Ian Abbott

Interactions between earthworms and their soil environment

Laboratory experiments were used to study the effect of food quantity and quality on the biomass of earthworms, and the influence of earthworms on plant growth and infiltration of water into soil. Earthworms with the most food gained weight faster than those with little or no supplementary food. The latter also failed to become reproductively mature. Earthworms lost weight on a nitrogenpoor diet, but this was not rectified by supplementing such food with inorganic nitrogen added to the soil 2 weeks before the worms. Ryegrass grown in soil in which earthworms (Allolobophora trapezoides) had been kept grew more slowly than in soil which had no previous worm activity, perhaps indicating that earthworms had converted relatively-available organic N into less available forms. Microscolex dubius gave the fastest infiltration rates of water into soil when clover mulch was present. With Eisenia foetida there was little effect of worm density on infiltration rates; the highest density significantly increased infiltration but only when clover hay had been mixed in the soil. The surface casting behaviour of the two earthworm species varied with the placing of the food offered.

Factors determining the number of land bird species on Islands around South-Western Australia

SummaryNew evidence from the passerine faunas of islands off Southwestern Australia agrees with the hypothesis that the passerine faunas of Australian and New Zealand islands are impoverished because most passerine species are poor colonizers. Dispersal of landbirds onto Carnac Island near Perth was infrequent, and many of those species that arrived were represented by single birds. Comparison of similarly structured island and mainland habitats showed that island habitats still have fewer passerine bird species than mainland habitats. Island bird faunas are more stable over short periods of time than over long periods; this is contrary to island avifaunas in the Northern Hemisphere.The following features typify the avifaunas of Australian islands: immigration of species of land birds occurs infrequently; (natural) extinction is rare; and the degree of saturation of the avifaunas is low. Without more direct evidence, competitive interactions should not be invoked to account for the species poverty of these insular avifaunas.

Finch numbers, owl predation and plant dispersal on Isla Daphne Major, Galpagos

SummaryPopulations of 4 geospizine finches were studied on Isla Daphne Major in April and December 1973. Finches were captured, banded, measured and released in both months, and censused in December. 1640±711 finches were estimated to be present in December, of which probably more than 1000 belonged to Geospiza fortis. G. fortis were 4 times more numerous than G. scandens. The overal density at this time was 27–54/ha. This is the first quantitative estimate of finch population sizes for a whole island in the Galápagos Archipelago. Some G. fuliginosa and magnirostris immigrated between study periods, but overall density remained nearly constant. There was no evidence of immigration of fortis and scandens. Survival rates of the two common species, fortis and scandens, from April to December were estimated, from banded birds, to be 86.9% and 91.3%. Up to 300 finches (fortis and scandens) disappeared between study periods. The amount of predation by owls (Asio flammeus), estimated from an analysis of 49 pellets, could account for more than 50% of the finch losses, but is likely to be less. The estimated loss due to predation was less than 10% of the populations in April.The discovery of the remains of house mice, Mus musculus, and black rats, Rattus rattus, in pellets indicates that owls hunt on one island (e.g. Santa Cruz or Baltra) and regurgitate on another (Daphne). Fruits of a Euphorb, Chamaesyce amplexicaulis (Hook. f.) Burch, that finches eat were found in two pellets that also contained finch remains. This suggests that seeds or fruits in the throat of a victim at the time of a kill may be transported unharmed inside an owl from one island to another. Indirect support to this suggestion is given by the results of flotation experiments with seeds and fruits of 22 species of plants. Most did not float, and are too heavy to be transported by normal winds. Many do not have hooks or sticky surfaces, and internal transport by birds (including owls) is therefore strongly suggested.

Do earthworms compete for food

Abstract Three species of non-native earthworms, Microscolex dubius (Fletcher), Eisenia foetida (Sav.) and Allolobophora trapezoides Duges are common and widespread in suburban gardens of Perth, Western Australia. Eisenia tends to dominate numerically mixtures of these species. Laboratory experiments were set up to detect intra- or interspecific competitive interactions. Changes of biomass of worms in mixed species populations indicate that Microscolex under the experimental conditions adopted is at a competitive disadvantage when with Eisenia . The biomass of Eisenia was adversely affected by conspecifics but not by Microscolex . Ratio diagrams of biomasses were used to illustrate the temporal dynamics of these processes. During the first 2 weeks of the experiment neither species had an advantage over the other, but between weeks 2 and 5 mixtures tended toward an equilibrium with Eisenia contributing 62–67% of the total biomass. After week 5 the advantage enjoyed by Eisenia became independent of its biomass. A similar experiment conducted with Eisenia and Allolobophora yielded a stable coexistence within 11 weeks. The object of competition is most likely food. Two possible mechanisms, involving differences in excretory or digestive physiology, that could account for the decline of Microscolex are outlined.

Conservation of the forest red-tailed black cockatoo, a hollow-dependent species, in the eucalypt forests of Western Australia

Surveys of the forest red-tailed black cockatoo (FRTBC), Calyptorhynchus banksii naso Gould, conducted in two consecutive breeding seasons, were used to examine the hypothesis that a shortage of suitable nest sites (hollows in standing trees) limits the distribution of the cockatoo. It was found that 36% of its original geographical range is currently unoccupied, presumably because of extensive clearance of woodland for agriculture. FRTBC were broadly distributed nearly all over the State Forest. Analysis of forest inventory data indicates that the supply of large trees (and hence suitable nesting hollows) is not limiting. The current population of FRTBC is estimated to be ca. 15 000 birds.

Impact of frequency and intensity of defoliation on growth of Jarrah (Eucalyptus marginata): an experimental study with saplings

Abstract Manual defoliation of saplings of Jarrah (Eucalyptus marginata), using 12 different combinations of frequency and intensity, reduced stem diameter growth. Growth loss was a linear function of the severity of defoliation. Slight defoliation did not stimulate stem growth. More frequent defoliations of low intensity reduced growth more than less frequent defoliations of higher intensity.

Aboriginal man as an exterminator of Wallaby and Kangaroo populations on Islands Round Australia

SummaryThe occurrence of kangaroos, wallabies and related species (Family Macropodidae) on islands of area 90 ha or more round Australia is non-random. Few islands adjacent to the northwestern, northern and eastern coasts have macropods present in contrast to a large number of islands near the mid-and southwestern coasts and most of the southern coastline. The latter group of islands was not visited by aborigines because they lacked watercraft, and most of the islands were apparently too small to support human populations. It is argued that Aboriginal man, through direct predation, his introduction of the Dingo, and his frequent use of fire, was chiefly responsible for the difference in representation of macropods on the two groups of islands.The median area of islands with at least one macropod species present and which are used by Aborigines is about six times larger than that of islands with at least one macropod species present and not visited or occupied by Aborigines. Several possible alternative hypotheses to account for the distribution pattern described above are discussed. For two of these hypotheses inadequate data are at hand to assess their significance.It is suggested that the median area of islands visited or occupied by Aborigines provides a guide to reserve sizes necessary for the conservation of macropods on mainland Australia. Areas of at least 5,000 ha are probably needed for the local long-term persistence of at least one species of macropod, and areas of 9,000 ha for the long-term survival in reserves of at least two macropod species.

The impact of canopy development on arthropod faunas in recently established Eucalyptus globulus plantations in Western Australia

Abstract Monthly samples of arthropods collected from foliage of newly planted bluegums (Eucalyptus globulus) during a period of 14 months revealed a diverse and abundant (35 000 individuals) fauna. Most species, however, were uncommon. Total arthropod biomass (relative to plant size) declined progressively, with minor peaks in late autumn and in the second spring. Sapsuckers dominated total biomass, with their biomass peaking in late autumn, nearly one year after planting. Chewers were the next dominant trophic level, but this was greatly biased by sporadic occurrence of large caterpillars. Predators and parasitoids each contributed A space-for-time study of bluegums aged 6, 18 and 30 months yielded 34 000 arthropods. Total biomass increased rapidly up to 16 months and then stabilized. The proportion of sapsucker biomass halved between 18 and 30 months, while the proportion of chewer biomass increased fourfold. The greater proportion of older leaves on larger plants may have provided more suitable habitat for predators, but was less suited to sapsuckers. Observations of 11 types of chewers were collated using a conceptual framework summarizing mechanisms potentially affecting distributions of these insects in bluegum plantations in Western Australia. All four chewer types originating from agricultural habitat and reported as damaging plantations have soil-dwelling stages. Four of the five damaging chewer types originating from remnant native vegetation have feeding or oviposition preferences which are influenced by canopy development.

When the ‘native cat’ would ‘plague’: historical hyperabundance in the quoll (Marsupialia : Dasyuridae) and an assessment of the role of disease, cats and foxes in its curtailment

Abstract. Since the European settlement of Australia in 1788, 25 mainland terrestrial mammal species have become extinct, more than on any other continent during this period. To determine if the causal factors are still active, it is necessary to better understand the species and their status preceding these regional extirpations or extinctions, and examine the historical record for clues to the cause(s) of these declines. From an extensive review of historical material, primarily newspaper accounts, we collated >2700 accounts of quolls. We discovered 36 accounts that demonstrate the propensity for quolls to become hyperabundant. The geographical distribution of accounts implies that most refer to Dasyurus viverrinus, but an account from Normanton district (Queensland) likely applies to D. hallucatus. More than 110 accounts demonstrate that disease/parasite epizootics occurred in south-eastern Australia, commencing on mainland Australia possibly in the goldfields region of Victoria in the 1850s, or in south-eastern South Australia and south-western Victoria in the mid to late 1860s, and implicate these as the initial primary factor in the regional extirpation of Australia’s quolls. The loss of D. viverrinus populations in south-eastern Australia was reportedly from population abundances and densities that were sporadically extraordinarily high, hence their loss appears more pronounced than previously suspected. Accounts describing the widespread, rapid and major loss of quolls suggest the possible involvement of several pathogens. Ectoparasites such as Uropsylla tasmanica and ticks appear to be described in detail in some accounts. A few others state comortality of Felis catus and Canis lupus familiaris, suggestive of a disease of either or both of these species, such as Canine Distemper Virus, a morbillivirus with a propensity to be non-host specific, that may have caused the decline of the quolls, perhaps vectored by the reported ectoparasites. We also collated 23 presumed independent accounts of cats negatively impacting quolls, two of which describe significant mortality, and three presumed independent accounts of fox predation. These highlight the capacity of both of these introduced predators to have reduced quoll distribution and abundance.

The role of quoll (Dasyurus) predation in the outcome of pre-1900 introductions of rabbits (Oryctolagus cuniculus) to the mainland and islands of Australia.

Abstract. We investigated two questions: Why did most historical releases of rabbits on the Australian mainland fail? And why did many releases of rabbits on islands around Australia persist? We reviewed historical sources and present here nearly 300 records of the importation, sale, transportation and release of rabbits in the period 1788–1900, with >90 records before the popularly cited 1859 Barwon Park (near Geelong, Victoria) release by Thomas Austin. Similarly, we present records of localised impact of quolls (especially Dasyurus viverrinus) on rabbits and poultry, indicative of the great abundance of quolls. Rabbits were often imported and traded and releases were frequent and widespread. This evidence implicates native predators, particularly quolls (Dasyurus spp.) as responsible for the widespread and early failure of rabbits to establish on mainland Australia. In contrast, rabbits thrived on many islands, nearly all of which lacked cursorial natural enemies. We suggest that these accounts support the establishment of rabbits from several locations, with Barwon Park being a primary location and rabbit source.