Robert L. Livezey

Bio: Robert L. Livezey is an academic researcher. The author has contributed to research in topics: Desmognathus & Taricha. The author has an hindex of 3, co-authored 6 publications receiving 97 citations.

A Synoptic Key to the Salientian Eggs of the United States

Abstract: Data for the present paper were gleaned from the examination of what preserved material has been available, almost entirely in the museum of Cornell University, a few specimens of fresh egg masses that the writers have been able to collect, and primarily, from the literature of previous authors. In the past only scattered notes on the eggs of the Salientians of this country were published and to date no comprehensive work has been done along this line. It is hoped that such an organization of information as is here presented will be of some use to other workers in the field. Furthermore, by pointing out a few of the difficulties, discrepancies, and lack of information regarding the eggs and egg laying habits of frogs and toads of the United States, it is hoped that others may find it worth their while to attempt to correct the existing state of affairs.

Some Observations on Pseudacris nigrita triseriata (Wied) in Texas

Abstract: The observations hcrein presented are based on studies carried out primarily in the vicinity of Huntsville, Walker County, Texas, from November, 1946 through May, 1949. Because of existing conditions and available time, the most consistent seasoln of observations was conducted in 1949 with emphasis being placed upon the activities of that year. Huntsville is located in a transitional area between the humid, mixed pine-hardwoods of the east and the drier, oak-prairies to the west. Such an area provides abundant varied habitats and breeding sites for amphibians.

An Intergrade Population of the Texas Subspecies of Desmognathus fuscus

Abstract: The range and status of Desmognathus fuscus brimleyorum and D. f. auriculatus in East Texas has been an open question. Sanders and Smith (1949) reported a 1938 collection from Hardin County which greatly extends the southern range of brimleyorum and records for the first time auriculatus from that state. Burger, Smith, and Smith (1949) recorded auriculatus from Orange County, two additional specimens from FHardin County, and a specimen of brimleyorum from Jasper County. Since Bishop's summary (1943) of our knowledge of these races, little has been added to the life history or ecology of the forms.

Influence of Amphibian Larvae on Primary Production, Nutrient Flux, and Competition in a Pond Ecosystem

Abstract: In a pond ecosystem near St. Louis, Missouri, natural variations in tadpole biomass during 1971-1972 were accompanied by shifts in patterns of nutrient cycling and primary production, particularly when metamorphoses caused abrupt removal of these transient consumers. In the field, increased tadpole biomass was associated with: (I) reduced standing crop of suspended particles, including phytoplankton, the tadpoles' major food source; (2) a shift in the state of nitrogen from largely particulate to largely dissolved; (3) reduced rates of primary production, from both H14CO:t uptake and diurnal oxygen methods; (4) a nonlinear effect on phytoplankton specific growth rates; (5) a shift in phytoplankton community structure away from filamentous blue-green algae; and (6) a reduced proportion of active chlorophyll a in the photosynthetic pigments of phytoplankton. From laboratory experiments, the potential impact of tadpoles on nitrogen flux, through feeding and nutrient release, was estimated. Several conclusions were made: (1) Suspension feeding by tadpoles reduced concentrations of suspended particles. Under condi- tions of low particles:high tadpoles, the specific growth rates of tadpoles were reduced. Recruitment was absent except under conditions of high particles:low tadpoles; the most diverse community of new tadpole recruits (four species) was observed under such conditions. All four species (three genera) had similarly sized particles in their guts. These field observations are consistent with an hypothesis of competition among the tadpoles. (2) Tadpoles apparently were regulatory consumers; they became a large component with respect to phytoplankton. Nitrogen flux through tadpoles was within the same order of magnitude, and some- times exceeded the estimated N uptake by phytoplankton. (3) Tadpoles probably regulated primary production by both reducing standing crop and altering specific growth rates of algae. At maximum tadpole biomass, suspended particle concentrations were stabilized near the laboratory-determined threshold concentration for feeding by these Rana tadpoles. When metamorphosis removed these transient consumers, rates of primary production increased dramatically. (4) Interactions within the pond ecosystem apparently determined aquatic-terrestrial nutrient bal- ances for the amphibian communities. Some species deposited more nutrient in their eggs than was assimilated by larvae, but the community as a whole extracted nutrient from the ecosystem. Nutrient input in eggs was much less than that assimilated by autotrophs.

Evolution and ecology of lizard body sizes

Abstract: Aim Body size is instrumental in influencing animal physiology, morphology, ecology and evolution, as well as extinction risk. I examine several hypotheses regarding the influence of body size on lizard evolution and extinction risk, assessing whether body size influences, or is influenced by, species richness, herbivory, island dwelling and extinction risk. Location World-wide. Methods I used literature data and measurements of museum and live specimens to estimate lizard body size distributions. Results I obtained body size data for 99% of the world’s lizard species. The body size‐frequency distribution is highly modal and right skewed and similar distributions characterize most lizard families and lizard assemblages across biogeographical realms. There is a strong negative correlation between mean body size within families and species richness. Herbivorous lizards are larger than omnivorous and carnivorous ones, and aquatic lizards are larger than non-aquatic species. Diurnal activity is associated with small body size. Insular lizards tend towards both extremes of the size spectrum. Extinction risk increases with body size of species for which risk has been assessed. Main conclusions Small size seems to promote fast diversification of disparate body plans. The absence of mammalian predators allows insular lizards to attain larger body sizes by means of release from predation and allows them to evolve into the top predator niche. Island living also promotes a high frequency of herbivory, which is also associated with large size. Aquatic and nocturnal lizards probably evolve large size because of thermal constraints. The association between large size and high extinction risk, however, probably reflects a bias in the species in which risk has been studied.

The integumentary skeleton of tetrapods: origin, evolution, and development

Abstract: Although often overlooked, the integument of many tetrapods is reinforced by a morphologically and structurally diverse assemblage of skeletal elements. These elements are widely understood to be derivatives of the once all-encompassing dermal skeleton of stem-gnathostomes but most details of their evolution and development remain confused and uncertain. Herein we re-evaluate the tetrapod integumentary skeleton by integrating comparative developmental and tissue structure data. Three types of tetrapod integumentary elements are recognized: (1) osteoderms, common to representatives of most major taxonomic lineages; (2) dermal scales, unique to gymnophionans; and (3) the lamina calcarea, an enigmatic tissue found only in some anurans. As presently understood, all are derivatives of the ancestral cosmoid scale and all originate from scleroblastic neural crest cells. Osteoderms are plesiomorphic for tetrapods but demonstrate considerable lineage-specific variability in size, shape, and tissue structure and composition. While metaplastic ossification often plays a role in osteoderm development, it is not the exclusive mode of skeletogenesis. All osteoderms share a common origin within the dermis (at or adjacent to the stratum superficiale) and are composed primarily (but not exclusively) of osseous tissue. These data support the notion that all osteoderms are derivatives of a neural crest-derived osteogenic cell population (with possible matrix contributions from the overlying epidermis) and share a deep homology associated with the skeletogenic competence of the dermis. Gymnophionan dermal scales are structurally similar to the elasmoid scales of most teleosts and are not comparable with osteoderms. Whereas details of development are lacking, it is hypothesized that dermal scales are derivatives of an odontogenic neural crest cell population and that skeletogenesis is comparable with the formation of elasmoid scales. Little is known about the lamina calcarea. It is proposed that this tissue layer is also odontogenic in origin, but clearly further study is necessary. Although not homologous as organs, all elements of the integumentary skeleton share a basic and essential relationship with the integument, connecting them with the ancestral rhombic scale.

Out of the blue: a novel, trans-Atlantic clade of geckos (Gekkota, Squamata)

Abstract: Phylogenetic relationships among gekkotan lizards were estimated from five nuclear protein-coding genes in separate and combined analyses using maximum parsimony, maximum likelihood and Bayesian analyses. All analyses recovered a monophyletic trans-Atlantic gecko clade (Phyllodactylidae) consisting of the genera Asaccus, Haemodracon, Homonota, Phyllodactylus, Phyllopezus, Ptyodactylus, Tarentola and Thecadactylus. No other phylogenetic or taxonomic hypotheses have proposed linking these genera, which have been consistently grouped with other taxa outside of the clade. In this paper, we determine the relationships of this new clade to other major gekkotan groups, evaluate previous phylogenetic hypotheses regarding constituent members of this novel clade, and critically examine the use of historically important morphological characters in gekkotan systematics as they relate to this novel clade, specifically — phalangeal formulae, hyoid morphology and external structure of the toe-pads.