Abundance matters: a field experiment testing the more individuals hypothesis for richness–productivity relationships

The more individuals hypothesis (MIH) postulates that productivity increases species richness by increasing mean equilibrium population size, thereby reducing the probability of local extinction. We tested the MIH for invertebrates colonizing microcosms that simulated tree holes by manipulating productivity through additions of leaf or animal detritus and subsequently determining the relationships among richness, total abundance, abundance per species, and measures of productivity. We quantified productivity as the rate of microorganism protein synthesis, microorganism metabolic rate, nutrient ion concentration, and type and amount of detritus. Microcosms with animal detritus attracted more species, more individuals per species, and more total individuals than did microcosms with similar amounts of leaf detritus. Relationships between richness or abundance and productivity varied with date. Richness in June increased as a linear function of productivity, whereas the power function predicted by the MIH fit best in July. Abundance in June and July was best described by a power function of productivity, but the linear function predicted by the MIH fit best in September. Abundance per species was best described by a power function of productivity in June and July. Path analysis showed that the indirect effect of productivity through abundance on richness that is predicted by MIH was important in all months, and that direct links between productivity and richness were unnecessary. Our results support many of the predictions of the MIH, but they also suggest that the effects of abundance on richness may be more complex than expected.     

‘Rigid’ internal timing in the circadian rhythm of flight activity in a tropical bat

Summary The timing of the emergence activity of a colony of the bat Taphozous melanopogon occupying a cave environment in Madurai (lat. 9°58 N, long. 78°10 E) and consisting of approximately 150–180 animals of both sexes was studies at 10-day intervals for one year. Even though the time of sunset during the eyar varied over a range of 41 min, the bats displayed an astonishingly rigid time of emergence that was restricted to a narrow gate of 16 min from 18:25 to 18:41 h. The timing of the termination of the activity was less precise in all seasons. Light/dark cycles are clearly the Zeitgeber. Even so, the bats began flying when it was very dark (0.1 lx) during shorter days, and they flew out as the sun was disappearing in the evening horizon (50 or more lx) during long days. Evidently there is no invariant, fixed lower threshold intensity that uniformly elicits the onset of activity throughout the year as reported earlier by other authors (Aschoff, 1969; Erkert, 1974). It is proposed that the bats undergo a systematic seasonal shift in the threshold sensitivity to light in response to the photic Zeitgeber of the environment. The result is a remarkable precision in terms of the hours of the civil/calendar day in the emergence of Taphozous melanopogon.     

Strong spatial genetic structure in five tropical Piper species: should the Baker–Fedorov hypothesis be revived for tropical shrubs?

Fifty years ago, Baker and Fedorov proposed that the high species diversity of tropical forests could arise from the combined effects of inbreeding and genetic drift leading to population differentiation and eventually to sympatric speciation. Decades of research, however have failed to support the Baker-Fedorov hypothesis (BFH), and it has now been discarded in favor of a paradigm where most trees are self-incompatible or strongly outcrossing, and where long-distance pollen dispersal prevents population drift. Here, we propose that several hyper-diverse genera of tropical herbs and shrubs, including Piper (>1,000 species), may provide an exception. Species in this genus often have aggregated, high-density populations with self-compatible breeding systems; characteristics which the BFH would predict lead to high local genetic differentiation. We test this prediction for five Piper species on Barro Colorado Island, Panama, using Amplified Fragment Length Polymorphism (AFLP) markers. All species showed strong genetic structure at both fine- and large-spatial scales. Over short distances (200-750 m) populations showed significant genetic differentiation (Fst 0.11-0.46, P < 0.05), with values of spatial genetic structure that exceed those reported for other tropical tree species (Sp = 0.03-0.136). This genetic structure probably results from the combined effects of limited seed and pollen dispersal, clonal spread, and selfing. These processes are likely to have facilitated the diversification of populations in response to local natural selection or genetic drift and may explain the remarkable diversity of this rich genus.     

Is the littoral zone taxonomically and functionally more diverse? Investigating the rotifer community of a tropical shallow lake

Limnology - We investigated the taxonomic and functional diversity of rotifers in the littoral, intermediate, and pelagic zones of a tropical lake. Rotifers were collected at 10 sampling stations...     

Hormonal correlates of individual quality in a long-lived bird: a test of the ‘corticosterone–fitness hypothesis’

Measuring individual quality in vertebrates is difficult. Focusing on allostasis mechanisms may be useful because they are functionally involved in the ability of an individual to survive and reproduce in its environment. Thus, a rise in stress hormones levels (corticosterone) occurs when an organism has to cope with challenging environmental conditions. This has recently led to the proposal of the ‘cort–fitness hypothesis’, which suggests that elevated baseline corticosterone levels should be found in individuals of poor quality that have difficulty coping with their environment. We tested this hypothesis by comparing an integrative measure of individual quality to baseline corticosterone in black-browed albatrosses (Thalassarche melanophrys). We found that individual baseline corticosterone levels were related to individual quality and highly repeatable from one breeding season to the next. Importantly, this relationship was found in males, but not in females. Therefore, we suggest that the relationship between quality and baseline corticosterone levels may depend on the environmental and energetic constraints that individuals have to cope with.     

Towards a cohesive strategy for the conservation of the United States’ diverse and highly endemic crayfish fauna

The fossil record of cichlids is sparse, and every new discovery can provide new insights into the evolutionary history of this speciose freshwater fish family. In this article, we describe †Rebekkachromis gen. nov. from the middle-to-late Miocene (c. 11 MYA) of the Central Kenya Rift within the East African Rift system. †Rebekkachromis is represented by two species that differ from all other fossil and extant African cichlids, except Etia, in possessing the unique character combination of two supraneural bones and a set of robust tricuspid oral teeth in the outer row of the dentition. Furthermore, †Rebekkachromis exhibits the only proposed morphological synapomorphy of the Haplotilapiini, namely the presence of tricuspid teeth in the inner row of the oral dentition. We show that †Rebekkachromis constitutes the oldest reliably identified fossil record of a haplotilapiine. The evolution of cichlid fishes possessing tricuspid teeth in the rivers and lakes of the Central Kenya Rift during the middle-to-late Miocene could have been facilitated by volcanic activity, as repeated ash falls may well have fostered the growth of algae and in particular diatoms. These fishes could thus have had a major advantage, because they could exploit the newly available, rich food resources.

     

Testing the ‘plant domestication-reduced defense’ hypothesis in blueberries: the role of herbivore identity

Domestication is predicted to reduce resistance of agricultural crops against insect herbivores; however, its impact on herbivores with different feeding modes and evolutionary histories needs investigation. To this end, we conducted greenhouse experiments to explore the effects of domestication of blueberries (Vaccinium corymbosum), a crop native to North America, on the performance of two chewing herbivores [the native Sparganothis fruitworm (Sparganothis sulfureana (Clemens)) and non-native gypsy moth (Lymantria dispar L.)], and one piercing-sucking herbivore [the blueberry aphid (Illinoia azaleae (Mason))]. Lymantria dispar performed better (i.e., larvae gained more mass, damaged more leaves, and had greater survival) on cultivated V. corymbosum than on its wild counterpart. In contrast, domestication had no impact on the native S. sulfureana larval mass, consumption, and survivorship. Domestication increased survivorship, but not offspring production, of the aphid I. azaleae. To examine changes in plant chemistry due to domestication, we measured phenolic and nutrient (macro- and micro-elements) content in wild and cultivated V. corymbosum leaves. Although there were no differences in total phenolic content, two compounds were absent, while two were at lower and one at higher concentration in domesticated than in wild plants. Wild V. corymbosum leaves had higher amounts of phosphorus, sulfur, and sodium than cultivated leaves; the opposite was found for aluminum. While our findings provide support for the ‘plant domestication-reduced defense’ hypothesis, the effects of domestication were dependent on feeding modes and adaptations of the herbivores such that the non-native chewing species was more positively affected than the chewing and the piercing-sucking natives.     

The ‘Psychic Surgeon’ and the schizophrenic patient: Crisis in a ‘Medicodrama’

This paper is concerned with a Filipino psychic surgeon confronted by a particularly challenging case of a kind perhaps unprecedented in his practice. The paper describes and analyzes how the practitioner modified his usual clinical performance and adapted his actions to demands of an extremely difficult situation. The case is viewed in wider perspective relative to the significance of performative acts of healing in a pluralistic medical setting.     

Leaf hydraulic vulnerability influences species’ bioclimatic limits in a diverse group of woody angiosperms

The ability of plants to maintain water flow through leaves under water stress-induced tension (assessed as the leaf hydraulic vulnerability; P50 _leaf) is intimately linked with survival. We examined the significance of P50 _leaf as an adaptive trait in influencing the dry-end distributional limits of cool temperate woody angiosperm species. We also examined differences in within-site variability in P50 _leaf between two high-rainfall montane rainforest sites in Tasmania and Peru, respectively. A significant relationship between P50 _leaf and the 5th percentile of mean annual rainfall across each species distribution was found in Tasmania, suggesting that P50 _leaf influences species climatic limits. Furthermore, a strong correlation between P50 _leaf and the minimum rainfall availability was found using five phylogenetically independent species pairs in wet and dry evergreen tree species, suggesting that rainfall is an important selective agent in the evolution of leaf hydraulic vulnerability. Greater within-site variability in P50 _leaf was found among dominant montane rainforest species in Tasmania than in Peru and this result is discussed within the context of differences in spatial and temporal environmental heterogeneity and parochial historical ecology.     

Linking environmental stress, feeding-shifts and the ‘island syndrome’: a nutritional challenge hypothesis

Adaptation to insular environments often arises from changes and innovations in feeding behaviour allowing expanded foraging habits and an increased niche breadth. These shifts and innovations have traditionally been thought to be related to community-wide processes, but could also be the direct result of environmental constraints determining the abundance, availability and suitability of a particular food providing specific nutrients for survival, growth and reproduction. The link between environmental constraints on nutrients and life-history of insular organisms can help in understanding the convergent set of adaptations sustaining the ‘island syndrome’. We tested whether a potential insular nutrient shortage can drive diet shifts, nutritional biochemistry and growth stress, thus contributing to the modulation of life-history traits in a large passerine bird, the red-billed chough (Pyrrhocorax pyrrhocorax). Results supported the insular nutritional challenge hypothesis, linked to an insular insect shortage. An insect shortage may in turn have determined the reduced consumption of this source of protein but increased consumption of other arthropods, and notably fruits, by insular nestlings and fully-grown individuals. Island birds showed comparatively low circulating levels of nutrients and metabolites associated with the consumption of protein-rich animal matter as opposed to carbohydrate-rich vegetal matter, as well as high growth stress reflected in poor feather quality. We propose that feeding shifts derived from an insular insect shortage may exert a strong influence on the allocation of limited time, energy and nutrients among competing functions associated with physiological changes and investment in reproduction and self-maintenance. Traits and patterns generally defining the insular syndrome could thus be linked to particular insular nutrient constraints forcing feeding shifts and nutritional challenges with physiological, demographic and life-history consequences.     

Mollusk species diversity in the Southeastern Pacific: why are there more species towards the pole?

The most ubiquitous and well recognized diversity pattern at large spatial scales is the latitudinal increase in species richness near the equator and decline towards the poles. Although several exceptions to this pattern have been documented, shallow water mollusks, the most specious group of marine invertebrates, are the epitome of the monotonic decline in species diversity toward higher latitudes along the Pacific and Atlantic coasts of North America. Here we analyze the geographic diversity of 629 mollusk species along the Pacific South American shelf. Our analyses are based on the most complete database of invertebrates assembled for this region of the world, consisting of latitudinal ranges of over 95% of all described mollusks between 10° and 55°S. Along this coast, mollusk diversity did not follow the typical latitudinal trend. The number of species remained constant and relatively low at intermediate latitudes and sharply increased toward higher latitudes, south of 42°S. This trend was explained by changes in shelf area, but not by sea surface temperature, unlike the pattern documented for Northern Hemisphere mollusks. Direct sampling of soft bottom communities along the gradient suggests that regional trends in species richness are produced by increased alpha diversity, and not only by artifacts produced by the increase in sampling area. We hypothesize that increased shelf area south of 42°S, geographic isolation produced by divergence of major oceanic currents, and the existence of refugia during glaciations, enabled species diversification. Radiation could have been limited by narrow continental shelves between 10°–42°. Asymmetries in latitudinal diversity trends between hemispheres show that there is not a single general factor determining large-scale diversity patterns.     

Racial,ethnic and religious social distance in Surinam: An exploration of the ‘strategic alliance hypothesis’ in a Caribbean community

The poly‐ethnic Caribbean can be seen as a laboratory for the study of the evolution of inter‐ and intra‐ethnic relationships. Using the Caribbean experience as context, the present study begins by focusing on the dynamics of Muslim‐Hindu relations in Surinam and then extends its analysis to South Asian‐Creole relations. Building on the work of van der Burg and van der Veer (1986), the study develops and examines a ‘strategic alliance hypothesis’: that Hindus and Muslims have avoided overt conflict in their Surinamese homeland in order to advance their common interests against the country's other major ethnic groups, and, by extension, South Asians have joined multi‐ethnic coalitions to advance these same interests. To explore these strategic alliance hypotheses, 376 secondary‐school students in western Surinam were administered a modified Bogardus (1925) social distance scale in order to measure the degree of reciprocal tolerance that the sample's respondents expressed towards Surinam's prominent ethno‐religious groups. The survey results offered qualified support for the strategic alliance hypothesis ‐ the degree of preferential closeness Hindus and Muslims in the sample would tolerate for each other fell approximately midway between the social distance they would allow between themselves and the Creoles, their major competitors, and the distance preferred for members of other sects within their own religion. These data are contextualized within Surinam's ongoing struggle to restore the independent and civilian constitutional government that was overthrown in a 1980 military coup.     

Assessing the ‘deep reef refugia’ hypothesis: focus on Caribbean reefs

Coral reefs in shallow-water environments (<30 m) are in decline due to local and global anthropogenic stresses. This has led to renewed interest in the ‘deep reef refugia’ hypothesis (DRRH), which stipulates that deep reef areas (1) are protected or dampened from disturbances that affect shallow reef areas and (2) can provide a viable reproductive source for shallow reef areas following disturbance. Using the Caribbean as an example, the assumptions of this hypothesis were explored by reviewing the literature for scleractinian corals—the reef framework builders on tropical reefs. Although there is evidence to support that deep reefs (>30 m) can escape the direct effects of storm-induced waves and thermal bleaching events, deep reefs are certainly not immune to disturbance. Additionally, the potential of deep reefs to provide propagules for shallow reef areas seems limited to ‘depth-generalist’ coral species, which constitute only ~25% of the total coral biodiversity. Larval connectivity between shallow and deep populations of these species may be further limited due to specific life history traits (e.g., brooding reproductive strategy and vertical symbiont acquisition mode). This review exposes how little is known about deep reefs and coral reproduction over depth. Hence, a series of urgent research priorities are proposed to determine the extent to which deep reefs may act as a refuge in the face of global reef decline.     

Aromatic herbs in Corsican blue tit nests: The ‘Potpourri’ hypothesis

This study reports that Corsican blue tit (Parus caeruleus ogliastrae) nests contain between one to five aromatic herb species between the onset of egg laying till the chicks’ finished growth 13 d after hatching. An herb removal experiment during the chick stage shows that blue tits bring fresh aromatic material 1–5 d after herb removal. Nests with a series of distinct odour classes easily perceived by humans have never been reported in birds. A new ‘Potpourri’ hypothesis is proposed that may explain the functional significance of this behaviour.     

Freezing tolerance in Draba chionophila,a ‘miniature’ caulescent rosette species

Summary Freezing tolerance as a cold resistance mechanism is described for the first time in a plant growing in the tropical range of the Andean high mountains. Draba chionophila, the plant in which freezing tolerance was found, is the vascular plant which reaches the highest altitudes in the Venezuelan Andes (approximately 4700m). Night cycles of air and leaf temperature were studied in the field to determine the temperature at which leaf freezing began. In the laboratory, thermal analysis and freezing injury determinations were also carried out. From both field and laboratory experiments, it was determined that freezing of the leaf tissue, as well as root and pith tissue, initiated at a temperature of approximately-5.0°C, while freezing injury occurred at approximately-12.0°C for the pith, and below-14.0°C for roots and leaves. This difference in temperature suggests that the plant still survives freezing in the-5.0 to-14.0°C range. Daily cycles of leaf osmotic potential and soluble carbohydrate concentration were also determined in an attempt to explain some of the changes occurring in this species during the nighttime temperature period. A comparison between Andean and African high mountain plants from the point of view of cold resistance mechanisms is made.     

Making a living in the tropical forest: Yuquí foragers in the Bolivian Amazon

Questions concerning the availability of resources in tropical rain forests have given rise to the current debate centering on whether human subsistence based solely on foraging is possible in these biomes without agricultural subsidies. This paper takes the position that changing perspectives on ecological pattern and process in tropical forests and the significant variation among tropical forests on a worldwide as well as regional scale must be taken into consideration. Human disturbance is also proposed as a cause of dependence on agriculture by modern human foragers rather than as a necessary precondition for successful exploitation of the tropical forest. These issues are discussed against the background of a case study of the Yuquí, who, until very recently, were true foragers in the Bolivian Amazon. For the Yuquí, the sustainability of their subsistence system depended on a finegrained knowledge of their environment and the freedom of movement over a large territory to access resources within it.