is calculated to be 500–1,000. This groundwater is depleted of calcium and magnesium supporting the early deductions that these elements have precipitated as calcrete. There is also a large depletion of silicate and potassium that probably have precipitated as well forming the clayey soils typical of the islands. The central island groundwater is dominated by sodium, bicarbonate and dissolved organic matter. The gradual increase of salinity here causes a periodic let off of this water through a density-driven process to deeper layers. This process together with island growth through precipitation of solutes are the two major sink processes of inflowing solutes and explains why the Okavango Delta is at present a freshwater system. The whole island complex is calculated to be 100,000–400,000 years old while some intensely studied islands may be younger: 80,000–240,000 years. The discrepancy is explained by a biassed selection of islands currently in flooded areas with better growth conditions. The uniqueness of the Okavango Delta and ideas for future research are discussed.     

COMPARISON OF VERTICAL AERIAL PHOTOGRAPHIC AND GROUND CENSUSES OF STELLER SEA LIONS AT AÑO NUEVO ISLAND, JULY 1990-1993

Counts of Steller sea lion ( Eumetopias jubatus ) pups and non-pups (adults and juveniles) from aerial photographs of rookeries at Año Nuevo Island between 1990 and 1993 were significantly higher than those made on the ground. Based on regression of natural logs of photographic counts versus year, the number of pups declined at a rate of −0.099yr while non-pup numbers declined at −0.315/yr. Examination of ground count data for the same period revealed a significant decline in non-pups (−0.139/yr), but no trend was detected in the ground counts of pups. The regression coefficients from photographic and ground counts of non-pups did not differ significantly. Power analyses using the program TRENDS indicated that detectable rates of change in abundance from four annual surveys were much lower for counts of pups than counts of non-pups where sampling precision was based on fits to linear models.     

Biogeography and the structure of coral reef fish communities on isolated islands

Aim To determine the applicability of biogeographical and ecological theory to marine species at two remote island locations. This study examines how biogeography, isolation and species geographic range size influence patterns of species richness, endemism, species composition and the abundance of coral reef fishes. Location Christmas Island and the Cocos (Keeling) Islands in the tropical eastern Indian Ocean. Methods Published species lists and underwater visual surveys were used to determine species richness, endemism, species composition and abundance of reef fishes at the islands. These data were statistically compared with patterns of species composition and abundance from the neighbouring ‘mainland’ Indonesian region. Results The two isolated reef fish communities were species‐poor and contained a distinct taxonomic composition with an overrepresentation of species with high dispersal potential. Despite low species richness, we found no evidence of density compensation, with population densities on the islands similar to those of species‐rich mainland assemblages. The mix of Indian and Pacific Ocean species and the proportional representations of the various regional faunas in the assemblages were not influenced by the relative proximity of the islands to different biogeographical provinces. Moreover, species at the edge of their range did not have a lower abundance than species at the centre of their range, and endemic species had substantially higher abundances than widespread species. At both locations, endemism was low (less than 1.2% of the community); this may be because the locations are not sufficiently isolated or old enough to promote the evolution of endemic species. Main conclusions The patterns observed generally conform to terrestrial biogeographical theory, suggesting that similar processes may be influencing species richness and community composition in reef fish communities at these remote islands. However, species abundances differed from typical terrestrial patterns, and this may be because of the life history of reef fishes and the processes maintaining isolated populations.     

Factors affecting the responses of female Canada Geese to disturbance during incubation

During incubation, Canada Geese (Branta canadensis) and other waterfowl flush from their nests in response to the approach of potential predators and subsequently return to nests after the threat of predation has abated. Differences among individuals in their responses to such disturbance (e.g., how close a potential predator approaches before flushing) are thought to reflect variation in female age, the reproductive value of clutches, and nest site characteristics. From 26 April to 26 May 2010, we examined the possible effects of these factors on the behavior of female Canada Geese (B. c. interior) on Akimiski Island, Nunavut. We used humans as surrogate predators and flushing distance and return time after disturbance as response variables. The distance at which females flushed in response to approaching humans was best explained by the density of vegetation around nests, with females on better concealed nests flushing at closer distances. We also found a weak relationship between return time and clutch size, with females with larger clutches returning to nests sooner. The frequency of human visits did not affect either female flushing distance or return time. Female Canada Geese in our study appeared to minimize risk of their own injury or death (future reproductive potential) in escape decisions, whereas return times appeared to minimize the risk of nest predation (current reproductive investment).     

Metazoan parasites of sticklebacks on Sable Island, Northwest Atlantic Ocean: biogeographic considerations

Three species of sticklebacks ( Apeltes quadracus, Gasterosteus aculeatus , and Pungitius pungitius ( n = 236) were collected from five ponds on Sable Island. The nematodes Pseudoterranova decipiens, Contracaecum sp., Paracuaria adunca , and Cosmucephalus obvelatus , and the cestode Diphyllobothrium ditremum parasitized three-spined sticklebacks ( G. aculeatus ) and four-spined sticklebacks ( A. quadracus ) inhabiting four brackish water ponds. All the parasites except P. decipiens infected nine-spined sticklebacks ( P. pungitius ) from a freshwater pond. In addition, the cestode Schistocephalus pungitii , the copepod Thersitina gasterostei , and the monogenean Gyrodactylus canadensis occurred in nine-spined sticklebacks from the freshwater pond. The two cestodes, the copepod, and the sealworm, P. decipiens , were the most common parasites encountered. The remaining helminths were relatively rare. Most of the parasite species were larval forms which use gulls or seals as definitive hosts. These parasites probably colonized Sable Island with their definitive hosts, whereas only two species ( T. gasterostei and G. canadensis ) successfully colonized the island ponds with their fish hosts. The low parasite species richness encountered is attributed to the impoverished nature of the host fauna of Sable island, and the difficulty of colonization as a result of the island's isolation with respect to the mainland.     

A new pipoid frog (Anura,Pipimorpha) from the Paleogene of Patagonia. Paleobiogeographical implications

The aim of the present contribution is to describe a new genus and species of Pipoidea from the Huitrera Formation (Eocene) from Patagonia, Argentina. The new genus shows a unique combination of characters indicating that it is a valid taxon different from other pipimorphs, including the coeval Llankibatrachus truebae. The phylogenetic analysis resulted in the nesting of the new taxon within a previously unrecognized endemic clade of South American aglossans. This new clade turns out to be the sister-group of crown-group Pipidae. This phylogenetic proposal reinforces the hypothesis sustaining the dispersal of pipids between Africa and South America through an island chain or a continental bridge across the Atlantic Ocean by Early Tertiary times.