How do Water Regime and Grazing Alter the Reproductive Capacity of Aquatic Plants?
Dr Margaret A. Brock
Botany, Rural Science and Natural Resources,
University of New England
Environment Australia, 2000
Attachment H
Pilot Study on the Influence of Water Regime on Frog Species Richness, Abundance and Reproduction in the UNE Experimental Wetlands
Michael Healey, Centre for Natural Resources, NSW Dept. of Land and Water Conservation, University of New England, Armidale NSW, 2351.
Introduction
Wetland hydroperiod has been shown to influence amphibian community structure and diversity overseas (Pechmann et al. 1989). In Australia, Humphries (1979) suggests that pond levels and changes to pond levels were more important to some frog species calling and breeding activity than the influence of rainfall events. Water level fluctuations have been shown to be an important factor in controlling larval metamorphosis in at least one Australian frog, Crinia signifera (Williamson and Bull 1999). Few studies on frog populations in the New England Tablelands of Northern New South Wales have occurred (see Heatwole et al. (1995) and Harris (1995)). None of these studies have investigated the influence of water regime on frog communities.
This study aims to investigate the relationship between different water regimes in the UNE Experimental Wetlands and frog species richness, species abundance and reproductive events.
Methods
All sampling was undertaken at UNE Experimental Wetlands located 10km north of Armidale (see Attachments c,d, and report Figure 1 for water regimes in wetlands). Sampling commenced in September 1999 with monthly visits to each wetlands. Sampling is expected to occur for a minimum of twelve months and will probably be extended to develop a long term data set. Unknown observed adult frogs and frog calls difficult to identify were checked against Barker et al. (1995) and Stewart (1998).
Adult frog activity (male calls)
Recording of male calls commenced in November 1999. Adult frog activity was measured by recording male frog calls for individual species at each pond approximately one hour after dusk. To prevent the possibility of disturbance (moving between ponds) affecting frog calls at each pond, one minute was allowed to elapse before recording calls. The abundance of each frog species calling was recorded for five minutes at each pond. Mean species richness and mean numbers of all frogs calling in each of the water regime treatments were evaluated.
Frog reproductive activity (egg masses and tadpoles)
Measurements of egg masses and tadpoles commenced in September 1999. Frog reproductive activity was measured by recording the number of egg masses (floating and submerged) and tadpole occurrence in each pond. Searches for egg masses and tadpoles were undertaken during early mornings. In each pond, five minutes was spent searching for frog egg masses (floating and submerged) in areas of aquatic vegetation (and flooded grass) followed by observations for tadpoles while walking around the entire edge of a pond. Tadpoles were placed into three size classes (>10mm, 5-10mm, <5mm) to examine if there were different tadpole cohorts occurring in each pond. Mean numbers of egg masses in each of the water regime treatments are evaluated.
Preliminary Results
A total of eight frog species from two Families have been observed at the Experimental Wetlands (Table h1).
| Family | Species Name | Common Name |
|---|---|---|
| Hylidae |
Litoria fallax |
Eastern dwarf tree frog Broad-palmed frog Peron's tree frog Verreaux's tree frog |
| Myobatrachidae | Uperoleia laevigata Limnodynatses tasmaniensis Crinia parinsignifera Crinia signifera |
Smooth toadlet Spotted grass frog Easterrn sign-bearing froglet Common froglet |
Adult frog activity (male calls)
The mean species richness (number of frog species calling) in autumn fill and spring filled treatments followed a pattern associated with increase on filling and decrease on drying (Figure h1 and report Figure 1). This pattern was also evident in the twice annual fill treatment. Similar numbers of species calling occurred across these three treatments (Figure h1). At similar sampling times, more species of frogs were found to be calling in the permanent and mimic treatments compared to the other treatments (Figure h1). To date, the highest number of species calling at two sampling times were recorded in permanently flooded treatments.
The mean number individuals (of all frogs calling, pooled for all species) across sampling times followed a similar pattern to the number of species calling in each treatment (Figure h2). Permanent and mimic treatments generally had more individual frogs calling at sampling times than other treatments at 70 percent and 57 percent respectively (Figure h2).
Frog reproductive activity (egg masses and tadpoles)
Frog reproductive activity was estimated by egg mass counts (pooled for submerged and floating egg masses) in each treatment. Patterns related to filling and drying were not as strong as for calling activity (Figure h3). The increase in the number of egg masses during the filling phase for spring and the first filling cycle for the twice annual fill treatments is possibly due to frog reproductive seasonal effects (Figure h3). More egg masses were recorded during December 1999 in the spring fill treatment compared to the twice annual fill ponds. This may be related to the twice annual fill ponds being half filled while the spring fill treatments were full and had more emergent aquatic vegetation and more shallow areas of flooded grass.
There were differences between the floating and submerged egg masses being deposited in particular water regime treatments (Figure h4). Floating egg masses are associated with the Family Myobatrachidae and submerged egg masses with the Family Hylidae. Floating egg masses were recorded in all treatments with most detected during spring and early summer sampling (Figure h4). Small numbers of floating egg masses were also detected in Autumn and twice annual fill treatments in March 2000 during the initial water filling phase. Submerged egg masses were only detected in spring and twice annual fill treatments during the early to mid filling phase (Figure h4). In December 1999, more submerged egg masses were recorded in the spring filled treatment than the twice annual fill treatment. During this sampling time more submerged egg masses were recorded than floating egg masses in the spring fill treatment.
No tadpole data has been evaluated to date due to a number of confounding factors. Tadpole observations were made difficult at most sampling times due to either dense aquatic vegetation preventing proper counts or high levels of water turbidity. At some times these two factors combined in some ponds. Considering these issues, tadpole data will be gathered as a bi-catch of the macroinvertebrate samples collected from another associated project that has recently commenced.
Conclusions
On the basis of this pilot study, further studies of frog activity associated with water regime are warranted. In particular studies on seasonal activity of frogs and tadpoles related to vegetation patterns and water regime are being planned
Mean frog species richness (+ 1 standard error) related to calling males across water regime treatments and over time. Newholme experimental wetlands, Armidale. Letters along the X axis represent the first letter of each month (eg. in each water regime, S = September 1999 at the start of project and the final M = May 2000 representing the last set of field data recorded.
Figure h2. Mean frog abundance: Mean number (+ 1 standard error) of individuals (all frogs calling,pooled for all species) across water regime treatments and over time. Newholme experimental wetlands, Armidale. (For explanation on the letters along the X axis see Fig. 1).
Figure h3. Mean number of frog egg masses (+ 1 standard error) across water regime treatments and over time (pooled floating and submerged). Newholme experimental wetlands, Armidale. (For explanation on the letters along the X axis see Fig. 1).
Figure h4. Mean number of floating egg masses (black bars) and submerged egg masses (clear bars) (+ 1 standard error) across water regime treatments and over time. Newholme experimental wetlands, Armidale. (For explanation on the letters along the X axis see Fig. 1).
References
Barker, J., Grigg, G. C., & Tyler, M. J. (1995). A field guide to Australian frogs. Chipping Norton, NSW.: Surrey Beaty & Sons.
Harris, K. H. (1995). Impacts of predation by the introduced fish Gambusia holbrooki (Girard, 1859) on two native species of anuran in New South Wales, Australia. Unpublished B. Sc. Hons thesis, University of New England, Armidale, New south Wales.
Heatwole, H., de Bavey, J., Webber, P., & Webb, G. (1995). Faunal survey of New England. IV. The frogs. Memoirs of the Queensland Museum, 38(1), 229-249.
Humphries, R. B. (1979). Dynamics of a breeding frog community. Unpublished PhD thesis, Australian National University, Canberra.
Pechmann, J. H. K., Scott, D. E., Gibbons, J. W., & Semlitsch, R. D. (1989). Influence on wetland hydroperiod on diversity and abundance of metamorphosing juvenile amphibians. Wetlands, Ecology and Management, 1(1), 3-11.
Stewart, D. (1998). Australia frog calls: subtropical east. (CD). Nature Sound, Mullumbimby, NSW.
Williamson, I., & Bull, C. M. (1999). Population ecology of the Australian frog Crinia signifera: larvae. Wildlife Research, 26, 81-99.
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