Slope Habitats Research Articles

Intra-seasonal variation in foraging behavior among Adélie penguins (Pygocelis adeliae) breeding at Cape Hallett, Ross Sea, Antarctica

We investigated intra-seasonal variation in foraging behavior of chick-rearing Adelie penguins, Pygoscelis adeliae, during two consecutive summers at Cape Hallett, northwestern Ross Sea. Although foraging behavior of this species has been extensively studied throughout the broad continental shelf region of the Ross Sea, this is the first study to report foraging behaviors and habitat affiliations among birds occupying continental slope waters. Continental slope habitat supports the greatest abundances of this species throughout its range, but we lack information about how intra-specific competition for prey might affect foraging and at-sea distribution and how these attributes compare with previous Ross Sea studies. Foraging trips increased in both distance and duration as breeding advanced from guard to creche stage, but foraging dive depth, dive rates, and vertical dive distances travelled per hour decreased. Consistent with previous studies within slope habitats elsewhere in Antarctic waters, Antarctic krill (Euphausia superba) dominated chick meal composition, but fish increased four-fold from guard to creche stages. Foraging-, focal-, and core areas all doubled during the creche stage as individuals shifted distribution in a southeasterly direction away from the coast while simultaneously becoming more widely dispersed (i.e., less spatial overlap among individuals). Intra-specific competition for prey among Adelie penguins appears to influence foraging behavior of this species, even in food webs dominated by Antarctic krill.

Squat lobster assemblages on seamounts differ from some, but not all, deep‐sea habitats of comparable depth

AbstractThis study was carried out to test the hypothesis that benthic communities on seamounts are distinct from those of other deep‐sea habitats at comparable depths. Analysis of the squat lobster fauna of deep‐sea habitats in the Southwestern Pacific revealed that the species composition of assemblages on seamounts was not statistically dissimilar from assemblages on slope and plateau habitat at comparable depths. However, compositional differences were observed between seamount and rise and ridge habitat. Differences in assemblage composition between seamount and ridge habitat were statistically significant for two of the four ridge systems examined. Assemblages on seamounts that were distinct from non‐seamount ridge habitat were typically dominated by small‐bodied species with an abbreviated larval stage. Various environmental variables were correlated with the observed assemblage patterns observed; depth‐related variables may account for differences between seamount and rise assemblages, whilst differences in POC flux likely play a role in determining the assemblage compositional patterns between seamount and non‐seamount ridge habitat. Extensive pre‐analysis data treatment was required to ensure that multivariate analyses of assemblage data from seamount and non‐seamount habitats were robust. Our results confirm the findings of recent studies that found no compositional differences in assemblages from seamount and slope habitats, and support the idea that dissimilarity between seamount assemblages on different ridge systems increases with geographic distance. Further research will be required before the generality of these findings can be confirmed.

Hawaiian hotspots: enhanced megafaunal abundance and diversity in submarine canyons on the oceanic islands of Hawaii

AbstractSubmarine canyons are important sources of habitat heterogeneity on the slopes of continents and islands, but the study of canyon ecology has been largely restricted to continental margins. Here we use visual and video surveys from 36 submersible dives to evaluate the role of canyons as abundance and diversity hotspots for megafauna in the Hawaiian Archipelago, an island chain embedded in an oligotrophic ocean. We surveyed megafauna in canyon and slope settings at depths of 350–1500 m along the margins of four islands: the low ‘islands’ of Nihoa and Maro Reef, and the high islands of Oahu and Moloka’i. Megafaunal communities in canyons differed significantly from those in nearby slope habitats at all depths. Highly mobile fishes and invertebrates were consistently more abundant in canyons than on nearby slopes at the same depth off all islands, suggesting that canyons may be important sources of larvae for surrounding habitats. In the few cases where megafaunal abundances were similar or higher on the slope, the differences were typically driven by higher slope abundance of sessile suspension feeders or animals with limited mobility, i.e. by organisms which are likely to have difficulty with high currents and sediment transport in canyons. Megafaunal species richness and diversity generally trended higher within canyons, especially for the highly mobile taxa. Canyons contained 41 megafaunal species never observed on the slope, and increased estimated regional species richness by 25–30 species, indicating that canyons enhanced beta and gamma (regional) biodiversity. An expected trend of greater enhancement of diversity and abundance in canyons on the margins of high versus low oceanic islands was not observed, although megafauna were generally more abundant in both canyon and slope habitats on the high islands (Oahu and Moloka’i). We conclude that submarine canyons on both low and high islands in the Hawaiian Archipelago may provide keystone structures, enhancing megafaunal abundance, providing source populations for the open slope, and enhancing local and regional species diversity.

Seasonal and spatial variation in water availability drive habitat associations in a tropical forest

Associations with topographic units or soil types that vary in water availability are widespread in plant communities and are one of the main structuring aspects for local species distribution patterns, yet the underlying mechanisms are poorly understood. We hypothesized that differential seedling performance across habitats, particularly during the dry season, leads to habitat associations in seasonal tropical forests. We expected this pattern to be most pronounced in particularly dry years, such as those associated with El Niño Southern Oscillation (ENSO) events. We assessed performance of 36 native tree and shrub species in a moist forest in central Panama across the dry and wet seasons in two topographic habitat types during a year in which dry-season precipitation was reduced due to an ENSO event. At the community level, we found lower growth and higher mortality in the dry season relative to the wet season and higher mortality in the drier plateau habitat relative to the wetter slope habitat. There was large variation in species' responses to season and habitat. Species' mortality and growth rates were significantly correlated with experimentally assessed drought sensitivity, but only during the dry season in the plateau habitat. Slope specialists had significantly higher survival, but not growth, in the slope vs. plateau habitat during the dry season. In contrast, plateau specialists showed no performance differences between habitats. The data suggest that associations with plateau habitats result from a numerical advantage of drought-tolerant species in dry habitats in which seedlings of drought-sensitive species are unable to persist. Overall, our results support the idea that seasonal and spatial variation in water availability, particularly in dry years, drive seedling dynamics, which in turn shape local species distributions. Predicted shifts in rainfall patterns caused by global and regional climate change are therefore expected to alter the dynamics, composition, and diversity of seasonal tropical forests.

Taxonomic revision of Ascidiacea (Tunicata) from the upper continental slope off north-western Australia

A collection of ascidians from 100–1000 m deep off the north-western coast of Australia has yielded 19 species, including one new, two possibly endemic to the north-western coast of Australia, four well-known Indo-west Pacific tropical species and 12 species known from the deeper waters of the western Pacific, of which 11 had not previously been recorded from off the western Australian coast or from other parts of the Indian Ocean. A third of these 12 species displays adaptations for a reduction in filter-feeding capacity, as do other known species from deeper slope and abyssal habitats. Nevertheless a connection with fauna of deep ocean basins of the Indian Ocean is not apparent at this stage. The full range of characters associated with species, genera and families are discussed, and those contributing to the identification of immature or mutilated specimens, as well as those relevant to an assessment of phylogenetic relationships, are emphasized.

Bioenergetic model estimates of interannual and spatial patterns in consumption demand and growth potential of juvenile pink salmon (Oncorhynchus gorbuscha) in the Gulf of Alaska

A bioenergetic model of juvenile pink salmon (Oncorhynchus gorbuscha) was used to estimate daily prey consumption and growth potential of four ocean habitats in the Gulf of Alaska during 2001 and 2002. Growth potential was not significantly higher in 2002 than in 2001 at an alpha level of 0.05 (P ¼ 0.073). Average differences in growth potential across habitats were minimal (slope habitat ¼ 0.844 g d � 1 , shelf habitat ¼ 0.806 g d � 1 , offshore habitat ¼ 0.820 g d � 1 , and nearshore habitat ¼ 0.703 g d � 1 ) and not significantly different (P ¼ 0.630). Consumption demand differed significantly between hatchery and wild stocks (P ¼ 0.035) when examined within year due to the interaction between hatchery verses wild origin and year. However, the overall effect of origin across years was not significant (P ¼ 0.705) due to similar total amounts of prey consumed by all juvenile pink salmon in both study years. We anticipated that years in which ocean survival was high would have had high growth potential, but this relationship did not prove to be true. Therefore, modeled growth potential may not be useful as a tool for forecasting survival of Prince William Sound hatchery pink salmon stocks. Significant differences in consumption demand and a two-fold difference in nearshore abundance during 2001 of hatchery and wild pink salmon confirmed the existence of strong and variable interannual competition and the importance of the nearshore region as being a potential competitive bottleneck. Published by Elsevier Ltd.

Does Prey Availability Determine Seasonal Patterns of Habitat Selection in Texas Ratsnakes

An animal's requirements (e.g., food vs. shelter) from its environment are likely to vary seasonally and, therefore, so too should habitat selection. Here, we test the hypothesis that Texas Ratsnakes (Elaphe obsoleta) choose habitats based on prey availability during their active season and on cover during winter. We examined snake habitat selection at three spatial scales and compared that to abundance of small mammals and nesting birds, which we confirmed by diet analysis to be the snakes' principal prey. Small mammal trapping and avian point counts showed that overall prey abundance was higher on mesas and slopes compared to savannahs. Compared to availability of habitats within the entire study area, snakes selected home ranges with a high proportion of slope habitat. Within home ranges, however, selection for slopes was exhibited only during winter when foraging is at a minimum and snakes are relatively inactive. Snakes did not use habitat within home ranges selectively during the active season or during the avian breeding season. The latter result suggests that ratsnakes are effective avian nest predators despite preying on birds opportunistically. However, it is also possible that some individual ratsnakes specialize on birds, whereas the majority preys on mammals. Microhabitat analysis comparing winter and active season sites showed that snakes preferentially used areas of high canopy cover and rock ground cover during winter. Collectively these results provide limited support for the hypothesis that ratsnakes use habitats based on prey availability but do indicate that ratsnakes select winter habitat based on cover availability.

Four new species of Rhodophyceae from Fiji, Polynesia and Vanuatu, South Pacific

SUMMARYFour new species of Rhodophyceae are described from the South Pacific, with type localities in Fiji, French Polynesia and Vanuatu. Chondria bullata from the Tuamotus (French Polynesia), Vanuatu, Palmerston Atoll (Cook Islands) and Fiji is unique owing to its non‐constricted axes with markedly protruding, bubble‐like cortical cells. Halymenia nukuhivensis, from the Marquesas Islands in French Polynesia, is distinguished from others in the genus by its dichotomous, papery blades issued from a strap‐shaped basal region, and the equal proportion of anti‐clinal, periclinal and oblique filaments in its medullary layer. Jania articulata, so far known only from the Tuamotus in French Polynesia and Manihiki in the Northern Cook Islands, superficially resembles the genus Amphiroa with its articulated branches with numerous genicula between successive dichotomies, and its large axis diameter. Meristotheca peltata from the Fiji Islands is unique among the genus by its distinctly peltate, erect habit. The recent high number of newly described species from the South Pacific region emphasizes the need for more in‐depth surveys, particularly in deeper outer reef slope habitats, which remain for the most part unexplored and could yield particularly interesting new taxa or distributional records.

Fishes of three North West Shelf atolls off Western Australia: Mermaid (Rowley Shoals), Scott and Seringapatam Reefs

The biodiversity of fishes on the Australian North West Shelf atolls is known to be the richest in the state. In recent years however, there has been minimal focus on comprehensive taxonomic fish surveys in this region. Since the atolls are subjected to an increasing frequency of pressures such as major cyclones, coral bleaching, tourism, fishing and natural resource exploitation, it is critical to monitor this region to have the information to safeguard the biodiversity for the future. To obtain current data that would complement ongoing quantitative surveys in the region, the Western Australian Museum undertook a taxonomic and semi-quantitative survey of the shallow water reef fishes and other major phyla at Mermaid, Scott and Seringapatam Reefs in September 2006. Thirty nine underwater visual surveys were conducted, supplemented by limited intertidal collecting, angling and surface observations. Analysis of the fish fauna across atolls demonstrated close similarities between North Scott, South Scott and Seringapatam Reefs, and, as a group, these reefs showed certain differences from the more southerly Mermaid Reef. Significant differences were found between lagoonal and outer reef slope habitats. At each atoll, the outer reef slope habitats were more homogeneous and had a greater diversity of fishes than the lagoon habitats, with South Scott lagoon housing a unique mix of both outer reef slope and lagoon species. Fish diversity was found to increase towards the northern atolls, supporting previous research in the region. The fish fauna at all four atolls had more in common with fish assemblages at equivalent clear-water reefs in Indonesia than with those on the northwest coastal mainland and, as such, are unique within Western Australian waters.

Potential reversal of a phase shift: the rapid decrease in the cover of the invasive green macroalga Dictyosphaeria cavernosa Forsskål on coral reefs in Kāne‘ohe Bay, Oahu, Hawai‘i

The native green macroalga Dictyosphaeria cavernosa dominated most of the reef slope habitat in Kāne‘ohe Bay, Hawai‘i for 40 years prior to 2006 and had displaced corals from the habitats they created. This has been one of the most oft-cited examples of a phase shift occurring on a coral reef. After decades of relatively constant, high abundance of the alga, percent cover declined dramatically throughout the bay between February and June 2006. The sudden decrease in cover of this alga appears to be the result of an unusually protracted cloudy, rainy period in March 2006, which may have reduced irradiance and caused the alga to lose weight. Corals and red macroalgae living at the same depths and in some of the same habitats were apparently not affected by this 42-day period of rain and overcast skies. Competition between corals and D. cavernosa for space on reef slopes has been virtually eliminated by the death of this alga, but the unstable rubble formations, which remain in much of the area formerly covered by D. cavernosa may not be conducive to rapid increase in cover by the remaining corals or to establishment by coral recruits. Two years later, there was still no recovery of D. cavernosa. This represents a rare example of decline in macroalgal dominance on a reef and a partial reversal, possibly only temporary, of a phase shift.

Fine- and landscape-scale spatial genetic structure of cushion rockjasmine, Androsace tapete (Primulaceae), across southern Qinghai-Tibetan Plateau

The cushion rockjasmine, Androsace tapete (Primulaceae), is among the angiosperms with highest altitudal distribution in the world. Cushion rockjasmine is a prominent pioneer species in alpine deserts and alpine flowstone slope habitats up to 5,300 m on Qinghai-Tibetan Plateau. In this study, we use inter simple sequence repeat (ISSR) markers to investigate the spatial genetic structure of A. tapete at both fine-scale and landscape-scale, with emphasis on testing the hypothesis that the low-altitude valley of the Brahmaputra River, running from west to east across Qinghai-Tibetan Plateau, has significant effects on the spatial population structure of A. tapete. A total of 235 individuals were collected from five populations in disjunct ridges (i.e. two populations located in the north, and three in the south of the Brahmaputra River), including 158 individuals that were spatial explicitly sampled from a 30 m x 90 m plot. At fine scale, spatial autocorrelation analysis indicates a significant genetic structure within a short distance (less than 10 m), which is probably due to limited gene dispersal via pollen and/or seeds. At landscape scale, however, AMOVA suggests that most of the total genetic variation (85%) is among individuals within populations; and the Brahmaputra River plays a weak role in shaping the spatial population structure of A. tapete. In addition, the results of PCA and STRUCTURE assignment show significant genetic associations between the populations across the Brahmaputra River. The historical gene exchanges and slow genetic drift may be responsible for the lack of deep genetic differentiation among topographically separated populations in A. tapete.

Short-term temporal variability in fish community structure at two western Mediterranean slope locations

Short-term temporal variability in deep-sea demersal fish assemblages is described for two slope areas characterised by different oceanographic conditions, which are situated north (Balearic sub-basin, BsB) and south (Algerian sub-basin, AsB) of the Balearic Islands (western Mediterranean). A total of 75 hauls were analysed from six bottom trawl surveys carried out in the two sub-basins. At BsB, surveys were designed for sampling different slope habitats during April 1991, December 1991, March 1992 and July 1992: (i) a submarine canyon at a depth of around 450 m, (ii) the upper slope at a depth of 600–650 m, and (iii) the middle slope at a depth of around 1200 m. At AsB, surveys were carried out during October 1996 and May 1998, along a continuous transect on the upper, middle and lower slope. The taxonomic composition, ecological parameters (number of species, abundance and biomass) and biomass spectra of the assemblages, as well as the length frequency distribution of the main species, were compared for different seasons and bathymetric ranges. Forty-four demersal species were captured in BsB and 38 in AsB. Helicolenus dactylopterus and Trachyrinchus scabrus were more abundant in BsB, and Hoplostethus mediterraneus, Galeus melastomus and Centroscymnus coelolepis in AsB. Depth was the determinant factor in all the analyses. Species-specific densities (abundance and biomass) showed significant differences between surveys, depth strata and their interaction in BsB. However, survey and its interaction with depth, were not significant in AsB. We also found significant differences in relation to depth and season for the three ecological parameters tested in BsB, but only significant differences in relation to depth in AsB. Biomass spectra showed large differences in relation to depth but only slight between-survey differences, which mainly occurred in the upper slope. The length frequency distributions of single species presented short-term temporal variations, mainly due to the varying presence of a larger proportion of small or large individuals. Depth, geographic area and sampling time were the main factors determining the species composition and structure of deep-sea slope demersal fish assemblages. The effects of short-term temporal variations were observed in both the replacement and the size structure of some dominant and subdominant species throughout the year. The different temporal variation effects observed between the two sub-basins might be related to differences in productivity and its transport to the benthos.

Cuvier's beaked whale distribution in the Mediterranean Sea: results from small boat surveys 1996–2007

A total of 17,651 km of sailboat survey effort obtained with very good sighting conditions was pooled over the period 1995 to 2007 to provide an insight into Cuvier's beaked whales' (Ziphius cavirostris) distribution in the western and central Mediterranean Sea. Although only six confirmed sightings were obtained under such conditions, complementary sightings made a total of eleven confirmed records. Their distribution showed that only slope habitat, and its close proximity, was favourable to the species. In contrast to regions pointed out in the recent literature, such as the Alboran, Ligurian and Ionian Seas, it appeared that the Tyrrhenian Sea was likely to be an important area for Cuvier's beaked whales in the Mediterranean. Sighting rates of 0.1–0.25 sighting/100 km and sighting rates for individuals of 0.2–0.5 individual/100 km were obtained in favourable regions. When compared to sighting rates obtained on Risso's dolphinsGrampus griseusduring the same surveys, the Cuvier's beaked whale appeared to be quite a frequent species in its favoured habitats. The present study contributes a better knowledge of this poorly-known species, in the context of increasing and threatening anthropogenic noises.

Temporal variation in dwarf sperm whale (Kogia sima) habitat use and group size off Great Abaco Island, Bahamas

AbstractDwarf sperm whales (Kogia sima) are among the most commonly stranded yet least known pelagic cetaceans. Few studies have occurred at sea, and none have quantified temporal and spatial variation in dwarf sperm whale abundance and group size. We assessed seasonal and spatial variation in dwarf sperm whale group size and abundance off Great Abaco Island, Bahamas using surveys within a 126 km2 study area with depths between 2 and 1,600 m. After correcting for survey effort and variation in sighting efficiency among sea states, we found that dwarf sperm whale group size and habitat use varied seasonally. In summer, dwarf sperm whale groups were small (median = 2.5, range = 1–8) and were found only in the two deep habitats within the study area (slope 400–900 m, deep 900–1,600 m). In winter, group sizes increased (median = 4, range = 1–12) and sightings were almost six times higher in the slope habitat, where vertical relief is highest, than other habitats. Our results suggest that studies of pelagic cetaceans and conservation plans must explicitly account for seasonal variation in group size and habitat use.

Leaf traits of natural populations of Adiantum reniforme var. sinensis, endemic to the Three Gorges region in China

Leaf mass per unit area (LMA), carbon and nitrogen contents, leaf construction cost, and photosynthetic capacity (P max) of Adiantum reniforme var. sinensis, an endangered fern endemic to the Three Gorges region in southwest China, were compared in five populations differing in habitat such as soil moisture and irradiance. The low soil moisture and high irradiance habitat population exhibited significantly higher LMA, area-based leaf construction (CCA), and carbon content (CA), but lower leaf nitrogen content per unit dry mass (NM) than the other habitat populations. The high soil moisture and low irradiance habitat populations had the lowest CCA, but their cost/benefic ratios of CCA/P max were similar to the medium soil moisture and irradiance habitat population due to their lower leaf P max. Hence A. reniforme var. sinensis prefers partially shaded, moist but well-drained, slope habitats. Due to human activities, however, its main habitats now are cliffs or steeply sloped bare rocks with poor and thin soil. The relatively high energy requirements and low photosynthetic capacity in these habitats could limit the capability of the species in extending population or interspecific competition and hence increase its endangerment.

Mating system variation in the hermaphroditic brooding coral, Seriatopora hystrix

Self-compatible, hermaphroditic marine invertebrates have the potential to self-fertilize in the absence of mates or under sperm-limited conditions, and outcross when sperm is available from a variety of males. Hence, many hermaphroditic marine invertebrates may have evolved mixed-mating systems that involve facultative self-fertilization. Such mixed-mating strategies are well documented for plants but have rarely been investigated in animals. Here, I use allozyme markers to make estimates of selfing from population surveys of reef slope and reef flat sites, and contrast this with direct estimates of selfing from progeny-array analysis, for the brooding coral Seriatopora hystrix. Consistent heterozygote deficits previously reported for S. hystrix suggests that inbreeding (including the extreme of selfing) may be common in this species. I detected significant levels of inbreeding within populations (F(IS)=0.48) and small but significant differentiation among all sites (F(ST)=0.04). I detected no significant differentiation among habitats (F(HT)=0.009) though among site differentiation did occur within the reef slope habitat (F(SH)=0.06), but not within the reef flat habitat (F(SH)=0.015). My direct estimates of outcrossing for six colonies and their progeny from a single reef flat site revealed an intermediate value (t(m) (+/-s.d.)=0.53+/-0.20). Inbreeding coefficients calculated from progeny arrays (F(e)=0.31) were similar to indirect estimates based on adult genotype frequencies for that site (F(IS)=0.38). This study confirms that the mating system of this brooding coral is potentially variable, with both outcrossing and selfing.

Spatio-temporal variations of biomass and abundance in bathyal non-crustacean megafauna in the Catalan Sea (North-western Mediterranean)

The spatio-temporal variations in diversity, biomass and abundance of bathyal invertebrates (excluding decapod crustaceans, which have been analysed elsewhere) from the North-western Mediterranean margin are described. The upper canyon (∼450 m), middle slope (∼650 m) and lower slope (∼1,200 m) habitats were investigated throughout the year. The first two sites are visited daily by a specialised commercial fisheries’ fleet, while the deeper site has not been impacted by fishing activities. A total of 140 species from 12 phyla were collected from the 3 study areas. Of these, the Mollusca, Echinodermata, Polychaeta and Cnidaria were the most speciose groups. The patterns of species diversity (H′) and evenness (E) were similar in time and space. The upper canyon and middle-slope sites were dominated by echinoderms and molluscs, while the lower-slope site was dominated by cnidarians and sponges. Multifactorial ANOVA showed significant spatio-temporal differences in the biomass and/or abundance only in echinoderms, molluscs, cnidarians and polychaetes. The faunal differences observed were explained by habitat type, but not by season. The role of submarine canyons and commercial fishing on shaping the diversity and biomass of bathyal Mediterranean invertebrates is discussed.

Halimeda pygmaea and Halimeda pumila (Bryopsidales, Chlorophyta): two new dwarf species from fore reef slopes in Fiji and the Bahamas

H. Verbruggen, D.S. Littler and M.M. Littler. 2007. Halimeda pygmaea and Halimeda pumila (Bryopsidales, Chlorophyta): two new dwarf species from fore reef slopes in Fiji and the Bahamas. Phycologia 46: 513–520. DOI: 10.2216/07-01.1Halimeda pygmaea and Halimeda pumila, two diminutive calcified green algal species, are described from material collected on Fijian and Bahamian reef slopes, respectively. The species resemble Halimeda cryptica in having a single siphon traversing the nodes between subsequent calcified segments and living in sheltered fore-reef slope habitats. They differ from H. cryptica by their diminutive size and various anatomical features. Molecular sequence data (tufA) underpin the identity of H. pygmaea and reveal its phylogenetic position as a sister taxon to H. cryptica in the Halimeda section Micronesicae.

Habitat niche partitioning by 16 species of Myristicaceae in Amazonian Ecuador

The distribution and spatial pattern of plants in tropical forests have important implications for how species interact with each other and their environments. In this article we use a large-scale permanent census plot to address if the coexistence of 16 co-occurring species of Myristicaceae is aided by topographic and light gradient niche partitioning. We used a second order spatial pattern analysis based on Ripley’s K function to describe species’ distributions and associations among species, and a torus translation procedure to test for associations with three topographically defined habitats. A majority of species displayed spatial aggregation and over half had one or more significant habitat associations. Four species were associated with the ridge habitat, four species with slope habitat, and two with valley habitat. Seven other species showed no habitat association. Within each habitat group, species exhibited a variety of distributions in relation to light availability. However, habitat associations were largely unexplained by differential rates of mortality, growth or recruitment over a 5-year interval. We conclude that although in principle partitioning of the topographic and light environments may double or treble the number of species able to coexist, there is no evidence that partitioning of physical habitats can explain the coexistence of all 16 of these closely related species.

Developmental changes in habitat associations of tropical trees

Summary 1 Recent studies have documented local-scale associations between tree species and topographic and edaphic habitat types in forests worldwide. To determine whether such associations form at early life stages, we compared species’ positive associations with five habitat types (high plateau, low plateau, slope, streamside, and swamp) at two life stages for 80 tree and shrub species in a Panamanian lowland forest. 2 Nineteen significant, positive habitat associations were detected at the small tree stage (seedlings and saplings ≥ 20 cm tall and < 1 cm d.b.h.), and 18 at the large tree stage (individuals ≥ 1 cm d.b.h.), according to results of torus-translation randomization tests. The majority of species did not show consistent associations at the two stages. Of the 30 species significantly associated with a habitat, only five were associated with the same habitat at both stages. Overall, more species were associated with the wetter slope habitat at the large tree stage compared with the small tree stage. 3 For a subset of species, we examined the relationship between observed habitat associations and seed dispersal and seedling establishment patterns by using species-specific seed dispersal kernels to predict seed rain into each habitat. 4 Two-thirds of species associated with a habitat at the large tree stage had higher predicted seed densities in the associated habitat relative to other habitat types, indicating that limited seed dispersal acts to reinforce habitat associations for most species. In contrast, only one-third of the species associated with a habitat at the large tree stage showed evidence of higher seedling establishment rates in the associated habitat compared with other habitats, and an equal number of species appeared to have lower rates of establishment in the habitat that large trees of the species were associated with. 5 Overall, our results indicate that habitat associations of large trees typically do not form at early life stages. Rather, many species appear to exhibit different ecological habitat preferences across life stages. Future studies of species’ habitat associations should therefore include multiple life stages in order to detect developmental shifts in ecological preferences.