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Overview
Amphibians are among the most globally endangered groups of vertebrates with more than one-third of species being assessed as declining or threatened. This book is designed to help those carrying out amphibian surveying and monitoring so that the results of their surveys can be used effectively.
Product Details
| ISBN-13: | 9781784270032 |
|---|---|
| Publisher: | Pelagic Publishing |
| Publication date: | 10/17/2015 |
| Series: | Conservation Handbooks |
| Pages: | 140 |
| Product dimensions: | 6.69(w) x 9.71(h) x 0.41(d) |
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Read an Excerpt
CHAPTER 1
Introducing amphibians
Today's amphibians are descended from the first terrestrial vertebrates that evolved from bony-finned fishes some 360 million years ago. A few tens of millions of years later, early amphibians gave rise to reptiles, and ultimately therefore to both birds and mammals. Your ancestors were amphibians!
The majority of amphibians develop from gelatinous eggs laid in water, which hatch into aquatic larvae (tadpoles or polliwogs) and gradually metamorphose into terrestrial juveniles resembling the adults. Many species, however, have evolved variations on this theme. Some salamanders, for example, reach sexual maturity in their larval form and never attain true adulthood, and some frogs produce eggs within which the tadpole stage takes place, hatching into fully formed froglets. Still others undergo the typical amphibian metamorphosis but remain aquatic throughout their lives. For a fuller overview of the diverse range of amphibian life histories, see Cloudsley-Thompson (1999), Halliday and Adler (2002) or Wells (2007).
1.1 Amphibian diversity
Modern amphibians number more than 7,000 species in three orders (see below). This number is only a fraction of the diversity present when amphibians were the dominant terrestrial vertebrates during the Carboniferous and Permian periods, more than 300 million years ago.
Amphibians are now among the most threatened of vertebrate groups, with more than 30% of amphibian species falling into IUCN threat categories (Stuart et al., 2004). Though some amphibians are declining to extinction – many more than would be without the influence of humans (McCallum, 2007) – the number of known amphibian species is actually rising as a result of taxonomic research and advances in methods used for separating species (see Box 1.1 on page 7).
Many factors are contributing to global amphibian declines, including emerging diseases and pollution, but by far the most serious threats to amphibians are the loss and fragmentation of their habitats. The modern, human-dominated world is a hostile place for many amphibians, which have particular ecological needs, including, for example, the need to migrate between hibernation sites and breeding ponds. Despite this, many amphibian species persist and thrive alongside human activities where the features on which they depend are still present in the landscape. Often, it is habitat fragmentation and the rate of landscape-scale change that prevent amphibians from colonizing new habitats, such as urban ornamental and sustainable urban drainage system (SUDS) ponds (e.g. Gledhill and James, 2008). For more information on global amphibian declines, see the reviews by Beebee and Griffiths (2005), McCallum (2007), Hamer and McDonnell (2008) and Blaustein et al. (2011).
The fact that many amphibians, even familiar and widespread species such as the common toad (Bufo bufo) in Europe, are declining (Carrier and Beebee, 2003) is one of the factors driving the need for effective and informative surveys. Whether conducting a site species inventory or carrying out detailed monitoring of a single population, survey results provide invaluable information that can lead to better conservation decision making. Your surveys can therefore inform positive action that will help prevent further declines in these critical components of our ecosystems.
1.2 Order Anura (frogs and toads)
The anurans are the most diverse and numerous of the amphibians, with more than 6000 species in more than 50 families. The familiar frogs and toads are anurans, though the distinction between the two is an artificial one: anurans that jump and have smooth skin are referred to as 'frogs', and those with warty skin and a tendency to walk or hop are called 'toads'. The midwife toads (genus Alytes) and fire-bellied toads (family Bombinatoridae) are more closely related to frogs than are the poison-dart frogs (Dendrobatidae) and treefrogs (Hylidae), which are allied to the true toads (Bufonidae).
Anurans lack tails and usually have a moist, scale-less skin that can be smooth or glandular and warty. Most species are also characterized by their prominent eyes, used for locating moving prey, and many species produce distinctive calls, most often as a way for the males to attract a mate. They breed, typically, in water (see Fig. 1.1), using external fertilization and laying eggs singly, in clumps or in strings, in a variety of aquatic situations from small, temporary puddles to large, permanent lakes. The jelly-covered eggs hatch into swimming larvae (tadpoles or polliwogs) that develop over days, weeks or (sometimes) years into smaller versions of their parents. Some of the many exceptions include the viviparous Nectophrynoides (see Fig. 1.2) and the Neotropical genus Eleutherodactylus. The eggs of the latter undergo direct development, hatching into fully formed froglets. Some species of anuran (e.g. the red-eyed treefrog, Agalychnis callidryas) deposit eggs on leaves over ponds or in other situations where the tadpoles can wriggle into the water when they hatch, reducing the risk of their eggs being eaten by predators. Other species, including members of the Dendrobatidae, reduce this risk by practising advanced parental care. Eggs are cared for and kept moist by one or both of the parents and the tadpoles are carried to suitable puddles or reservoirs of water in epiphytic plants to develop in relative safety. Some dendrobatids even produce unfertilized eggs that provide a regular source of nourishment for the growing tadpoles.
1.3 Order Caudata (newts and salamanders)
The order Caudata contains more than 600 species in 10 families. Though there are many fewer species than in the Anura, caudates nevertheless display a remarkably diverse range of life histories. Caudata includes the pond-breeding newts (see Fig. 1.3) of Europe, Asia and North America (family Salamandridae) but, again, the distinction between newts and salamanders is an artificial one based on their life histories. Many salamanders are more terrestrial than newts but equally others, such as the axolotl of Mexico (Ambystoma mexicanum) and members of the family Proteidae (including the olm, Proteus anguinus, of Europe), are paedomorphic, never leaving the water and never usually developing into an adult form. They retain their larval characteristics and breed, effectively, as tadpoles.
More than half of the species of caudate, however, belong to the family Plethodontidae. This family has a few species in Europe and many in the Americas, and is the only caudate family with many species in the Southern Hemisphere. The majority of this family are terrestrial (see Fig. 1.4), though some live aquatically, and quite a few small, Neotropical species have evolved to be arboreal, using direct development of their eggs to conduct their entire, tiny lives above ground. Plethodontid salamanders are lungless, obtaining all the oxygen they need through their skin.
Unlike anurans, all caudates have tails and a low-slung, lizard-like body pattern. Fertilization is predominantly internal, being facilitated by a spermatophore (packet of sperm) that the female picks up. Many caudates have an intricate and complex courtship ritual that is unique to their species. Eggs can be single or laid in groups/clumps and may be cared for by one or both parents. A few species, like the fire salamander (Salamandra salamandra), retain their eggs and give birth to tadpoles or even completely metamorphosed terrestrial baby salamanders. Caudate tadpoles typically possess branched, prominent external gills (these are internal or less obvious in anuran tadpoles). They undergo gradual metamorphosis into adult form in the same way as anurans.
1.4 Order Gymnophonia (caecilians)
The least numerous and least known of the amphibians, the order Gymnophonia currently contains around 200 species in 10 families. Part of the reason for this group being relatively poorly known is that most species are burrowers in leaf litter and moist soil, though some are aquatic. They can therefore be difficult animals to survey and study effectively, and detailed information about their distribution and fascinating ecology is only just becoming known. Caecilians are restricted to the tropics.
All caecilians share the same basic body pattern (Fig. 1.5): an elongated, limbless and virtually tail-less body like that of a large earthworm (for which they are sometimes mistaken). The eyes are tiny and indistinct. Their skins are smooth but appear scaly in species that have segmented rings (annuli) around their bodies. All the amphibian groups have extraordinary characteristics and caecilians are no exception. They have (uniquely) evolved a small, mobile tentacle below each eye. These retractable tentacles aid in sensing prey items and mates in the caecilians' underground world where good eyesight would be useless. Additionally, though primitive and simplistic in appearance, they utilize different reproductive strategies. Fertilization is internal, with about half of all species producing eggs that hatch into gilled larvae, and the others giving birth to young that have developed within the female. Courtship in this group is very poorly known.
Some female caecilians, depending on the species, produce a kind of internal milk to feed their developing embryos, and some, like Boulengerula taitanus of Kenya, even grow and shed special layers of skin for their hatched larvae to eat. The larvae rasp this skin off their mother's body with special baby teeth (see Kupfer et al., 2006). The resemblance to earthworms is therefore entirely coincidental!
CHAPTER 2
Before you start surveying
2.1 Types of survey
Defining the type of survey you are intending to carry out will help make sure you have everything in place to make it a success, as well as avoiding the mistake of having unrealistic expectations about what the results can show you. Broadly, and irrespective of which survey methods are used, amphibian surveys can be divided into three categories.
• Census or inventory surveys: these surveys are usually confined to a predefined area (e.g. a particular pond, protected area or region) and can reveal the presence/absence of amphibian species there and their relative distributions within that area. Inventory surveys can also be used comparatively to inform ecological questions such as How do the amphibian species present in Area A differ from those present in Area B? when combined with other information specific to the areas being studied (e.g. pond size and depth, surrounding vegetation types, geology). Inventory surveys are generally intended as one-off exercises, though careful data collection will mean they can inform more extensive surveys and be referred to for comparisons over time (e.g. if a grassland area gradually becomes woodland, the composition of the amphibian species present may change). The potential for future inventories of the area in question may be unknown, but any inventory survey should be carried out with the possibility in mind that someone will refer back to it in future.
• Surveillance: this is a programme of repeated surveys intended from the outset to detect changes over time. The intention might be simply to check that the same species previously recorded in an area continue to be present, or to assess the effects of habitat works or landscape changes: How has the construction of a new housing estate affected the species composition of amphibians breeding at Pond X?, Are the most sensitive species still present after five years?, etc. Effective surveillance will usually include information additional to simple species presence/absence, such as an estimate of population size/s, and each survey must include some comparative information to be useful. It is interesting (though saddening) when surveillance shows a protected species is no longer using a pond five years after a road was built next to it ... but what is the actual change that has caused the loss of that species? Changes causing observable effects on amphibians can be many and varied; in the example of the construction of a new road, the changes could be loss of terrestrial habitat, fragmentation of the habitat, harmful runoff from the road's surface, or perhaps simply that amphibians are being killed by traffic on their way to the pond. It is often the case that such factors combine to affect amphibians, so it's useful (but sometimes difficult) to predict and record systematically (i.e. in exactly the same way each time your survey is repeated) a variety of related information (see Section 3.3).
If population size information is included in surveillance, it can be used to detect trends. It is essential to note, however, that many amphibian populations fluctuate substantially over time and that separating a 'real' decline from natural fluctuations may require many years of data (e.g. Pechmann et al., 1991; Blaustein et al., 2011). For example, a new road might result in the recording of slightly fewer amphibians at a time of population 'boom' but might equally cause local extinction of a species if the road construction happens at a time of low numbers of breeding adults. This problem also emphasizes the importance of systematic long-term surveillance of amphibian populations to the investigation of declines, and as an aid to effective conservation.
• Monitoring: this is very similar to surveillance, but with the added dimension of having a target or threshold value that is pre-defined and that informs us about the conservation status of the species involved. Monitoring relative to pre-defined values can help keep track of the status of species in an area almost irrespective of the known tendency of amphibian populations to fluctuate (see above). In reality, few amphibians are well-known enough in any area to establish such target values, but this should be the goal of any long-term monitoring. You may, for example, have long-term data that tell you Newt Species Q populations in State Park Z fluctuated between 75 and 250 breeding adults over a 20-year period. So a monitoring target could be to detect at least 75 breeding adults every year. Fewer than this number would trigger more intensive surveys and/or an investigation into a possible 'real' decline and subsequent remedial action. Monitoring thresholds can also be defined in other ways, for example Is there, in any given year, evidence of breeding (eggs detected) of Newt Species Q in at least 12 of the 17 ponds in State Park Z? Every monitoring target will be specific to species and area, the critical aspect being that values are based on systematic surveys over a sufficient length of time for them to be both robust and useful (see Section 2.2). As I said, few amphibian populations are well-known enough to establish adequate target values, but monitoring with targets as defined here can still be enshrined in legal instruments. Member states of the European Union (EU), for example, have a list of species (including the great crested newt, Triturus cristatus, and natterjack toad, Epidalea calamita) for which they have to report on the conservation status every six years. This responsibility comes from the EU Habitats Directive of 1992. The metrics (population, habitat, range and future prospects) are defined, and status is favourable only when all four metrics can be said to exceed Favourable Reference Values (FRVs). Target (FRV) values against which to monitor, however, are currently poorly explored, so Favourable Conservation Status (FCS) is frequently interpreted or quantified differently by individual EU member states! Many countries use the date when the Directive came into force in their country (often 1994) as a reference threshold, and concentrate their reporting on trying to prove that a species' status has not dropped below that level. In most cases, though, there are no data to say that status was 'Favourable' at that point. Current discussions on monitoring and FCS at EU level may nevertheless eventually lead to useful guidance on setting targets that will hopefully be adopted widely.
Perhaps inevitably, many concepts originating within the EU tend towards complication and I don't intend to explore further the EU's take on monitoring. It is useful to be aware, however, that governments do attempt to measure status through monitoring in this way. More information on FCS can be found at http://jncc.defra.gov.uk/PDF/comm02D07.pdf, and the reports on the status of species by each EU country can be seen at http://bd.eionet. europa.eu/article17/index_html/speciesreport. The real value of the concept of FCS, of course, is to define appropriate conservation targets that can relate back to tangible conservation action: Has the habitat management carried out in State Park Z improved the conservation status of Newt Species Q there? If we can monitor amphibian populations against targets in a protected area or a defined region, target values can also be aggregated to produce country values and even eventually describe the status of a species across its entire range. So even irregular species inventories of the amphibians breeding in the pond at your local nature reserve can, if conducted systematically, provide valuable evidence on which practical conservation methods can be based in the long term.
(Continues…)
Excerpted from "Amphibian Survey and Monitoring Handbook"
by .
Copyright © 2015 John W. Wilkinson.
Excerpted by permission of Pelagic Publishing.
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Table of Contents
List of figures, ix,
List of tables, xi,
Foreword, xiii,
Preface, xv,
Acknowledgements, xvii,
1 Introducing amphibians, 1,
2 Before you start surveying, 9,
3 During your survey: amphibian survey methods, 29,
4 After your survey, 75,
5 Resources to help you, 95,
References, 107,
Glossary, 112,
Index, 115,