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Frog breeding in rain-fed wetlands after a period of severe drought: Implications for predicting the impacts of climate change



Globally, rain-fed wetlands provide critical habitat for a wide range of amphibian species, however, information on the use of rain-fed wetlands by Australian frog species is extremely limited. This study examined the distribution of frog breeding in rain-fed wetlands following the first significant rain event after a period of severe drought (2002–2009) in order to predict how frog communities may be affected in the future by changed climate. Tadpole communities along with vegetation and water quality variables were described in 35 rain-fed wetlands across the South West Slopes and Riverina bioregions of inland south-eastern Australia. In addition, weekly tadpole surveys were conducted in a subset of these wetlands to describe temporal patterns of occupancy. Despite the protracted dry period prior to this study 50% of the rain-fed wetlands surveyed contained tadpoles. However, frog communities were species poor with only five species recorded. The majority of wetlands were dominated be a single species, Limnodynastes tasmaniensis which is also common within permanent waterbodies such as farm dams and irrigation infrastructure in both bioregions. Tadpoles of two burrowing species L. interioris and Neobatrachus sudelli were restricted to a small number of wetlands mostly in the South West Slopes. The composition of tadpole communities changed over time, and Crinia parinsignifera was the only species that continued to breed over winter. The dominance of generalist species within rain-fed wetlands indicates that characteristics such as dispersal capability, flexibility in breeding times and the ability to utilise created habitats may be more important than burrowing ability and longevity when predicting vulnerability to climate change.
Frog breeding in rain-fed wetlands after a period of severe drought: implications for predicting the impacts
of climate change
Wassens, S.a*, Walcott, Ab., Wilson, A.a and Freire, R.b
a Institute of Land Water and Society, School of Environmental Sciences, Charles Sturt University, LMB 588,
Wagga Wagga, NSW, 2678, Australia
b School of Animal and Veterinary Sciences, Charles Sturt University, LMB 588,Wagga Wagga, NSW, 2678,
*Correspondence to:
Dr Skye Wassens
School of Environmental Sciences
Charles Sturt University
LMB 588 , Wagga Wagga, NSW, 2678, Australia
Tel: (02) 69 332843
Word count: 6672
Globally, rain-fed wetlands provide critical habitat for a wide range of amphibian species, however information on
the use of rain-fed wetlands by Australian frog species is extremely limited. This study examined the distribution of
frog breeding in rain-fed wetlands following the first significant rain event after a period of severe drought (2002-
2009) in order to predict how frog communities may be affected in the future by changed climate. Tadpole
communities along with vegetation and water quality variables were described in 35 rain-fed wetlands across the
South West Slopes and Riverina bioregions of inland south-eastern Australia. In addition, weekly tadpole surveys
were conducted in a subset of these wetlands to describe temporal patterns of occupancy. Despite the protracted dry
period prior to this study 50% of the rain-fed wetlands surveyed contained tadpoles. However frog communities
were species poor with only five species recorded. The majority of wetlands were dominated be a single species,
Limnodynastes tasmaniensis which is also common within permanent waterbodies such as farm dams and irrigation
infrastructure in both bioregions. Tadpoles of two burrowing species Limnodynastes interioris and Neobatrachus
sudelli were restricted to a small number of wetlands mostly in the South West Slopes. The composition of tadpole
communities changed over time, and Crinia parinsignifera was the only species that continued to breed over winter.
The dominance of generalist species within rain-fed wetlands indicates that characteristics such as dispersal
capability, flexibility in breeding times and the ability to utilise created habitats may be more important than
burrowing ability and longevity when predicting vulnerability to climate change.
Key words: amphibians; tadpoles; rain-fed wetlands; climate change; drought
Rain-fed wetlands are of major economic and ecological importance, providing many benefits such as surface water
storage, floodwater protection, nutrient cycling and water quality maintenance. In addition these wetland ecosystems
provide vital habitat for unique biota in an otherwise dry environment where rainfall is highly variable (Jolly et al.,
2008). Temporary rain-fed wetlands support a wide range of species including non-vascular and vascular plants
(Casanova & Brock, 2000), microinvertebrates (Boix et al., 2001; Gleason et al., 2004) , macroinvertebrates (Lee
Foote & Rice Hornung, 2005) and amphibians (Homan et al., 2004; Trauth et al., 2006; Baldwin & deMaynadier,
Rain-fed wetlands are vulnerable to changes in rainfall and evaporation rates, including those driven by increases in
atmospheric CO2 and enhanced green house effect, because their hydrological regime is driven largely by local
weather patterns (Acreman et al., 2009; Brooks, 2009) . The impacts of climate change on rain-fed wetlands and
their dependent faunal communities are difficult to quantify due to the high level of uncertainty regarding future
changes to local weather patterns, particularly changes in precipitation. However, a number of climate models for
Australia predict a long-term shift to higher temperatures, increased evaporation rates and more extreme
hydrological events (Smith & Chandler, 2010). For example, the drought experienced between 2002 and 2009 may
have been more severe than previous drought events because reduced rainfall has also been accompanied by higher
temperatures and evapotranspiration rates (Murphy & Timbal, 2008).
Rain-fed wetlands provide important habitat for a range of native frogs (Williams, 1985; Beja & Alcazar, 2003;
Vignoli et al., 2007b; Babbitt et al., 2009; Gómez-Rodríguez et al., 2009). Unlike more persistent water bodies, rain-
fed wetlands are typically free of large predators, particularly fish, making them important breeding habitat for
species with predator-sensitive tadpoles (Gillespie & Hero, 1999; Adams, 2000; Baber & Babbitt, 2003; Goldingay,
2008). However, water level fluctuations result in variable physio-chemical conditions and frog species utilising
rain-fed wetlands must trade-off the reduced risk of predation with the increased risk of breeding failure due to
desiccation and declining water quality (Vignoli et al., 2007a; Gahl et al., 2009; Gómez-Rodríguez et al., 2009).
Life-cycle adaptations such as plastic developmental times and bet-hedging in tadpoles (Dziminski & Alford,
2005), burrowing and aestivation (Penman et al., 2004; Tracy et al., 2007; Kayes et al., 2009), and emigration under
adverse conditions (Wassens et al., 2008) are common characteristics of Australian frog species in temperate, semi-
arid and arid environments. Dispersal capability may be a critical factor influencing the ability of both burrowing
and non-burrowing species to recover following periods of drought because it enables them to rapidly recolonise
newly created rain-fed wetlands. The spatial distribution of permanent waterbodies and soil types suitable for
burrowing may also influence recolonisation of rain-fed wetlands (Mazerolle & Villard, 1999) although the latter
issue has received little attention.
Despite their many adaptations to the use of variable resources, amphibians that preferentially breed in rain-fed and
temporary pools are considered to be extremely sensitive to changes in temperature and precipitation occurring as a
result of climate change (Blaustein et al., 2010). While long-term shifts in precipitation are difficult to predict, a
number of recent studies have demonstrated the negative impact of severe drought on amphibian community
composition and breeding success (Rohr & Madison, 2003; Piha et al., 2007; McMenamin et al., 2008; Mac Nally et
al., 2009; Rohr & Raffel, 2010). Increased climatic variability and increased frequency of extreme weather events
can have a number of direct and indirect impacts on amphibian populations, including increased mortality during
extreme dry or extreme cold events (Blaustein et al., 2010), reduced breeding success and recruitment (Babbitt &
Tanner, 2000; Piha et al., 2007) and increased susceptibility to disease (Rohr & Raffel, 2010). It can however, be
difficult to separate the normal inter-annual variability in amphibian population dynamics and distributions from
potential long-term shifts caused by climate change. For example some population declines attributed to extreme
drought and climate change may have been a result of normal variability in occupancy patterns caused by
individuals retreating back to areas of core habitat during extended drought, only to recolonise formerly occupied
wetlands with a return to favourable conditions (Patla et al., 2009).
Much of our understanding of the impacts of climate change on amphibians in rain-fed waterbodies is derived from
studies in the northern hemisphere where vernal pools are important habitat for a wide range of species e.g.
(Blaustein et al., 2010; Blaustein et al., 2011). Knowledge of the importance of rain-fed wetlands for frogs in
Australian temperate and semi-arid regions is extremely limited making predictions on the impacts of future climate
change difficult. Frog communities in the dry temperate and semi-arid regions of south-eastern Australia are
typically species poor compared with the wetter temperate, tropical and monsoonal regions of Australia (Caughley
& Gall, 1985). The Riverina and South West Slopes Bioregions support 15 frog species, the majority of which occur
across a range of aquatic habitats including seasonally flooded wetlands associated with the Murrumbidgee River
system (Wassens, 2006). Only two species Notaden bennettii and Pseudophryne bibronii are considered to be rain-
fed wetland specialists and are active only after heavy rain (Cogger, 2000).
The use of rain–fed wetlands by resident frog species is primarily driven by the timing of filling and drying
(seasonality of rainfall) and the hydrological regime (duration of inundation, and the length time between filling
events). A large number of frog species have restricted activity periods which are often linked to temperature
(Carroll et al., 2009) and as a result tadpole communities within the same rain-fed wetland can vary considerably
between years depending on the timing of inundation (Paton & Crouch, 2002; Jakob et al., 2003). Those species
which follow specific breeding times may suffer more from altered seasonality of rainfall under climate change, than
those with long breeding periods or opportunistic breeding.
Tadpole development times are species specific and this is reflected in the hydroperiod of the wetlands that these
species inhabit. Species with rapid tadpole development times typically have a higher breeding success rate in
temporary waterbodies, while species with long development times may be excluded (Lane & Mahony, 2002;
Popescu & Gibbs, 2009). Tadpole mortalities due to desiccation are a common result of hydroperiods which fail to
extend over the given species complete developmental time frame (Williamson & Bull, 1999; Babbitt & Tanner,
2000; Brodman et al., 2003; Jakob et al., 2003). Predicted increases in potential evapotranspiration, especially
during summer may contribute to reduced hydroperiods within rain-fed wetlands and increased frequency of
recruitment failure due to tadpole desiccation.
The aims of this study were to:
1) identify which frog species utilise rain-fed wetlands after a period of severe and extended droughts and
2) describe temporal patterns of breeding activity by frogs within rain-fed wetlands in order to better
understand the impacts of potential shifts in the timing of significant rain events.
Study area
Regional scale surveys were conducted at a total of 35 rain-fed wetlands, located in the South West Slopes bioregion
(n=18) and in the Riverina bioregion centred on the Hay Plain (n=17) in south west New South Wales, Australia
(Figure 1). Vegetation of the South West Slopes is diverse, with the original vegetation dominated by open
woodlands containing white box (Eucalyptus albens, Benth), yellow box (E. melliodora, Cunn. ex Schauer) and
blakelys red gum (E. blakelyi, Maiden) the vast majority of which has been cleared. Black box (Eucalyptus
largiflorens, Muell) communities occur along intermittent creeks and wetlands and river red gum forests (E.
camaldulensis, Dehnh) occur close to permanent rivers and seasonally flooded wetlands in both bioregions. The
Riverina bioregion is a flat, largely treeless plain dominated by Atriplex communities and native grasslands. The
dominant land use is pastoral grazing and along with extensive areas of irrigated crop production.
Climate and rainfall patterns
The annual mean rainfall in the South West Slopes is 572 mm, summer temperatures are hot, averaging between 29
and 32 degrees Celsius and winter temperatures range from overnight minimums of three to daily maximums of 12
to 14 degrees Celsius (Bureau of Meteorology 2010). The climate in the Riverina is semi-arid (mean annual rainfall
365 mm), with very hot summers, mean maximum temperatures of 33 degrees Celsius, and cool winters (average
min. 3.5 to average max. of 15 degrees Celsius) (Bureau of Meteorology 2010). Rainfall is slightly winter dominant,
although high intensity summer thunderstorms of short duration are common during wetter years.
Inter-annual variability in precipitation is extremely high in both bioregions, between 1941 and 2010 the annual
precipitation ranged from 164.9 mm to 836.8 mm in the Riverina (variance 21094.9) measured at Hay and between
165.7 mm and 1019.2 mm in the South West Slopes (variance = 28345.1) measured at the nearby town of Wagga
Wagga (Bureau of Meteorology 2010). In both bioregions, 2002, 2006 and 2008 were in the top 12 driest years
between 1941 and 2010, while 2010 was the wettest year for that period in Wagga Wagga and the 4th wettest year in
Hay (Figure 2) (Bureau of Meteorology 2010).
As the distribution of rain-fed wetlands is poorly documented, air photos and consultation with property owners and
Murrumbidgee Catchment Management Authority staff were initially employed to identify potential wetlands for
investigation. In February 2010 a low pressure system brought significant rainfall to the Riverina and the South
West Slopes, this was followed by an inland trough in early March which brought a second significant rain event
(record highest rainfall in Wagga Wagga) to both regions (Bureau of Meteorology 2010) (Figure 3). Further
significant rain events occurred in May, July and August. All wetlands included in this study first filled in February
2010 with subsequent top-up falls in March and May after which time the smaller shallower wetlands dried out,
before refilling in June. Larger wetlands retained water throughout the study period for six to nine months. All
wetlands were dry during the severe drought conditions experienced through 2009.
Habitat parameters
Regional scale surveys of tadpole communities, vegetation characteristics and water quality were conducted
between the 15th and 31st of March 2010. In addition to regional scale surveys, repeat weekly sampling was
conducted at a subset of wetlands between the 31st of March and 10th of August, 2010. Wetland type and size were
classified according to (Semeniuk & Semeniuk, 1995) as Playa (n = 20)(intermittently flooded basin), Sumpland (n
= 7)(seasonally inundated basin) or Wadi (n = 8) (intermittently flooded channel). Wetlands fell into one of two
size classes, Leptoscale (n = 24) less than 100 x 100m, and mesoscale (n = 3) between 500 x 500m to 1000 x
1000m. Wadi channels were all classified as microscale (n = 8) less than 10m across and 100m long (Semeniuk &
Semeniuk, 1995).
Three replicate measures of water quality (turbidity, conductivity, pH, dissolved oxygen and temperature) were
taken on each survey occasion using a hand held YSI 6820 V2 multi-parameter sonde at approximately one metre
from the water’s edge. Vegetation was assessed by visual estimation of the proportion of microhabitats (fringing
vegetation, tall emergent vegetation, short emergent vegetation, submerged vegetation, floating vegetation and
timber within the water body) comprising five metre wide bank to bank sections of the wetland. Fringing vegetation
was considered to include all plant classes present within two meters of the shoreline, or where the there was an
abrupt change in vegetation communities from semi-aquatic and riparian vegetation to terrestrial grassland and
Atriplex communities. Tall emergent vegetation was classified as vegetation greater than 20 cm above the water
level (e.g. Typha sp.), whilst short emergent vegetation included sedges and short rushes less than 20 cm above the
water level. Submerged vegetation included all plant species present below the water surface, including vegetation
recently inundated due to rising water levels. Floating vegetation was any vegetation that floated on the water’s
surface and included both attached and free floating species.
Tadpole surveys
Tadpoles were surveyed using sweep nets, targeting the range of water depths and habitats within the wetland. This
is a common and effective technique for sampling tadpoles within rain-fed water bodies (Anstis, 2002). Sweeping
was conducted at each wetland for 20 minutes. Visual searches for tadpoles and metamorphs were also conducted by
walking the entire wetland perimeter, or in the case of larger systems, walking a 50 m transect. Tadpoles were
collected in a soft mesh sweep net ( mesh size 2 mm, 40 cm wide), and immediately transferred to a container where
they were identified to species, measured and their development stage described based on the extent of limb
development (Grosner, 1960) before being released at the point of capture.
Temporal occupancy patterns
Change in tadpole communities over time was assessed at a subset of five wetlands on 14 occasions (weekly), from
the 31st of March to the 10th of August, 2010. Wetlands were selected on the basis of their tadpole communities with
the aim of including all species likely to occur in both the South West Slopes and Riverina bioregion sites. In order
to conduct intensive surveys of wetlands on a weekly basis and to minimise potential variability in tadpole responses
caused by regional variation in temperature and rainfall, we aimed to select wetlands within a 15 km radius of one
another which contained all five species. Three key species, Crina parinsignifera Main, Litoria peronii Tschudi and
Neobatrachus sudelli Lamb, were restricted to a small number of wetlands in the South West Slopes, as a result
wetlands containing these three species formed the basis for our search area with the remaining wetlands selected
from within the 15 km radius that contained the more common and widespread species.
In order to limit potential confounding effects caused by land use disturbance, all wetlands were selected from
within nature reserves. Vegetation and water quality data were collected on each survey occasion, as described for
the broad-scale occupancy surveys, along with collection of additional tadpole data for body size. Tadpoles were
identified to species and stage of development via visual assessment (Anstis, 2002).
Data analysis
General Linear Models (GLMs) and Bonferroni post-hoc tests were employed to analyse univariate data using SPSS
(SPSS for Windows Release 17.0 SPSS Inc 2005). The mean values of temperature, salinity, turbidity, dissolved
oxygen, conductivity and pH were compared between regions and among wetland types. Differences in the
composition of tadpole communities between bioregions and between seasons, autumn (n = 7) and winter (n = 7)
(temporal occupancy patterns) were tested using Analysis of similarities (ANOSIM) with a Bray Curtis Similarity
matrix. Data were square-root transformed prior to analysis (Clarke & Warwick, 2001).
Two-tailed t-tests were used to compare the means for conductivity, pH, turbidity, percent cover of open water,
floating, submerged, fringing and short emergent vegetation, and total percent cover of aquatic vegetation, total
percent cover of aquatic vegetation for vacant and occupied wetlands from the broad-scale data.
Habitat parameters
Water quality was variable between regions and among wetlands, reflecting the wide geographic spread of wetlands
included in this study. Conductivity was high in playa wetlands (mean 1.088 mScm-1 SE 0.086) within the Riverina
compared to range of 0.054 to 0.426 mScm-1 for other wetland types resulting in significant differences among
wetland types (GLM F = 3.779, p = 0.039), however there was no significant difference in conductivity between
bioregions. In contrast pH differed significantly between bioregions, with mean pH significantly higher in the
Riverina (mean 10.20 SE 0.04) than in the South West Slopes (mean 8.38 SE 0.11) (GLM F = 15.711, p = 0.001).
Aquatic vegetation communities were variable across wetlands in both regions and there were no significant
differences in the structural diversity of aquatic vegetation, aquatic or fringing vegetation cover between bioregions
or among wetland types.
Broad scale patterns of tadpole occupancy
A total of 310 tadpoles of five species were collected from 17 of the 35 wetlands (49%) surveyed. The proportion of
wetlands containing tadpoles was similar across the two bioregions, seven out of 17 wetlands in the Riverina and
nine out of 18 wetlands in the South West Slopes contained tadpoles. Three species, Neobtrachus sudelli (n = 3),
Crinia parinsignifera (n = 2) and Litoria peronii (n = 1) occurred only in the South West Slopes (Figure 4). Of the
remaining two species Limnodynastes interioris Fry occurred in both bioregions but was rare (n = 4) while
Limnodynastes tasmaniensis Günther, was widespread and abundant in both the bioregions. Consequently, species
richness was on average higher in the South Western Slopes (0.94) than the Riverina (0.47) but this difference was
not significant (GLM; F = 1.680; P = 0.204). It was not possible to identify statistically significant differences in
community composition between the two bioregions due to lack of statistical power as the vast majority of wetlands
in both bioregions contained just one species (L. tasmaniensis) (ANOSIM; Global R= 0.011; P = 0.435).
As the majority of species were very rare, we were only able to analyse the relationship between presence/absence
and habitat and water quality variables for L. tasmaniensis. There were no significant relationships for mean water
quality and vegetation attributes measured in wetlands where L. tasmaniensis tadpoles were present and where they
were absent.
Temporal patterns in tadpole occupancy
Significant rain events occurred from the 13th and 16th of February (60mm) and the 6th to the 8th of March (164 mm),
the smallest of the five wetlands dried out in late may and was refilled in June (see Figure 3). Water temperature
decreased over time at the five weekly monitoring sites from a mean of 25oC in March to 10oC in late July and
August. While conductivity also decreased from a mean high of 0.099mScm-1 in March to a low of 0.062 mScm-1 in
August. The percent cover of aquatic vegetation also decreased over time mainly due to fluctuating water levels,
ranging from a mean of 37 % in March to 6% in August.
Tadpoles of five frog species (L. peronii, C. parinsignifera, L. interioris, N. sudelli and L. tasmaniensis) were
monitored over the duration of the study within the five wetlands. The tadpole communities differed significantly
between autumn and winter (ANOSIM Global R=0.278, p=0.01) and according to location (discrete wetlands)
(ANOSIM Global R= 0.683, p = 0.01). Tadpole communities in autumn were typically more diverse, with four
species, C. parinsignifera, N. sudelli, L. tasmaniensis and L. interioris present, while the winter tadpole
communities were generally dominated by C. parinsignifera (Figure 5).
Tadpole abundance for the majority of species declined over time with the exception of C. parinsignifera which
declined and then increased following winter rainfall. Neobatrachus sudelli was present for the shortest period of
time (no longer recorded after the 15th of May) and its abundance was initially high and steadily decreased over time
with late stage tadpoles ( grosner stages 37 and above) recorded in early May. Crinia parinsignifera was the only
species to undergo two breeding events, early stage tadpoles were recorded in March and April, with later stage
tadpoles (grosner stages 37 and above) were collected in mid-May. The site containing C. parinsignifera dried out
briefly and then refilled following significant rain events on 26 and 29 of May (26 and 20 mm respectively) (see
figure 4). Egg masses and very early stage tadpoles (stage 26) located from the 2nd of June through July, mid stage
tadpoles (grosner stages 32) (Grosner, 1960) were present when surveys ceased on the 10th August.
Tadpoles were relatively widespread in the rain-fed wetlands of both bioregions, but communities were species
poor. Only five of the 15 species known to occur in both bioregions were recorded within rain-fed wetlands in this
study (Wassens, 2006). The vast majority of wetlands contained only one species, the habitat generalist
Limnodynastes tasmaniensis. Despite the lower survey effort in this study, tadpoles occurred at a far higher
proportion of wetlands than reported by McNally et al (2009) in their study in south-eastern Victoria. This probably
reflects the different focus of that study on more persistent waterbodies which were present during the drought
period in 2006 and 2007.
Wetlands are subject to a wide range of disturbances and threatening processes including draining, damming,
grazing and cultivation (Finlayson & Rea, 1999). The spatial context of rain-fed wetlands has also been altered
within agricultural landscapes with dams and canals increasing the availability of permanent habitats, while the
availability of temporary waterbodies has decreased (Brock et al., 1999). These shifts in habitat availability have
undoubtedly altered frog communities (e.g McNally et al 2009), with a potential shift towards generalist species
capable of utilising more persistent waterbodies as well as the opportunistic use of rain-fed waterbodies when they
are available.
The results of this study suggest that dispersive generalist frog species, rather than burrowing frog species tend to
dominate rain-fed wetlands in modified agricultural landscapes after periods of extended drought. Limnodynastes
tasmaniensis has a number of adaptations that make it highly suited to the opportunistic use of rain-fed wetlands, it
has comparably good dispersal ability (Schauble, 2004 ), and utilises a wide range of aquatic habitats including
farm dams (Hazell et al., 2001) and irrigation infrastructure (Wassens, 2006) which provide a more constant source
of water during drought periods. Studies of other vertebrate taxa consider dispersal ability to be a critical factor in
determining the risk from climate change, however this typically relates to large scale movements which reflect
range shifts (Pearson & Dawson, 2003; Thomas et al., 2004). At local scales dispersal ability may be a key factor
influencing the ability of aquatic and semi-aquatic fauna to recover from severe climate perturbations such as
drought because it influences their ability to seek out permanent refuge sites and recolonise waterbodies following
local extinctions (Harrison, 1994; Smith & Green, 2005).
Burrowing ability is a specific adaptation of frogs to variable rainfall and allows individuals to persist for extended
dry periods (Tracy et al., 2007; Kayes et al., 2009). On this basis burrowing ability might be seen as lowering the
susceptibility of species to future climate changes, with large-bodied, long-lived species such as Limnodynastes
interioris being comparatively resilient to drought compared to the shorter lived, non-burrowing species. However
there have been few studies on the actual capacity of these species to aestivate for extended periods. Many
burrowing species are active throughout the year, but this activity is closely linked to meteorological conditions,
particularly rain and humidity (Penman et al., 2004). Extended drought may limit the ability of these species to
forage and this, along with their requirement for wetlands with extended hydroperiods to support breeding, may
explain their rarity in rain-fed wetlands in the drier Riverina bioregion. Non-cocoon forming species such as L.
interioris may also burrow deeper during extended dry periods in order to maintain moisture balance (Thompson et
al., 2005) and retreating water tables or increased groundwater salinity could potentially limit the survival of these
species during periods of extended drought.
Weekly monitoring of tadpole communities within selected wetlands was used in this study to assess change in
tadpole communities over time. This study was conducted outside the reported core calling periods of L.
tasmaniensis (Lemckert & Mahony, 2008) but despite this, tadpoles of this species were abundant, which
demonstrates the ability of this species to respond to unusual weather conditions. Crinia parinsignifera was the only
species able to respond to winter rain events and underwent two distinct breeding events between March and
August. This high level of flexibility and rapid breeding times may increase the resilience of this species to changes
in the seasonality of rain events. Studies conducted in the Northern Hemisphere have reported on changes in
breeding phenology, including earlier calling times in response to increased spring temperatures (Neveu, 2009;
Blaustein et al., 2010; Todd et al., 2010). These studies focused on areas where the availability of wetland habitat
was unchanged but where changes in temperature altered breeding cues. Assessing the impacts of altered rainfall
patterns on frog breeding is more complex because both the temporal patterns of habitat availability, and the
temperature driven breeding cues are altered. For frogs to respond to a rain event it must occur within their activity
window and for tadpoles to successfully develop, wetlands must retain water for a sufficient period of time. Shifts
towards summer dominated rainfall may allow breeding for many species but higher temperature and evaporation
rates may reduce wetland hydroperiod excluding those species with longer and less flexible development times, such
as Limnodynastes interioris.
Marked inter-annual variation in rainfall, wetland hydrology and subsequent variability in frog breeding and
community composition has also been widely reported for rain-fed wetlands systems (Jakob et al., 2003; Piha et al.,
2007; Gómez-Rodríguez et al., 2009). This high level of variability presents a significant challenge for predicting
impacts of future climate change on frogs within rain-fed wetland systems. In this respect predictive models that
consider species distributions with respect to climate variability, for example variability in the duration of wet-dry
periods, may be more informative when predicting the impacts of climate change on species in variable landscapes
than models based on temperature shifts alone. The long-term study of frog communities in rain-fed wetlands and
better assessment of their hydrological requirements and distributions will also greatly assist our understanding of
population processes in systems that already have a high level of inter-annual variability.
David Read (Wagga Wagga City Council) and Dr Patricia Murray (Murrumbidgee Catchment Management
Authority) greatly assisted in the identification and selection of survey wetlands. Two anonymous reviewers
provided valuable advice which greatly improved the quality of this paper. Vanessa Griese and Sarah Cordell
assisted with data collection. We thank land holders for giving us access to study sites on their property. This
research was conducted under a NSW National Parks and Wildlife Service Licence (S12393). Ethics approval was
granted by Charles Sturt University Animal Care and Ethics Committee (10/042).
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List of figures
Figure 1. Location of rain-fed wetland study sites within the Riverina (Riv) and South West Slopes (SWS).
Figure 2. Annual precipitation over a 50 year period (1940-2010) in the Riverina at Hay (75031) and South West
Slopes at Wagga Wagga (72150). Reference line shows median precipitation for the same period. Source:
Commonwealth Bureau of Meteorology 2010.
Figure 3. Total monthly rainfall (mm) and mean daily air temperature recorded at 3pm at Wagga Wagga (72150)
and Hay (75031) between February 1st 2010 and August 31st 2010. Source: Commonwealth Bureau of Meteorology
Figure 4. Proportion of wetlands occupied by tadpoles in the Riverina and South West Slopes for surveys conducted
between the 15th and 31st of March
Figure 5. Temporal changes in tadpole numbers of each species between March 31st and August 10th 2010 at five
wetlands within the South West Slopes near Wagga Wagga.
0 100 200 30050 Km
Wagga Wagga
Figure 1. Location of rain-fed wetland study sites within the Riverina (RIV) and South West Slopes (SWS).
Figure 2. Annual precipitation from1940-2010in the Riverina at Hay (75031) and South West Slopes at Wagga
Wagga (72150). Reference line shows median precipitation for the same period. Source Commonwealth Bureau of
Figure 4. Proportion of wetlands occupied by tadpoles in the Riverina and South West Slopes.
Figure 5. Temporal changes in tadpole numbers of each species between March 31st and August 10th 2010 at five
wetlands within the South West Slopes near Wagga Wagga.
... In some cases availability of water habitats has been linked to concerns regarding climate change. Wassens, Walcott, Wilson, and Freire (2013) discuss the availability of rain-fed wetlands for frogs in inland Australia after a period of extreme drought. Other studies have been focussed on the availability of water in landscapes where the water supply is largely regulated both for individual species (e.g. ...
... Heard et al., 2004;Popescu et al., 2013). Hydroperiod and water availability have also been found to influence frog occupancy (Otto, Forester, & Snodgrass, 2007;Wassens & Maher, 2011;Wassens, Walcott, Wilson, & Freire, 2013). Waterbody size and water depth have also been considered important factors (Hunter et al., 2009;Welch & MacMahon, 2005). ...
... It was observed that in periods of heavy rain, when these areas were flooded, Sloane's Froglets actively called from them, however the period of time that these areas retained water has not been ascertained; and the duration of Sloane's Froglet stay in them and their use of these areas have not been studied. These areas may be analogous with the rain-fed wetlands examined by Wassens et al. (2013) in their recent study of tadpole response to rainfall events. Shallow ephemeral overflows may also exhibit similarities with the well-studied vernal ponds of the northern hemisphere (Calhoun, (Hazell et al., 2001, p. 69). ...
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Sloane’s Froglet, Crinia sloanei, is a threatened and little-known frog with a historical distribution in the Australian states of New South Wales (NSW) and Victoria (Vic). I investigated Sloane’s Froglet distribution and habitat (chapters 2, 3 and 4). As my intention was for the ecological knowledge generated to be applied, I undertook a transdisciplinary case study approach, and used social research methods to explore knowledge exchange between researchers and practitioners, and advocacy (chapters 5 and 6). I discuss the research approach in Chapter 7. I undertook distribution studies from 2010 to 2013 and established the presence of an important extant population of Sloane’s Froglet in southern NSW and northern Vic, within a highly modified landscape that is quickly becoming more densely settled by humans. I investigated the habitat characteristics of waterbodies occupied by Sloane’s Froglet in winter, its peak breeding period, by comparing the physical and vegetation characteristics of 54 occupied and 40 unoccupied waterbodies. I determined a core calling period for Sloane’s Froglet and detection probabilities for the surveys undertaken. Sloane’s Froglet occupied both constructed and “natural” waterbodies with a variety of features, including differing hydroperiods and surrounding landuse. The waterbodies that Sloane’s Froglet occupied differed from unoccupied waterbodies by containing a greater percent cover of small stem-diameter emergent vegetation; often connecting with adjacent ephemeral shallow overflows; having gently sloping banks; and less bare ground on the banks within two metres of the waterbody. I explored the microhabitat and relative spatial positioning of Sloane’s Froglet within waterbodies by comparing the characteristics of 54 sites around individual male Sloane’s Froglet with 57 randomly selected unoccupied sites. Sloane’s Froglets were found to always call from within the waterbody rather than on the bank, distinguishing them from other sympatric Crinia species. Sloane’s Froglets occurred at sites with less of the site above the water level, and at significantly shallower water depths, than unoccupied sites. Sloane’s Froglets were closer to other Sloane’s Froglets and other calling male frogs at occupied sites, suggesting clustering behaviours. Recommendations for applying this knowledge to benefit Sloane’s Froglet are included in chapters 2 to 4. I used an autoethnographical approach to describe the advocacy I undertook during the research process and to reflect on knowledge exchange between me as a researcher-advocate, environmental practitioners and the broader community. I further investigated the constraints and enablers of knowledge sharing and utilisation by exploring the insights of 11 environmental practitioners whose work can benefit water-dependent biodiversity. Exploration of the semi-structured interviews suggests that exchange and utilisation of new knowledge is impacted by: how knowledge and knowledge sharing processes are perceived; the media for knowledge communication; continual learning and adaptive management; personal values and the role of advocacy; and, external filters such as political will and institutional processes. The transdisciplinary case study results suggest that my applied research will not be utilised without an advocative approach, preferably with the support of an influential person and validation of an established organisation. In addition, a collaborative research approach or the coproduction of knowledge with practitioners will enable the management application of the ecological research. In Chapter 7 I present a framework that I call “intentional ecology” based in conservation biology, systems and contemporary feminist theories to support the transdisciplinary and applied research approach. Intentional ecology provides a platform for the use of multiple methodologies and an imperative for action in which knowledge exchange and advocacy are understood as implicit to ecological research with management implications.
... Studies of wildlife responses to drought are uncommon but increasingly needed because research suggests that population-level effects can be substantial, especially in arid and semi-arid regions and when combined with other stressors such as habitat fragmentation, non-native predators, or disease (Vicente-Serrano et al., 2020). Ecological drought is a concern for many amphibians because of their dependence on surface water and certain environmental characteristics associated with wetland and riparian habitats (Fellers and Drost, 1993;Clemann et al., 2013;Walls et al., 2013;Wassens et al., 2013;Ryan et al., 2014;Ray et al., 2016;Hossack et al., 2017;MacNally et al., 2017;Zylstra et al., 2019). For example, most amphibians in arid environments breed in intermittent pools or chains of ponds that form along streambeds after spring spates or when snow melt subsides (Hazell et al., 2003) wetlands that are less likely to fill and more likely to dry quickly during drought years. ...
... Thus, frog recruitment rates responded to pond excavation more strongly than changes in NDVI at this particular location. The diversity of responses observed highlights the complexity of demographic responses to drought given environmental conditions (e.g., habitat) and context (Wassens et al., 2013;Cayuela et al., 2016). Some of this variability could be related to changes in prey availability (i.e., arthropods) and predators (e.g., garter snakes [Thamnophis sirtalis]), neither of which were assessed in this study. ...
Increasing frequency and severity of droughts have motivated natural resource managers to mitigate harmful ecological and hydrological effects of drought, but drought mitigation is an emerging science and evaluating its effectiveness is difficult. We examined ecohydrological responses of drought mitigation actions aimed at conserving populations of the Columbia spotted frog (Rana luteiventris) in a semi-arid valley in Nevada, USA. Abundance of this rare frog had declined precipitously after multiple droughts. Mitigation included excavating ponds to increase available surface water and installing earthen dams to raise water tables. We assessed responses of riparian vegetation to mitigation using a 30-year time series of satellite-derived Normalized Difference Vegetation Index (NDVI) and gridded weather data. We then analyzed a 23-year mark-recapture dataset to evaluate the effects of drought mitigation and NDVI on the probability of frog survival and rates of recruitment. After accounting for interannual precipitation variability, we found that NDVI increased significantly from before to after drought mitigation, suggesting that mitigation influenced the hydrology and vegetation of the meadows. Frog survival increased with NDVI, but mitigation had a stronger effect than NDVI suggesting that excavated mitigation ponds were particularly important for frog survival during drought. In contrast, frog recruitment was associated with NDVI more than mitigation, but only in meadows where NDVI was dependent on precipitation. At meadows with available groundwater, recruitment was associated with mitigation ponds. These findings suggest that mitigation ponds are critical for juvenile frogs to recruit into the adult population, but recruitment can also be increased by raising water tables in meadows lacking groundwater sources. Lagged recruitment (i.e., effects on larvae and juveniles) was negatively associated with NDVI. This study illustrates the ecohydrological complexity of drought mitigation and demonstrates novel ways to assess the effectiveness of drought mitigation using time series of readily available satellite imagery and organismal data.
... Similarly, droughts usually precede wildfire events and can reduce the availability of suitable breeding habitat and refuges which can lead to reductions in amphibian populations and communities before the passing of a wildfire Cayuela et al., 2016;Wassens et al., 2013). ...
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Aim Changes to the extent and severity of wildfires driven by anthropogenic climate change are predicted to have compounding negative consequences for ecological communities. While there is evidence that severe weather events like drought impact amphibian communities, the effects of wildfire on such communities are not well understood. The impact of wildfire on amphibian communities and species is likely to vary, owing to the diversity of their life‐history traits. However, no previous research has identified commonalities among the amphibians at most risk from wildfire, limiting conservation initiatives in the aftermath of severe wildfire. We aimed to investigate the impacts of the unprecedented 2019–2020 black summer bushfires on Australian forest amphibian communities. Location Eastern coast of New South Wales, Australia. Methods We conducted visual encounter surveys and passive acoustic monitoring across 411 sites within two regions, one in northeast and one in southeast New South Wales. We used fire severity and extent mapping in two multispecies occupancy models to assess the impacts of fire on 35 forest amphibian species. Results We demonstrate a negative influence of severe fire extent on metacommunity occupancy and species richness in the south with weaker effects in the north—reflective of the less severe fires that occurred in this region. Both threatened and common species were impacted by severe wildfire extent. Occupancy of burrowing species and rain forest specialists had mostly negative relationships with severe wildfire extent, while arboreal amphibians had neutral relationships. Main Conclusion Metacommunity monitoring and adaptive conservation strategies are needed to account for common species after severe climatic events. Ecological, morphological and life‐history variation drives the susceptibility of amphibians to wildfires. We document the first evidence of climate change‐driven wildfires impacting temperate forest amphibian communities across a broad geographic area, which raises serious concern for the persistence of amphibians under an increasingly fire‐prone climate.
... In contrast to our initial prediction, total frog abundance was not a significant factor in explaining Ngabi detection patterns, a result consistent with Shelton et al. (2020), who also found habitat use by the pale-headed snake (Hoplocephalus bitorquatus) was not influenced by frog abundance. Our findings may be due to the ubiquitous distribution and abundance of the most common frog species in this system (Wassens et al. 2013;Littlefair et al. 2021), spotted marsh frog (Limnodynastes tasmaniensis) and barking marsh frog (L. fletcheri), and due to homogeneous distribution in frog abundance between our sites. ...
... The impacts of drought can be influenced by habitat characteristics and species-dependant responses (Scheele et al. 2012, Clemann et al. 2013, Hossack et al. 2013, Anderson et al. 2015, Zylstra et al. 2019. Drought and heatwaves lead to a net-reduction in amphibian diversity due to local extinction of drought intolerant species and persistence of pre-adapted species (Blaustein et al. 2010, Wassens et al. 2013. Heatwaves can rapidly dry ephemeral wetlands, which can result in mass mortality of tadpoles (Amburgey et al. 2012) and lead to population decline due to lack of recruitment (Weinbach et al. 2018, Swartz et al. 2019). ...
Full-text available
Biodiversity is in global decline during the Anthropocene. Declines have been caused by multiple factors, such as habitat removal, invasive species, and disease, which are often targets for conservation management. However, conservation interventions are under threat from climate change induced weather extremes. Weather extremes are becoming more frequent and devastating and an example of this was the 2019/2020 Australian drought and mega-fires. We provide a case study the impacts of these extreme weather events had on a population of the threatened frog Litoria aurea that occurs in a constructed habitat which was designed to reduce the impact of introduced fish and chytrid-induced disease. We aimed to determine what factors influenced persistence so that the design of wetlands can be further optimised to future-proof threatened amphibians. We achieved this with 4 years (2016–2020) of intensive capture–recapture surveys during austral spring and summer across nine wetlands ( n = 94 repeat surveys). As hypothesized, drought caused a sharp reduction in population size, but persistence was achieved. The most parsimonious predictor of survival was an interaction between maximum air temperature and rainfall, indicating that weather extremes likely caused the decline. Survival was positively correlated with wetland vegetation coverage, positing this is an important feature to target to enhance resilience in wetland restoration programs. Additionally, the benefits obtained from measures to reduce chytrid prevalence were not compromised during drought, as there was a positive correlation between salinity and survival. We emphasize that many species may not be able to persist under worse extreme weather scenarios. Despite the potential for habitat augmentation to buffer effects of extreme weather, global action on climate change is needed to reduce extinction risk.
... Depending on the targeted amphibian species and study site, the effects of earlier onset of breeding phenology on survival and population abundance can be positive or negativefor example a longer snow-free season can be favorable for growth, reproduction and resource acquisition in energy-limited mountain environments (Carey and Alexander, 2003;McCaffery and Maxell, 2010). It can also be negative (Reading, 2007;Tomaševic et al., 2007;Blaustein et al., 2010;Todd et al., 2010;Garner et al., 2011;Wassens et al., 2013;Carter et al., 2018;Fitzpatrick et al., 2020), for instance if earlier breeding phenology increases the risk of exposure of embryos to cold air temperatures or drought (Loman, 2009;Benard, 2015). Hence, with the documented earlier onset of snowmelt occurring in response to warmer winter and spring temperatures in documented in the European Alps (Beniston, 2012;Hall et al., 2015;Klein et al., 2016), surface pond embryos may be exposed to a greater risk of frost, which in turn would influence embryonic survival (Beattie, 1987;Frisbie et al., 2000;Muir et al., 2014) and population dynamics. ...
Full-text available
The alarming decline of amphibians around the world calls for complementary studies to better understand their responses to climate change. In mountain environments, water resources linked to snowmelt play a major role in allowing amphibians to complete tadpole metamorphosis. As snow cover duration has significantly decreased since the 1970s, amphibian populations could be strongly impacted by climate warming, and even more in high elevation sites where air temperatures are increasing at a higher rate than at low elevation. In this context, we investigated common frog ( Rana temporaria ) breeding phenology at two different elevations and explored the threats that this species faces in a climate change context. Our objectives were to understand how environmental variables influence the timing of breeding phenology of the common frog, and explore the threats that amphibians face in the context of climate change in mountain areas. To address these questions, we collected 11 years (2009–2019) of data on egg-spawning date, tadpole development stages, snowmelt date, air temperature, rainfall and drying up of wetland pools at ∼1,300 and ∼1,900 m a.s.l. in the French Alps. We found an advancement of the egg-spawning date and snowmelt date at low elevation but a delay at high elevations for both variables. Our results demonstrated a strong positive relationship between egg-spawning date and snowmelt date at both elevations. We also observed that the risk of frost exposure increased faster at high elevation as egg-spawning date advanced than at low elevation, and that drying up of wetland pools led to tadpole mortality at the high elevation site. Within the context of climate change, egg-spawning date is expected to happen earlier in the future and eggs and tadpoles of common frogs may face higher risk of frost exposure, while wetland drying may lead to higher larval mortality. However, population dynamics studies are needed to test these hypotheses and to assess impacts at the population level. Our results highlight climate-related threats to common frog populations in mountain environments, but additional research should be conducted to forecast how climate change may benefit or harm amphibian populations, and inform conservation and land management plans in the future.
... They provide roosting and nesting habitat for waterbirds, with each species requiring specific depth and duration of inundation beneath nests if successful fledging is to occur (Arthur et al., 2012;Rogers and Ralph, 2011;Wakeley et al., 2007). Overbank flows fill floodplain depressions (cut-off meanders), subsequently utilised by frogs, turtles and some species of fish (Chessman, 2011;Wassens et al., 2013). Groundwater is recharged as water flows over and percolates into porous soils (Cendón et al., 2010;Doble et al., 2012), important in the maintenance of vegetation condition during extended drought (Doody et al., 2014;Overton et al., 2006). ...
The ephemeral inundation of floodplains in semi-arid and arid zone climates is an essential driver of biological productivity. Natural biota depend on floodplain inundation to support critical reproductive life phases. In historical times, grazing industries have developed taking advantage of phases of high productivity associated with the overbank flow. However, the modelling of inundation in lowland floodplains is challenged by the complexity of topographic and hydrodynamic constraints. Here we apply a spatially explicit fine-scale inundation model to compare floodplain inundation regimes associated with current hydrological development on the Darling River floodplain, Australia, and pre-development, conceptualised as the removal of hydrological control structures. Our results suggest that hydrological developments in the Darling River catchment have substantially increased inter-flood period, an effect particularly pronounced during dry climatic phases. The result explains the decline in waterbird utilisation in this section of the Darling River, the low resilience of outer floodplain vegetation to the recent drought, and the reduction in grazing capacity. Water resource development had less impact on large inundation events.
... However, the patterns of occurrence and the use of space by anuran larvae result from a complex interaction between biotic factors, such as competition, predation and the presence of aquatic vegetation (Morin 1983, Hecnar & M'Closkey 1997, Strauß et al. 2013, Johnson et al. 2015, and abiotic factors, such as rainfall distribution, humidity and temperature, in addition to physicochemical characteristics (e.g. pH, dissolved oxygen, salinity) (Aichinger 1987, Degani & Kaplan 1999, Bernabò et al. 2013, Wassens et al. 2013. Potentially competing tadpoles can directly affect the growth, maximum metamorphosis size, and larval length of other amphibians, as they capture environmental resources more efficiently (Petranka 1989, Cabrera-Guzmán et al. 2013; however, the presence of aquatic vegetation favors survival, as it provides refuges against predators (Babbitt & Jordan 1996, Kopp et al. 2006. ...
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Microhabitat choice by tadpoles is related to several physical or biological characteristics, and variations in these factors have a direct influence on their distribution and abundance at different scales (e.g. time, space). Our work sought to investigate how Pithecopus nordestinus tadpoles use water bodies at a Caatinga site and quantify how biotic and abiotic variables affects the occurrence of this tadpole species. We developed the study in the Protected Area Monumento Natural Grota do Angico/Sergipe, from December 2009 to November 2010 and collected samples (408 plots) using a "throw trap". In addition to the tadpoles collected in the plots, we quantified five variables (competitors, percentage of emergent and aquatic vegetation, predators and depth) and acquired variation of some data throughout the year (size, maximum depth and hydroperiod) for each water bodies. Tadpoles were found in lentic water bodies that fit their habits and that were also suitable for mating by their adult relates. Most of the studied environments maintained water throughout the period of the study, with P. nordestinus tadpoles being present from April to October, with abundance peak both in July and May. The absence of P. nordestinus tadpoles from February to March may allow the establishment of other species during this period, minimizing the competition between them. The larvae of P. nordestinus showed an aggregate distribution (Id > 1) in most of the water bodies throughout the year, which may reduce the predation. This could explain the positive relation that was found between the tadpole abundance and the predator's presence. The aggregations were not intensified by the reduction of water bodies as the drought progressed. Among the ecological variables, the presence of competitors (other tadpoles) and the percentage of emergent and aquatic vegetation did not favor tadpole abundance. Interspecific competition can drastically reduce the amount of resources and damage metamorphosis in periods when there is still water regularity in the environments. Branching and abundant vegetation can damage the habit of P. nordestinus tadpoles, which are nektonic suspension-raspers, requiring that this portion of the space is unoccupied.
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Globally, river regulation has degraded wetlands, including parts of the Murray-Darling Basin (MDB), an ecologically significant basin in Australia. Frogs in a floodplain environment largely depend on habitats created by river flows, but little is known about how frogs in the northern MDB are impacted by river regulation. We tested how wetland inundation affected frogs in a catchment of the northern MDB. We surveyed frogs between 2015 and 2019 to determine long-term changes in the community composition associated with wetland inun-dation from river flows. Additionally, we recorded nightly soundscapes for four days before and after the arrival of river flows between 2019 and 2020. The abundance and richness of frog species increased during larger inundation events leading to altered community composition (beta diversity). Warmer temperatures increased frog species richness, and frog community dominance decreased with decreasing vegetation cover (i.e., the relative abundance became more even across species). The abundance of five frog species (Limnodynastes tas-maniensis, Limnodynastes fletcheri, Crinia parinsignifera, Litoria peronii, and Litoria latopalmata) was higher in response to increased inundation extent. The total species richness of chorusing frogs increased after the arrival of river flows; six species chorused over the four nights preceding flow, whereas eight species chorused following the flow arrival, but the responses varied among species and sites. Frog species richness increased at three sites after flows, but not at others. After inundation, the choruses of Limnodynastes tasmaniensis increased whereas Limnodynastes fletcheri decreased. Our findings indicate that wetland inundation is beneficial for frog communities and suggest that chorusing behaviour varied in response to river flows inundating floodplain wetlands.
The Andalusian International University held a workshop entitled Temporary wetlands’ future in drylands under the projected global change scenario in March 2020 in Baeza, Spain, with 26 participants from 10 countries. The workshop objectives were to promote international cooperation and scientific exchange on the conservation and protection of temporary wetlands. The participants highlighted the extreme conditions that temporary and permanent wetlands, ponds, and shallow lakes are currently facing and predicted a dismal future for these systems due to climate change. To foster a holistic view of these ecosystems, the workshop included wetland watersheds. It was concluded that the main threats are those affecting water quality and quantity as well as egg-seed banks, species population dynamics, and food webs. The inherent characteristics of waterbodies in drylands, including high resilience and resistance to harsh conditions, are already negatively impacted by direct human actions and climate change. Another threat is the time lag between scientific warnings about threats and the social and political concern leading to mitigating actions. Thus, more effective actions to protect and conserve temporary wetlands are essential. Research networks could help stimulate the necessary conservation actions, but the global recession due to the COVID-19 pandemic will pose a challenge as economies are burdened with urgent expenditure.
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In many temporary wetlands such as those on the Northern Tablelands of New South Wales Australia, the develop-ment of plant communities is largely the result of germination and establishment from a long-lived, dormant seed bank, and vegetative propagules that survive drought. In these wetlands the pattern of plant zonation can differ from year to year and season to season, and depth is not always a good indicator of the plant community composition in different zones. In order to determine which aspects of water regime (depth, duration or frequency of flooding) were important in the development of plant communities an experiment using seed bank material from two wetlands was undertaken over a 16 week period in late spring–early summer 1995–1996. Seed bank samples were exposed to 17 different water-level treatments with different depths, durations and frequencies of flooding. Species richness and biomass of the communities that established from the seed bank were assessed at the end of the experiment and the data were examined to determine which aspects of water regime were important in the development of the different communities. It was found that depth, duration and frequency of inundation influenced plant community composition, but depth was least important, and also that the duration of individual flooding events was important in segregating the plant communities. Species were grouped according to their ability to tolerate or respond to fluctuations in flooding and drying. The highest biomass and species richness developed in pots that were never flooded. Least biomass and species richness developed in pots that were continuously flooded. Short frequent floods promoted high species richness and biomass especially of Amphibious fluctuation-tolerator species and Amphibious fluctuation-responder species that have heterophylly. Terrestrial species were able to establish during dry phases between short floods. Depth was important in determining whether Amphibious fluctuation-tolerator or Amphibious fluctuation-responder species had greater biomass. Longer durations of flooding lowered species richness and the biomass of terrestrial species. Experiments of this kind can assist in predicting vegetation response to water-level variation in natural and modified wetlands.
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We used records of calling male frogs to quantitatively assess the calling patterns of the frogs found in mesic, eastern New South Wales, Australia. We obtained 17,461 calling records for 67 species and determined the core calling months for 46 species. Forty-three species have clearly defined core calling periods in which > 90% of calling records fall, all of which are based around the warmer spring-summer months. We consider two species to be essentially year- round callers. Increasing latitude usually, but not always, leads to a small reduction in the core calling period. This information can be used to better target the timing of surveys, improving opportunities for research, management, and conservation.
An increasing proportion of ecological studies examine landscape effects on the phenomena they address. We reviewed studies which simultaneously considered landscape-scale and patch-scale effects in order to answer the following question: does the inclusion of landscape characteristics as explanatory variables increase our ability to predict species presence and abundance when local (i.e., habitat patch) conditions are known? The 61 studies selected cover a wide array of taxa, landscape types, and explanatory variables, but many (36%) focused on avian communities in forests fragmented by agriculture. Patch-scale variables (e.g., habitat characteristics) had a significant effect on invertebrates, amphibians, reptiles, birds, and mammals in all landscape types. Landscape-scale characteristics (e.g., area of suitable habitat within a certain radius of a patch) also were significant predictors of species presence and abundance for vertebrates, but not for the majority of invertebrates in the studies we reviewed. Thus, our results indicate that both patch and landscape characteristics should be included in models investigating the distribution and abundance of animals, at least for vertebrates. However, distinguishing between local (or patch) and landscape scales for particular taxa is often problematic. Analyzing movements of individuals and their influence on larger-scale population dynamics could potentially solve this dilemma, but other approaches, such as the analysis of context effects using nested sampling grids covering several different spatial scales may represent a more practical alternative. Results from this review suggest that the inclusion of landscape characteristics will enhance conservation strategies if the landscape scale is properly defined with respect to the taxon or taxa under investigation.
A primary threat to amphibians in North America is the loss of wetland areas used for reproduction, especially small, temporary, and isolated wetlands. The Illinois chorus frog (Pseudacris streckeri illinoensis) is particularly vulnerable and exists today in a highly fragmented distribution limited to a few isolated populations in Arkansas, Illinois, and Missouri. Precision land-leveling combined with seasonal drought conditions has resulted in a significant population decline and range contraction for this species in Arkansas. Distributional surveys conducted from 1987 through 2004 indicate a 61% range contraction from a maximum of 59 km² to a current range of approximately 23 km². Additionally, there has been a lack of recruitment the past 2 years for a species that typically possesses a 2–3-year lifespan. Because the Clean Water Act will only protect isolated vernal pools if the continued existence of a threatened or endangered species is jeopardized, the future of this subspecies of chorus frog in Arkansas is both tenuous and problematic. In the absence of immediate protection and habitat modification through the reintroduction of depressions, we argue extirpation of this species in Arkansas may be imminent. The increasing use of precision land-leveling may have implications for other amphibian species worldwide.
We examined larval anuran assemblages at 12 temporary wetlands occurring on the MacArthur Agro-Ecology Research center (MAERC) in southcentral Florida. MAERC is an active cattle ranch, and the wetlands on the site are heavily influenced by an extensive series of ditches that drain the landscape. Ditching has resulted in a change from a historically extensive marsh system to a series of isolated wetlands surrounded by upland habitats. Because a majority of anurans in Florida breed exclusively or facultatively in wetlands whose drying regime excludes fish, we were interested in determining the value of these modified wetlands as breeding sites. We examined the effect of wetland size and hydrology on anuran use, and compared breeding activity across three summers that varied greatly in rainfall pattern. We sampled tadpoles from May 93 to August 93 and from May 94 to September 95. A total of 3678 tadpoles from 11 species was collected. Rana utricularia was the most abundant species and the only species found in every wetland Species richness was related positively to wetland size (r=0.65, p=0.023) but not hydroperiod (r=0.03, p=0.93). Tadpole abundance was not related to wetland size (r=0.35, p=0.29) nor hydroperiod (r=0.40, p=0.22). Annual variation in rainfall resulted in significant changes in species composition. A drought during 1993 resulted in no breeding. A high water table in the spring of 1995 resulted in localized flooding in early summer on part of the ranch. Wetlands in these areas were exposed to spillover of water from ditches containing fishes. Wetlands so impacted showed significant changes in species composition from the previous year (x2=1008, p < 0.0001), whereas wetlands that were not impacted did not differ in composition. The wetlands at MAERC provide dynamic habitats that offer varying breeding opportunities that are highly dependent on meteorological conditions.
Riverine forests had fewest species of reptiles and frogs. The other forests divided into eastern, central and western zones on the basis of faunal composition, the change on an E-W gradient marking the transition from coastal and montane (Bassian) fauna to inland (Eyrean) fauna. Over 75% of the recorded species reach their geographic limits within the slopes. The transition lies in the centre of the region and the fauna there was depauperate. Western forests were also depauperate, containing only 50% of the Eyrean fauna known to occur in the region and <25% of species found 200 km further west. The forests of the region serve principally to maintain the range of species. Most are of sufficient size to conserve the majority of their component herpetofauna, the exceptions being small western forests (c300 ha) surrounded by agriculture. -from Authors
In many permanent ponds throughout western North America, the introduc- tion of a variety of exotic fish and bullfrogs (Rana catesbeiana) correlates with declines in native amphibians. Direct effects of exotics are suspected to be responsible for the rarity of some native amphibians and are one hypothesis to explain the prevalence of amphibian declines in western North America. However, the prediction that the permanent ponds occupied by exotics would be suitable for native amphibians if exotics were absent has not been tested. I used a series of enclosure experiments to test whether survival of northern red-legged frog (Rana aurora aurora) and Pacific treefrog (Hyla regilla) larvae is equal in permanent and temporary ponds in the Puget Lowlands, Washington State, USA. I also examined the direct effects of bullfrog larvae and sunfish. Survival of both species of native anuran larvae was generally lower in permanent ponds. Only one permanent pond out of six was an exception to this pattern and exhibited increased larval survival rates in the absence of direct effects by exotics. The presence of fish in enclosures reduced survival to near zero for both native species. An effect of bullfrog larvae on Pacific treefrog larval survival was not detected, but effects on red-legged frog larvae were mixed. A hypothesis that food limitation is responsible for the low survival of native larvae in some permanent ponds was not supported. My results confirm that direct negative effects of exotic vertebrates on native anurans occur but suggest that they may not be important to broad distribution patterns. Instead, habitat gradients or indirect effects of exotics appear to play major roles. I found support for the role of permanence as a structuring agent for pond communities in the Puget Lowlands, but neither permanence nor exotic vertebrates fully explained the observed variability in larval anuran survival.