Northern Range Of Trinidad Research Articles

Chasitermespax, a new genus and species of soldierless termite (Termitidae, Apicotermitinae) from the island of Trinidad.

Chasitermespax Scheffrahn & Carrijo gen. et sp. nov. is described from workers collected from a single colony in the Northern Range of Trinidad. The shape and texture of the unsclerotized enteric valve, tubular shape of the enteric valve seating, and prominent spherical mesenteric tongue of C.pax are the diagnostic characters for both the genus and species. A Bayesian phylogenetic analysis using the COI gene and including all neotropical Apicotermitinae genera described to date supports the new genus as a distinct terminal.

Resistance from a resident heterospecific affects establishment success of a globally invasive freshwater fish

Abstract The role of biotic resistance is a subject of debate in our understanding of invasions. We used a well‐known system in the Northern Range of Trinidad, where ephemeral conditions in small pool habitats lead to repeated colonisation by two native species (guppies, Poecilia reticulata, and killifish, Anablepsoides hartii), to ask questions about the role of biotic resistance and intraguild predation in natural, small‐water habitats. Using horticultural containers under forest cover, alongside constructed bankside mesocosms, we established populations of each species to test hypotheses concerning the conditions under which the guppy, a globally successful invasive species with the potential to establish populations from a single female, could be excluded by a resident intraguild predator, the killifish. Recruitment success of the guppy depended on founder numbers (propagule size) and introduction order (whether first or last to arrive in the habitat). Single founder guppies always failed to recruit in pools with resident killifish, which we posit is directly attributable to biotic resistance from the resident. However, increased propagule pressure (introduction attempts and propagule number) greatly increased the probability of successful invasion. Our results have two main implications. The first is that guppies are capable of being successful colonisers even in the presence of a resident intraguild predator. The second is to highlight the role that biotic resistance can play in preventing establishment in small‐water habitats, especially under circumstances of low propagule pressure. While previous studies have shown that guppies are strong colonisers outside of their native range, our findings suggest that this may not always be the case when there are other small‐bodied fish present. Accordingly, we argue that in small‐water habitats, biotic resistance and intraguild predation relationships should be important considerations when the ability to establish is being assessed for a taxon.

Geothermometric constraints on the thermal architecture, metamorphism, and exhumation of the Northern Range, Trinidad

AbstractThe Northern Range of Trinidad is composed of Mesozoic passive margin sedimentary rocks that underwent ductile deformation and subgreenschist‐ to greenschist‐facies metamorphism in the early Miocene. Previous studies suggested a two‐stage formation of the Northern Range between the Caribbean and South American plates: an initial collision drove mountain building in the Miocene and subsequent strike‐slip plate motion preferentially exhumed the western segment, producing a westward increase in the metamorphic thermal gradient. However, these studies were not able to resolve whether this gradient was discrete or continuous so the tectonic model awaits testing. In this study we use Raman spectroscopy on carbonaceous material (RSCM), an empirical geothermometer, to constrain peak temperatures across the Northern Range with a greater resolution than was available in previous studies. The RSCM temperatures show an abrupt increase from 337°C ± 10°C in the east to 442°C ± 16°C west of Chupara Point, where a range‐cutting fault (Chupara Fault) had been inferred in previous geologic mapping campaigns. Thus, the discrete thermal discontinuity of ~100°C very likely represents the Chupara Fault. Our RSCM‐derived peak metamorphic temperatures are 50°C to 100°C higher than those from previous estimates, requiring revision of tectonic models to account for deeper burial and greater exhumation. The peak metamorphic conditions determined here, and the deduced timing of faulting from published thermochronological data, are consistent with the two‐stage tectonic model proposed in previous studies.

Multivariate geospatial analysis for predicting soil variability along a toposequence of a watershed in the humid tropics

Spatiotemporal patterns of edaphic properties can be useful in modeling underlying mechanisms and controls of watershed processes, however, few studies have quantified the spatial variability of soils in watersheds in the humid tropics. A multivariate geostatistical approach was used to examine the relationships between soil apparent electrical conductivity (ECa) and measured soil and landform parameters, as well as to assess the temporal and spatial stability of ECa in a 50 × 150 m sub-watershed with three distinct land uses (forest, savannah grassland, and cultivation) in the Northern Range of Trinidad. Soil samples (0–0.2 m), and ECa measured at shallow (0 – 0.5 m; ECas) and deep (0 – 1.6 m; ECad) depths of exploration using a DUALEM-1S EC meter, were taken approximately 4 m apart along a 120 m transect in the toposequence. Although ECa and soil properties (e.g., soil depth and texture) differed among the steeply sloping forest, gently sloping savannah grassland, and flat cultivated area, there was no evidence of an effect of land use on soil properties other than what could be explained by the slope gradient. Sixty-one percent of the variability in ECas was explained by soil depth and water-stable aggregates whereas, 87% of the variation in ECad was explained by soil depth, clay content, and soil pH. Soil depth explained the greatest proportion of the variability in ECa in both models. Additionally, repeated ECa mappings revealed that ECas and ECad were spatiotemporally stable. Thus, ECad which is strongly influenced by the underlying bedrock can be used to model the spatial variability in soil depth, whereas ECas may be better for predicting surface soil properties. Models developed using this approach can predict field-scale variations of soil depth, thereby improving the accuracy of hydro-ecological models.

A Remote Sensing Approach to Understanding Patterns of Secondary Succession in Tropical Forest

Monitoring biodiversity on a global scale is a major challenge for biodiversity conservation. Field assessments commonly used to assess patterns of biodiversity and habitat condition are costly, challenging, and restricted to small spatial scales. As ecosystems face increasing anthropogenic pressures, it is important that we find ways to assess patterns of biodiversity more efficiently. Remote sensing has the potential to support understanding of landscape-level ecological processes. In this study, we considered cacao agroforests at different stages of secondary succession, and primary forest in the Northern Range of Trinidad, West Indies. We assessed changes in tree biodiversity over succession using both field data, and data derived from remote sensing. We then evaluated the strengths and limitations of each method, exploring the potential for expanding field data by using remote sensing techniques to investigate landscape-level patterns of forest condition and regeneration. Remote sensing and field data provided different insights into tree species compositional changes, and patterns of alpha- and beta-diversity. The results highlight the potential of remote sensing for detecting patterns of compositional change in forests, and for expanding on field data in order to better understand landscape-level patterns of forest diversity.

Contrasting trends in biodiversity of birds and trees during succession following cacao agroforest abandonment

Abstract Understanding how transformed habitats act as reservoirs of biodiversity is a key challenge at a time when ecosystems are under unprecedented pressure. Here we compare tree and bird biodiversity in actively cultivated and abandoned cacao agroforests, and use a space for time approach to ask how this diversity has changed over 100 years of succession. Tree and bird communities were surveyed in cacao agroforests, secondary forests at different stages of succession and primary forests in the Northern Range of Trinidad, West Indies, to test the prediction that there are consistent temporal trends in alpha and beta‐diversity across taxa. Temporal alpha‐diversity was taxon dependent. We found that tree alpha‐diversity increased with forest age. In contrast, there was no temporal trend in bird alpha‐diversity. Tree and bird species richness were negatively correlated. Tree and bird composition varied with forest age and environmental distance. A greater proportion of native trees, and of highly forest‐dependent and insectivorous birds were found in older forests. Our analyses show that actively cultivated and young abandoned cacao agroforests can sustain high bird alpha‐diversity, despite lower levels of tree alpha‐diversity. Old secondary and primary forests have unique species compositions including more sensitive and specialist species. Compositional shifts with successional stage for both trees and birds produce a patchwork of habitats that contribute to regional gamma‐diversity. Synthesis and applications. Our research highlights the value of actively cultivated cacao agroforests and secondary forest alongside primary forests as reservoirs of biodiversity. By supporting both biodiversity and livelihoods, traditionally grown shade‐cacao agroforests fall within a people and nature framework. Taken together, these results emphasise the contributions of secondary forests, which are often overlooked, to conservation.

Ceramic Production and Interaction in the Northern Range of Trinidad

ABSTRACTRegional syntheses based on data recovered mostly from outside of the Northern Range have characterized the mountainous region in northern Trinidad as a boundary between two distinct interaction spheres during the Early Ceramic Age (ca. AD 350–650/800) (Boomert 2000). Changes occurring on Trinidad, other islands of the southern Lesser Antilles, and the South American mainland resulted in the disintegration of these earlier style zones during the final centuries of the Early Ceramic (Boomert 2000, 2010). This period of Late Ceramic cultural realignment was characterized by climate change, the renegotiation of political and social networks, and demographic transformations. We consider newly recovered ceramic evidence from the central Northern Range in order to evaluate the characterization of the region as a boundary and the region's role in broader Caribbean trends. We examine participation in interaction spheres to provide a more nuanced understanding of regional dynamics as they were expressed locally. Ceramic data indicate that occupants of the central Northern Range interpreted regional styles using locally derived materials, thus simultaneously engaging regional traditions and constructing local patterns of resource exploitation.

Hemipenial Morphology in the Semifossorial Snakes of the GenusNiniaand a New Species from Trinidad, West Indies (Serpentes: Dipsadidae)

The hemipenial morphology of nine species in Ninia is described for the first time. A total of 65 hemipenes of all recognized species of Ninia were examined. As a result of the evaluation of the hemipenial and caudal morphology, Ninia diademata labiosa is elevated to full species status and a new species is described from 240 m above sea level in the Northern Range of Trinidad. The new species exhibits several diagnostic features, including (1) a primary temporal scale that is extremely long and contacts the upper labial scales 5–7; (2) a temporal scale formula 1 2, with the primary temporal scale three times longer than the lower posterior temporal; and (3) forked hemipenes. The male genitalia of Ninia are excellent indicators of species limits and an effective tool to clarify the identity of cryptic species in the genus.

Selection at the MHC class IIB locus across guppy (Poecilia reticulata) populations

The highly diverse genes of the major histocompatibility complex (MHC) are important in the adaptive immune system and are expected to be under selection from pathogens. Thus, the MHC genes provide an exceptional opportunity to investigate patterns of selection within and across populations. In this study, we analyzed genetic variation at the MHC class IIB gene and six microsatellite loci across 10 populations of guppies (Poecilia reticulata) in the northern range of Trinidad. We found a high level of diversity at the MHC, with a total of 43 alleles in 142 individuals. At the population level, we found that neutral evolution could not fully account for the variability found at the MHC. Instead, we found that MHC F(ST) statistics were lower than F(ST) derived from the microsatellite loci; 33 of 45 population pairwise estimates for the MHC were significantly lower than those for the microsatellite loci, and MHC F(ST) estimates were consistently lower than those predicted by a coalescent model of neutral evolution. These results suggest a similar selection acting across populations, and we discuss the potential roles of directional and balancing selection. At the sequence level, we found evidence for both positive and purifying selection. Furthermore, positive selection was detected within and adjacent to the putative peptide-binding region (PBR) of the MHC. Surprisingly, we also found a purifying selection at two sites within the putative PBR. Overall, our data provide evidence for selection for functional diversity at the MHC class IIB gene at both the population and nucleotide levels of guppy populations.

A field test of the Hamilton–Zuk hypothesis in the Trinidadian guppy (Poecilia reticulata)

The Hamilton–Zuk hypothesis proposes that females prefer male secondary sexual traits because they are honest indicators of parasite resistance. Despite the attention that this hypothesis has received, its role in sexual selection remains equivocal. This study presents the first field test in guppies of two key predictions of the Hamilton–Zuk hypothesis: (1) that within populations, the most highly ornamented males have the fewest parasites and (2) that among populations, males in high parasite populations have the most conspicuous ornaments. Five hundred male guppies from 19 distinct populations in the Northern Range of Trinidad were inspected for Gyrodactylus parasites and photographed. Eight measures of orange spot ornamentation were used to test the predictions: hue, saturation, lightness, relative area, number, and area-weighted hue, saturation, and lightness. Parasite load had no significant effect on any of these measures. There was also no relationship between orange spot ornamentation and parasite abundance among populations. Guppies from high-predation environments had significantly more parasites, and their orange coloration was lighter and less saturated than that in guppies from low-predation environments. Despite previous lab results, this study found no relationship between parasite load and male orange spot ornamentation.

CHROMOSOME BANDING OF SIX DENDROBATID FROGS (COLOSTETHUS, MANNOPHRYNE)

We conducted a chromosome banding analysis (heterochromatin, nucleolus organizer regions, DAPI fluorescence, distamycin A/mithramycin fluorescence) of six phylogenetically basal dendrobatid frog species (Colostethus chalcopis, C. leopardalis, Mannophryne herminae, M. neblina, M. olmonae, M. trinitatis). With the exception of C. chalcopis (2n = 22), all examined species had a chromosome complement of 2n = 24 chromosomes. The C- and Q-band analyses showed that constitutive heterochromatin is present at the centromeres of all species, with Q−-regions occurring at the positions of the nucleolus organizer regions (NORs) of C. leopardalis, M. olmonae, and M. trinitatis. The C-band polymorphisms were detected in M. herminae and M. neblina on chromosome No. 6 and in M. herminae on chromosome No. 7. Silver-staining and distamycin A/mithramycin fluorescence resolved a single pair of NORs in each species. The DAPI fluorescence revealed pericentromeric bands on chromosome No. 1 and 5 in M. trinitatis and on chromosome No. 1 and 4 in C. chalcopis. Chromosome data clearly allow a distinction between M. olmonae and northern Trinidadian M. trinitatis, laying to rest arguments that M. olmonae may not be a good species. In conjunction with chromosome information found in the literature, our data confirm that chromosome complements of phylogenetically basal dendrobatids can be quite variable, with both 2n = 24 and 2n = 22 complements present. Discrepancies in the karyotypes of M. trinitatis from near Caracas, Venezuela, and from the Northern Range of Trinidad indicate the possibility of cryptic species within M. trinitatis. The notion that a reduction in chromosome number by up to three chromosome pairs has taken place among Dendrobatidae from a putative ancestral 2n = 24 karyotype is shown to be congruent with current molecular hypotheses of dendrobatid relationships.

RAIN FOREST CANOPY COVER, RESOURCE AVAILABILITY, AND LIFE HISTORY EVOLUTION IN GUPPIES

Life history traits in guppies (Poecilia reticulata) vary geographically along a predator assemblage gradient, and field experiments have indicated that the association may be causal; guppies introduced from high predation sites to low predation sites have evolved the phenotype associated with low predation in as few as seven generations. It has long been recognized, however, that low predation sites tend to have greater forest canopy cover than high predation sites. Stream differences in canopy cover could translate into stream differences in resource availability, another theoretically potent agent of selection on life history traits. Moreover, new computer simulations indicate that the high predation phenotype would outcompete the low predation phenotype under both mortality regimes. Thus, predation alone may not be sufficient to explain the observed life history patterns. Here we show that food availability for guppies decreases as forest canopy cover increases, among six low predation streams in the Northern Range of Trinidad. Streams with less canopy cover received more photosynthetically active light and contained a larger standing crop of algae (the primary food of guppies), as measured by algal pigments (chlorophylls and carotenoids) on both natural cobble and artificial tile substrates, but did not contain a greater biomass of guppies (per square meter of streambed). Consequently, algae availability for guppies (in micrograms of algal pigments per milligram of guppy) increased with decreasing canopy cover. The biomass of guppies and algae both decreased after a series of floods, with no net effect on algae availability. Field mark–recapture studies revealed that female and juvenile guppies grew faster, and that the asymptotic size of mature males was larger, in streams with less canopy cover. Canopy cover explained 84% of the variation among streams in algae availability which, in turn, explained 93% of the variation in guppy growth rates. Laboratory “common garden” experiments indicated that the stream differences in growth and adult male size in the field were largely environmental (nongenetic). These results strongly suggest that stream differences in canopy cover result in consistent stream differences in food availability, independent of predation. Our preliminary data indicate that some life history traits (offspring size and litter size) vary genetically along the canopy cover gradient, among low predation streams, in the same direction as along the predation gradient. Another recent study shows that food availability is higher at high predation sites than at low predation sites, partly as an indirect effect of predators reducing guppy densities. Further research is required to disentangle the direct effects of predation from those of resource availability in the evolution of life histories.

Calcite and quartz microstructural geothermometry of low-grade metasedimentary rocks, Northern Range, Trinidad

The Northern Range of Trinidad is a mountainous exposure of deformed metasedimentary rocks with Mesozoic depositional ages and Tertiary metamorphic ages located in the Caribbean–South American plate boundary zone. These rocks lack precise mineralogical indicators of metamorphic grade. Using temperature-sensitive quartz and calcite microstructures, and fission track data, we identify, describe, quantify, and map a nearly continuous spectrum of relatively low (>l50°C) to relatively high (250–400°C) deformation temperatures from east to west across the range. Average estimated rock exhumation rates also increase systematically along this trend. The analysis illuminates a sharp, east–west-trending, major thermal discontinuity (i.e. a fault) along the southern boundary of the range. Kinematic analysis of faults and shear bands adjacent to this boundary and modeling indicate that the fault probably dips southward at 80–85° and accommodated normal dip-slip at rates that decreased from west to east. Earlier experimental studies at high strain rates illustrated a strong strain rate dependency for quartz microstructural transitions. Our work indicates a possible strong temperature control for quartz microstructural transitions at natural strain rates.

Plate Boundary Forces in the Vicinity of Trinidad: the Transition from Transpression to Transtension in the Southern Caribbean Plate Boundary Zones

Deformation in the southern Caribbean plate boundary zones as recorded in the Northern Range of Trinidad initiated in the Oligocene with northward vergent gravity sliding of Northern Range sediments due to uplift and oversteepening of the previously passive margin by the eastward migration of the Caribbean flexural forebulge. Progressive east-southeast transvergence of the Caribbean Plate with respect to South America overthrust incorporated the Northern Range sediments into the Caribbean accretionary prism, thrusting them south-southeast to produce a Middle Miocene transpressive foreland fold and thrust belt in southern Trinidad. Late Miocene deformation within Trinidad was increasingly dominated by right-lateral strike-slop (RLSS) faulting, at the expense of transpressive compressional features. Right-stepping of RLSS motion initiated the Gulf of Paria and Caroni pull-apart basins, Since Early Pliocene these basins and other areas to the north of Trinidad have undergone north-south extension in addition to east-west trending RLSS. Such extension caused the northward withdrawal of Caribbean terranes from atop of the Northern Range, Resulting in rapid isostatically induced uplift (approximately 0.5 mmyr[sup -1]). This change in deformation style may relate to a hitherto unrecognized shift in the relative motion of the eastern Caribbean Plate with respect to South America: from east-southeast-directed transpression to east-northeast-directedmore » transtension.« less

Preliminary Observations on Quaternary Reverse Faulting Along the Southern Front of the Northern Range of Trinidad

Several geomorphological evidences of Quaternary reverse faulting are observed along the southern front of the Northern Range in Trinidad between Port-of-Spain and Matura Point. Such a mountain front is associated to a reverse fault system showing an imbricated pattern southward. In the north, the system is limited by a structural feature showing an important vertical component. Southward this system progressively changes to low angle faults. This geometry is corroborated by seismic profiling in the continent shelf. The active faulting evidences consist in lateral drainage offsets, fault trenches, sag-ponds, triangular facets, and saddles. Some quaternary terraces show fault scarps and tilting. We postulate that these reverse fault systems as Arima Fault instead of El Pilar fault as it is not actually connected to the San Sebestian-El Pilar right-lateral slip system, due to the southward prolongation of the southern limit of the Caribbean Plate through the fault system of Los Bajos-El Soldado.

Geological Studies in Eastern Venezuela and Trinidad: From Cretaceous Passive Margin to Neogene Transpressional Thrust Belt

Sedimentological and structural analyses of Trinidad's Northern and Central ranges and Venezuela's Serrania del Interior have led to new interpretations of northeastern. South America's tectonic evolution within the Southern Caribbean Plate Boundary Zone. Medial ( ) Jurassic through early Cenozoic passive margin sediments make up the majority of these areas and were deposited somewhat to the WNW (between 80 and 130 km for Northern Range of Trinidad) of their present positions prior to structural shortening. Neogene southeastward displacement of Jurassic-Cretaceous passive slope and rise sediments (Northern Range) drove propagation of thrusts southward into the Serrania and Central ranges. Displacements were driven by migration of the Caribbean Plate relative to South America. Thus, the Serrania and Central ranges are the western hemisphere's only exposed Mesozoic-Cenozoic passive Atlantic margin stratigraphic section. As such, they provide a Cretaceous-Paleogene record of passive margin sedimentation at a thermally subsiding margin where the complicating effects of tectonism are absent. This makes these sections especially suited for studies of eustatic sea level behavior. Preliminary assessments are shown which suggest that sea level changes for Cretaceous to Paleogene time are not as pronounced as the frequent large and rapid sea level falls and rises that are promoted bymore » some.« less

Cenozoic Plate tectonic history of the northern Venezuela‐Trinidad Area

Geological and geophysical data, coupled with recent plate tectonic reconstructions, suggest that the Cenozoic geologic history of the northern Venezuela‐Trinidad area has been dominated by strike‐slip displacement of discrete crustal blocks. Allochthonous terranes within the area include metavolcanic rocks of the Cretaceous Villa de Cura Group and metamorphic rocks of the Precambrian to Cretaceous Cordillera de la Costa. A relatively competent crustal block (Margarita Block) is defined by an outline around the metamorphic basement of Margarita Island, the Araya/Paria peninsula, the Northern Range of Trinidad, and Tobago Island. Reconstruction of the Margarita Block to its original position requires at least partial closure of the Falcon Basin, closure of the Bonaire and Cariaco basins, and restoration of about 50 km of motion on both the Oca and Bocono faults. Post middle Eocene eastward translation of the Caribbean plate caused eastward motion of the Margarita Block. A minor change in relative plate motion during the late Oligocene or early Miocene produced a right step in the Moron fault, forming the Cariaco pull‐apart basin and El Pilar fault zone. Maximum offset on El Pilar fault is estimated to be no more than 125 km, though displacement along the entire fault zone may have been greater. Transpressional stresses between the Caribbean plate and northern South America caused folding of the Serrania del Interior of Venezuela and the Central Range of Trinidad. Eastward migration of transpressional stresses at the southeastern corner of the Caribbean‐South American plate boundary is being accommodated by formation of oblique thrusts, transpressive anticlines, and downwarping of the crust. Bouguer gravity data suggest that Jurassic‐aged Atlantic oceanic crust is being depressed as the Caribbean plate expands into the Demerara Plateau area. This study suggests that the faults and transtensional/transpressional/compressional structures identified in this study are the result of stresses produced during the large eastward translation of the Caribbean plate since the Paleocene, and are not the product of a shear couple.

The mineralogy and metamorphic geology of low-grade metasediments, Northern Range, Trinidad

Forty-one low-grade metasediments from the Northern Range of Trinidad and from the neighbouring island of Tobago, West Indies, were investigated by microscopic, X-ray powder diffraction, Guinier camera technique and electron microprobe methods. The following minerals were encountered (in order of decreasing abundance): quartz, muscovite, chlorite, paragonite/muscovite mixed-layer, paragonite, organic material, calcite, pyrophyllite, dolomite, albite, hematite, chloritoid, pyrite, rutile, titanite, rectorite, stilpnomelane. The chemical composition of muscovite is dependent on the mineral assemblage, with Si = 6.1–6.2 per formula unit in two high alumina assemblages, versus Si = 6.6 in a low alumina assemblage. Microprobe analyses indicate that muscovite, paragonite and pyrophyllite are sometimes intergrown on a micrometre scale. Chlorite composition estimated from X-ray data shows good correspondence with microprobe data for two Al-poor samples but is less satisfactory for an Al-rich sample. Observed mineral assemblages in AKNa are indicative of the pyrophyllite-paragonite-albite fades. For the first time, chemical data for coexisting pyrophyllite, chlorite (M = MgO/(MgO+ FeO) = 0.377) and chloritoid (M = 0.110) are given. This assemblage is indicative of the low or medium pressure range of the lower greenschist facies. Pressure conditions during metamorphism are not well constrained but a minimum pressure of 2 kbar, corresponding to 5–6 km of overburden, can be estimated from the Na M4 content of actinolite. Temperatures derived from the calcite-dolomite geothermometer range between 300 and 350°C and are consistent with the presence of the assemblage pyrophyllite + calcite + quartz.

LEK BEHAVIOUR AND BREEDING OF GUY'S HERMIT HUMMINGBIRD PHAETHORNIS GUY

SummaryGuy's Hermit Phaethornis guy, a large forest hummingbird, was studied for 21/2 years in the Northern Range of Trinidad. Regular observations made at a lek of 16 males showed that leks are occupied from November until the beginning of July, and that individual birds retain their lek territories from year to year and use the same perches.The usual song is a monosyllabic note regularly repeated, but the quality of the note varied between different leks and between different parts of a lek, and a few males had a disyllabic song. Young males join the lek between April and June and learn the song of their immediate neighbours. Their plumage, when they first join, is similar to a female's, with distinct pale super‐ and subciliary stripes. The acquisition of the dark head of the adult male probably takes four years.Before they land on their lek perches, males perform an elaborate aerial display in which the red gape is flashed open and a loud tock is uttered. When males visit each other they rapidly change places on the lek perch, the airborne bird performing the tock‐display over the perched bird. A similar tock‐displaying with changing of place occurs when females visit males; twice these were seen to culminate in mounting. Periodically all males at the lek ‘false‐mate’ with a leaf or other piece of vegetation near their lek perches, after tock‐displaying above it. Young males false‐mate much more frequently than older males.The breeding season lasts for eight months, the peak of breeding coinciding closely with the period when the two most important sources of nectar (Heliconia bihai and Pachystachys coccinea) are available. Males occasionally visit nests, and possibly assist in defending them. Undefended nests are quickly dismantled by other birds in search of nest‐material. Of 19 nests found before the clutch was complete, five (26%) were successful. The incubation period is 17–18 days, and the fledging period 21–23 days.

Experiments on the Demography of Tropical Butterflies. I. Survival Rate and Density in Two Species of Parides

Estimations of number of individuals and survival rate for Parides anchises and P. neophilus have been made in an area in the Northern Range, Trinidad, West Indies, where the insects are particularly common. The change in numbers observed reflects the onset of the wet season, during which the species become most abundant. The estimated survival rate is 0.84 per day, indicating an expectation of life of between 5 and 10 days. This is much shorter than the possible duration of life known from observation of specimens in insectaries, and is similar to the values obtained for a variety of Lepidoptera in temperate regions. It is suggested that one factor contributing to low survival is the very heavy rain showers that were experienced. NEOTROPICAL BUTTERFLIES ARE noted for the striking mimetic associations found among them. Although mimicry is of great significance in the experimental study of evolution, there is as yet little information available on the density, longevity, or dispersal behaviour of the species involved. Such information is essential for a full understanding of the processes giving rise to mimicry. The present observations concern the ecology of two miillerian mimics, Parides anchises (Linnaeus) and P. neophilus (Hiibner), studied in the Northern Range of Trinidad. These butterflies occur in clearings and along paths in the lower montane rain forest of the Northern Range and in the secondary scrub on the lowland. As a rule they are solitary in behaviour, and although during July and August one or two individuals would almost certainly be encountered during a few hours collecting along the traces in the forest, it is not easy to predict a locality for them with any precision. The estimation was carried out in an area where they were more than usually common. Being distasteful and robust insects, we expected them to exhibit a high survival rate in this natural colony.