The relationship between body length, age and sexual maturity in the common toad, Bufo bufo

An investigation of the relationship between the onset of sexual maturity, age and body size in common toads Bufo bufo was started in 1984 at a pond in southern England. During the toad breeding seasons of 1984 and 1985, 7259 common toad'metamorphs'were captured and permanently marked so that if captured as adults their true age would be known. Although a very small proportion of males and females reached sexual maturity at ages of two and four years respectively, most did so much later and asynchronously. The body size of toads breeding for the first time was relatively constant for each sex and not correlated with age. The rational behind our understanding of the mechanism of female choice is discussed in the light of these results.     

Population dynamics in a Danish metapopulation of spadefoot toads Pelobates fuscus

If an amphibian species has a high degree of site fidelity to its natal pond, subpopulations do not mix, and this may have implications: the subpopulations may get different because of genetic drift, and their status may be affected due to stochastic events. During a four-year period (1994–1997), demographic parameters of a Danish metapopulation consisting of ca 1000 adult Pelobates fuscus in five subpopulations were investigated with the aim of quantifying exchange of individuals in subpopulations and potential differences in demographic parameters, and to clarify population regulating mechanisms. This was done through the use of drift fences surrounding the five breeding ponds, individual marking (PIT-tagging) and weight recordings of the adult females. Metamorphs were recorded when leaving the pond. There was no significant differences between ponds in sex ratio, eggs laid per female, fraction of females breeding and survival of eggs to froglets and of adults. However, there was a significant difference in juvenile survival (52% in one pond and 31% in the others). Sex ratio was 1.70 males:1 female. Mean number of eggs laid per female in the pond was 1762. The number of eggs laid was age-specific, fecundity peaking at age five. Larval survival rate was density dependent: decreasing in an overcompensating fashion at high densities. Exchange rate between ponds was low; 1.09% of the marked and recaptured adult population was found to change pond during the study period. The low exchange rate was confirmed in a simple translocation experiment. This population shows features of a source-sink metapopulation where the identity of the source pond changes due to succession. It is presumably regulated either in the larval stage by density dependent mechanisms (in the subpopulations with many adults) or in the adult stage by density independent mechanisms (in the subpopulations with few adults).     

The declining spadefoot toad Pelobates fuscus: calling site choice and conservation

We investigated whether local biotic and abiotic conditions could explain the occurrence of calling males of the declining spadefoot toad Pelobates fuscus in 72 ponds in southern Sweden. The ponds covered the entire distribution range of P. fuscus and were monitored during the breeding season in 2000. Calling males were found in 33 ponds, representing ca 50% of all known ponds for the species in Sweden. They had a non-random distribution and a discriminant analysis including 19 environmental variables successfully classified 86% of the ponds as with or without calling males. A stepwise discriminant analysis selected eight of these variables and classified 85% of the ponds correctly. Ponds with calling males were classified mainly on characteristics of the ponds, whereas composition of the terrestrial habitat close to the ponds and traffic load within 500 m had little influence on the distribution of calling males. Ponds with P. fuscus were large, permanent and eutrophic with high concentrations of oxygen and high spring temperatures. They also had a high proportion of shoreline with steep banks. Permanent ponds with calling males typically had a low abundance of predatory fish and crayfish; only two of the ponds with P. fuscus contained predatory fish. The results of this study indicate that interactions between physical factors (e.g. pond drying) and predation determine the presence of P. fuscus. Because P. fuscus has specific habitat requirements necessary for its survival and high site fidelity, it is particularly vulnerable to local changes in the condition of its natural breeding ponds. The situation is particularly serious for this species because the majority of the ponds that are within its dispersal range do not seem to be suitable for P. fuscus because of physical constraints.     

The effect of winter temperatures on the timing of breeding activity in the common toad Bufo bufo

A 19-year study of a common toad population in south Dorset, UK, was carried out between 1980 and 1998. The daily arrival of sexually mature male and female toads at a breeding pond was recorded each year. The timing of the main arrival of toads at the breeding pond was highly correlated with the mean daily temperatures over the 40 days immediately preceding the main arrival. When the temperatures were higher than average, breeding occurred significantly earlier in the year than if they were either average or lower than average. During the study, the toad breeding seasons were early (2–13 February) in 5 years (1989, 1990, 1993, 1995, 1998), late (16–23 March) in 2 years (1986, 1996) and average (25 February–8 March) during the remaining 12 years. Evidence was found suggesting that common toads have a daylength threshold of about 9 h, below which the migration to the breeding pond does not occur. Evidence was also found indicating that common toads in southern England have a threshold temperature for activity of about 6°C and that the onset of breeding activity is highly correlated with the number of days during the 40 days prior to the main arrival at the breeding pond that were at or above this temperature. Predicting the start of the main breeding migration to a pond in any year may be possible by comparing the pattern of the 40-day running mean daily temperatures from 21 December the preceding year with those from previous years when the start of breeding activity is known. Although all five of the earliest recorded toad breeding years occurred during the last 10 years, and were associated with the occurrence of particularly mild winters, a significant trend towards earlier breeding in recent years compared with previous years was not found. Received: 16 July 1998 / Accepted: 14 September 1998     

Life stage specific variation in the occupancy of ponds by Litoria aurea,a threatened amphibian

Breeding aggregations are a reproductive strategy to increase mate finding opportunity. However, because aggregations skew the distribution of mature animals through conspecific attraction, rather than resource availability, the distribution of breeding sites may be reduced, so that not all suitable breeding sites are used. To examine the relationship between landscape and reproductive strategies of a threatened frog, Litoria aurea, we studied its distribution at Sydney Olympic Park over two breeding seasons. We aimed to: (i) determine the distribution and predictors of breeding ponds; and (ii) assess the significance of dispersal in the juvenile age‐class. We found that the distribution of the calling males was highly skewed and occurred in large, well‐connected ponds. Despite this, breeding ponds were not aggregated; pond size was the single factor explaining the distribution of breeding ponds. Juvenile frogs dispersed from breeding ponds and were not associated with a specific pond characteristic. Less breeding occurred in the second season during which fewer ponds were used for breeding including many different ponds from the previous year. These changes suggest that breeding effort and breeding pond choice are dynamic and therefore knowledge of the factors that drive breeding events will be a powerful tool in managing species, particularly in light of changing climatic regimes.     

Male breeding behaviour and mate acquisition in the Common toad, Bufo bufo

The breeding behaviour of a Common toad ( Bufo bufo ) population was studied at a breeding pond on Portland, Dorset. Major toad movements towards the breeding pond occurred on warm, wet nights when the temperature did not fall below 6°C. Males arrived earlier than females resulting in an initially exaggerated sex ratio which then slowly reduced as the breeding season progressed. No size assortative pairing was found although large males were more successful at mating than small males. Although males demonstrated no ESS (evolutionary stable strategy) in searching for a female between sites within the pond evidence suggesting the existence of one between the pond and an undefined area surrounding it was found.     

Patterns of synchrony in natterjack toad breeding activity and reproductive success at local and regional scales

Empirical studies of the spatiotemporal dynamics of populations are required to better understand natural fluctuations in abundance and reproductive success, and to better target conservation and monitoring programmes. In particular, spatial synchrony in amphibian populations remains little studied. We used data from a comprehensive three year study of natterjack toad Bufo calamita populations breeding at 36 ponds to assess whether there was spatial synchrony in the toad breeding activity (start and length of breeding season, total number of egg strings) and reproductive success (premetamorphic survival and production of metamorphs). We defined a novel approach to assess the importance of short‐term synchrony at both local and regional scales. The approach employs similarity indices and quantifies the interaction between the temporal and spatial components of populations using mixed effects models. There was no synchrony in the toad breeding activity and reproductive success at the local scale, suggesting that populations function as individual clusters independent of each other. Regional synchrony was apparent in the commencement and duration of the breeding season and in the number of egg strings laid (indicative of female population size). Regional synchrony in both rainfall and temperature are likely to explain the patterns observed (e.g. Moran effect). There was no evidence supporting regional synchrony in reproductive success, most likely due to spatial variability in the environmental conditions at the breeding ponds, and to differences in local population fitness (e.g. fecundity). The small scale asynchronous dynamics and regional synchronous dynamics in the number of breeding females indicate that it is best to monitor several populations within a subset of regions. Importantly, variations in the toad breeding activity and reproductive success are not synchronous, and it is thus important to consider them both when assessing the conservation status of pond‐breeding amphibians.     

Female polyandry and size‐assortative mating in isolated local populations of the Japanese common toad Bufo japonicus

In anurans, female polyandry under male harassment is distributed across taxa because of external aquatic fertilization. According to the sexual selection theory, male–male competition for access to females is affected by the operational sex ratio (OSR) and population density. The Japanese common toad, Bufo japonicus, is widespread in mainland Japan, and like the European common toad, B. bufo, it engages in explosive breeding. In this study, we observed the breeding behaviour of B. japonicus in isolated local populations for over four years in two breeding ponds with different population sizes and densities: large‐low (L‐pond) and small‐high (S‐pond). We analysed the relative polyandry ratio in egg clutches laid by females and estimated the size‐assortative mating pattern to be an indicator of male–male competition in the two ponds. Both ponds tended to exhibit a size‐assortative mating pattern; however, the frequency of polyandry was different in the two ponds (L‐pond = 20% and S‐pond = 90%). Our results showed that polyandry could occur without multiple amplexus with a high population density, i.e. eggs were often fertilized by free‐swimming sperm in the small shallow pond. We propose that high female polyandry ratios without continuous male harassment are generated because of a male‐biased OSR and a high population density in the small pond. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 236–242.     

Pathways of ornamental and aquarium fish introductions into urban ponds of Epping Forest (London,England): the human vector*

To examine the role of humans in the non‐native fish introductions, we measured the frequency of occurrence and density of non‐native fishes in ponds (Epping Forest, Essex, England) that had been restored (drained of water and voided of fish or treated with rotenone) on a known date and into which no piscivorous or non‐native fishes had subsequently been stocked intentionally. For each pond, the period of time since pond restoration, pond area, distance to nearest residential housing, distance to nearest footpath, distance to nearest water body or stream, and the proportion of pond vegetated were measured. The occurrence of both non‐native and unexpected native fish species was non‐random, and the number of ornamental varieties was found to increase as pond distance from the nearest road decreased. Variety richness of each of three categories of fish (non‐native, goldfish Carassius auratus and native) was significantly correlated with at least two of the following variables: distance from nearest road, nearest footpath and nearest pond. The rate of non‐native fish introductions (adjusted variety richness per year) could also be estimated from pond distance to the nearest road, being about 3.5 ornamental varieties introduced per year in ponds adjacent to roads, but the rate appears to be much greater in ponds that had recently (<1.5 years) undergone restoration. Implications for conservation and management, as well as the potential role of societal issues such as recreational activities, cultural and religious practices, are discussed.     

Measuring dispersal in a metapopulation using stable isotope enrichment: high rates of sex-biased dispersal between patches in a mayfly metapopulation

Dispersal affects a wide array of ecological and evolutionary processes, but has been difficult to estimate empirically. A ¹⁵Nitrogen stable isotope enrichment technique was used to passively mark all developing Callibaetis ferrugineus hageni (Eaton) mayfly larvae in a beaver pond that had previously been shown to be a patch in a source-sink metapopulation. After enrichment during the larval stages, dispersal among ponds by adult females was demonstrated by the presence of unmarked females ovipositing in the labeled pond, and marked females in an unlabeled pond. Observed frequencies of marked females suggested incomplete mixing between ponds. In contrast, males rarely dispersed from their natal pond, which was consistent with the unusual mating system in this species – adult Callibaetis are short-lived, do not feed, and females are sexually receptive immediately after emerging from the larval habitat. The frequent dispersal demonstrated using the stable isotope technique was a critical component of the source-sink dynamic observed in this metapopulation, and further use of this technique will provide insights into patterns of dispersal in spatially structured habitats.     

Modeling spatial distribution of amphibian populations: a GIS approach based on habitat matrix permeability

Predictions of occurrence of two amphibian species, the common toad and the alpine newt, were made using information on land use surrounding breeding ponds. A geographical information system (GIS) was used to compile a landuse map, from which permeability estimates (friction) were derived. Potential migration zones based on friction and maximum migration distance were then modeled. Contacts between several migration zones suggest the potential for migration between ponds by adult individuals. The ability of the migration zones to enhance predictions of species occurrence was tested using generalized additive models (GAMs), and several landscape variables were selected as determinants of amphibian presence. The area of a migration zone and the number of ponds within that zone were positively related to both toad and newt presence, suggesting the importance of buffer habitats around each pond in amphibian conservation. Toad presence declined with cultivated field area and newt presence declined with vineyard area, suggesting the negative effect of agricultural activity on amphibians. The friction-based modeling approach improved the prediction of toad presence when compared to a more classical analysis of habitat composition within a circular zone centered on the focal pond. Prediction of newt presence was, however, less accurate than prediction of toad presence. Despite its exploratory nature and the subjectivity of permeability estimates, this study shows the usefulness of GIS in the functional analysis of a landscape, with potential applications in biological conservation. It also highlights the need for improving our knowledge of habitat use by animals.     

Emergence of the damselfly Pyrrhosoma nymphula (Sulzer) (Zygoptera: Coenagrionidae) from two adjacent ponds in northern England

Emergence of the damselfly Pyrrhosoma nymphula was followed closely at two similar and adjacent ponds in northern England. Males emerged earlier than females at both ponds (significantly so at one). The sex ratio was significantly male biased at both ponds. Size of emerging adults declined through the emergence period at both ponds. Adults emerging from one pond did so significantly earlier and were significantly larger than those from the other pond. The density of larvae was approximately twice as high in the pond from which larvae emerged early; this pond was also slightly deeper and usually achieved higher maximum daily water temperatures. These findings are discussed in the light of the conventional view of seasonal regulation in a spring-emerging damselfly.     

Wetland Restoration for Amphibians: Should Local Sites Be Designed to Support Metapopulations or Patchy Populations?

Pond-breeding amphibians have been characterized as having metapopulation structure, and a goal of many local restoration projects is to establish viable metapopulations. However, recent studies suggest that metapopulation organization is unlikely at the local level because of high dispersal rates between neighboring ponds. Although many amphibians avoid ovipositing in habitats that pose high predation risk to their offspring, the spatial scale of avoidance is poorly resolved for natural systems and could involve wholesale movements between ponds. To determine the scale of avoidance, we monitored annual habitat use by the Wood frog ( Rana sylvatica ), American toad ( Bufo americanus ), and Spotted salamander ( Ambystoma maculatum ) at a restoration site in western North Carolina, U.S.A. Wood frogs consistently used most fish-free ponds, but rapidly curtailed use following fish invasions. American toads rarely used the same breeding site from year to year, and adults strongly avoided ovipositing in habitats with predatory Wood frog tadpoles. Spotted salamanders exhibited a predator avoidance response to fish that was weaker than the predator avoidance response of anurans. Our data indicate that the spatial scale of predator avoidance by ovipositing amphibians often exceeds that of an individual pond and that the focal species at this site are organized as patchy populations rather than as metapopulations. At local restoration sites, ponds that are placed in spatial arrays to create metapopulations may not accomplish their goal and may limit the extent to which ovipositing adults can express an adaptive antipredator behavior. We discuss an alternative design that is more likely to enhance the long-term persistence of local populations.     

Interrelationships between breeding frequency,timing and outcome in King Penguins Aptenodytes patagonicus: are King Penguins biennial breeders?

King Penguin Aptenodytes patagonicus chick growth is interrupted by a winter fast which extends the length of the breeding cycle (laying to chick independence) to 14–16 months, so that continuous annual successful breeding appears to be impossible. The 3–month laying period imposes further constraints with respect to timing of breeding attempts in relation to the onset of fasting. By the frequent resighting of individually marked birds at Marion Island, we examined the frequency of breeding and the relationships between timing, outcome and frequency in the same and in consecutive years. A total of 3101 adult King Penguins were banded between 1984 and 1991, yielding continuous breeding histories spanning a maximum of 5 years. Most penguins attempted to breed in consecutive years, although the likelihood of taking a year off increased with the number of consecutive attempts. In any one season, about 19% of potentially breeding adults did not breed. Early breeders were more likely to succeed than late breeders and comprised 84% of breeding attempts of known timing. Successful birds in one season usually bred late in the following season, whereas failed attempts were usually followed by an early attempt. Non-breeding was more likely to occur after a successful outcome than a failed one, and after a year off 93% of birds bred early. It is incorrect to refer to the King Penguin as a biennial breeder.     

Breeding site fidelity and natal philopatry in the Redshank Tringa totanus

This paper presents the results of a study carried out on breeding Redshank in the Ribble Marshes, Lancashire, England.
Redshank tend to return to the same breeding area year after year. There was no detectable sex bias in return rates. Experienced birds were more site faithful than inexperienced birds, with previously successful birds exhibiting the highest degree of breeding site fidelity. Older, more experienced birds were more successful at hatching eggs than inexperienced birds.
Breeding dispersal was the same both within and between years. Faithful pairs and males nesting with a new mate dispersed significantly shorter distances than females nesting with a new partner. Dispersal distances in female Redshank were affected by breeding success: unsuccessful females, nesting with a new mate, dispersed significantly farther than successful females. A pair's breeding success influenced the following year's mate fidelity. However, other factors such as overwintering survival and date of return may also have influenced mate fidelity.
Redshank were highly faithful to their natal area; a high proportion of birds that survived post-fledging mortality returned to breed in their area of birth. No sex bias in natal dispersal was detected. Approximately 50% of Redshank breed in their first year of life.     

Demography of Bristle-thighed Curlews Numenius tahitiensis wintering on Laysan Island

We studied the nonbreeding ecology of Bristle-thighed Curlews Numenius tahitiensis from 1988 to 1991 on Laysan Island in the Northwestern Hawaiian Islands. Using capture-recapture analysis, we estimated that 300–350 curlews wintered on the island. Annual survival was >85% for adults and 92% for first-year birds. Young birds remained on the island until at least their third calendar year, when some individuals made "exploratory" visits to other islands in the Northwestern chain. Most of the birds marked in their first year migrated north to the breeding grounds when they were 3 years old; several birds remained on the island until they were at least 4 years old. Adults returned to the same discrete home ranges year after year, whereas subadults (which do not migrate) tended to use a greater portion of the island. At least 60% of the subadults marked from 1988 to 1990 returned to the island to winter as adults. Because young curlews arrived after adults and experienced high survivorship while on the island, there did not appear to be intense competition for space at Laysan even though the island is at the northern end of the species' winter range.     

THE BREEDING CYCLE OF THE SOUTHERN SEA LION, OTARIA BYRONIA

Daily counts of Southern sea lions ( Otaria byronia ) made at Punta Norte, Argentina, during four consecutive breeding seasons (1980–1984) yielded similar results in the time of the reproductive events. Males and females began to arrive during the second week of December. Males reached peak numbers (100–110) between 15 and 21 January. Females reached maximum numbers (300–350) at the end of January. About 380–430 pups were born between December 20 and February 2, and 70–80 percent of births occurred between 10 and 25 January. Copulations peaked during the third week of January. The sex ratio of adult males to adult females at peak season fluctuated from 1:3.7 to 1:4.2. By the first week of February, coinciding with the maximum number of young males (25–50), 90 percent of the adult males had abandoned the area and the number of females fluctuated greatly. Since 1980 the number of females and pups has shown a slight increase, particularly during the 1983–1984 breeding season.     

Temporal and spatial variation in dispersal in the greater flamingo (Phoenicopterus ruber roseus)

We studied movements of individually marked greater flamingos (Phoenicopterus ruber roseus) born in the Camargue, southern France, between their two most important breeding colonies in the western Mediterranean (Camargue and Fuente de Piedra, Spain) from 1986 to 1992. The two sites differ in the frequency with which they offer suitable conditions for breeding. Flamingos have bred each year in the Camargue since 1974, but in only 12 of the past 22 years at Fuente de Piedra. Higher colony fidelity is thus expected in the less variable environment (Camargue), but if dispersal occurs competition might be an important factor causing this dispersal. Following years during which breeding birds in the Camrgue were disturbed (1988 and 1990) a higher proportion of adults changed colonies between breeding attempts (= breeding dispersal, 12.4%), while only 0.4% of flamingos breeding in the Camargue dispersed in the other years. As expected, flamingos breeding at Fuente de Piedra showed a higher rate of breeding dispersal (8.14%). No differences were observed between males and females. The importance of breeding failure as a factor causing breeding dispersal in flamingos was also confirmed by the movements of individual birds. The proportion of young flamingos that moved from their natal colony to start breeding at Fuente de Piedra (= natal dispersal) was independent of sex and age, but increased when breeding access to the Camargue colony was more difficult. However, natal dispersal was also higher in 1988 and 1990 (40.5%) than in the remaining years (1.2%), as was breeding dispersal. We discuss possible ways in which the increased natal dispersal among inexperienced birds could be linked with the increased breeding dispersal of adults in the same year.     

Morphological and life history responses to predators in larvae of seven anurans

Amphibian larvae often face two major sources of mortality: pond desiccation and predation. Tadpoles of seven anuran species with different preferences for type of breeding habitat, on a hydroperiod scale, were tested for responses to the presence of predators by raising them experimentally in the presence and absence of a separately caged invertebrate predator that was fed on conspecific tadpoles. The species typically breeding in temporary or semi-permanent ponds ( Rana temporaria , Rana arvalis , Rana dalmatina and Hyla arborea ) – where invertebrate predator populations are predicted to vary considerably spatiotemporally – all showed marked induced increases in tail fin depth in response to predator presence. These species also tended to respond by reduced growth rates. The representative of the most ephemeral habitats, Bufo calamita , did not respond in any of these traits. Its congeneric, Bufo bufo , a toxic inhabitant of permanent ponds and lakes, tended to respond to predator presence by reducing its growth rate, though not by a tail depth increase. I argue that the rather poor swimming performance in Bufo tadpoles may opt for defences other than locomotor ability. The palatable, permanent pond species Pelobates fuscus did not alter either its growth rate or tail morphology. Possible explanations for this result are discussed.