A nesting association between semi-colonial Bullock's orioles and yellow-billed magpies: evidence for the predator protection hypothesis

Mixed-species nesting associations have been reported for many birds. However, few studies have shown that one species specifically chooses to nest close to another in order to obtain a direct benefit and only two studies have managed to adequately test the predator protection hypothesis for such associations. Here we demonstrate a nesting association between Bullock's orioles (Icterus galbula bullockii) and yellow-billed magpies (Pica nuttalli). The evidence indicates that this is an active association in which, given a choice of suitable habitat areas in which to nest, orioles choose those areas that contain magpie nests. Oriole nests associated with magpie nests have a significantly reduced predation rate compared to those without associated magpie nests. This suggests that orioles prefer to nest near to magpies and that this preference has evolved due to the protection provided by neighbouring magpies. The nesting association results in the clumping of oriole nests around magpie nests, and therefore provides a possible explanation for the semi-colonial nature of Bullock's orioles. Received: 23 November 1998 / Received in revised form: 25 May 1999 / Accepted: 30 May 1999     

Delayed plumage maturation in the orchard oriole (Icterus spurius): tests of winter adaptation hypotheses

Summary Explanations of delayed plumage maturation (DPM) in passerines have focused on potential breeding season advantages for non-definitive (subadult) plumage. In contrast, the molt constraint hypothesis (Rohwer and Butcher 1988) proposes that subadult plumage is a winter adaptation, increasing winter survivorship by decreasing intraspecific aggression (the winter status signaling hypothesis) or predation (the winter crypsis hypothesis). Under the molt constraint hypothesis, nondefinitive breeding plumage is non-adaptive, resulting from species-specific constraints on the number of feathers replaced during the pre-alternate (spring) molt. In studies conducted on an overwintering population of orchard orioles in Panama, I tested predictions of both the winter status signaling and molt constraint hypotheses. Contrary to predictions of winter status signaling, I found no evidence that subadult plumage reduces adult male aggression toward subadults. Agonistic encounters occurred at random with respect to plumage and the intensity of adult male/subadult male encounters was not lower than the intensity of encounters occurring within age classes. Contrary to the molt constraint hypothesis, I found no evidence that the number of feathers exchanged by subadults in their pre-alternate molt is the sole constraint on the development of subadult breeding plumage. The majority of feathers grown by molting subadult orioles during January and February were of non-definitive coloration. These results, together with results of earlier breeding season experiments which tested summer communication hypotheses for DPM in this species, suggest that subadult plumage in the orchard oriole may be non-adaptive and the result of constraints on plumage development. They also indicate, however, that the extent of the pre-alternate molt is not the sole source of that constraint.     

Coloration in New World orioles

Summary Although sexual dichromatism in birds is usually ascribed to sexual selection, some workers argue that avian coloration is better explained by predation-related selection pressures. Supporting evidence for these latter hypotheses comes primarily from broad interspecific comparisons, which can be biased by a variety of factors. This study examines the predation-based hypotheses of Baker and Parker (1979), particularly the Predator Deflection Hypothesis, with reference to two closely-related oriole species: Icterus parisorum, which is dichromatic, and I. gularis, in which both sexes are brightly coloured. To test the prediction that bright coloration serves to divert the attention of predators away from cryptic young, rates of predation on nests of conspicuous (2 years of age or older) and dull-coloured (first-year). I. parisorum males were compared. The results showed equal predation on the young of males in both age/plumage classes. The Predator Deflection Hypothesis also predicts that, once a predator has been detected, brightly-coloured birds should attempt to distract it, whereas cryptic individuals should not. Tests using models of avian predators showed that this was not the case: cryptic I. parisorum females responded as aggressively toward the model as did conspicuous conspecific males. The same was true for I. gularis. Overall, the results did not support the idea that bright coloration has evolved in response to predation pressure in these species.     

Effects of Restoring Oak Savannas on Bird Communities and Populations

Abstract:  Efforts to restore and maintain oak savannas in North America, with emphasis on the use of prescribed fire, have become common. Little is known, however, about how restoration affects animal populations, especially those of birds. I compared the breeding densities, community structure, and reproductive success of birds in oak savannas maintained by prescribed fire (12 sites) with those in closed-canopy forests (13 sites). All sampling was conducted in Illinois (U.S.A.). Of the 31 bird species analyzed, 12 were more common in savannas, 14 were not affected by habitat structure, and 5 were more common in forest habitat. The species favored by disturbance and restoration included Northern Bobwhites ( Colinus virginianus ), Mourning Doves (  Zenaida macroura ), Red-headed Woodpeckers (  Melanerpes erythrocephalus ), Indigo Buntings (  Passerina cyanea ), and Baltimore Orioles ( Icterus galbula ). Those more common in closed-canopy forest included Ovenbirds ( Seiurus aurocapilla ) and Wood Thrushes (  Hylocichla mustelina ). Few species were unique to one type of habitat, but overall avian community structure in oak savannas and closed-canopy forests was generally distinctive. Estimates of nesting success (derived from 785 nests) revealed that 6 of the 13 species considered experienced greater productivity in the savanna habitat. Rates of brood parasitism were unaffected by restoration and habitat structure. Within savannas, tract size had little effect on breeding abundances and reproductive success. My results illustrate that restoration techniques can significantly affect the ecology of constituent animal populations and communities and have key implications regarding avian conservation and the management of forest habitat in fragmented landscapes. Small patches of forest habitat that regularly function as population sinks may offer far better prospects for birds if they are subjected to disturbance and ecosystem restoration.     

Phylogenetic Reanalysis of the Saudi Gazelle and Its Implications for Conservation

Abstract: The identification of taxonomically appropriate populations of endangered species for captive breeding and reintroduction programs is fundamental to the success of those programs. The Saudi gazelle (   Gazella saudiya ) was endemic to the Arabian peninsula but is now considered extinct in the wild and is potentially a candidate for captive breeding and reintroduction. Using 375 base pairs of mitochondrial DNA (mtDNA) cytochrome b gene derived from museum samples collected from the wild prior to the presumed extinction of this species, we show that G. saudiya is the sister taxon of the African dorcas gazelle (  G. dorcas ). Reciprocal monophyly of G. saudiya mtDNA haplotypes with G. dorcas , coupled with morphological distinctiveness, suggests that it is an evolutionarily significant unit. These data indicate that captive populations identified previously as potential sources of G. saudiya for captive breeding appear incorrectly designated and are irrelevant to the conservation of G. saudiya. The polymerase chain reaction–restriction fragment length polymorphism ( PCR-RFLP) analysis of several private collections of living gazelles in Saudi Arabia provides no evidence for the survival of G. saudiya. We recommend that field surveys be undertaken to establish whether G. saudiya is indeed extinct in the wild and that other private collections within the Arabian peninsula be screened genetically. We urge caution when captive animals of unknown provenance are used to investigate the phylogenetics of cryptic species groups.     

Genetics, Taxonomy, and Conservation of the Threatened California Gnatcatcher

Abstract: The California Gnatcatcher (   Polioptila californica ) has become a flagship species in the dispute over development of southern California's unique coastal sage scrub habitat, a fragile, geographically restricted ecosystem with high endemism. One aspect of the controversy concerns the status of the subspecies of this bird in southern California coastal sage scrub that is currently listed as threatened under the U.S. Endangered Species Act. To investigate the recent population history of this species and the genetic distinctiveness of subspecies and to inform conservation planning, we used direct sequencing of mitochondrial DNA (mtDNA) for 64 individuals from 13 samples taken throughout the species' range. We found that coastal sage scrub populations of California Gnatcatchers are not genetically distinct from populations in Baja California, which are dense and continuously distributed throughout the peninsula. Rather, mtDNA sequences from this species contain the signatures of population growth and support a hypothesis of recent expansion of populations from a southern Baja California refugium northward into the southern coastal regions of California. During this expansion, stochastic events led to a reduction in genetic variation in the newly occupied range. Thus, preservation of coastal sage scrub cannot be linked to maintaining the genetic diversity of northern gnatcatcher populations, despite previous recognition of subspecies. Our study suggests that not all currently recognized subspecies are equivalent to evolutionarily significant units and illustrates the danger of focusing conservation efforts for threatened habitats on a single species.     

Effects of Artisanal Fishing on Caribbean Coral Reefs

Abstract:  Although the impacts of industrial fishing are widely recognized, marine ecosystems are generally considered less threatened by artisanal fisheries. To determine how coral reef fish assemblages and benthic communities are affected by artisanal fishing, we studied six Caribbean islands on which fishing pressure ranged from virtually none in Bonaire, increasing through Saba, Puerto Rico, St Lucia, and Dominica, and reaching very high intensities in Jamaica. Using stationary-point fish counts at 5 m and 15 m depth, we counted and estimated the lengths of all noncryptic, diurnal fish species within replicate 10-m-diameter areas. We estimated percent cover of coral and algae and determined reef structural complexity. From fish numbers and lengths we calculated mean fish biomass per count for the five most commercially important families. Groupers (Serranidae), snappers (Lutjanidae), parrotfish (Scaridae), and surgeonfish (Acanthuridae) showed order-of-magnitude differences in biomass among islands. Biomass fell as fishing pressure increased. Only grunts (Haemulidae) did not follow this pattern. Within families, larger-bodied species decreased as fishing intensified. Coral cover and structural complexity were highest on little-fished islands and lowest on those most fished. By contrast, algal cover was an order of magnitude higher in Jamaica than in Bonaire. These results suggest that following the Caribbean-wide mass mortality of herbivorous sea urchins in 1983–1984 and consequent declines in grazing pressure on reefs, herbivorous fishes have not controlled algae overgrowing corals in heavily fished areas but have restricted growth in lightly fished areas. In summary, differences among islands in the structure of fish and benthic assemblages suggest that intensive artisanal fishing has transformed Caribbean reefs.     

Long-Term Changes in the Avifauna of Barro Colorado Island, Panama, a Tropical Forest Isolate

Since its isolation from the mainland more than 85 years ago, 65 bird species have disappeared from Barro Colorado Island, Panama. Because of these extinctions the island is often used as a model for the study of faunal relaxation, or loss of species through time. The most recent survey of the island's bird community was completed in 1970. Between June 1994 and May 1996 I surveyed the island and observed 218 species, including 5 species never before recorded. Three relatively sedentary species have experienced severe population declines since Willis's 1970 survey and may be on the brink of disappearing from the island. Willis estimated 500 Slate-colored Grosbeaks ( Pitylus grossus ), whereas I found only two pairs of this conspicuous midstory-dwelling finch. Two cotingas—Speckled Mourner ( Laniocera rufescens ) and Rufous Piha ( Lipaugus unirufus )—have declined by 85–95%. I did not locate any individuals of 36 other species that were present during the 1970s. Most (21) of these are uncommon aquatic or nocturnal species, which I may have missed during my surveys, or are rare to uncommon edge species that probably move frequently to and from the island. Seven species, however, are primarily inhabitants of second-growth forest and have been lost probably because of continuing successional maturation of the forest, including changes in land use around the laboratory clearing. Seven forest-dwelling species disappeared during the 1970s and have not recolonized. I detected only one sedentary forest-dwelling species, Great Currasow ( Crax rubra ), that previously had been reported as missing from the island. The nearly complete lack of recolonizations by such forest-interior species suggests that local extinction from tropical forest isolates may be extremely persistent. Tropical forest reserves as small as Barro Colorado Island (1600 ha) may not preserve high levels of regional avian diversity over long periods of time.     

Genetic Variability in mtDNA of the Silvery Gibbon: Implications for the Conservation of a Critically Endangered Species

Abstract: The silvery gibbon (   Hylobates moloch ), endemic to the island of Java, relies on closed-canopy, lowland evergreen forest for its survival. Because Java has lost over 91% of its original forest, silvery gibbons currently occupy small, isolated forest fragments and are threatened with extinction. To contribute to a comprehensive conservation strategy for this species, we analyzed the mtDNA control region of 31 silvery gibbons representing most remaining populations. Our results suggest the presence of at least two genetically differentiated lineages: a "western" lineage, represented by the largest remaining natural population in Gunung Halimun National Park and a "central" lineage, consisting of smaller, more isolated populations in and around the Gunung Masigit/Simpang/Tilu complex, Gunung Gede/Pangrango, and Gunung Slamet. These two lineages, at a minimum, represent different management units that should, except in the most dire circumstances, be managed separately.     

Low Genetic Variability in the Hawaiian Monk Seal

The Hawaiian monk seal (   Monachus schauinslandi) is a critically endangered species that has failed to recover from human exploitation despite decades of protection and ongoing management efforts designed to increase population growth. The seals breed at five principal locations in the northwestern Hawaiian islands, and inter-island migration is limited. Genetic variation in this species is expected to be low due to a recent population bottleneck and probable inbreeding within small subpopulations. To test the hypothesis that small population size and strong site fidelity has led to low within-island genetic variability and significant between-island differentiation, we used two independent approaches to quantify genetic variation both within and among the principal subpopulations. Mitochondrial control region and tRNA gene sequences (359 base pairs) were obtained from 50 seals and revealed very low genetic diversity (0.6% variable sites), with no evidence of subpopulation differentiation. Multilocus DNA fingerprints from 22 individuals also indicated low genetic variation in at least some subpopulations (band-sharing values for "unrelated" seals from the same island ranged from 49 to 73%). This method also provided preliminary evidence of population subdivision (  F'_st estimates of 0.20 and 0.13 for two adjacent island pairs). Translocations of seals among islands may therefore have the potential to relieve local inbreeding and possibly to reduce the total amount of variation preserved in the population. Genetic variation is only one of many factors that determine the ability of an endangered species to recover. Maintenance of existing genetic diversity, however, remains an important priority for conservation programs because of the possibility of increased disease resistance in more variable populations and the chance that inbreeding depression may only be manifest under adverse environmental conditions.     

The Biogeography of Globally Threatened Seabirds and Island Conservation Opportunities

Seabirds are the most threatened group of marine animals; 29% of species are at some risk of extinction. Significant threats to seabirds occur on islands where they breed, but in many cases, effective island conservation can mitigate these threats. To guide island‐based seabird conservation actions, we identified all islands with extant or extirpated populations of the 98 globally threatened seabird species, as recognized on the International Union for Conservation of Nature Red List, and quantified the presence of threatening invasive species, protected areas, and human populations. We matched these results with island attributes to highlight feasible island conservation opportunities. We identified 1362 threatened breeding seabird populations on 968 islands. On 803 (83%) of these islands, we identified threatening invasive species (20%), incomplete protected area coverage (23%), or both (40%). Most islands with threatened seabirds are amenable to island‐wide conservation action because they are small (57% were <1 km²), uninhabited (74%), and occur in high‐ or middle‐income countries (96%). Collectively these attributes make islands with threatened seabirds a rare opportunity for effective conservation at scale. La Biogeografía de Aves Marinas Amenazadas Globalmente y las Oportunidades de Conservación en Islas     

Where is the western limit of the tropical Indian Ocean seaweed flora? An analysis of intertidal seaweed biogeography on the east coast of South Africa

New, large-scale collections have been made of marine benthic macroalgae (seaweeds) on the east coast of South Africa, and the distributions of shallow-water species were analyzed in detail by multivariate, clustering and -diversity methods. The two northernmost sites are distinct, with a predominance of tropical species, and it is concluded that the changeover from a tropical Indian Ocean flora to a temperate South African flora occurs most rapidly in the vicinity of St. Lucia, 135 km south of the Mozambique border. It is imperative that all future biogeographical studies on the South African inshore marine biota include detailed collections north of St. Lucia. The remaining 440 km of the South African east coast (southern and central Kwazulu-Natal Province) is populated by a mixture of tropical and temperate elements, with only 2% endemism in this data set. This, thus, represents a true overlap region, with relatively equal numbers of species with affinities in the temperate Agulhas and tropical Indo–West Pacific floras, rather than a distinctive sub-tropical marine province, as the South African east coast is considered to be by most previous authors. The distinction between this overlap region and the south coast (Agulhas) region proper is not as clearly distinct. The change from a temperate to a tropical flora shows a relative increase in green algae from 15% to 25% of the species present. Criteria for the delineation of marine biogeographical regions are critically discussed, and it is concluded that the monitoring of distributions of all species, including rare species, is necessary. This is particularly relevant with regard to using these data to assess effects of potential changes in seawater temperature, including those which may be caused by global warming. Criteria for the delimitation of biogeographic entities such as "marine provinces" need to be clearly spelt out in all investigations.Communicated by O. Kinne, Oldendorf/Luhe     

Low levels of genetic variation in mtDNA sequences over the western Mediterranean and Atlantic range of the sponge<Emphasis Type="Italic"> Crambe crambe</Emphasis> (Poecilosclerida)

Crambe crambe is a common encrusting sponge found in the Mediterranean and Atlantic littoral. An analysis of a partial sequence (535 bp) of the mitochondrial DNA (mtDNA) gene cytochrome oxidase subunit I (COI) was conducted in an attempt to determine population structure in this species. This is the first study of population genetics using this kind of marker in the phylum. Samples (N=86) were taken in eight populations separated by distances from 20 to 3,000 km, spanning from the western Mediterranean to the Atlantic. Low variability of this gene was found, as only two haplotypes were identified, along with low nucleotide diversity (=0.0006). However, the different frequencies found among populations revealed genetic structure and low gene flow between close populations, as expected from the dispersal biology of the species. The low variability found in sponges is in agreement with reports on cnidarians and points to a high conservation of mtDNA in diploblastic phyla.     

Evolution of Nesting Height in an Endangered Hawaiian Forest Bird in Response to a Non‐Native Predator

Abstract: The majority of bird extinctions since 1800 have occurred on islands, and non‐native predators have been the greatest threat to the persistence of island birds. Island endemic species often lack life‐history traits and behaviors that reduce the probability of predation and they can become evolutionarily trapped if they are unable to adapt, but few studies have examined the ability of island species to respond to novel predators. The greatest threat to the persistence of the Oahu Elepaio (Chasiempis ibidis), an endangered Hawaiian forest bird, is nest predation by non‐native black rats (Rattus rattus). I examined whether Oahu Elepaio nest placement has changed at the individual and population levels in response to rat predation by measuring nest height and determining whether each nest produced offspring from 1996 to 2011. Average height of Oahu Elepaio nests increased 50% over this 16‐year period, from 7.9 m (SE 1.7) to 12.0 m (SE 1.1). There was no net change in height of sequential nests made by individual birds, which means individual elepaios have not learned to place nests higher. Nests ≤3 m off the ground produced offspring less often, and the proportion of such nests declined over time, which suggests that nest‐building behavior has evolved through natural selection by predation. Nest success increased over time, which may increase the probability of long‐term persistence of the species. Rat control may facilitate the evolution of nesting height by slowing the rate of population decline and providing time for this adaptive response to spread through the population.     

Inter-ocean genetic divergence of istiophorid billfishes

Restriction fragment length polymorphism (RFLP) analysis of mitochondrial DNA (mtDNA) was used to investigate the taxonomic status of the following species-pairs of Atlantic and Indo-Pacific istiophorid billfishes: Atlantic blue marlin Makaira nigricans (Lacépède) and Indo-Pacific blue marlin M. mazara (Jordan and Snyder); Atlantic sailfish Istiophorus albicans (Latreille) and Indo-Pacific sailfish I. platypterus (Shaw and Nodder); and white marlin Tetrapturus albidus Poey and striped marlin T. audax (Phillippi). Tissue samples were collected from 1990 to 1992. Several mtDNA haplotypes were common to Atlantic and Indo-Pacific samples of blue marlin and sailfish, although there were significant differences in the distribution of haplotypes between samples from different oceans. For both blue marlin and sailfish, a single group of closely related mtDNA haplotypes was found among all indo-Pacific and some Atlantic individuals, while the remaining Atlantic specimens exhibited mtDNA haplotypes that differed by several consistent restriction site changes from the common haplotype. No restriction site differences were found to discriminate white marlin from striped marlin, and the mtDNA haplotypes of both species were very similar although significant differences were found in the distribution of haplotypes between the two species. Two of 26 haplotypes were shared between white and striped marlin, and the corrected mean nucleotide sequence divergence between species (0.06%) was not much greater than that observed between geographically distant samples of striped marlin from the Pacific Ocean (mean 0.03%). The presence of identical haplotypes in samples from both oceans for each of the three species-pairs of istiophorid billfishes suggests that specific status may not be warranted for any of the Atlantic and Indo-Pacific populations. The significant difference in the distributions of mtDNA haplotypes between Atlantic and Indo-Pacific populations, which contrasts sharply with the homogeneity reported for several species of tunas, indicates considerable population structuring within the highly vagile billfishes.     

Critique of the Evolutionarily Significant Unit as a Definition for "Distinct Population Segments" under the U.S. Endangered Species Act

The U.S. Endangered Species Act grants protection to species, subspecies, and "distinct population segments" of vertebrate species. Historically, Congress included distinct population segments into endangered species legislation to enable the U.S. Fish and Wildlife Service to implement a flexible and pragmatic approach in listing populations of vertebrate species. Recently, the U.S. Fish and Wildlife Service and the National Marine Fisheries Service have proposed a policy that would narrowly define distinct population segments as evolutionarily significant units based on morphological and genetic distinctiveness between populations. Historically, the power to list species or populations as distinct population segments has been used to tailor management practices to unique circumstances; grant varied levels of protection in different parts of a species' range; protect species from extinction in significant portions of their ranges as well as to protect populations that are unique evolutionary entities. A strict redefinition of distinct population segments as evolutionarily significant units will compromise management efforts because the role of demographic and behavioral data will be reduced. Furthermore, strictly cultural, economic, or geographic justifications for listing populations as threatened or endangered will be greatly curtailed.     

Avoidance Behavior by Prairie Grouse: Implications for Development of Wind Energy

Abstract:  New wind-energy facilities and their associated power transmission lines and roads are being constructed at a rapid pace in the Great Plains of North America. Nevertheless, little is known about the possible negative effects these anthropogenic features might have on prairie birds, one of the most threatened groups in North America. We examined radiotelemetry tracking locations of Lesser Prairie-Chickens ( Tympanuchus pallidicinctus ) and Greater Prairie-Chickens ( T. cupido ) in two locations in Oklahoma to determine whether these birds avoided or changed movement behavior near power lines and paved highways. We tracked 463 Lesser Prairie-Chickens (15,071 tracking locations) and 216 Greater Prairie-Chickens (5,750 locations) for 7 and 3 years, respectively. Individuals of both species avoided power lines by at least 100 m and Lesser Prairie-Chickens avoided one of the two highways by 100 m. Prairie-chickens crossed power lines less often than expected if birds moved randomly ( p < 0.05) but did not appear to perceive highways as a movement barrier ( p > 0.05). In addition, home ranges of Lesser Prairie-Chickens overlapped the power line less often than would be expected by chance placement of home ranges; this result was supported by kernel-density estimation of home ranges. It is likely that new power lines (and other tall structures such as wind turbines) will lead to avoidance of previously suitable habitat and will serve as barriers to movement. These two factors will likely increase fragmentation in an already fragmented landscape if wind energy development continues in prairie habitats .     

Population Declines, Viable Breeding Areas, and Management Options for Flamingos in Southern Africa

Habitat rehabilitation or intervention to prevent species declines are rarely employed in Africa. I argue that despite protection in national parks, active intervention is necessary to halt declines in southern Africa's Greater ( Phoenicopterus ruber ) and Lesser ( Phoeniconaias minor ) Flamingo populations. Flamingos are long-lived species that breed sporadically at only two localities in southern Africa: the Makgadikgadi Pans in Botswana and Etosha National Park in Namibia. Despite well-publicized breeding on Etosha Pan, flamingos have experienced only three major breeding events in 40 years. Breeding failure occurs when high evaporation rates rapidly dry the pan, and up to 100,000 flightless chicks may starve. Consequently, pairs breeding in Etosha exhibit extraordinarily low recruitment (0.040 young pair/year) and extrapolations indicate that adults can replace themselves only if they breed for 38 to 50 years and all offspring survive. Because survival of offspring from fledging to adulthood (5 years) is about 46%, this breeding lifespan rises to an unrealistic 83 years, making Etosha a nonviable breeding site. Alternative, suitable flamingo habitats in Africa are being mined for soda-ash, are damaged by pollution, or are unprotected. Accordingly, continent-wide estimates and those from southern Africa alone suggest a population decline of about 40% in both species over the last 15 years. Because Namibia regularly supports 84% of the Greater and 93% of the Lesser Flamingos in southern Africa, conservation strategies are best focused there. Simple but effective management methods, based on those employed in western Europe, could reverse these downward trends. In Etosha a small island surrounded by a water-filled depression would allow up to 4000 pairs to breed annually. The benefits of enhancing the breeding of flamingos in Etosha include research opportunities, tourism revenue, and a safe haven for two Red Data species.     

Comparison of larval fish assemblages in three large estuarine systems, KwaZulu-Natal, South Africa

 The structure of the larval fish assemblages in three large estuarine systems on the KwaZulu-Natal coast of South Africa was examined using a combination of univariate, distributional and multivariate techniques. The database was comprised of a full annual set of larval fish samples taken from each estuarine system: Durban Harbour, Richards Bay Harbour and St Lucia Estuary. The mean monthly densities of each species in each system were used in the species matrix, and the mean monthly values of salinity, temperature and turbidity were used in the environmental matrix. The mean species diversity and evenness index were significantly higher in Durban Harbour (H′ = 1.03, J′ = 0.65) than in the other two systems. The cumulative dominance curve showed that St Lucia Estuary has a high dominance of a few species, with Richards Bay Harbour intermediate and Durban Harbour being the most diverse. Classification and MDS (multiple-dimensional scaling) analyses of larval fish densities in all three systems grouped together into three main clusters on the basis of system. The species similarity matrix (inverse analysis) clustered into five groups at the 25% similarity level. The MDS analysis of the same matrix showed that the groups separated out according to the degree of estuarine association of a species and hence habitat type. The species most responsible for system groupings were: Glossogobius callidus, Gilchristella aestuaria, Stolephorus holodon, Croilia mossambica and Gobiid 12. The “best fitting” of the environmental variables to explain the larval fish community patterns in each system was turbidity on its own (weighted Spearman's rank correlation, ρ_w = 0.55). The relationship of larval densities to environmental conditions was shown to be species-specific with estuarine species (e.g. G. callidus and G. aestuaria), having a strong positive correlation with temperature and turbidity but negative correlations with salinity. In summary, much longer term studies with more sites within each system are needed to assess whether the larval fish assemblages are stable or at an equilibrium (both spatially and temporally) and whether these assemblages are indicative of the relative “health” and nursery function of the system. Received: 28 April 1999 / Accepted: 30 May 2000     

Adaptive Units for Conservation: Population Distinction and Historic Extinctions in the Island Scrub-Jay

Abstract:  The Island Scrub-Jay ( Aphelocoma insularis ) is found on Santa Cruz Island, California, and is the only insular bird species in the continental United States. We typed seven microsatellite loci and sequenced a portion of the mitochondrial DNA control region of Island Scrub-Jays and their closest mainland relative, the Western Scrub-Jay ( Aphelocoma californica ), to assess levels of variability and effective population size and to examine the evolutionary relationship between the two species. The estimated female effective population size, N _ef, of the Island Scrub-Jay was 1603 (90% confidence interval: 1481–1738) and was about 7.5% of the size of the mainland species. Island and Western Scrub-Jays have highly divergent control-region sequences, and the value of 3.14 ± 0.09% sequence divergence between the two species suggests a divergence time of approximately 151,000 years ago. Because the four northern Channel Islands were joined as one large island as recently as 11,000 years ago, extinctions must have occurred on the three other northern Channel islands, Santa Rosa, San Miguel, and Anacapa, highlighting the vulnerability of the remaining population. We assessed the evolutionary significance of four island endemics, including the Island Scrub-Jay, based on both genetic and adaptive divergence. Our results show that the Island Scrub-Jay is a distinct species of high conservation value whose history and adaptive potential is not well predicted by study of other island vertebrates.