A database of life-history traits of European amphibians

Abstract In the current context of climate change and landscape fragmentation, efficient conservation strategies require the explicit consideration of life history traits. This is particularly true for amphibians, which are highly threatened worldwide, composed by more than 7400 species, which is constitute one of the most species-rich vertebrate groups. The collection of information on life history traits is difficult due to the ecology of species and remoteness of their habitats. It is therefore not surprising that our knowledge is limited, and missing information on certain life history traits are common for in this species group. We compiled data on amphibian life history traits from literature in an extensive database with morphological and behavioral traits, habitat preferences and movement abilities for 86 European amphibian species (50 Anuran and 36 Urodela species). When it were available, we reported data for males, females, juveniles and tadpoles. Our database may serve as an important starting point for further analyses regarding amphibian conservation.


Introduction
Amphibians are ectotherms, and all aspects of their life history are strongly influenced by the external environment, including weather and climate. Amphibians are currently the most threatened taxonomic group worldwide (Temple andCox 2009, IUCN 2011). The major threats acting on amphibian populations are habitat loss and habitat fragmentation, pollution, global change or disease exposure (Beebee and Griffith 2005, Blaustein and Kiesecker 2002, Houlahan et al. 2000, Stuart et al. 2004). Habitat fragmentation is actually recognized as the major treat of amphibian decline (Chanson et al. 2008, Marsh andTrenham 2001) by its strong impact on population functioning, in particular in amphibians. Indeed, habitat fragmentation can decrease the size of habitat patches, and also the distances between habitat patches (Fahrig 2003, Chanson et al. 2008, Reh and Seitz 1990. Consequently, this loss of connectivity should negatively affect population functioning, by limiting dispersal events between patches and by increasing inbreeding risk (Sjögren-Gulve 1994).
The impact of global warming on amphibian populations has been reported several times (Beebee 2002, Blaustein et al. 2001, Blaustein and Kiesecker 2002, Corn 2003, Houlahan et al. 2000, Araujo et al. 2006, Alford et al. 2006. For example, the breeding phenology of anurans adapted to breeding in early spring might be shifted to even earlier breeding in recent years in response to warmer spring temperatures (Beebee 1995, Parmesan 2006, Klaus and Lougheed 2013. These responses may not be universal among amphibians and remain a matter of debate (Beebee 2002, Corn 2003, Reading 1998. It is undoubted that rising temperatures, changes in precipitation and UV-radiation are considered stressful and might be associated with disease outbreaks in amphibian populations (Blaustein and Kiesecker 2002, Kiesecker and Blaustein 1995, Walker et al. 2010). UV-B may, however, also enhance tadpole growth in some species (Pahkala et al. 2003), but with not yet anticipated effects on survival of metamorphs and population dynamics.
Our database on life history traits of 86 European Amphibian species is an important prerequisite for understanding change in amphibian life history, community composition and migration behavior. Such data is important to inform the Essential Biodiversity Variables (Pereira et al. 2013), develop new indicators and ultimately inform the decisionmaking process to improve amphibian conservation. Proportion of (a) Anura (N=50) and (b) Urodela species (N=36) within IUCN categories used in our database. Data were extracted in 2013 from information found on the IUCN website (IUCN 2011). IUCN categories: LC = least concern, NT = near threatened, VU = vulnerable, EN = endangered, CR = critically endangered.

Geographic coverage
Description: Our database included all amphibian species present in Europe (Frost et al. 2006, IUCN 2011. Four invasive species were included in the database (Anaxyrus americanus, Lithobates catesbeianus, Lithobates sylvaticus and Xenopus laevis). A particularity is that Bufotes viridis has been recently split in several species. To avoid biased data, we considered all populations to represent identical entities and therefore argued that they shared identical traits. By this way, we reported only traits referring to Bufotes viridis (formerly Bufo viridis) and we did not take into account traits related to new splited species.

Taxonomic coverage
Description: We based our taxonomic coverage on European species described on the IUCN website (IUCN 2011) and from the Amphibian Tree of Life (Frost et al. 2006). More details on species are given in Table 1 Table 1.

Morphological traits
We reported 14 morphological traits (32 modalities) for each European amphibian species: body lengths, body mass, limb lengths and details about webbing and fingers (Table 3). These traits were supposed to be relevant for amphibian conservation.

Sexual dimorphism
Difference in ornamentation (coloration) or in size (length of tail, size of head or body size) between sexes. In amphibians, females are generally bigger than males. This difference may be caused by natural selection of a large female size due to a fecundity advantage. This phenotypic difference in size is often explained by sexual selection. Modalities: Presence of sexual dimorphism.

Body mass
Body mass in males, females or both when sex specific data were not available.

Modalities:
Body mass in males Body mass in males, in grams.

Body mass in females
Body mass in males, in grams.
Adult body mass Body mass in adults, without distinction between males and females, in grams. This data was recorded when no sex specific data on body mass were available in the literature.
Body mass in juveniles Body mass in juveniles, in grams. No distinction between sexes was available.

Body length
A measurement of the longest dimension of a body, typically between two distinct ends of the body. In amphibians, the distance snout-to-vent length is usually measured. To take into account the tail length in Urodela, we also reported a total length for each species, in males, in females or both when sex-specific data were not available.

Snout-to-vent length in males
Measurement between the snout and the vent in males (in millimeters).

Snout-to-vent length in females
Measurement between the snout and the vent in females (in millimeters).
Adult snout-to-vent length Measurement between the snout and the vent in adults, when no sex specific data were available (in millimeters).

Total length
In Anura, this measure was similar to the snout-to-vent length. In Urodela, this measurement takes into account the tail length.
Definition of the 14 morphological traits and their modalities in the European amphibian database. For all traits recorded, DD (data deficient) means that no data were reported. When several values were available for a trait, we averaged them across studies (i.e. between populations).

Total length in males
Measure of the total body length in males, in millimeters.
Total length in females Measure of the total body length in females, in millimeters.
Adult total length Measure of the total body length in adults, when no sex specific data were available, in millimeters.

Head and body length proportion
Proportion of the head length compared to the body length. Modalities: Head length < Body length 0: Head length is not lower than body length. 1: Head length is lower than body length.
Head length = Body length 0: Head length is not similar to body length. 1: Head length is similar to body length.
Head length > Body length 0: Head length is not longer than body length. 1: Head length is longer than body length.

Limb length
Measurements of limb (foot, tibia and hind limb) in males, in females, or both when data were not sex specific available.

Foot length
Measurement of the foot in millimeters.

Modalities:
Foot length in males Measurement of the foot in males, in millimeters.
Foot length in females Measurement of the foot in females, in millimeters.
Adult foot length Measurement of the foot in adults, when no sex specific data were available, in millimeters.

Hind limb length
Measurement of the hind limb, in millimeters.

Modalities:
Hind limb length in males Measurement of the hind limb in males, in millimeters.

Hind limb length in females
Measurement of the hind limb in females, in millimeters.
Adult hind limb length Measurement of the hind limb in adults, when no sex specific data were available, in millimeters.

Tibia length
Measurement of the tibia, in millimeters.

Modalities:
Tibia length in males Measurement of the tibia in males, in millimeters.
Tibia length in females Measurement of the tibia in females, in millimeters.
Adult tibia length Measurement of the tibia in adults, when no sex specific data were available, in millimeters.

Fore and hind limb proportion
Proportion of the fore limb length compared to the hind limb length.

Modalities:
Fore limb length < Hind limb length 0: Fore limb length is not lower than hind limb length. 1: Fore limb length is lower than hind limb length.
Fore limb length = Hind limb length 0: Fore limb length is not similar to hind limb length. 1: Fore limb length is similar to hind limb length.
Fore limb length > Hind limb length 0: Fore limb length is not longer than hind limb length. 1: Fore limb length is longer than hind limb length.

Fingers and webbing
Presence of discs Some amphibians have adhesive discs at the ends of the toes and fingers.
Modalities: 0 Absence of adhesive discs 1 Presence of adhesive discs on fingers and/or on toes.

Webbing
Modalities: Presence of webbing 0: Absence of webbing.  (4), or if the individuals have less than 5 toes and 4 fingers.

Modalities:
Reduction on fingers only 0: Individuals have less than 5 toes and 4 fingers. 1: Individuals have 5 toes and 4 fingers.
Reduction on fingers and toes 0: Individuals have 5 toes and 4 fingers. 1: Individuals have less than 5 toes and 4 fingers.

Presence of metatarsal tubercle
Some species have a metatarsal tubercle on hind limb. A prominent inner metatarsal tubercle used for burrowing with the hind limbs. When available, the length of the tubercle is given. Modalities: 0 Absence of metatarsal tubercle.

Life history traits
We collected 17 life history traits (65 modalities), when available, for European amphibians (Table 4). Life history traits vary considerably between species, and between Anura and Urodela in particular. The database includes data about activity, survival rates, sexual maturity, mating systems, characteristics of eggs and clutch position, parental care, foot diet, defense system, communication and territoriality.

Activity
Details about the period of activity. Modalities:

Survival rates
Survival rate indicates the percentage of individuals who are alive for a given period of time.

Modalities:
Survival rates in males Survival rates in males.
Survival rates in females Survival rates in females.
Adult survival rates Survival rates in adults, when no sex specific data were available.

Sexual maturity
Sexual maturity in years.

Modalities:
Sexual maturity in males Sexual maturity in males, in years.
Sexual maturity in females Sexual maturity in females, in years.
Adult sexual maturity Sexual maturity in adults, when no sex specific data were available, in years.

Mating systems
Structuration of sexual behaviour relationships during the breeding season. We recorded 2 different types of mating systems through amphibians: polygyny when a male has mating relationships with several females; polyandry when a female has mating relationships with several males.

Eggs and young
Details about clutch size, egg laying mode, eggs and young characteristics.

Number of eggs/offspring
Modalities:

Viviparous: number of offspring
When the species is viviparous, number of offspring by female by clutch.

Ovoviviparous: number of eggs
When the species is ovoviviparous, number of eggs by female by clutch.

Ovoviviparous: number of offspring
When the species is ovoviviparous, number of offspring by female by clutch.

Egg laying mode
Modalities:

Eggs and larvae characteristics
Modalities: Metamorphosis size Measurement of the total body length of juveniles before metamorphosis, in millimeters.

Number of eggs
When the species is oviparous, number of eggs by female by clutch.
Egg diameter Egg diameter in millimeters. On surface on nonpermanent lentic ponds 0: Eggs are not laid on surface on non-permanent lentic ponds. 1: Eggs are laid on surface on non-permanent lentic ponds.

Breeding season
Breeding season can be prolonged or explosive (breeding periods of a few days to a few weeks).

Parental care
Parental care is defined as any behaviour of parents for increasing the fitness of their young. Most of amphibians do not perform parental care, but a few transport, guard and defend their eggs.

Movement
We reported 7 traits related to movement, by separating when possible migration (N subcategories) and dispersal events (21 modalities; Table 5). In contrast to migration, dispersal is defined as individual movement that induces gene flow (Ronce 2007). Amphibians regularly migrate between terrestrial and aquatic habitats, and some individuals also engage in dispersal, leaving their population of birth (or previous reproduction) to join another suitable habitat in the landscape. We used the maximum distance (and not the modal distance) recorded by species because long-distance dispersal movements have considerably higher impact on species spread, species persistence, and metapopulation functioning (Trakhtenbrot et al. 2005). All dispersal and migration values were estimated using mark-release-recapture or individual tracking. In general, amphibians are considered as low dispersal species (Boissinot 2009, Smith and Green 2005), but we detected several species for which dispersal and/or migration distances were > 10 km (Fig. 2).

Home range
Modalities: Home range Here, we consider home range as the area that an individual needs throughout a year. Home range recorded in the literature, in m².

Movement event
Modalities:  Definition of the 7 traits related to movement in the European amphibian database. For all traits recorded, DD (data deficient) means that no data were reported in the literature. When several values were available for a trait, we averaged them across studies (i.e. between populations).

Sex-biased dispersal
Dispersal abilities can be significantly different between genders. We reported here if sex-biased dispersal was identified in species (if males have faster or longer dispersal abilities than females).

Modalities:
Sex-biased dispersal 0: No sex-biased dispersal reported in the literature. 1: Significant sex-biased dispersal reported in the literature.

Mode of displacement
Modalities:

Habitat preferences and distribution
We collected habitat preferences and 2 traits related to spatial distribution (113 modalities; Table 6). Amphibians are often considered as specialized to certain habitat types, which make them particularly sensitive to landscape changes. Nevertheless, habitat preferences, and particularly terrestrial habitats of amphibian species request much clarification, especially given the recent changes induced by habitat fragmentation. We categorized habitats as follows (IUCN 2011): forest, savanna, shrubland, grassland, wetlands, rocky areas, caves and subterranean habitats (non-aquatic), deserts, artificial/terrestrial habitats, and other. We chose to use the following IUCN habitats because in our opinion it is the most conservative assumptions about species delimitations and also because these are the entities currently recognized by international conservation authorities and that is the actual aim of the database. Moreover, for this inter-specific database we avoided selecting too specific habitats, and chose relatively broad habitat categories which included all habitats in which species live. We also noted biogeographical regions (European Environment Agency 2010) where species were present, and the proportion of their distribution map on each continent.  Definition of the habitat preferences and the 2 traits related to the spatial distribution in the European amphibian database (IUCN 2011). For all traits recorded, DD (data deficient) means that no data were reported in the literature.

Wetlands
Permanent rivers/streams/creeks (including waterfalls) 0: The species does not live in permanent rivers/streams/creeks (including waterfalls) wetlands. 1: The species lives in tropical permanent rivers/streams/creeks (including waterfalls) wetlands.
Intermittent/irregular rivers/streams/creeks 0: The species does not live in intermittent/irregular rivers/streams/ creeks wetlands. 1: The species lives in tropical intermittent/irregular rivers/streams/ creeks wetlands.
Shrub dominated wetlands 0: The species does not live in shrub dominated wetlands wetlands. 1: The species lives in tropical shrub dominated wetlands wetlands.

Rocky areas
Inland cliffs, moutain peaks 0: The species does not live in rock areas as inland cliffs, moutain peaks. 1: The species lives in rock areas as inland cliffs, moutain peaks. Steppic 0: The species does not live in the steppic biogeographical region. 1: The species lives in the steppic biogeographical region.

Europe occupied UTM 50×50 km cells
Absolute Spatial distribution of the species in Europe, calculated with GIS tools, in km².

Asia
Distribution of the species in Asia.
Absolute Spatial distribution of the species in Asia, calculated with GIS tools, in km².
Punctual 0: The spatial distribution of the species is not rare. 1: The spatial distribution of the species is rare. < 10% 0: Less than 10% of the spatial distribution of the species is not in Asia. 1: Less than 10% of the spatial distribution of the species is in Asia. 80-90% 0: Between 80 and 90% of the spatial distribution of the species are not in Asia. 1: Between 80 and 90% of the spatial distribution of the species are in Asia.
> 90% 0: Up to 90% of the spatial distribution of the species is not in Asia. 1: Up to 90% of the spatial distribution of the species is in Asia.

Africa
Distribution of the species in Africa.

Absolute
Spatial distribution of the species in Africa, calculated with GIS tools, in km².
Punctual 0: The spatial distribution of the species is not punctual. 1: The spatial distribution of the species is punctual. <15% 0: Less than 15% of the spatial distribution of the species is not in Africa. 1: Less than 15% of the spatial distribution of the species is in Africa.
15-30% 0: Between 15 and 30% of the spatial distribution of the species are not in Africa. 1: Between 15 and 30% of the spatial distribution of the species are in Africa.
30-45% 0: Between 30 and 45% of the spatial distribution of the species are not in Africa. 1: Between 30 and 45% of the spatial distribution of the species are in Africa.
45-60% 0: Between 45 and 60% of the spatial distribution of the species are not in Africa. 1: Between 45 and 60% of the spatial distribution of the species are in Africa.
60-75% 0: Between 60 and 75% of the spatial distribution of the species are not in Africa. 1: Between 60 and 75% of the spatial distribution of the species are in Africa.
75-90% 0: Between 75 and 90% of the spatial distribution of the species are not in Africa. 1: Between 75 and 90% of the spatial distribution of the species are in Africa.
>90% 0: Up to 90% of the spatial distribution of the species is not in Africa. 1: Up to 90% of the spatial distribution of the species is in Africa.

North America
Distribution of the species in North America.
Absolute Spatial distribution of the species in North America, calculated with GIS tools, in km².

South America
Distribution of the species in South America.
Absolute Spatial distribution of the species in South America, calculated with GIS tools, in km².
Punctual 0: The spatial distribution of the species is not punctual. 1: The spatial distribution of the species is punctual. <25% 0: Less than 25% of the spatial distribution of the species is not in South America. 1: Less than 25% of the spatial distribution of the species is in South America.
25-50% 0: Between 25 and 50% of the spatial distribution of the species are not in South America. 1: Between 25 and 50% of the spatial distribution of the species are in South America.
50-75% 0: Between 50 and 75% of the spatial distribution of the species are not in South America. 1: Between 50 and 75% of the spatial distribution of the species are in South America. >75% 0: Up to 75% of the spatial distribution of the species is not in South America. 1: Up to 75% of the spatial distribution of the species is in South America.

Australia
Distribution of the species in Australia.
Absolute Spatial distribution of the species in Australia, calculated with GIS tools, in km².
Punctual 0: The spatial distribution of the species is not punctual. 1: The spatial distribution of the species is punctual. <50% 0: Less than 50% of the spatial distribution of the species is not in Australia. 1: Less than 50% of the spatial distribution of the species is in Australia.
>50% 0: Up to 50% of the spatial distribution of the species is not in Australia. 1: Up to 50% of the spatial distribution of the species is in Australia.

Global Distribution
Modalities: Ubiquity 0: The species is not ubiquist. 1: The species is ubiquist.

Threats
We collected information on three categories (22 modalities; Table 7) related to threats of amphibian species: The IUCN status (6 subcategories), population trend (4 subcategories), and major threats (12 subcategories).

IUCN status
IUCN threat status. Threatened species have one of the three following IUCN status: "vulnerable", "endangered", "critically endangered".

Population trend
Evolution of the population. Population trends vary between "decrease", "stable" and "increase".
Definition of the 3 traits related to threats in the European amphibian database. For all traits recorded, DD (data deficient) means that no data were reported in the literature.

Conclusion
Our database is the first comprehensive trait database in European amphibians. After an extensive research effort, our database highlighted the lack of data about amphibian traits and more generally, on amphibian's biology. Improve our knowledge on amphibians should certainly help for their management, which might strongly enhance their conservation plans. Morphological traits, which are easy to collect, are still unavailable for many species. Data about movement abilities (both dispersal and migration) were the least informed data of all database. In particular, we showed that movement traits, which are difficult to collect, were unknown for a majority of threatened species. This database could be an essential support for management and conservation plans, and should be more efficient when all data will be available.