Suchergebnisse

A repeatable index of population density for cane toads active around permanent water in the dry season
showed that, in the lowlands of the Gulf of Carpentaria, local populations rapidly increased in size following
colonization, and remained high (up to 2138 ha-1 on a single night) for at least 19 years. Long-established
populations ( ~ 47 years) around Townsville have declined to an average density of 82 ha-1 on a single
night. In this area toads are in poor body condition, are smaller, and have a lower proportion of reproductive
males than do younger populations. The sizes of fat bodies, and the numbers of ova carried by females,
do not appear to have declined in the Townsville populations. The index of population density was found
to represent approximately 20% of a Jolly-Seber, capture-recapture estimate of population density for a
2.5-year-old cane toad population. The Jolly-Seber estimate for this young population is up to 45 times
the densities of native cane toads in Panama. The numbers of toads captured, toad body sizes and proportions
of sexually mature toads in the Townsville populations are very similar to those in Panama.

Passive Integrated Transponder (PIT) tags were subject to a series of experimental manipulations designed
to simulate conditions operating during the course of trade in animals. Experiments were designed to
determine the effects of tag-wand angle of orientation, various barriers between tags and wands and
different wand-readers on the distance at which a reading could be made. The distances at which readings
can be made are subject to influences by all three variables. The effect of tag-wand angle of orientation is
likely to be trivial under most circumstances. Of more importance to the utility of PIT tags for animal trade
is environmental interference, particularly that due to metallic barriers (plate or mesh). Different wand-readers
produce idiosyncratic results in relation to orientation of the tag and wand and type of barrier. Implantation
of tags in cane toads (Bufo marinus) indicates that tags are long lived and reliable. Loss of tags from the
toads was relatively rare and probably due to error during the insertion of tags. PIT tags proved resistant to
preservation in formalin or ethanol, and to the decomposition of animals in which they had been inserted.
Tags inserted into 14 species of Australian mammal provided reliable identification of individuals, and
were lost only from species that fly (bats) or are arboreal and glide (a petaurid marsupial). PIT tags are
outstandingly reliable and provide for rapid identification of individual animals. Limitations to the use of
PIT tags in trade in animals are the inability to conduct readings from a distance (>50mm), and their
vulnerability to environmental interference. Technological improvements in taglscannerlreader design may
improve the distance from which readings may be made, and cages could possibly be designed in ways that
minimise environmental interference. Until these developments have occurred, the PIT tag does not provide
cost-effective improvements in the ability to identify animals used in trade.

A model of population growth of feral water buffalo is presented and used as a basis for simulating
buffalo control exercises. Simulations incorporated annual removal of constant numbers of buffalo,
annual allocations of constant amounts of control effort, or continous application of effort until control
density had been achieved. The models rely on data from helicopter-based shooting and shooting by
shooters on the ground (Bayliss 1986). Approximately 60% of a starting population had to be removed
per annum for control to extinction to be achieved within two years. Annual allocations of constant
levels of control effort resulted in failure to reach the control target within 150 years, control in about
40 years, or control within the first two years of operation, depending on the level of effort expended.
Addition of two helicopters to a team of four helicopters working for 20 days changed the result from
no control to control within two years. Optimal allocation of control effort requires continuous
application of control measures until the objective has been achieved. Lower levels of effort result in
prolonged campaigns that may not achieve desired objectives.

Recently metamorphosed Bufo marinus exhibit patterns of activity and habitat use that vary in relation
to changes in weather and moisture availability. Activity adjacent to water is greatest on moist substrates
at high daytime temperatures in windy weather. Conditions that inhibit evaporative cooling (no
wind, dry substrates, high humidity), or are likely to lead to low body temperatures (cool temperatures
at night under windy conditions) restrict activity. Activity in habitats away from permanent water is
dependent on metamorphlings having grown large enough to allow night-time activity on dry substrates.
Growth leads to a change in activity from diurnal as metarnorphlings, to nocturnal and diurnal as
juveniles (30-70 mm SVL), and to nocturnal as adulthood approaches. Size-dependent changes in patterns
of activity and habitat use are accompanied by changes in pelvic patch morphology and body pigmentation.
The morphological changes may have resulted from selection acting to minimise time spent
in the smaller size classes which are vulnerable to predators, competitors and the environment, and
size-dependent optimisation of chemical defences.

Aerial surveys of coastal waters (27 216 km2) in the western Gulf of Carpentaria during the dry season
of 1984 and wet season of 1985 indicated no major seasonal changes in distribution and relative
abundance of dugongs. Minimum population size in the dry season was estimated as 16 816 � 2946
(standard error), with a relative density of 0.62 k 0.11 km-2, and that for the wet season 16 846 + 3257,
with a relative density of 0.62 � 0.12 km-2. The estimates exclude 5% of observations which could
have been either dugongs or Irrawaddy dolphins, and were corrected for submerged dugongs and those
missed on the surface. Dugongs were unevenly distributed over the study area, and neither mean group
size nor proportion of calves varied between seasons. Dugong abundance was correlated with area of
available seagrass. The catch rate of dugongs by Aboriginal people off Numbulwar decreased six-fold
between the 1960s and 1985 (60 to 10 p.a.), possibly due to excessive hunting.

Four tropical Australian frog species do not alter their dry season patterns of habitat and/or food
utilisation following invasion by introduced Bufo marinus. Breadths of utilisation of habitat and food
resources by B. rnarinus are less than those of one or more native species. Levels of overlap of resource
use between B. marinus and native frog species are not different from those occurring among the native
species. Differences in body sizes of native species and B. marinus are not related to levels of resource
overlap. The population sizes of individual species, species richness and equitabilities of native frog
communities in the dry season are not influenced by the presence of B. marinus. B. rnarinus has
no observable impact on recovery of native frog communities or populations following experimental
perturbation. At the time of year when resources are likely to be most limiting (the dry season),
B. marinus is a relatively 'narrow-niched' invader with no measurable competitive impact on a native
frog community that may be in a state of disequilibrium.

Between 1980 and 1984, the cane toad, Bufo marinus, expanded its range westward from a small, isolated
and probably man-introduced population north-west of Burketown in Queensland, at an average rate of
27 km per year. The rate of range expansion is not influenced by rainfall (dry or wet season) and appears
to occur by continual colonization of new areas by small, sexually immature toads. If current rates of expansion
continue, cane toads will have colonized the 'Top End' of the Northern Territory by the year 2027. However,
the high frequency of toad dispersal assisted by man suggests that colonization will be more rapid.

Food habits and parasitism of cane toad, Bufo marinus, populations are documented in relation to time
since the populations were first established. Toads from populations less than 2 years old consume greater
dry weights of animal prey and greater numbers of prey items per unit time than do those from populations
3-47 years old. There are no significant differences among the dry weights of animal food and numbers
of prey items consumed by toads from areas colonized 3-47 years before the study. There are significant
regional and interpopulation differences in the taxonomic composition of prey consumed; these appear
independent of the age of particular cane toad populations. Rates of parasitism by protozoans and helminths
are low in a 2-year-old population, higher in populations 4-19 years old and low in a population
approximately 47 years old. Parasitism by Saccamoeba and the opalinate Zelleriella appears to promote
parasitism by other taxa. The rates of parasitism by particular taxa are independent of the age and size
of the cane toad population. Neither food shortage nor parasitism by helminths or protozoans appears
a likely cause for the decline in body condition in populations 47 years old. If this is due to the presence
of a microbial pathogen, the low rates of helminth and protozoan parasitism may reflect continuing
development of an interactive parasitic community in cane toad populations; isolation of the microbe
might provide a mechanism for slowing the rate of spread of cane toads, and reducing their impact on
the native fauna.

Cane toads from an urban population in Townsville, Qld, exhibit poor body condition and small body
size, as do toads in populations around Townsville which have declined in numbers. The small body
size and poor condition are associated with a high food intake and a low rate of parasitism. The results
suggest that decline of rural populations is not a product of parasitism, or food and or water shortages
related to unusually adverse seasonal conditions. Populations of cane toads around Townsville declined
more than 3 years before this study.