Lawrence G. Abele

Ecological Communities: Conceptual Issues and the Evidence

This work is the first to focus systematically on a much-debated topic: the conceptual issues of community ecology, including the nature of evidence in ecology, the role of experiments, attempts to disprove hypotheses, and the value of negative evidence in the discipline.Originally published in 1984.The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These paperback editions preserve the original texts of these important books while presenting them in durable paperback editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.

Island Biogeography Theory and Conservation Practice

The application of island biogeography theory to conservation practice is premature. Theoretically and empirically, a major conclusion of such applications—that refuges should always consist of the largest possible single area—can be incorrect under a variety of biologically feasible conditions. The cost and irreversibility of large-scale conservation programs demand a prudent approach to the application of an insufficiently validated theory.

REFUGE DESIGN AND ISLAND BIOGEOGRAPHIC THEORY: EFFECTS OF FRAGMENTATION

Coles theoretical conclusion that one large site generally contains more species than several small ones of equal total area is falsified by data in the literature, as is his contention that exceptions will only occur when the species in the sites are but a small fraction of those in the species pool. For a variety of taxa, for a number of different habitat types, and for a wide range of sizes of the biota as a fraction of the pool, either there is no clear best strategy, or several small sites are better than one large site. Since there are numerous idiosyncratic biological considerations, plus a number of nonbiological ones that bear heavily on refuge design, it is unlikely that a general reductionist model can generate useful predictions or advice on this matter.

Experiments on Competition and Predation Among Shrimps of Seagrass Meadows

A series of experiments was conducted to evaluate the distribution and abundance patterns of two species of macrophyte—inhabiting caridean shrimps found in Apalachee Bay, Florida, USA. Experiments using Palaemonetes vulgaris and Palaemon floridanus included microhabitat association and behavioral interactions. Predator—prey relationships, as they apply to habitat complexity and interspecifc interactions, were also examined using the pinfish, Lagodon rhomboides, a natural predator. Pt. vulgaris individuals were excluded from the experimental habitats by P. floridanus over a range of densities. We conclude that their nonoverlapping microgeographical distribution is primarily a consequence of interspecific competition rather than just microhabitat selection. Predation success on single species was inversely related to the physical complexity of the experimental habitat. However, when placed together, a significantly greater proportion of Pt. vulgaris is consumed than P. floridanus. We posit that the displacement of Pt. vulgaris from cover by P. floridanus significantly increases the formers risk of detection and capture. The importance of refuges in regard to: (1) seagrass predator strategies; (2) prey tactics, and (3) species abundance and richness patterns in macrophyte—dominated communities are discussed.

Crustacean phylogeny inferred from 18S rDNA

Resolution concerning issues of higher-order crustacean phylogeny remains elusive even after years of thorough morphological and palaeontological scrutiny. Surprisingly, there is as yet no consensus regarding even the number of constituent crustacean classes. One view (Schram, 1986) based on a cladistic analysis of morphological characters suggests there are four classes: Remipedia, Phyllocarida, Maxillopoda and Malacostraca (Figure 14.1(a)); an alternative cladistic analysis (Brusca and Brusca, 1990) suggests there are five: Remipedia, Branchiopoda, Cephalocarida, Maxillopoda and Malacostraca (Figure 14.1(b)). Still another view (Bowman and Abele, 1982), presented as a classification rather than a phylogeny, divides crustaceans into six classes: the five aforementioned groups and the Ostracoda (Figure 14.1(c)).

Natural history and social organization of the semiterrestrial grapsid crab Pachygrapsus transversus (Gibbes)

Pachygrapsus transversus (Gibbes) was studied in the intertidal zone of the Bay of Panama. Individuals are active at all low tides as soon as their habitat is exposed. Crabs on large rocks occupy holes and crevices that provide food, refuge from predators, and relief from thermal stress. Males and females move daily from the refuge rocks to flat smooth rocks where they graze on algae. P. transversus is omnivorous, feeding on algae, porcelain crabs, fish and conspecifics. Predators on the crabs include raccoons, fish, and birds. Behavioral displays of P. transversus are described. Males maintain non-exclusive core areas on the refuge rocks, with larger males defending larger areas. A typical area contains a single dominant male, zero to five subordinate males, three to eight mature females, and seven to 25 non-interacting juveniles. All observed matings occurred on these areas; dominant males copulated in 83–88% of the matings. We suggest that predation and heat stress are the selection pressures favoring use of holes as refuges. The fact that some holes are occupied by females may have led to the evolution of male dominance and defense of these areas.

Comparative species richness in fluctuating and constant environments: coral-associated decapod crustaceans.

The number of decapod species associated with the coral Pocillopora damicornis is compared between two regions on the Pacific coast of Panama which are of the same geologic age but differ in environmental characteristics. The relationship between number of species and coral head size does not differ between the two regions but species composition among coral heads is more variable in the fluctuating environment. Thus there are more species (55 compared to 37) associated with corals in the fluctuating environment than in the constant environment. These data impugn the concept that environmental constancy increases species richness. They support the hypothesis that species equilibrium within habitats is maintained by measurable ecological factors—in this case, the effects of a natural physical disturbance.

Phylogenetic Study of Cirripedes and Selected Relatives (Thecostraca) Based on 18s Rdna Sequence Analysis

ABSTRACT Sequence data from PCR-amplified 18S rDNA were used to infer phylogenetic relationships among the thecostracan crustacean taxa Ascothoracida (Ulophysema oeresundense), Acrothoracica (Berndtia purpurea, Trypetesa lampas), Rhizocephala (Loxothylacus texanus), and Thoracica (Calantica villosa, Lepas anatifera, Octolasmis lowei, Chthamalus fragilis, Chelonibia patula, Tetraclita stalactifera, Balanus eburneus). Sequence-divergence estimates ranged from 1.8% for 2 acrothoracican taxa to 24.3% for an ascothoracidan and a balanomorph thoracican. Parsimony, invariants, and neighbor-joining analyses all showed the Ascothoracida and Acrothoracica to be sister taxa and very early thecostracan lineages widely separated from the Rhizocephala, which in turn is the sister group to the Thoracica. A comparison of the secondary structure of the V3 variable domain in the 18S rRNA molecule for these taxa supports this result somewhat: the acrothoracican V3 structure is phenetically more similar to that of the ascothoracidan and branchiopods than to the other cirripedes. There is some disagreement between a morphology-based phylogeny and the current one based on molecular characters. It may result from molecular evidence suggesting an early origin and divergence of the Acrothoracica from the main cirripede lineage, as well as a substitution rate in the lineage leading to the Rhizocephala + Thoracica that is very much higher (10-12 times) than those in the other thecostracan lineages examined. Within the Thoracica, the sessile balanomorphs appear to be derived from a lineage related to scalpelloid lepadomorphs, but variation in the 18S molecule among balanomorphs is insufficient to permit inference of relationships within this group. We conclude that the Thecostraca, represented here by the subclasses Ascothoracida and Cirripedia (the latter including the Acrothoracica, Rhizocephala, and Thoracica), is a monophyletic taxon.

Ultrastructure and functional morphology of feeding and associated appendages in the tropical fresh-water shrimp Atya innocous (Herbst) with notes on its ecology

ABSTRACT Atya innocous (Atyidae) occurs in permanent and temporary fresh-water streams in Panama. Its microhabitat distribution depends in part on the presence of congeners. The propodus and dactylus of each cheliped of A. innocous bear about 300 setae modified for specific functions in food collection. These setae may be divided into three basic types: chemoreceptors, scrapers, and filtering setae. The latter two types also function as mechanoreceptors. The cheliped setae are probably extended by an increase in hemocoelic pressure, producing an efficient filtering fan. Mechanosensory and chemosensory bipolar neurons innervate the cheliped setae, presumably providing the shrimp with the ability to detect current velocity, particulate load, and quality of the food source. The external morphology and ulrastructure of these sensilla are described. No dually innervated receptors (mechanochemoreceptors) were found. In addition to food collection and sensory functions, the pereiopods are used to groom body parts and brooded embryos. Super-8 eine films show the important role mouthparts play in grooming. The third maxillipeds groom the antennae and antennules, while the ultimate segment of the second maxillipeds frees lodged debris from the chelipeds. The dactylar pectinate comb of the fifth pereopod grooms the dorsal surface of the abdomen and pleopods. Scanning electron microscopy showed pores in the cuticle leading to unicellular and multicellular glands within the epidermis. Three gland types were observed and their respective functions are described. Adaptations for a lotic habitat seem to be important to species of Atya, which have a wide array of morphological modifications for life in running water.

Peracarid monophyly and interordinal phylogeny inferred from nuclear small-subunit ribosomal DNA sequences (Crustacea: Malacostraca: Peracarida)

ABSTRACT Peracarids are a large group of malacostracan crustaceans whose systematics and phylogeny are uncertain. The present phylogenetic study of peracarids is, to our knowledge, the first that includes full-length nuclear (n) small-subunit (SSU) ribosomal DNA (rDNA) sequences for representatives of every peracarid order. Sequence length varied substantially (1807–2746 base pairs), and two variable regions (V4 and V7) contained long expansion segments. Variable regions also exhibited significantly greater heterogeneity in nucleotide frequencies than did core regions. Maximum-parsimony, maximum-likelihood, Bayesian, and distance phylogenetic estimates indicated a monophyletic Peracarida that excluded the Mysida and included the Thermosbaenacea. This peracarid clade received strong support under Bayesian, maximum-parsimony, and distance analyses, but not maximum likelihood. Further, the thermosbaenacean lineage does not occupy a basal position relative to other peracarids, as suggested by many morphology-based phylogenies. The phylogenetic position of the Mysida within the Malacostraca remains uncertain, but a sister-group relationship between Mysida and Lophogastrida (i.e., a monophyletic Mysidacea) was consistently rejected, a result that also differs from those of most morphology-based phylogenies. High Bayesian clade-credibility support was obtained for an (Isopoda + Tanaidacea + Cumacea) clade and a (Lophogastrida + [Spelaeogriphacea + Amphipoda]) clade. Within the peracarid clade, internal branches were considerably shorter than terminal ones, so relationships among some peracarid lineages were equivocal. Data partitions corresponding to stem and loop regions in a secondary-structure model for nSSU rRNA had congruent phylogenetic signal but differed in nucleotide composition and evolutionary model. Maximum parsimony and Bayesian phylogenetic estimates based on the loop partition generally shared more nodes in trees inferred from combined data than did those based on stems, even though the stem partition had roughly twice as many characters.