Demographic Forecasting in Koala Conservation

Abstract: The koala currently needs conservation intervention. There is clear evidence of decline in many populations, but the existence of other stable or expanding populations offers the possibility of a variety of creative solutions to their conservation problems. The 1998 National Koala Conservation Strategy emphasizes the need to obtain demographic information and to use this information to assess management options for koalas. We need accurate diagnoses of the status of koala populations and forecasts of their demographic future with and without particular management actions. In a qualitative fashion, this process has been undertaken many times on a local and national scale. Quantitative demographic forecasting tools are increasingly available, and koala management could benefit from their application both at the scale of individual populations and more broadly. There is already a considerable body of suitable data on the dispersal, effects of normal and catastrophic environmental variation on reproduction and survival, and on the effects of habitat change. Demographic forecasting, however, is hampered because the full suite of information is rarely available from a single population. In two Queensland populations, retrospective population viability analyses provided forecasts that were in agreement with observed population trends. Work is needed to determine whether data from one population can be applied to other populations. Models can then be developed to make projections at a multipopulation level on the basis of local population dynamics and dispersal. Certain koala populations, because of their long history of study, offer the opportunity to test demographic models retrospectively. These tests will not only aid in fine-tuning the models for koala biology and data but will also assist with the more general process of validating the models.     

Poisoned plusiines: toxicity of milkweed latex and cardenolides to some generalist caterpillars

Summary. Larvae of Trichoplusia ni Hübner (Lepidoptera: Noctuidae) that ingested latex from Asclepias curassavica L. (Asclepiadaceae) often regurgitated and convulsed with spasms before becoming immobile and unresponsive. Some larvae required over a day to recover sufficiently to feed. Latices from four other plant species in three families were all deterrent, but none caused detectable poisoning. The toxicity of A. curassavica latex was evidently due to cardenolides because pure cardenolides had similar effects when ingested by T. ni. Other species of noctuid caterpillars (Rachiplusia ou Guenée, Anagrapha falcifera Kirby, and Autographa precationis Guenée) sometimes also suffered spasms and temporary immobility when fed A. curassavica latex. A more distantly related noctuid, Spodoptera ornithogalli, was deterred by the latex, but showed no overt physiological responses at the dosage tested. T. ni larvae failed to develop on intact leaves of A. curassavica, on leaves with latex canals deactivated by midrib severance, and on excised leaves. Similarly, larvae reared on excised A. syriaca L. leaves to the final instar died when transferred to A. curassavica leaves with either intact or severed midribs. The final instar larvae sometimes suffered from spasms and immobility even when confined on leaves with depressurized canal systems. Evidently, cardenolides stored outside the latex system suffice to poison larvae. We conclude that cardenolides in A. curassavica have potent physiological effects on some generalist caterpillars and that the presence of these compounds both inside and outside laticifers effectively protects the plant. Received 30 June 1999; accepted 18 October 1999     

Effects of ecological factors on the diurnal activity rhythm of Yakutian black-capped marmots (Marmota camtschatica bungei) in the arctic

It is established that the activity of marmots (the genusMarmota) on the surface is timed to the daylight period. In the Arctic, under conditions of continuous illumination (the polar day), the diurnal rhythm of black-capped marmotsMarmota camtschatica bungei on the surface has a “daylight” pattern. The main external regulator of the diurnal rhythm is the altitude of the sun above the horizon. In the cold period, however, the effect of air temperature on animal activity becomes stronger.     

Life under Arctic sea ice – reproduction strategies of two sympagic (ice-associated) amphipod species, Gammarus wilkitzkii and Apherusa glacialis

The reproductive strategies of two gammaridean amphipod species, Gammarus wilkitzkii and Apherusa glacialis, that permanently inhabit the Arctic sea ice were investigated. G. wilkitzkii reaches sexual maturity at an age of 2 years and produces 128 ± 54 eggs fem.⁻¹ yr⁻¹. Mating takes place during fall and winter, and the development of the large eggs (0.60 to 0.80 mm diam.) lasts 6 to 7 months. The sex ratio of G. wilkitzkii was dominated by males in a proportion of 1.5:1. In vivo studies showed that juveniles are released in batches from the brood pouches of the females during April and May. A. glacialis reaches sexual maturity at the age of 1 year and produces 555 ± 151 eggs fem.⁻¹ yr⁻¹. The eggs are between 0.18 and 0.23 mm in diameter, and are the smallest known for gammaridean amphipods. Eggs are kept in packages of two to eight in the brood pouches of females. The sex ratio of A. glacialis was dominated by females in a proportion of 3:1. The high fecundity of both amphipod species, the release of juveniles in batches over a period of time, a high proportion of females (A. glacialis), and an elongated life-span with multiple spawnings (G. wilkitzkii) are discussed as possible adaptations to the specific and highly variable conditions under Arctic sea ice. Received: 29 December 1999 / Accepted: 8 March 2000     

Occurrence of the semi-catadromous European eel Anguilla anguilla in the Baltic Sea

Strontium (Sr) and calcium (Ca) contents in the otoliths of yellow and silver European eels [Anguilla anguilla (L.)] collected from coastal waters of the Baltic Sea and a freshwater lake in Sweden were examined by wavelength dispersive X-ray spectrometry with an electron microprobe. The mean Sr/Ca ratios from elver check to otolith edge were significantly higher for the eels from coastal waters (5.39 ± 1.09‰) than for those from the lake (0.71 ± 0.89‰). The evidence indicates that European eels in the Baltic Sea do not necessarily migrate into freshwater streams during the growth phase. Received: 30 September 1999 / Accepted: 6 April 2000     

Parthenogenetic reproduction of Diaphanosoma celebensis (Crustacea: Cladocera): influence of salinity on feeding, survival, growth and neonate production

 Effect of salinity on the feeding rate and parthenogenetic reproduction of asexual females of the cladoceran Diaphanosoma celebensis Stingelin was studied. Short-term (10 h) grazing experiments were conducted using Isochrysis galbana as feed at 5, 17, 25 and 30 psu salinity. Gut pigment concentration showed a significantly higher rate of feeding at lower salinities. Survival, growth, maturity attainment and neonate production of asexual females reared in the above four test salinities indicated preference for lower salinities (5 and 17 psu). The mean size of adult females decreased from 909 to 593 μm, mean life span from 24 to 5 d, mean neonate production from 12 to 2 and mean size of neonates from 434 to 400 μm as the salinity increased from 5 to 30 psu. Salinity variations also affected the size and age of primiparous females. Resting egg formation and sexual reproduction did not occur at the tested salinities. The results indicate that D. celebensis is adapted to low saline, estuarine environments. Received: 14 January 2000 / Accepted: 24 March 2000     

Mating behaviour of Macrophthalmus hirtipes (Brachyura: Ocypodidae)

 We examined the mating behaviour of the New Zealand ocypodid crab Macrophthalmus hirtipes in the laboratory between February and June 1998. This species has a discrete breeding season. Mating and moulting were not linked and only intermoult females with mobile gonopore opercula were attractive to males. Allometry and compatibility of gonopods and gonopores of different-sized crabs was investigated. Under laboratory conditions, the opercula of intermoult females remained mobile on average for 11.4 d, but the duration of receptivity did not appear to be under female control. The operational sex ratio in the laboratory fluctuated greatly, but was always male-dominated. During the period of opercular mobility, females mated many times with several different males. Matings in the absence of burrows were relatively short (mean duration = 23 min, max. = 122 min) and the mating behaviour of M. hirtipes lacked courtship and mate-guarding. Males used a search-intercept method to acquire mates, with very low levels of intrasexual competition. There was no evidence of mate preference in M. hirtipes, and males spent just as long mating with ovigerous females as with non-ovigerous ones. Although M. hirtipes has ventral-type spermathecae, as do several other ocypodid crabs, it is unclear whether this promotes last-male sperm precedence. The role of burrows in modifying the mating behaviour of M. hirtipes in the field remains to be established. Received: 7 January 2000 / Accepted: 5 June 2000     

Phylogeny and biogeographic history of hake (genus Merluccius), inferred from mitochondrial DNA control-region sequences

 Phylogenetic analyses of the left domain of the mitochondrial DNA control-region sequence have been used to examine the relationships among species of the genus Merluccius (Rafinesque, 1810), and to compare these with hypotheses based on morphological, meristic and allozyme characters. Analysis of aligned sequences revealed that transition bias was much lower than in mammalian mtDNA, and that nucleotide composition of control-region sequences was biased toward A and T. We have roughly calibrated a molecular clock for the genus, based on the rise of the Isthmus of Panamá, which is believed to have created a barrier to dispersal between marine species of the Atlantic and Pacific Oceans. Our mtDNA-based phylogeny was highly congruent with allozyme-based phylogenies, but poorly so with a previously described phylogeny based on morphology. Specifically, our phylogeny resolved two well-supported principal clades, one of American (west Atlantic and east Pacific) species and the other of Euro–African (east Atlantic) species. This suggests an evolutionary history during which the ancestral lineage of Merluccius was divided between two geographic regions, with subsequent dispersal and vicariant events resulting in the evolution and distribution of extant taxa. However, the relationships between some taxa within the American clade could not be resolved. We suggest that this is consistent with an hypothesis of a rapid origin and radiation of these taxa. Received: 12 December 1998 / Accepted: 15 October 1999     

Grazing rates of organic matter and living fungal biomass of decaying Spartina alterniflora by three species of salt-marsh invertebrates

 The pathway for the flow of salt-marsh grass production into marsh food-webs is still not well defined. We compared the abilities of three marsh macroinvertebrates [salt marsh periwinkles, Littoraria irrorata (Say) (=Littorina irrorata), salt-marsh coffee-bean snails, Melampus bidentatus (Say); and a talitrid amphipod, Uhlorchestia spartinophila Bounsfield and Heard] to access standing-dead leaves of smooth cordgrass (Spartina alterniflora Loisel). The invertebrates were incubated with naturally-decaying leaves, and the rates of removal of organic matter and living fungal biomass (ergosterol) were measured. The impact of invertebrate activity upon fungal growth rates was measured as rates of fungal-membrane synthesis (incorporation of radioacetate into ergosterol). The removal rates of organic leaf biomass per mg individual biomass were highest for amphipods (700 μg mg⁻¹ d⁻¹) and lowest for periwinkles (90 μg mg⁻¹ d⁻¹), but the relatively large biomass of the snails made their removal rates per individual greater than those of amphipods. Net removal of ergosterol by all three invertebrates was >50% for yellow-brown (early-decay) leaf blades. For fully-brown (advanced-decay) blades, >50% removal of ergosterol was found only for periwinkles; exposure to coffee-bean snails and amphipods resulted in a net ergosterol reduction of ≤20%. The lower net reduction of living fungal biomass by coffee-bean snails and amphipods may have been due to fungal-growth stimulation (2.3-fold stimulation in coffee-bean snails and 1.5-fold stimulation in amphipods). Grazing by periwinkles did not stimulate fungal growth, possibly because of its high intensity. Grazing by these three salt-marsh shredders may affect marsh-grass shoot-decay in different ways. Periwinkles may abbreviate the period of fungal production, and incorporate the decaying material relatively quickly into snail biomass and fecal-pellet rain to the sediments. Coffee-bean snails and amphipods may enhance and prolong fungal production, along with the formation of fecal-pellet rain. All three invertebrates fed preferentially on leaf blades rather than leaf sheaths, and feeding rates of gastropods were higher during the night than during the day. Received: 25 November 1998 / Accepted: 4 November 1999     

Cadmium accumulation in the female shore crab Carcinus maenas during the moult cycle and ovarian maturation

 The influence of moulting and ovarian maturation on cadmium accumulation in the tissues of female shore crabs Carcinus maenas exposed to 1 mg Cd l⁻¹ in the water was investigated. Cadmium accumulation in all tissues examined was markedly increased in crabs in the postmoult stages (A and B) compared to crabs in all other moult stages. During the moult cycle, average cadmium accumulation in the midgut gland ranged from 29 μg Cd g⁻¹ dw at premoult stage (D₂) to 589 μg Cd g⁻¹ dw at postmoult stage (A). Average cadmium concentrations in the haemolymph ranged from 0.56 μg Cd ml⁻¹ at intermoult stage (C₄) to 4.6 μg Cd ml⁻¹ at postmoult stage (A), while the gills accumulated from 103 μg Cd g⁻¹ dw in intermoult stage (C₃) to 352 μg Cd g⁻¹ dw in postmoult stage (A). Cadmium concentration in gills and haemolymph was also significantly higher in crabs in late premoult stage (D₃) compared to C₄-crabs, while midgut gland cadmium concentration remained elevated in C₁- and C₃- intermoult stages relative to C₄. During ovarian maturation the cadmium accumulation in midgut gland, gills, ovaries and haemolymph decreased. Average cadmium concentration in the midgut gland decreased from 63 μg g⁻¹ dw in ovarian Stage I to 19 μg g⁻¹ dw in ovarian Stage VI. The same pattern was observed for gills, haemolymph and ovaries. The present study demonstrates that cadmium accumulation in the female shore crab strongly depends on the physiological status of the animal. A possible association between physiological calcium requirements and cadmium accumulation during moulting is discussed. Received: 20 January 2000 / Accepted: 20 July 2000