CONTENTS
1.
Introduction…………………………………………..
1
2.
Amphibians…………………………………………... 1
3.
Farm pond ecology…………………………………... 2
4. Habitat requirements for Amphibians……………...
3
5.
Post-breeding habitat use ………………………….... 3
6.
Water Chemistry and Toxicity of Ponds…………… 3
7.
Amphibian Larval ……………………………………
3
8. Summary……………………………………………… 4
9. References…………………………………………….. 5
Introduction
Constructed farm ponds
represent significant breeding, rearing, and over-wintering habitat for
amphibians in the Driftless Area Ecoregion of southeastern Minnesota, western
Wisconsin, and northeastern Iowa, a landscape where natural wetlands are
scarce.Despite intensive agricultural use adjacent to the ponds, these ponds
harbor an abundance of frogs and toads
The purpose of these farm
ponds is to prevent soil erosion and create wildlife habitat, yet no studies
have been conducted to determine how the ponds benefit wildlife. Habitat and
water quality in these ponds directly affects livestock health where grazing is
practiced. The karst geology of the area promotes rapid water movement from
surface waters into ground water used for human consumption. Minnesota has been
plagued by the discovery of frog deformities in some agricultural areas; farm
ponds have not been examined to determine if amphibian deformities are a
problem in the Driftless Area. Based on our experience and study results, we
will recommend screening/monitoring methods suitable for assessing the health
of amphibian populations in farm ponds. We will also develop a guide to the
design, construction, and management of farm ponds for use by contractors,
private landowners, and state and federal agencies.
What is meant by Native?
Living or growing naturally in a
particular place or region; indigenous. Occurring in nature on its own,
uncombined with other substances. Copper and gold are often found in native form. Of or relating to the naturally occurring
conformation of a macromolecule, such as a protein.
Amphibians
Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. Modern amphibians are all Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Thus amphibians typically start out
as larvae living
in water, but some species have developed behavioural adaptations to bypass
this. The young generally undergo metamorphosis from larva with gills to an adult
air-breathing form with lungs. Amphibians use their skin as a secondary
respiratory surface and some small terrestrial salamanders and frogs lack
lungs and rely entirely on their skin. They are superficially similar to lizards but,
along with mammals and birds, reptiles are amniotes and do not require water bodies in
which to breed. With their complex reproductive needs and permeable skins,
amphibians are often ecological indicators;
in recent decades there has been a dramatic decline in amphibian
populations for
many species around the globe.
The earliest amphibians evolved in the Devonian period
from sarcopterygian fish with lungs and bony-limbed fins,
features that were helpful in adapting to dry land. They diversified and became
dominant during the Carboniferousand Permian periods, but were later displaced by
reptiles and other vertebrates. Over time, amphibians shrank in size and
decreased in diversity, leaving only the modern subclass Lissamphibia. The three modern orders of amphibians are Anura (the frogs
and toads), Urodela (the
salamanders), and Apoda (the caecilians). The number of known amphibian species
is approximately 7,000, of which nearly 90% are frogs. The smallest amphibian
(and vertebrate) in the world is a frog from New Guinea with a length of just 7.7 mm
(0.30 in). The largest living amphibian is the 1.8 m (5 ft 11 in) Chinese giant salamander
but this is dwarfed by the extinct 9 m (30 ft) Prionosuchus from
the middle Permian of Brazil. The study of amphibians is called batrachology, while the study of both reptiles and amphibians
is called herpetology.
Farm pond ecology
Ponds consist of complex systems that support various
forms of life. The basis of aquatic life in a farm pond is phytoplankton. These
are small, usually single-celled, photosynthetic organisms, also known as
algae. Other small organisms that live in ponds are called zooplankton, which
are members of the animal kingdom that are suspended in the water column.
Common examples of zooplankton are rotifers, cladoceras (water fleas), and
copepods. Zooplankton, insects, crustaceans, and tadpoles that live in the
pond consume phytoplankton. Larger invertebrates, including gastropods
(snails), bivalves (fingernail clams), oligochaetes (worms), annelids (leeches),
decapods (crayfish), and insects consume these smaller animals, creating the
complex food webs that occur in the farm pond ecosystem. The typical farm pond
ecosystem can support an extensive array of plants, insects, amphibians,
reptiles, fish, and birds.
Habitat requirements for Amphibians
Habitat requirements
and principles Amphibians have complex life cycles. This refers to the fact
that the life cycle includes a larval (tadpole) stage which is terminated by
metamorphosis into a juvenile which has a completely different morphology and
lifestyle. The pre-metamorphic stage is dependent on an aquatic environment;
the post-metamorphic stages (juvenile and adult) include long periods living on
land. Even in the terrestrial habitat, amphibians are heavily dependent on
water. They have permeable skins which make them prone to desiccation, although
tolerance of arid conditions varies between species. The best amphibian
breeding sites also tend to be ‘good wildlife ponds’. Much of the advice given
in this handbook mirrors that provided by Pond Conservation regarding high
quality pond habitats (Williams et al., 2010 and the Pond Creation Toolkit).
Terrestrial habitat requirements for most native species are fairly generic, as
amphibians can occupy a variety of different habitat types. The natter jack
toad is an exception, requiring sparsely vegetated sites that are inhospitable
to the other species.
Post-breeding habitat use
We worked to refine methods of attaching radio-transmitters
to leopard frogs (Rana pipiens) for purposes of describing post-breeding
habitat use. Beginning 1 August 2000, frogs were captured in a wet meadow
adjacent to a natural pond, one of the farm pond reference sites, and outfitted
with radio transmitters. We could not obtain radio prior to August, due to a
backlog of orders at the manufacturer. The frogs were outfitted with radio
transmitters attached to each frog’s back with a harness. The frogs experienced
problems with skin erosion and they slipped out of the transmitters with all
combinations of materials and strapping methods we tried. We decided to hold
the frogs in enclosures while we worked on refining our methods. The frogs were
confined for observation in 1.8 X 1.8 m cages on the periphery of the pond.
We tried nickel bead chain, aluminum bead chain, plastic
cable ties, and sewing elastic as harness materials. Frogs were located and
their health status evaluated every 2-4. Removed the harness and transmitter
and released frogs that developed skin lesions.
Water Chemistry and Toxicity of
Ponds
Water
samples were collected approximately 1 m from the shoreline at mid-depth. All
water samples were labeled and immediately placed in coolers on ice. Sample
numbers and codes were assigned to each sample to ensure blind testing of each
sample by laboratory staff. Water for chemical analysis (100 ml) was frozen
until analysis. Water samples for the FETAX and MICROTOX analyses (200 ml,
described below) were collected in chemically clean amber bottles with Teflon
caps and reduced head space (to minimize volatilization), transported on ice to
the laboratory, and stored in the dark at 4 C until use.
Amphibian
Larval
The presence of
larvae is good evidence that breeding was successful and that site conditions
support larval development. There are a number of methods used to survey
amphibian larvae We recommend defining a search area for larval larvae
collected during a 20-min dip net effort in a bucket. We then identified larvae
by species and recorded their abundances (Appendix B). The ability to
successfully collect larvae depends on the density of larvae and the habitat
characteristics. Small, temporary ponds may have relatively high densities of
larval amphibians that can be collected with little effort. Larger,
interconnected, permanent wetlands tend to have more dispersed populations of
larval amphibians that increases the effort required. Most amphibian larvae can
be found among aquatic vegetation or other sheltering objects, where they seek
food and refuge from predators. Toad tadpoles can often be seen in large
schools in shallow, open water. Amphibian larvae with a dip net requires
walking carefully and slowly through the water, sweeping the net through stands
of aquatic vegetation. In shallow, turbid, sparsely vegetated areas, larvae can
often be found resting on the bottom. To prevent the escape of larvae, work
from deeper water towards shallower areas. Immediately place collected larvae
in a bucket containing water from the site. Put 2 to 3 L of water in the bucket
and place it out of direct sunlight to prevent the larvae from overheating.
Funnel traps are another tool for collecting larvae. Funnel traps are useful
when it is logistically feasible to deploy and check them regularly and when
dense vegetation impedes the use of dip nets or seines. Because of the
logistical considerations of sampling many sites, we collected the same species
with less time using dip nets. Identifying larvae in the field can be difficult
for novices. Training by a herpetologist in the field is the best way to learn
to identify larvae. Keys to amphibian larvae and are useful in identifying
species or groups of species. Some species can only be differentiated during
the larval stage by examination of larval tooth patterns with the aid of a
microscope .We recommend this only if you have training in amphibian larval
identification. If you are unsure of your identifications, options include
consulting a herpetologist or raising the larvae in the laboratory and making
an identification from a metamorph or juvenile amphibian.
Summary
American toads, green frogs, spring
peepers, chorus frogs and leopard frogs at >32 ponds, making them the most
common species identified. Common and scientific names for all species are
based on the Integrated Taxonomic Information System. Pickerel frogs, tiger
salamanders, and wood frogs were less common; these species were found at 13 or
fewer ponds. Calling surveys had the best correlation with the total number of
ponds where each species was identified, followed by dipnetting and visual
search for adults (Table 1). Egg mass surveys were least successful in
identifying species presence (Figs. 4 and 5). However, egg mass surveys were
useful for wood frogs and American toads because their egg masses are easily
observed and identified. Calling surveys were not as useful for leopard frogs
and pickerel frogs, missing about ½ of the ponds where these species were ultimately
found. For leopard frogs and pickerel frogs, adult visual search was the most
successful survey method. We recommend calling surveys plus dipnetting and egg
mass surveys for most species. In addition, adult visual search should be used
where leopard or pickerel frogs are suspected. For tiger salamanders,
dipnetting and funnel traps are the best methods of identification. We found
drift fences with pit traps to be too time-intensive for our purposes. Humane
treatment of animals requires that traps be set and checked on a strict
timetable to avoid mortality. Drift fences will be most useful when the number
of sites is very low and travel distances to check them short. Salamanders were
the only non-calling species in our ponds, and they were easily identified in
the larval stage by dipnetting.
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