This study investigated the utility to vertebrates of upland linear riparian rainforest fragments on the Atherton and Evelyn Tablelands in the Australian Wet Tropics region, north Queensland. Similar linear fragments were selected, that varied in forest age and their connectivity to large areas of continuous forest:- (connected primary (N=6), isolated primary (N=5), connected secondary (N=6) and isolated secondary (N=7)). Primary sites had either never been cleared or only subject to selective logging, while secondary forest had been completely cleared and allowed to regenerate for at least 30 years. These linear fragments were contrasted with riparian sites within continuous forest sites (N=6 to 7), which were situated in State Forest or National Parks, and sites within the cleared matrix (pasture, N=6). Vertebrates surveyed were birds, ground-dwelling mammals and reptiles, particularly leaf-litter skinks. All surveys were conducted between September and December in 2001 and/or 2000. Chapter 2 investigates the effects of forest age, isolation and structural vegetation features on bird assemblages within linear riparian fragments of rainforest. Bird surveys and structural vegetation assessments were conducted within connected and isolated primary and secondary linear fragments, and compared with those of continuous forest habitat (N=6) and pasture. There were strong effects of forest age; all three types of primary rainforest had higher values than secondary rainforest for most measured attributes of vegetation structure (including canopy height and cover; and frequency of large-diameter trees, lianes, epiphytes, strangler figs; and woody debris), but lower frequencies of tree ferns and thorny scramblers. Sites within primary rainforest also had a greater frequency of many bird species across different guilds of habitat, feeding and movement. Assemblages of rainforest-dependent birds showed an effect of isolation, although its strength was less than that of forest age. Isolated fragments of primary rainforest differed significantly from continuous primary rainforest in their rainforest-dependent bird species assemblages (and had lower species richness), and isolated fragments of secondary rainforest differed from those that were connected. There was a significant association between the species composition of rainforest birds and some measured vegetation parameters across all sites, but not within primary or secondary sites. Vegetation differences did not explain the lowered frequency of several species in isolated fragments. Limited dispersal seems unlikely to be a main cause, and causal processes probably vary among species. Specialist rainforest species endemic to the Wet Tropics region showed stronger responses to present-day rainforest age and fragmentation than those not endemic. Variation in nest depredation levels associated with rainforest fragmentation (edge effects) is examined in Chapter 3. Artificial nests were placed in the forest understorey at seven edge sites where continuous forest adjoined pasture, seven interiors (about one kilometre from the edge), and six primary linear riparian forest remnants (50-100 m wide) that were connected to continuous forest. Four nest types were compared, representing different combinations of two factors; height (ground, shrub) and shape (open, domed). At each site, four nests of each type, containing one quail egg and two model plasticine eggs, were interspersed about 15 m apart within a 160 m transect. Predators were identified from marks on the plasticine eggs. The overall depredation rate was 66.5% of 320 nests' contents damaged over a three-day period. Large rodents, especially the rat Uromys caudimaculatus, and birds, especially the spotted catbird Ailuroedus melanotis, were the main predators. Mammals comprised 56.5% and birds 31.0% of identified predators, with 12.5% of unknown identity. The depredation rate did not vary among site-types, or between open and domed nests, and there were no statistically significant interactions. Nest height strongly affected depredation rates by particular types of predator; depredation rates by mammals were highest at ground nests, whereas attacks by birds were most frequent at shrub nests. These effects counterbalanced so that overall there was little net effect of nest height. Mammals accounted for 78.4% of depredated ground nests and birds for at least 47.4% of shrub nests (and possibly up to 70.1%). The main predators were species characteristic of rainforest, rather than habitat generalists, open-country or edge specialists. For birds that nest in the tropical rainforest understorey of the study region, it is unlikely that edges and linear remnants presently function as ecological population sinks due to mortality associated with increased nest depredation. The use of linear riparian remnants by small ground-dwelling mammals and reptiles (mainly leaf litter skinks), is reported in Chapter 4. Site types were continuous rainforest, connected and isolated linear fragments of both uncleared primary rainforest and secondary regrowth rainforest. Mammals were also surveyed in pasture sites. Neither reptile species richness nor abundance varied significantly among site types. Although mammal species richness varied significantly between site types, with isolated primary sites containing highest species richness, overall mammal abundance did not differ significantly among site types. Pasture sites differed significantly from all rainforest sites in their mammal species composition, and were dominated by the introduced house mouse (Mus musculus). This species was absent from all rainforest sites, which were characterised by moderate abundances of bush rat/Cape York rat Rattus fuscipes/leucopus, fawn-footed melomys Melomys cervinipes and giant white-tailed rat Uromys caudimaculatus. None of these species varied significantly in abundance among site types, although the giant white-tailed rat showed a trend (P=0.09) for reduced abundance in isolated secondary sites. A single reptile species, the prickly forest skink Gnypetoscincus queenslandiae, occurred in sufficient numbers for individual analysis, and its abundance varied significantly among the forested site types, being less abundant in all linear fragments than in continuous forest sites. The utility of linear riparian rainforest for vertebrates appears to be species-specific and involves many factors. However, overall, species endemic to the Wet Tropics (which are hence of the highest conservation significance) appear to be the most sensitive to fragmentation. These species were most likely to show altered abundances or frequencies of occurrence due to isolation, forest age, and habitat linearity. The ecology of species within this group warrants further investigation within fragmented and non-fragmented regions of the Tablelands. For many other vertebrates examined in this study, there appears to be sufficient functional connectedness between remnants on the Tablelands to minimise the effects of fragmentation. Nevertheless, the lower density of many of these species in pasture may indicate that their long-term persistence within the fragmented rainforest areas could benefit from the maintenance or establishment of habitat linkages. Certainly, if the current rainforest vegetation cover were further reduced, or if the land use in the matrix became more intensive, the establishment of specific habitat linkages could become more important as existing dispersal routes could be lost. It also appears that nest depredation levels are unlikely to limit the value of linear rainforest remnants and other small rainforest remnants as breeding habitat for birds (at least for understorey-nesting species), relative to more intact rainforest, in the study region.
| Identifer | oai:union.ndltd.org:ADTP/195138 |
| Date | January 2004 |
| Creators | Hausmann, Franziska, n/a |
| Publisher | Griffith University. Australian School of Environmental Studies |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.gu.edu.au/disclaimer.html), Copyright Franziska Hausmann |
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