The rate of accumulation and the composition of the forest floor litter were studied in an open eucalypt forest at Seal Rocks, New South Wales. The forest is subject to frequent fires and its recent fire history is well documented. The height of the understorey vegetation was shown to be a good indication of the time since fire. Litter accumulation in eucalypt forests can be adequately described by a modified exponential equation with two parameters, steady-state accumulation (Χss) and rate of accumulation (k). Both parameters are functions of the annual litter fall, which is assumed to be continuous in this model. The steady-state accumulation of litter in the Seal Rocks forest was found to be 1.67 kg m-2, reached after c. 10 years. The model should be recognized as a gross simplification of the many factors which affect litter accumulation, in particular the assumption of a constant value for k. The components of the litter on the forest floor change in relative importance with time owing to differing rates of accumulation and decomposition.
The importance of habitat structure has been illustrated for many groups of animals. A method to objectively measure the vegetation structure of animal habitats is presented. Factors contributing to the index are evaluated and an attempt is made to show how this index relates to other methods of measuring habitat structure. A technique to measure crop leaf area is adapted and applied to assessing structure (the vertical distribution of vegetation) in natural vegetation. A light meter is used to determine a vegetation index for each of several layers. The index is compared with projected cover, cover estimated with a cover board and cover repetition using pin contacts. All correlations are highly significant. In heath the dry weight of clipped vegetation contributed more to the vegetation index than did the leaf area, reflecting a greater contribution of woody stems and branches than of the small ericoid leaves. The technique has been successfully applied to the measurement of habitat requirements for small mammals and an example of such an application is included.
This paper reports successful laboratory hybridization of R. lutreolus lutreolus (2n = 42) and R. fuscipes assimilis (2n = 38). Hybrid offspring grew rapidly (hybrid vigour) to age 24 days. Only one individual survived past 50 days but is fertile. Although intermediate for many characteristics the hybrids resemble R. lutreolus more than R. fuscipes. The hybridization indicates a closer relationship between these species than previously accepted, but there is no evidence of natural hybrids, perhaps due to an ecological separation observed in the field and to behavioural obstacles to mating observed in the laboratory. Hybrid animals (2n = 40) have single fused chromosomes from each of the two pairs of submeta- centrics in the R. fuscipes karyotype. Chromosome arm length measurements and rankings show that one centric fusion (CF1) comprises two longer chromosomes (4 + 8) and the second fusion (CF2) comprises the two shorter chromosomes (10 + 12). These fusions appear to be identical with those we observed in other R. fuscipes populations in New South Wales. The chromosome numbering determined by measurement of unbanded chromosomes in this study appears to differ from the numbering convention currently in use. This emphasizes the need to establish a standard sequence of chromosomes for Australian Rattus.
Information on development (to 40 days) and growth (to adult size) was obtained from 26 litters of Pseudomys gracilicaudatus (Gould, 1845). Animals were laboratory-raised, the breeding stock originating from Myall Lakes, N.S.W. Young are precocial at birth and early development is rapid. Lower incisors have erupted at birth and upper incisors at 1(0-4) day. Head and shoulders are furred at birth and a full pelage is present by 6 days. Ears and eyes open at 9 (7-11) and 11 (9-12) days, respectively. Weaning occurs during the fourth week and the first moult begins at about 30 days. Adults show significant sexual dimorphism (males, 90 g; females; 69 g; P<0.05), which becomes apparent after an age of 1 month. Head length, hind foot length and head + body length do not show significant differences until after an age of 2 months. Growth in the first 40 days is multiphasic, changes in growth rate being related to developmental events. Inverse index of growth (20-90% of adult weight) is 110 days in females and 125 days in males. The rapid early development, which may be related to increasing juvenile survival, contrasts markedly with the slow growth rate.
Little is known about the biology and ecology of the eastern chestnut mouse (Pseudomys gracilicaudatus), let alone the details of its diet. In this paper, we examined the dietary composition, diversity and variation among individuals of this species in a coastal heathland of New South Wales, by means of microscopic examination of its faecal pellets. From 200 faecal samples, P. gracilicaudatus was found to consume considerable amounts of fungi (20% overall) and insects (over 10% on average). Seed was the most abundant food in its diet from August to February, accounting for 39%, with stem contributing 28% of the diet. Stem was dominant at other times, accounting for 34%, with seed contributing 24%. Although cohort-dependent foraging strategies have been reported in many small mammals, age-dependent foraging only occurred in autumn; sex-dependent foraging was not observed in P. gracilicaudatus. Analysis of dietary diversity (H') and among-individual variation (CVp,) showed that there were significant variations in the diet of P. gracilicaudatus in different seasons and successional stages. Negative association between H' and CVp, for seasons and vegetation succession suggested that individuals of P. gracilicaudatus consumed a range of food items, producing maximum dietary diversity. These results indicate that P. gracilicaudatus is a generalist herbivore, opportunistic in foraging and less specialised in food selection than any other Pseudomys species reported so far.
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