Littoral infauna of a West African estuary: An oil pollution baseline survey

Littoral infaunal density was recorded from December 1983 to October 1984 throughout the Bonny Estuary in the Niger delta, Nigeria, to provide a baseline for the monitoring of oil pollution. Results on the most abundant faunal elements, polychaetes and the fiddler crabUca tangeri L., are presented. In the upper reaches, polychaete density peaked in January — due to increases in the abundance of the principal species. In the lower reaches, euryhaline and stenohaline polychaetes exhibited maxima in April to July and lesser peaks earlier and later in the year. There were no wide fluctuations in the middle reaches, due to the lack of truly estuarine species — exceptU. tangeri which was most abundant between December and April. Features such as the salinity/substrate zones, faunistic components and reduction of species upstream, are typical of estuaries elsewhere. Others, including the low abundance of all species in the middle reaches, and the occurrence of species minimum far downstream of 5 S, are atypical, and pollution from the Okrika oil terminal, oil from outboard engines, and substrate disturbance by shipping, are suggested as causative factors.     

Reciprocity and trades in wild West African chimpanzees

Why do animals help other individuals and provide benefits to the recipient, sometimes at personal cost? In this study, we aim to determine if some of the helpful behaviors observed in a group of wild chimpanzees (Taï chimpanzee group, Côte d'Ivoire, West Africa) are exchanged among individuals resulting in a net benefit for both participants. We adopted an inclusive view of exchanges by considering that all commodities (i.e., social behaviors as grooming, sex, support, as well as resources, such as meat) can be exchanged. This would result in “market” type social interactions in which debts of one commodity can be met by giving the same or other commodities. We investigated whether both in-kind exchanges and trades of commodities occurred. The Taï chimpanzees reciprocated the amount of grooming they received and were more likely to give support in agonistic conflicts to those who also supported them. In addition, they traded support for meat and meat for sex. Both male and female chimpanzees exchanged many different commodities, which seemed to result in long-term balanced relationships. Our results suggest that wild chimpanzees rely on other group members to obtain many of the important commodities they need.     

Oxygen consumption of the West African blood clamAnadara senilis

The West African blood clamAnadara senilis (L.) is one of a small number of bivalve species which have haemoglobin in their haemolymph. In the investigation reported here, in which the musselMytilus edulis (L.) was also studied for comparative purposes, it was shown thatA. senilis was an oxygen regulator between oxygen tensions corresponding to 50 and 100% air saturation. Oxygen uptake increased by about 128% after 24 h at zero pO₂; although the haemoglobins ofA. senilis were found to be responsible for about 34% of oxygen uptake at 25°C (a proportion unaffected by pO₂), there was clearly insufficient haemoglobin present in the haemolymph to act as an effective oxygen store during prolonged exposure to anoxic conditions.     

Rates of Movement of Threatened Bird Species between IUCN Red List Categories and toward Extinction

Abstract:  In recent centuries bird species have been deteriorating in status and becoming extinct at a rate that may be 2–3 orders of magnitude higher than in prehuman times. We examined extinction rates of bird species designated critically endangered in 1994 and the rate at which species have moved through the IUCN (World Conservation Union) Red List categories of extinction risk globally for the period 1988–2004 and regionally in Australia from 1750 to 2000. For Australia we drew on historical accounts of the extent and condition of species habitats, spread of invasive species, and changes in sighting frequencies. These data sets permitted comparison of observed rates of movement through the IUCN Red List categories with novel predictions based on the IUCN Red List criterion E, which relates to explicit extinction probabilities determined, for example, by population viability analysis. The comparison also tested whether species listed on the basis of other criteria face a similar probability of moving to a higher threat category as those listed under criterion E. For the rate at which species moved from vulnerable to endangered, there was a good match between observations and predictions, both worldwide and in Australia. Nevertheless, species have become extinct at a rate that, although historically high, is 2 (Australia) to 10 (globally) times lower than predicted. Although the extinction probability associated with the critically endangered category may be too high, the shortfall in realized extinctions can also be attributed to the beneficial impact of conservation intervention. These efforts may have reduced the number of global extinctions from 19 to 3 and substantially slowed the extinction trajectory of 33 additional critically endangered species. Our results suggest that current conservation action benefits species on the brink of extinction, but is less targeted at or has less effect on moderately threatened species.     

Effects of Forest Fragmentation and Habitat Degradation on West African Leaf-Litter Frogs

Abstract:  Habitat degradation alters the dynamics and composition of anuran assemblages in tropical forests. The effects of forest fragmentation on the composition of anuran assemblages are so far poorly known. We studied the joint influence of forest fragmentation and degradation on leaf-litter frogs. We specifically asked whether the processes structuring leaf-litter anuran assemblages in fragmented forests are the same as those in continuous forests. We analyzed anuran assemblages with respect to habitat characteristics, including fragmentation and degradation parameters. In comparison with continuous forests, species richness and diversity were lower and assemblage composition was altered in forest fragments. These changes seemed to be mainly caused by habitat degradation rather than forest fragmentation. Availability of aquatic sites for breeding, vegetation structure (including those variables indicating degradation), and leaf-litter cover had the most influence on the presence of single species. The comparatively small impact of fragmentation on anurans might be due to the location of the study area; it still possessed large tracts of continuous forest. These forest blocks may stabilize the regional rainforest climate and thus weaken the effects of fragmentation .     

Evaluating the Predicted Local Extinction of a Once-Common Mouse

Abstract:  In an earlier paper ( Pergams & Nyberg 2001 ) we found that the proportion of the prairie deer mouse ( Peromyscus maniculatus bairdii ), among all local Peromyscus museum specimens collected in the Chicago region, had significantly declined over time. This proportion changed from about 50% before 1900 to <10% in the last 25 years. Based on this proportion a regression model predicted the local extinction of the prairie deer mouse in 2009. To evaluate that prediction, we estimated current deer mouse abundance by live trapping small mammals at 15 preserves in Cook and Lake counties, Illinois (USA) at which prairie deer mice had previously been caught or that still contained their preferred open habitat. In 1900 trap nights, 477 mammals were caught, including 251 white-footed mice ( P. leucopus ), but only one prairie deer mouse. The observed proportion of Peromyscus that were prairie deer mice, 0.4%, was even lower than the 4.5% predicted for 2000. Here we also introduce a simple, new community proportions model, which for any given geographic region compares the proportions of species recently caught with the proportions of species in museums. We compared proportions of seven species collected in Cook and Lake counties and examined by Hoffmeister (1989) with proportions of these species that we caught. Ten percent of the museum community was prairie deer mice, but only 0.2% of our catch was. The current local scarcity of the prairie deer mouse is consistent with the regression-based prediction of its eminent local extinction. More conservation attention should be paid to changes in relative abundance of once-common species.     

Extinction of a Species of Land Snail Due to Infection with a Microsporidian Parasite

Snails of the genus Partula are highly endangered, with many species occurring solely in captivity. Captive populations experience periodic crashes, some of which have resulted in extinction. Pathologic investigations of the last individuals of a species that had undergone such a crash ( Partula turgida ) showed infection with a protozoan parasite as the cause of death. The parasite was identified as a member of the microsporidian genus Steinhausia , other members of which are known to cause mortality in aquatic pulmonate snails. We believe this is the first definitive report of an infectious disease causing the extinction of a species.

Extinción de una especie de Caracol Terrestre Debido a una Infección por un Parásito Microsporidio

Los caracoles del género Partula estan altamente amenazados junto con muchas especies existiendo únicamente en cautividad. Las poblaciones cautivas experimentan colapsos periódicos, algunos de los cuales han resultado en extinciones. Investigaciones patológicas de los últimos individuos de una especie que ha pasado por este tipo de colapso ( Partula turgida ) muestran infecciones de un protozoario parásito como la causa de su muerte. El parásito ha sido identificado como un miembro del género Steinhausia , otros miembros de este género han sido identificados como los causantes de mortalidades en caracoles pulmonados acuáticos. Creemos que este es un reporte definitivo de una enfermedad infecciosa causante de la extinción de una especie.     

Predicting the Risk of Extinction through Hybridization

Abstract: Natural hybridization threatens a substantial number of plant and animal species with extinction, but extinction risk has been difficult to evaluate in the absence of a quantitative assessment of risk factors. We investigated a number of ecological parameters likely to affect extinction risk, through an individual-based model simulating the life cycle of two hybridizing annual plant species. All parameters tested, ranging from population size to variance in pollen-tube growth rates, affected extinction risk. The sensitivity of each parameter varied dramatically across parameter sets, but, overall, the competitive ability, initial frequency, and selfing rate of the native taxon had the strongest effect on extinction. In addition, prezygotic reproductive barriers had a stronger influence on extinction rates than did postzygotic barriers. A stable hybrid zone was possible only when habitat differentiation was included in the model. When there was no habitat differentiation, either one of the parental species or the hybrids eventually displaced the other two taxa. The simulations demonstrated that hybridization is perhaps the most rapidly acting genetic threat to endangered species, with extinction often taking place in less than five generations. The simulation model was also applied to naturally hybridizing species pairs for which considerable genetic and ecological information is available. The predictions from these "worked examples" are in close agreement with observed outcomes and further suggest that an endemic cordgrass species is threatened by hybridization. These simulations provide guidance concerning the kinds of data required to evaluate extinction risk and possible conservation strategies.     

Extinction Rates of North American Freshwater Fauna

Abstract: Since 1900, 123 freshwater animal species have been recorded as extinct in North America. Hundreds of additional species of fishes, mollusks, crayfishes, and amphibians are considered imperiled. Using an exponential decay model, we derived recent and future extinction rates for North American freshwater fauna that are five times higher than those for terrestrial fauna. Assuming that imperiled freshwater species will not survive throughout the next century, our model projects a future extinction rate of 4% per decade, which suggests that North America's temperate freshwater ecosystems are being depleted of species as rapidly as tropical forests.     

The Consistency of Extinction Risk Classification Protocols

Abstract:  Systematic protocols that use decision rules or scores are seen to improve consistency and transparency in classifying the conservation status of species. When applying these protocols, assessors are typically required to decide on estimates for attributes that are inherently uncertain. Input data and resulting classifications are usually treated as though they are exact and hence without operator error. We investigated the impact of data interpretation on the consistency of protocols of extinction risk classifications and diagnosed causes of discrepancies when they occurred. We tested three widely used systematic classification protocols employed by the World Conservation Union, NatureServe, and the Florida Fish and Wildlife Conservation Commission. We provided 18 assessors with identical information for 13 different species to infer estimates for each of the required parameters for the three protocols. The threat classification of several of the species varied from low risk to high risk, depending on who did the assessment. This occurred across the three protocols investigated. Assessors tended to agree on their placement of species in the highest (50–70%) and lowest risk categories (20–40%), but there was poor agreement on which species should be placed in the intermediate categories. Furthermore, the correspondence between the three classification methods was unpredictable, with large variation among assessors. These results highlight the importance of peer review and consensus among multiple assessors in species classifications and the need to be cautious with assessments carried out by a single assessor. Greater consistency among assessors requires wide use of training manuals and formal methods for estimating parameters that allow uncertainties to be represented, carried through chains of calculations, and reported transparently.     

Extinction, recolonization, and dispersal through time in a planktonic crustacean

Dormant propagule banks are important reservoirs of biological and genetic diversity of local communities and populations and provide buffering mechanisms against extinction. Although dormant stages of various plant and animal species are known to remain viable for decades and even centuries, little is known about the effective influence of recolonization from such old sources on the genetic continuity of intermittent populations under natural conditions. Using recent and old dormant eggs recovered from a dated lake sediment core in Kenya, we traced the genetic composition of a local population of the planktonic crustacean Daphnia barbata through a sequence of extinction and recolonization events. This was combined with a phylogeographic and population-genetic survey of regional populations. Four successive populations, fully separated in time, inhabited Lake Naivasha from ca. 1330 to 1570 AD, from ca. 1610 to 1720 AD, from ca. 1840 to 1940 AD, and from 1995 to the present (2001 AD). Our results strongly indicate genetic continuity between the 1840-1940 and 1995-2001 populations, which are separated in time by at least 50 years, and close genetic relatedness of them both to the 1330-1580 population. A software tool (Colonize) was developed to find the most likely source population of the refounded 1995-2001 population and to test the number of colonists involved in the recolonization event. The results confirmed that the 1995-2001 population most probably developed out of a limited number of surviving local dormant eggs from the previous population, rather than out of individuals from regional (central and southern Kenya) or more distant (Ethiopia, Zimbabwe) populations that may have immigrated to Lake Naivasha through passive dispersal. These results emphasize the importance of prolonged dormancy for the natural long-term dynamics of crustacean zooplankton in fluctuating environments and suggest an important role of old local dormant egg banks in aquatic habitat restoration.     

Rapid Extinction of Mountain Sheep Populations Revisited

Abstract: Predicting extinction probabilities for populations of various sizes has been a primary focus of conservation biology. Berger (1990) presented an empirically based extinction model for mountain sheep ( Ovis canadensis ) populations in five southwestern states that predicted disappearance within 50 years of all populations estimated to number 50 sheep or fewer, but essentially no loss in that time period of populations estimated at over 100. The majority of the 122 populations he used in his analysis were from California, but his analysis did not use many of the historical size estimates for these populations. I tested Berger's (1990) model using the complete data set from California and found—contrary to his results—that, for all size classes of population estimates, at least 61% of the populations persisted for 50 years. Also, two predictions from Berger's model were not consistent with the data from California: (1) 10 populations have increased from estimates of 50 or fewer animals to over 100, whereas the Berger model predicted that these populations would only decline to extinction; and (2) of 27 extant populations with long enough records, 85% were estimated at least 50 years ago to be 50 individuals or fewer and should therefore be extinct by now. Berger's model has now failed tests in three states and therefore does not support the strong population size effect on extinction probability that it first appeared to provide, and it may serve conservation poorly through misdirected effort if it is used as the basis for setting policies or taking actions.     

Between-group contest competition for food in a highly folivorous population of black and white colobus monkeys (Colobus guereza)

In theory, between-group contest (BGC) competition for food can greatly influence female social relationships and reproductive success in primates, but few studies have investigated whether such effects occur and, if so, under what ecological conditions. There is evidence that adult male black and white colobus monkeys (Colobus guereza, “guerezas”) defend the food their mates need against other groups, suggesting that BGC competition is important in this species. Using data on feeding, ranging, vegetation patterns, and intergroup encounters between six neighboring guereza groups, I provide evidence that the highly folivorous guerezas at Kanyawara, Kibale National Park, Uganda, engaged in BGC competition over unevenly dispersed, relatively high-quality feeding areas or “core areas”. Intergroup aggression was common, and groups’ home ranges overlapped. Groups were more likely to initiate high-level aggression if they encountered another group within or near their core area, and groups that initiated and won encounters often fed in the same areas in which losing groups had fed. Guerezas fed selectively on species with contagious (clumped) distributions and concentrated their feeding efforts in areas of the forest that contained the most food (core areas). Groups could be ranked in a linear dominance hierarchy, and group rank number was inversely related to the quantity and quality of food in groups’ core areas. This study not only provides good evidence that BGC competition occurs in primates but it also reinforces the idea that folivore food resources may be worth defending.     

Annelids of a west African estuarine system

Annelids collected from eight stations in the western part of Lagos Lagoon between May, 1996 and February, 1998 were reported. Rainfall, salinity and sediment type influenced distribution of annelids, which were either dry season species, wet season species or euryhaline species. A total of fifty-five species were collected, thirty-one not recorded in earlier studies. Pollution indicators, Polydora sp., Capitella capitata, Nereis sp. and Tubifex sp. were collected in both dry and wet seasons.