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Further Notes on Pseudophryne australis (Myobatrachidae)


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Posted by Richard Wells on March 17, 2002 at 20:56:12:

Hello all,
For those interested in the Family Myobatrachidae I offer you my considerations regarding the genus Pseudophryne in Australia - specifically on Pseudophryne australis - which were recently published in the AUSTRALIAN BIODIVERSITY RECORD, 2002 (No 4): 1-28 (March, 2002)
A copy of this article is attached below, but owing to its size, I shall send it in parts:

Herein please find the second part which concerns the ecology and conservation of the species:

Kind Regards from

Richard Wells

Ecology
Usually small colonies are found scattered along ridges, their distance apart being variable, and coinciding with the positions of suitable refuges such as drainage lines or other breeding sites.

It is likely that individuals move between these ‘colonies’ during periods of suitably wet weather and this would explain the occurrences of isolated specimens that are occasionally discovered sheltering under small exfoliated rocks and the like on parts of a ridge that are less than ideal.

Given the relative close proximity of these small colonies it would be reasonable to assume that they are functioning as a metapopulation, so the loss of any of these smaller colonies from a ridge would likely have a deleterious impact on the species’ overall presence in an area.

A colony usually contains at least several pairs of adult frogs within a few square metres of ideal site conditions, but in some areas of more extensive, undisturbed habitat colonies in excess of 50 individuals have been found during peak breeding weather.

However such large numbers are nowadays unusual - colonies in excess of 20 individuals are regarded as very large, with less than 10 individuals being about the average situation across much of the species’ range. It is also apparent that these smaller ‘colonies’ may merge into a few (or even one) refuge sites such as during drought conditions. As conditions improve, the population disperses across the habitat to again fragment into the smaller groups or colonies.

Larvae would on occasions be washed downslope into gullies far removed from their nesting habitat and some movement into new ridge habitat must eventually occur from successful metamorphs but the population dynamics of this species are still too poorly known to be sure of this.

Once transformation has occurred, most of this species’ life is spent under some form of cover, such as rocks, deep leaf-litter, or in rock crevices, with any surface activity being only at night, and then largely only during periods of heavy rainfall in summer.

When not breeding, Red-crowned Toadlets are thought to disperse over wider areas of its sandstone habitat, (i.e. into non-breeding areas) and certainly many individuals have been observed sheltering under cover that would really be unsuitable for egg-laying. However, it is likely that such ‘dispersion’ is really only in the order of a few tens of metres from suitable breeding areas.

This is really quite a localised species that appears to be largely restricted to the immediate vicinity of suitable breeding habitat, so recruitment rates into other areas of habitat would probably be low.

Information on the natural predators of Red-crowned Toadlet is scant. Snakes are known to eat this species, but the consequences are largely unknown. An immature Tiger Snake found road-killed contained an adult Red-crowned Toadlet in its stomach. However as mentioned earlier, a juvenile Red-bellied Black Snake that ate one in captivity rolled over onto its back and died within minutes of consuming it.

The bold red markings of the species have been taken to represent some form of warning pattern against potential predators, but it is difficult to imagine how such a strategy would help a mainly fossorial and nocturnal species. Perhaps this colour pattern may have evolved in association with the litter-foraging behaviours of some birds and small mammals, that could be expected to uncover the species while foraging for invertebrates.

There is a prominent glandular region on the thighs, and these flat femoral glands (one on each hindlimb) are mostly covered by a bold white thigh spot, but their function is unknown. The skin also exudes a chemical secretion which has an unknown function at present. It may act as an anti-predator defence strategy, or possibly be utilised as an anti-bacterial or anti-fungal agent as is the case with some other frog skin secretions. Analytical studies in the 1950’s on Pseudophryne secretions indicated that it was much more toxic than strychnine, but little follow-up work has apparently been undertaken indicating a potential for pharmacological investigation.

This species has a relatively long life span with adults surviving over 5 years in captivity. It is believed that this species may attain an age of at least 10 or even 15 years.

How to Detect the Red-crowned Toadlet
Some techniques for detecting the Red-crowned Toadlet might also be of interest to those interested in its conservation.

With its nocturnal and largely fossorial lifestyle, the Red-crowned Toadlet can easily be overlooked in an area of suitable habitat without a combination of active search both during the day and night.

Although this species is active throughout the year, the best time to search for Red-crowned Toadlets is during periods of heightened activity in Spring, Summer and early Autumn. It is much more difficult to detect in the colder months or during dry weather conditions when activity is reduced.

Detection of this species may be through call identification or active searching of microhabitats - preferably both.

Additionally, pit-trapping has been employed but has had limited success and then only during ideal weather conditions. Pit-trapping on an adequate scale in the rugged sandstone habitat of this species is often extremely difficult or even impossible due to the shallow soils. It can also seriously disturb a site and trap many other non-target organisms.

When pit-trapping is employed, there are two strategies - known as ‘wet’ or ‘dry’. In the case of ‘wet’ pit-traps, the pits contain a form of chemical killing agent/fixative such as formalin. ‘Dry’ pit-traps are without such agents and generally do not result in the death of the captured fauna if checked frequently and a few basic modifications are employed (such as placing a bed of damp leaf-litter in the pit as a refuge for trapped specimens. If such pit-trapping is used to survey for Red-crowned Toadlets, the ‘dry’ technique is preferred, modified slightly with the addition of wet litter in the trap to prevent dehydration.

Call detection is the commonest method used to locate this species, however, a few words of caution are appropriate. The call of the Red-crowned Toadlet may vary somewhat depending upon the particular conditions at the time (eg repetition-rates may vary with the prevailing weather conditions).

Where possible, it is always preferable to follow a frog call to its source to verify its identity as the call of this species may be mistaken for other species. Caution should be observed by survey works when targeting this species solely on the basis of call.

It is important that field biologists should be able to accurately discriminate between the call of the Red-crowned Toadlet and those of Pseudophryne coriacea, Pseudophryne bibronii, Uperoleia fusca, Uperoleia laevigata, and even Ranidella signifera. On occasions both experienced and less experienced observers have confused the call of the Red-crowned Toadlet with all of these species and vice versa. Thus, call misidentification may result in a false record of the Red-crowned Toadlet’s presence in an area, or even the species’ exclusion from the survey results because it was believed to one of the common species mentioned above.

It is known that Red-crowned Toadlets will call in response to unusual noises (such as people talking or shouting) and such a technique has been used with success by some survey workers. However this technique is not always successful and it could actually result in call suppression.

The use of tape-recorded calls of this species to elicit a response call (known as the call-playback technique) apparently has also some value for survey, but it has on occasion appeared to have had the effect of silencing calling Red-crowned Toadlets as well.

This could be indicative of another potential problem with call detection - call variations between ‘populations’ of Red-crowned Toadlets. No detailed studies on the call structure have been undertaken on this species as yet, but I have observed subtle differences between the calls of Red-crowned Toadlet from different parts of its range. Whether the use of a tape-recorded call of a population far removed from the surveyed population influences the results or not, must remain speculative until further study, but it would be better not to rely solely on call-playback to detect this species.

Active searching of this species’ habitat is an invaluable adjunct to call detection. This must be done with care as the best places to find Red-crowned Toadlets are fragile and likely critically important to their survival in area.

The two main microhabitats that should be examined are accumulations of leaf-litter along the beds of the non-perennial feeder streams, and exfoliated sandstone rocks along both the ridges and on the first tallus slope at the base of the uppermost escarpment or benchline.

When examining the leaf-litter be mindful of its moisture retention role and rake the litter back into position on the creek bed or wherever it was originally laying after your examination.

When checking sandstone rocks, ensure that they are replaced exactly as they were found and be aware that the rocks may be easily damaged or broken. They are the products of thousands of years of weathering so will not be replaced quickly if damaged. As the best time for locating this species is during periods of wet weather, the rocks favoured by Red-crowned Toadlets will be even more fragile at this time due to moisture content and can be easily damaged if one is not very careful.

Details on the ecology of the Red-crowned Toadlet have already been mentioned above and it is really through an appreciation of such knowledge that the species may be detected in an area of suitable habitat.

Threats to the Red-crowned Toadlet
I would also like to briefly mention some of the threats to this species survival and offer a few suggestions for their amelioration. Although there have been few studies on the life-cycle of this species, enough is now known to identify a range of potential threats to the species.

In general terms, among the potential threats to the survival of this species are the removal of bush-rock for the landscaping industry, expanding urbanisation, water pollution, changed hydrological regimes, and the frequency and severity of bushfires.

The various destructive land-use practices adopted across this species’ range over the last two centuries must have had a range of impacts that have varied in their intensity from one area to another.

It has been estimated that around 15-20% of this species’ total available habitat has been subjected to development and therefore by implication, is no longer suitable for the species. I think that this percentage is far too high, but it would still be a significant amount in some areas because of the fragmented nature of the species’ distribution.

Consequently it is now held that the range of this species has experienced a contraction since European colonisation. Obviously, those parts of the species’ past range now occupied by the northern and eastern suburbs of Sydney have been very significantly affected. In the area extending from South Head through what is now most of the Sydney CBD, across to the eastern suburbs, to as far south as La Perouse, it is clear that almost total loss of habitat (over 95%) has now occurred and the species is now believed to have been extirpated from that part of its former range.

On the Hornsby Plateau between the Parramatta River and the Hawkesbury River which now includes most of Sydney’s northern suburbs, over half of this species’ former range has now been totally lost. Red-crowned Toadlets still occur in most of the larger reserves and National Parks of the Hornsby Plateau, but there is concern that these refuges are being continuously degraded by the edge-effects of existing and continuing urbanisation. Of the remainder of this species’ habitat left on the Hornsby Plateau, almost all of this area has been affected by, and is still being subjected to, severe bushfires and this should be a matter of concern.

The population on the central coast between the Hawkesbury River and the Hunter River and west to the Putty Road is highly fragmented, but with most of its original habitat still extant, relatively minimal reductions have probably occurred since colonisation. However, most of the remaining Red-crowned Toadlet habitat has been degraded to a varying extent. Many areas have been subjected to repeated bushfires that have been regarded as severe, and the removal of sandstone exfoliations by bushrock collectors from the ridges has been widespread in this part of its range.

The habitat in Wollemi National Park is largely intact and represents a stronghold for the species. The removal of sandstone rocks by the activities of ‘bushrock’ collectors though has devastated much of the eastern edge of Wollemi National Park and in so doing destroyed much of the habitat of Red-crowned Toadlets in the Culoul Range section of the Park. Additionally, most of its remaining habitat in Wollemi National Park has been subjected to repeated severe bushfire and this appears to have had a very serious impact in places.

To the south, the original habitat for the Red-crowned Toadlet in the Blue Mountain National Park is still extant and the species is still present, although possibly declining in some areas due to the low numbers now reported. Much of the frog’s habitat also continues to experience repeated bushfires of a severe nature, and additionally, the area has been affected by the past removal of bushrock on a large scale. The consequences of this habitat degradation for the species in the Blue Mountains National Park are at present unknown, but they must be considered as potentially serious in places. Another matter of concern is the urbanisation of the Blue Mountains City region - for example how pollution impacts on the surrounding National Park. The Blue Mountains City region also contains a significant part of the distribution of the Red-crowned Toadlet, but most of this original habitat has now been lost and of the remainder, much is in a very degraded state due to various human-induced disturbances.

That part of the species’ range that encompasses the northern Moss Vale Plateau across to the southern part of the Blue Mountains National Park was likely already fragmented at European colonisation, and subsequent agricultural development of some parts have had a limited impact. The species is still present here, but is patchy in its occurrence, and therefore at greater risk of loss through localised disturbances.

On the southern part of the species’ range Red-crowned Toadlets appear to be less-often recorded and the reason for this is unknown. The area between the Woronora Plateau and the Moss Vale Plateau includes large areas of water catchment lands which have been long-protected from disturbance - other than periodic bushfires - and most of the original habitat is still intact. Consequently the species is still present and appears to be doing well here.

The southern extreme of its range - from the Woronora Plateau to the Nowra area - has been heavily affected by the loss of bushrock which has devastated many ridges over last few years. The extent of repeated severe bushfire is considerable here also.

Although the species is still present at the limits of its distribution, its core distribution has experienced disturbances of a nature and intensity that must be considered counter to the species’ survival needs. It is likely that many years may be required for a colony of this species to recover from the impact of some disturbances.

Within these areas of disturbance, some of the possible contributing factors implicated in this species’ decline are as follows:

The Potential Impact of Fire
I think that by far the most widespread factor apparently affecting this species’ habitat is fire. It has recently been suggested that fire is having a major effect on this species’ habitat, and as a consequence impacting upon the survival of the species.

The potential deleterious impact of bushfire on this species though is a matter of hot debate, for it must be appreciated that fire has been long part of the natural ecology of the Red-crowned Toadlet - as readily seen by the adaptations that have evolved with the flora of this species’ habitat.

Significantly, the issue of fire-effects on this species obviously revolves less on its occurrence, and more on its frequency and severity. What is the ideal fire-regime for this species’ habitat? A suggestion of 10 year intervals between burns has been touted, but I know of no objective basis for this particular frequency.

It is clear that fire-effects on Red-crowned Toadlet habitat vary greatly both within and between affected areas. The actual intensity of a fire, the extent of refuges within an affected area, the history of rainfall, the rate of subsequent vegetation regeneration, and of course even the time of the year the site is subject to a burn are only a few of the considerations necessary when one tries to determine the impact of fire on this species.

However, it is known that some sites where Red-crowned Toadlets were known prior to severe fire, appear to have lost the species. Even sites subject to regular hazard-reduction burns appear to have smaller populations of Red-crowned Toadlets than areas of habitat left unburnt.

But this said, it must also be appreciated that virtually every consideration of fire-effects to date depends upon anecdotal or fragmentary observations which could easily be misleading.

While scientific studies supporting the proposition that frequent or severe fire has a deleterious impact on this species are lacking, the disturbing absence or rarity of Red-crowned Toadlets in areas subjected to regular burns or wildfire is worrying to naturalists experienced with this frog. At the very least a serious scientific investigation on the effects of fire on this species is urgently required.

The Potential Impact of the loss of Bushrock
Habitat loss or damage through exploitation of sandstone as a building material was among the earliest impacts on this species but was usually confined to a few quarries.

The use of sandstone changed with the times however, and with the widespread fashion for bushrock gardens over the last 40 years, vast areas of this species’ habitat was affected by the removal of the actual exfoliated rocks utilised as shelter sites by the Red-crowned Toadlet and numerous other species.

With the removal of hundreds of thousands of tonnes of the material (translated into millions of individual rocks) the most readily accessible areas began to be stripped by the early 1970s, and soon after widespread illegal removal from the National Parks expanded in ernest and continued right up until precipitous canyons prevented further access.

This problem became so serious, that the NPWS had to patrol ridges with helicopters looking for bushrock collectors. A police report to the NPWS at the time also indicated the kind of people involved - police intelligence had revealed that many known to be undertaking the activity of illegal bushrock collection had serious criminal records and were considered armed and potentially dangerous. Not surprisingly, the number of prosecutions was appallingly small in relation to their impact on the conservation reserves in the Sydney Basin.

The NSW Threatened Species Conservation Act 1995 eventually listed bushrock removal as a key threatening process on the Red-crowned Toadlet and other species.

The past and continuing illegal collection of exfoliated sandstone rocks from the habitat of this species appears to certainly have had a destructive impact. Habitat that has lost this resource is ecologically disrupted through the reduction of shelter sites and food supply for many species, including the Red-crowned Toadlet.

The Potential Impact of Urbanisation
Another potential threat of concern, although fairly limited in the area of its occurrence is the clearing of ridge-top habitats for urbanisation.

Ridge-tops, although less suitable for breeding, may be used as important foraging habitat, so activities that disturb these areas may have consequences for the species in nearby relatively undisturbed breeding habitat.

Housing developments along some sandstone ridges may directly threaten Red-crowned Toadlets through direct habitat destruction, pollution or siltation of watercourses and alterations to the local hydrological regime.

Its specialised terrestrial reproductive strategy and reliance on ephemeral water flow means that it may be particularly vulnerable to a range of activities that impact on water quality. As discussed above, breeding sites have been found to be associated with shallow temporary ponds and slow water seepage from ridges upslope of its breeding site and have a soil pH ranging from 5.5 to 6.5. Under these conditions the water is of a very high purity. Indeed, Red-crowned Toadlets have not been recorded breeding in waters that are even mildly polluted, or from permanently flowing watercourses.

In some parts of the species’ range, clearing of ridgetops and related development activities have resulted in seriously degraded water conditions as a result of altered hydrological patterns as well as eventual urban run-off, increased sedimentation and higher nutrient levels of the feeder watercourses. Even run-off from blue-metal and bitumen roads upslope of Red-crowned Toadlet habitat is believed to directly affect this species’ breeding habitat by increasing the pH of waters downslope.

Although there have been no studies for the Red-crowned Toadlet to determine the effects of garden biocides and other potentially toxic chemicals known to occur in urban run-off, it is likely a reasonable proposition that their larvae could also be deleteriously affected by such chemicals.

It is not an unreasonable assumption to take the next step and conclude that any or all of these above factors may have deleterious consequences for a population exposed to such conditions when one is familiar with this species’ highly specialised breeding requirements. It is most likely that the resultant increased flow rates, higher pH and consequent erosion of head-waters could negatively impact on the critical habitat required by the Red-crowned Toadlet for breeding.

The Potential Impact of Drought
The effects of prolonged drought on the Red-crowned Toadlet must also be considered, for although usually regarded as a ‘natural’ feature, its impact may be exacerbated by other disturbances that are man-induced.

During the last two decades of the 20th century, much of the Southern Hemisphere experienced record periods of drought and above-average temperatures. In eastern Australia during this period, maximum summer temperatures were in places the highest recorded since record-keeping began and such conditions also coincided with droughts that in some cases lasted over 5 years.

During this period of reduced rainfall and increased temperatures much of the habitat of the Red-crowned Toadlet was also subjected to severe burning through wildfires as well as repeated hazard-reduction burns and numerous other degrading influences.

In recent years it has become apparent that man-induced climatic changes are now occurring, and indications are that the Red-crowned Toadlet is a prime candidate to be directly effected due to the potential impact of global warming on its montane environment.

The cumulative effect on the Red-crowned Toadlet of these impacts must at present remain speculative, but an increasing body of anecdotal evidence suggests that this species could be at the very least in a state of widespread decline.

So, in summary, the Red-crowned Toadlet presently survives across its entire range as a number of apparently isolated populations - and this has likely been the case since the end of the last Glacial period thousands of years ago.

Its current distribution pattern of a fragmented or isolate nature suggests that it had naturally contracted to a post-glacial montane refuge situation by the time of European settlement. Some of these isolates however are becoming increasingly fragmented due to various human-induced changes such as roads, urban developments and other activities that destroy parts of the habitat of the Red-crowned Toadlet within a particular area.

It is possible, that given the species’ ancient evolutionary history as derived from molecular data, and the known climatic history of the region, that it has expanded and contracted in range many times in its existence.

Thus, expansion of the species’ range during future glaciations or ice-ages could be compromised by the loss of any of its existing populations and habitat. The further fragmentation of already naturally restricted areas of habitat may have unforeseen consequences for the survival of an isolate or even the entire species itself.

Conservation Status
The Red-crowned Toadlet is presently listed as a Vulnerable Species on Schedule 2 of the NSW Threatened Species Conservation Act 1995 (TSC Act).

All existing colonies of the Red-crowned Toadlet that are successfully reproducing and recruiting new members into the breeding population must be regarded as viable. The presence of calling individuals, gravid females, deposited eggs and larvae strongly supports the notion that a site has resources available to the species to support a viable local population.

The viability of any local population of this species is likely to be compromised by the above threatening processes if they result in a decrease in the quality of breeding and/or foraging habitat.

Additionally, protection of habitat surrounding these viable local populations may also be essential as connectivity between different colonies allows gene flow between them, thus ensuring viability in the long-term.

Populations of this species are currently reserved in Sydney Harbour National Park, Royal National Park, Heathcote National Park, Morton National Park, Garigal National Park, Ku-ring-Gai Chase National Park, Muogamarra Nature Reserve, Nattai NR, Brisbane Water National Park, Popran National Park, Marramarra National Park, Wollemi National Park, Bargo SRA, Parr SRA, Dharawal SRA, Blue Mountains National Park, Dharug National Park, Yengo National Park, Lane Cove National Park, and Barren Grounds National Park. Additionally the species also occurs in a number of State Forests and Water Catchment areas.

Although the species is protected in a number of conservation reserves, it is not known whether the genetic variation of the species is adequately reserved at present. There may be considerable genetic variation between isolated populations of this species.

What Can Be Done to Save the Red-crowned Toadlet?
Some potential management strategies for the conservation of the Red-crowned Toadlet might include:

*Ensuring more environmentally sympathetic housing developments on sandstone ridges. The present situation is one of almost total localised destruction of the habitat of this species so as to maximise the number of dwellings per hectare with the result of minimal habitat conservation. Housing development and the conservation of this species should not be regarded as mutually exclusive alternatives.

*Development and implementation of fire management plans with an appropriate fire regime for known areas of habitat. This should include appropriate buffers and a mosaic burn strategy where necessary. Hazard-Reduction and Prescribed Burn operations need to be mindful of the potential impact on this species;

*Active prevention of bushrock removal;

*Development of erosion, sediment and flow control measures at the urban bushland interface;

*Prevention of stormwater and other runoff from ridgetop developments and existing urban areas altering the natural hydrological cycle of Red-crowned Toadlet habitat.

*Support for scientific studies on all aspects of this species’ biology.





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