DEVELOPMENTAL MODE AND SPECIES GEOGRAPHIC RANGE IN REGULAR SEA URCHINS (ECHINODERMATA: ECHINOIDEA)

Among marine benthic organisms, the ability to disperse, primarily during the larval stage, is widely thought to influence the extent of species geographic range. Because related species often differ in their modes of larval development (pelagic, feeding larvae; pelagic, nonfeeding larvae; or brooded development), and these can have dramatically different planktonic intervals, the mode of development may influence geographic range. A global survey of 215 regular echinoids shows that species with pelagic, feeding larvae have significantly larger ranges than those with pelagic, nonfeeding larvae, but there is no difference in ranges between species with pelagic, nonfeeding larvae and those with brooded development. These patterns are maintained within the Cidaroida and the Temnopleuroida, which account for the great majority of species with pelagic, nonfeeding development and brooded development. This limited effect of developmental mode on geographic range is found among species occurring predominantly in waters shallower than 100 m. For species occurring deeper than 100 m, there is no significant difference in geographic range related to type of development. The relationship between developmental mode and species range was examined more closely for circa 30 species for which the developmental period was known from laboratory observations. Adjusting the developmental times to a common temperature, 20°C, using realistic values for Q₁₀ from 2.0 to 3.6, showed a highly significant, negative correlation between egg volume and developmental time, indicating the potential for developmental mode to influence the planktonic interval. However, there was no relationship between time in the plankton, estimated from unadjusted developmental times, and extent of species geographic range. These results suggest that developmental mode may influence extent of species geographic ranges indirectly through the consequences of dispersal for gene flow or recovery from disturbance.     

The effects of host-plant distribution and local abundance on the species richness of agromyzid flies attacking British umbellifers

Abstract. 1. The number of agromyzid species (Diptera: Agromyzidae) attacking British Umbelliferae generally increases with the size of the geographic range of the host, measured as occupied 10 km squares in the Atlas of the British Flora (Lawton & Price, 1979). 2. In the present study we tried to explain the large, residual variation in this species—area relationship using two new variables, namely the local abundance of the host plant, and the number of habitats within which it grows. 3. Local abundance was estimated from eight floras that map plant distributions within English countries by tetrads (2 times 2 km squares). Local abundance was defined as: Total number of occupied tetrads Total number of available tetrads within occupied 10 km squares 4. The number of habitats occupied by each host plant was taken from the only county flora to record plant habitats objectively, that for Warwickshire. 5. We expected to find a correlation between local abundance and the residuals from the national species—area relationship, with locally scarce plants having fewer agromyzids than expected from the sizes of their national ranges, and vice versa. 6. What we found was that size of geographic range and local abundance were highly correlated; hence their relative contributions to agromyzid species richness were difficult to disentangle. Residuals from the national species—area relationship were positively correlated with local abundance, but the relationship marginally failed to achieve statistical significance (P= 0.06). 7. In contrast, the number of habitats occupied by each species of umbellifer in Warwickshire had a marked effect upon agrornyzid species richness, with plants that grow in more habitats supporting more species of insects. Not surprisingly, local abundance and number of habitats occupied were highly correlated. 8. Lawton & Price's observation that aquatic umbellifers are faunally impoverished now emerges as part of the general effect of number of habitats occupied by the host plants on agromyzid species richness. 9. Once the number of habitats occupied by each host plant in Warwickshire was entered into a multiple regression, the effect of size of host geographic range on agromyzid species richness was no longer statistically significant. 10. A combination of the number of habitats occupied, and leaf-form of the host (the latter taken from Lawton & Price, 1979), explains 61% of the variation in agromyzid species richness on British Umbelliferae.     

Tropical dry forest trees and the relationship between local abundance and geographic range

Aim To test the macroecological principle that a positive relationship exists between local abundance and geographic range size for tree communities in the tropical dry forest. Location Two tropical dry forest (TDF) regions on the Pacific coast of Mexico: one near Chamela, Jalisco; the other near Huatulco, Oaxaca. Methods We recorded species presence and relative abundance of trees and lianas from over 40 locales in each of the study regions using transects across an elevational gradient. We then compared the field data with occurrence data from national and online databases to examine how local patterns of abundance relate to putative geographic range areas and latitudinal breadth. Results We found no significant correlation between abundance and range size. Overall, many more locally abundant species had small ranges than large ones. We found that most species occupy the majority of the TDF range north of Colombia, and those species present in South America occupy the majority of that continent’s TDF range as well. This pattern was independent of local abundance. We also found no relationship between range size and local niche breadth as measured by elevation, or between local abundance and distance to the range centre. Main conclusions The macroecological tenet that posits a positive correlation between local abundance and geographic range size does not appear to hold for TDF trees. The finding that many locally abundant species had narrow ranges also suggests that dry forest endemics may be particularly well adapted to local conditions and make important contributions to community structure. We hypothesize that the absence of abundant species with large ranges is due to opposing environmental constraints that prevent a species from thriving everywhere.     

Biogeographic and bathymetric ranges of Atlantic deep-sea echinoderms and ascidians: the role of larval dispersal

Dispersal plays an important role in the establishment and maintenance of biodiversity and, for most deep-sea benthic marine invertebrates, it occurs mainly during the larval stages. Therefore, the mode of reproduction (and thus dispersal ability) will affect greatly the biogeographic and bathymetric distributions of deep-sea organisms. We tested the hypothesis that, for bathyal and abyssal echinoderms and ascidians of the Atlantic Ocean, species with planktotrophic larval development have broader biogeographic and bathymetric ranges than species with lecithotrophic development. In comparing two groups with lecithotrophic development, we found that ascidians, which probably have a shorter larval period and therefore less dispersal potential, were present in fewer geographic regions than elasipod holothurians, which are likely to have longer larval periods. For asteroids and echinoids, both the geographic and bathymetric ranges were greater for lecithotrophic than for planktotrophic species. For these two classes, the relationships of egg diameter with geographic and bathymetric range were either linearly increasing or non-monotonic. We conclude that lecithotrophic development does not necessarily constrain dispersal in the deep sea, probably because species with planktotrophic development may be confined to regions of high detrital input from the sea surface. Our data suggest that more information is necessary on lengths of larval period for different species to accurately assess dispersal in the deep sea.     

Colonization,abundance, and geographic range size of gravestone lichens

Macroecological studies often find that species with large geographic range sizes are also locally abundant. Superior colonization ability of species with large ranges is a possible/plausible explanation for this pattern, yet direct measures of colonization ability are difficult, and thus the relationship between colonization ability and range size is rarely investigated directly. Using a data set of gravestone lichens spanning more than 300 years, we investigated relationships among colonization ability, abundance, and geographic range size. Pairwise correlations were used to compare colonization ability and local abundance with area of occupancy (a measure of range size) and spore size within England, Scotland, and Wales on two different types of gravestones. Indices of colonization ability and abundance were positively correlated with area of occupancy. Colonization ability was significantly positively correlated with local abundance, but it was not at all related to propagule size. When lichen species were grouped categorically by colonization ability, the strongest area-occupancy relationships were observed within the subset of species that were the best colonizers. Significant differences among genera were found in spore size but not for other variables. Lichen species that occupy the largest geographic area were the best colonizers: they were the first species present on newly erected stones. These results complement the more commonly observed macroecological pattern that widespread species are also locally abundant.     

Correlates of range size and dispersal ability: a comparative analysis of sphingid moths from the Indo-Australian tropics

Aim  We tested various species-level traits for their potential to explain species' range sizes and dispersal abilities.
Location  Southeast Asia and Malay Archipelago.
Methods  We used published maps of geographical distribution estimates for sphingid moths to calculate range areas and classify species according to their dispersion across (present or historical) water straits in the Malay Archipelago. We tested forewing length (FWL), wing load (thorax width/FWL), presence or absence of a functional proboscis (i.e. adult feeding), larval diet breadth and larval diet composition for univariate correlations with range size and inter-island dispersion. We used multivariate, phylogenetically controlled models to test for independent effects of parameters.
Results  Range size correlated strongly with larval diet breadth, a result that was also confirmed in the multivariate model. Adult feeding had a significant impact on range sizes only within the multivariate model, but not in the univariate correlation. Dispersal class also correlated with larval diet breadth, but was additionally influenced by forewing length, wing load and larval diet composition. A univariate effect of adult feeding became non-significant in the multivariate, phylogenetically controlled model.
Main conclusions  Larval diet breadth is the best predictor of range size as well as inter-island dispersion, confirming the importance of niche breadth on the geographic ranges of species. A number of other factors are shown to have additional impact on predictions of range size or inter-island dispersal ability. Our analyses cannot determine the causal mechanisms of these correlations, but may stimulate further research on the adaptive significance of traits affecting range size and dispersal in this system.     

Connections between ecology,biogeography, and paleobiology: Relationship between local abundance and geographic distribution in fossil and recent molluscs

Summary We used data on Contemporary and Pleistocene molluscs at one site in the Gulf of California to evaluate and extend earlier ideas about the relationship between local abundance and geographic distribution. For each species whose shells occurred in one Recent and two Pleistocene deposits, we measured its abundance in the sample and relative latitudinal position within its contemporary geographic range. Species near the edges of their ranges showed uniformly low abundances, whereas those near the centres exhibited a wide range of abundances. Species near the edges of their ranges also appear to have exhibited greater changes in abundance, including more colonization and extinction events, between the Pleistocene interglacial sample and the Recent one. The constraint of location in the geographic range on maximal local and regional abundance appears to offer an example of a connection between patterns and processes on local, regional, and geographical scales. Characteristics of community structure, such as relative abundance of individual species and frequency of local co-existence of multiple species, may be influenced by the location of the sample site with respect to the geographic ranges of the constituent species. These results demonstrate emergent, statistical features of population ecology and community organization that are manifest over geographic space and evolutionary time.     

Rarity and extinction risk in coral reef angelfishes on isolated islands: interrelationships among abundance, geographic range size and specialisation

Determining the species most vulnerable to increasing degradation of coral reef habitats requires identification of the ecological traits that increase extinction risk. In the terrestrial environment, endemic species often face a high risk of extinction because of an association among three traits that threaten species persistence: small geographic range size, low abundance and ecological specialisation. To test whether these traits are associated in coral reef fishes, this study compared abundance and specialisation in endemic and widespread angelfishes at the remote Christmas and Cocos Islands in the Indian Ocean. The interrelationships among traits conferring high extinction risk in terrestrial communities did not apply to these fishes. Endemic angelfishes were 50–80 times more abundant than widespread species at these islands. Furthermore, there was no relationship between abundance and ecological specialisation. Endemic species were not more specialised than widespread congeners and endemics used similar resources to many widespread species. Three widespread species exhibited low abundance and some degree of specialisation, which may expose them to a greater risk of local extinction. For endemic species, high abundance and lack of specialisation on susceptible habitats may compensate for the global extinction risk posed by having extremely small geographic ranges. However, recent extinctions of small range reef fishes confirm that endemics are not immune to the increasing severity of large-scale disturbances that can affect species throughout their geographic range.     

Larval ecology, geographic range, and species survivorship in Cretaceous mollusks: organismic versus species-level explanations

The observation that geographic range size in Cretaceous mollusks is correlated with species survivorship and is heritable at the species level has figured repeatedly in discussions of species selection over the past two decades. However, some authors have suggested that the relationship between mode of larval development and geographic range supports the reduction of this example to selection on organismic properties. Our reanalysis of Jablonski's work on heritability at the species level finds that geographic range is significantly heritable (using a randomization test) in both bivalves and gastropods, even within a single larval mode. Further, generalized linear models show that geographic range size is more important than larval mode in predicting extinction probability in both gastropods and bivalves. These results reaffirm the role and heritability of geographic range as a species-level property that can promote species selection; the model-based approach applied here may help to operationalize "screening off " and related approaches to evaluating hierarchical explanations in evolution.     

Reserve mass and dispersal investment in relation to geographic range of plant species: phylogenetically independent contrasts

Recent studies have reported conflicting evidence about correlations between seed size and plant species geographic range sizes. Using phylogenetically independent contrasts (PICs) within genera, we found no consistent differences in reserve mass between species with similar dispersal morphology and «wide>> versus «narrow>> geographic ranges. There was also no tendency within genera for broad ranged species to be those that allocate a larger percentage of the resources invested in each diaspora to dispersal structures. PICs were also constructed between species having a tenfold difference in seed size. In these PICs, the larger seeded species often occupied a greater number of regions than species with smaller seed sizes. This result was generated primarily through the comparison of species from different genera, families or higher level taxa which differed not only in seed mass but also in dispersal modes and growth forms. Finally, comparing species within Acacia and Eucalyptus having similar seed size but different dispersal modes, we found that bird dispersal (in Acacia ) and possession of a wing for wind dispersal (in Eucalyptus ) was associated with wider geographic range compared to lower-investment dispersal modes. Taken together, these comparisons indicate that seed size is not itself important as a factor influencing breadth of geographic range. Dispersal mode and growth form may have an influence, however, and seed size differences may be associated with contrasts in dispersal mode or growth form.     

Range size: disentangling current traits and phylogenetic and biogeographic factors

The range size of a species can be determined by its current traits and by phylogenetic and biogeographic factors. However, only rarely have these factors been studied in combination. We use data on the geographic range sizes of all 26 Sylvia warblers to explicitly test whether range size was determined by current species-specific traits (e.g., body size, dispersal ability), phylogenetic factors (e.g., age of the lineage), or environmental, biogeographic factors (e.g., latitudinal position of the range). The results demonstrated that current traits and phylogenetic and biogeographic factors were interrelated. While a number of factors were significant in simple regression analyses, only one factor determined range size in the multiple regression analyses--dispersal ability. Species with better dispersal ability had larger ranges than species with poorer dispersal ability. Apparent increases of range size with latitude or with the age of the species resulted from correlations with dispersal ability. While the most significant factor that influences the range size of a group of species might differ from one group to the next, these results demonstrate that studies that focus only on a single, for example, phylogenetic, factor might yield misleading results.     

Patterns in the distribution, abundance and body size of carabid beetles (Coleoptera: Caraboidea) in relation to dispersal ability

The effects of dispersal ability, measured as two wing size categories (brachypterous vs. macropterous), on the distribution, abundance and body size, and on the relationships between these variables were examined in eighty-four species of carabid beetles over twenty-two sites in the northern Iberian peninsula. Geographic ranges of species (restricted to the northern Iberian peninsula vs. widespread—European or wider range) were also taken into account in the analyses because macropterous species significantly tended to exhibit wider geographic ranges than did brachypterous species. Regional distributions were wider in brachypterous-restricted and brachypterous-widespread species than in macropterous-widespread species. The three groups did not differ in abundance. Differences in regional distributions between groups may be explained by referring to a trade-off between dispersal ability and establishment ability indicated in the literature. Macropterous species would occupy relatively few sites due to a high frequency of unsuccessful colonizations. The relationships between regional distribution and abundance were positive for all the three groups, brachypterous-restricted, brachypterous-widespread and macropterous-widespread species. The regression line for the last group showed a lower elevation than those for brachypterous-restricted and brachypterous-widespread species. This fact was probably due to differences in regional distributions between groups. No relationship between abundance and body size was significant. Regressions of regional distribution on body size were positive in brachypterous-restricted and brachypterous-widespread carabids, but the relationship was not significant in macropterous-widespread carabids. These results were interpreted in terms of differences in body size–dependency of travelling velocities between flying and running carabids.     

Geographic locale and relative dominance patterns among North American passerine communities

Numerous studies have addressed variation in the local occurrence and abundance of species, but only recently have investigators begun considering the influence of spatial context on community structure. We examined the influence of geographic position within a species’ range on its dominance (relative abundance) within the community. Our three primary questions were: 1) Does dominance within a community vary across a species’ range? 2) Do dominance‐location trends differ between widely and narrowly distributed species? and 3) Does dominance within a guild vary across a species range? We examined 40 passerine species (20 widely distributed, 20 narrowly distributed) and their communities using North American Breeding Bird Survey data, of which, a subset of 11 species belonging to a single foraging guild were used for addressing guild effects. Data were gathered from communities at the center (10 locations) and periphery (10 locations) of each species’ range. Focal species were significantly less dominant at locations on the periphery of their ranges compared to central locations, and did not differ between widely and narrowly distributed species. In examining factors influencing these patterns, it was found that narrowly distributed species occur in communities of fewer individuals and fewer species compared to widely distributed species irrespective of locale. Within the foraging guild, dominance was also lower at the periphery than at the center of focal species’ ranges. However, guild abundance was also lower at the periphery of ranges while guild richness did not vary with locale. Specifically, focal species abundance decreased at a greater rate than abundance of other members of the foraging guild. Contrary to overall community data, widely distributed species were more dominant members of their guild at the center of their ranges. No significant patterns were found between distribution and guild dominance at the periphery of ranges.     

Low dispersal ability and habitat specificity promote extinctions in rare but not in widespread species: the Orthoptera of Germany

Local extinctions are often non‐randomly associated with range size, dispersal ability and habitat specificity, as well as body size, sexual dimorphism and phylogeny. We used a large data set of the Orthoptera species (bush crickets, crickets, grasshoppers) occurring in Germany and compared the number of occupied grid cells before 1980 to those occupied after 1980, corrected for monitoring intensity. The number of grid cells in which a species went extinct was non‐linearly related to the number of occupied grid cells per species. Using generalized linear modelling we analysed extinction in relation to national distribution (the number of occupied grid cells before 1980), dispersal ability (derived from a large body of literature concerning wing development, colonization dynamics and within‐habitat mobility), habitat specificity (moisture specialists versus generalists), potential reproduction (the number of ovarioles), the degree of sexual size dimorphism and phylogeny (twelve clades). Species with a large global range size also had a large national range size. Species with a large range experienced more total extinction events than species with smaller ranges but relatively fewer compared to range size. The latter relationship was largely shaped by the dispersal ability of the species: the interactions of range size×dispersal ability and range size×habitat specificity explained almost one third of the variation in the number of extinction events. Species with high dispersal ability went extinct in a similar number of grid cells irrespective of their range size. By contrast, species with low dispersal ability went extinct in proportion to their range size. Therefore, comparing the speed of extinction across species in the conventional way of extinction rates (that is the percentage of range contraction) might be flawed because it only applies to species with low dispersal ability. Sexual size dimorphism was not a significant predictor of extinction. Extinction was not concentrated on particular clades.     

Persistence and transport of fauna on drifting kelp (Macrocystis pyrifera (L.) C. Agardh) rafts in the Southern California Bight

Drifting rafts of Macrocystis pyrifera may connect isolated kelp forests in the Southern California Bight. To determine which species might utilize this dispersal mechanism, faunal samples from natural drifting rafts and attached M. pyrifera plants were collected during five cruises between March 1995 and December 1997. These rafts, which can be considered as floating islands, were aged and the macroinvertebrate assemblage enumerated. There was no significant relationship between raft age and species richness, or between species richness and distance offshore, which contrasts with predictions based on island biogeography. Species richness, however, was related to raft weight. Patterns of species presence and density were investigated relative to raft age for the species most frequently associated with rafts. Only one species, the isopod Idotea resecata, was found on all sampled rafts. Some species increased in frequency with raft age and others decreased, but only one relationship, a decline in the frequency of the anemone Epiactis prolifera with raft age was significant. When species density was examined over all cruises, only I. resecata had a significant change in density (an increase) with raft age, but additional significant relationships were found when species density patterns were considered by cruise. The results of all the tests were combined to provide a measure of "raft success". Nine of the most frequent 19 species had a positive score, indicating a favorable response to rafting, seven were unaffected, and two species had negative responses to rafting. Extinction times were calculated using species abundance and raft age relationships. Two species (E. prolifera and Paracerceis cordata), were predicted to persist on rafts for only about 100 days, which is the maximum estimated raft lifetime. All other species were predicted to persist for longer periods if the rafts floated longer. Kelp fauna that begin rafting appear to be largely unaffected by rafting, and hence dispersal on kelp rafts is possible for many members of the kelp forest community.     

Geographic range structure in North American landbrids: variation with migratory strategy, trophic level, and breeding habitat

We investigated the relationship between abundance and geographic range structure of 258 North American landbirds. For this purpose we used six measures of range structure based upon fractal geometry and geostatistics, and three ecological characteristics that can influence avian distribution. Permanent residents (PRs) that were abundant showed little fragmentation of their abundance surface at the periphery of their breeding range. Conversely, common Neotropical migrants (NTMs) exhibited low fragmentation of their central populations the abundance surface was smoother for PRs than NTMs or short-distance migrants (SDMs). indicating that changes in abundance occurred more gradually across space for this group. The areas of high abundance for grassland species had little demographic fragmentation, but other populations showed little spatial autocorrelation in abundance. Species that bred in late-successional forests were relatively rare compared to species breeding in other habitat types. Among carnivores. PRs had a higher average abundance than either NTMs or SDMs. Although carnivores had more distributional gaps within their ranges than other trophic groups, the number of gaps did not differ between rare and abundant species, indicating that increased abundance did not change their presence. absence distribution maps. Knowledge of patterns and variations of geographic range structure among species may provide insights into processes that shape and maintain the biodiversity of a continent.     

The frog filter: amphibian introduction bias driven by taxonomy,body size and biogeography

Aim Invasive species often exhibit a highly non‐random suite of traits relative to non‐invasive taxa, and these biases reflect strong selection at a series of steps along the invasion pathway. Here we investigate traits that are favoured in the first of these steps: the introduction of species outside their native geographic range. We use the global introduction of amphibians as our case study. Location Global. Methods We examined whether taxonomy, body size and attributes of the native geographic range predict the likelihood of an introduction event in amphibians. We then determined whether these characteristics differed between amphibian species that have been introduced intentionally and those that have been introduced unintentionally (i.e. stowaways). Results Comparisons of introduced and non‐introduced amphibians reveal significant biases with respect to taxonomic position (c. 50% of all introduced species originate from only 5% of all families), and characteristics of the native geographic range (most introduced species originate from the Northern Hemisphere, occupy a wide geographic range and are sympatric with high densities of humans). Many of these biases presumably reflect the ease and likelihood of capturing and transporting such animals. Additionally, intentionally introduced species are of larger than average body size, occupy higher elevations in their native ranges, and are more likely to originate from the Northern Hemisphere than unintentionally introduced species. Main conclusions Introduced amphibian species are not a random subset of the global amphibian fauna with respect to taxonomic affiliation and biogeography, and this restricts our ability to make robust generalizations regarding the ecological determinants of introduction success. Nevertheless, many of our findings are similar to those revealed by previous analyses of vertebrate and invertebrate introductions. Thus, our study suggests that biases in the anthropogenic mechanisms involved in transporting species around the globe are surprisingly consistent across broadly divergent taxa.     

Eukaryotic microbes, species recognition and the geographic limits of species: examples from the kingdom Fungi

The claim that eukaryotic micro-organisms have global geographic ranges, constituting a significant departure from the situation with macro-organisms, has been supported by studies of morphological species from protistan kingdoms. Here, we examine this claim by reviewing examples from another kingdom of eukaryotic microbes, the Fungi. We show that inferred geographic range of a fungal species depends upon the method of species recognition. While some fungal species defined by morphology show global geographic ranges, when fungal species are defined by phylogenetic species recognition they are typically shown to harbour several to many endemic species. We advance two non-exclusive reasons to explain the perceived difference between the size of geographic ranges of microscopic and macroscopic eukaryotic species when morphological methods of species recognition are used. These reasons are that microbial organisms generally have fewer morphological characters, and that the rate of morphological change will be slower for organisms with less elaborate development and fewer cells. Both of these reasons result in fewer discriminatory morphological differences between recently diverged lineages. The rate of genetic change, moreover, is similar for both large and small organisms, which helps to explain why phylogenetic species of large and small organisms show a more similar distribution of geographic ranges. As a consequence of the different rates in fungi of genetic and morphological changes, genetic isolation precedes a recognizable morphological change. The final step in speciation, reproductive isolation, also follows genetic isolation and may precede morphological change.     

Antifouling properties of 10beta-formamidokalihinol-A and kalihinol A isolated from the marine sponge Acanthella cavernosa

Many soft-bodied sessile marine invertebrates such as sponges and soft corals defend themselves against fouling directly through the production of antifouling compounds, or indirectly through regulating the epibiotic microbes that affect larval settlement. In this study, 10beta-formamidokalihinol-A and kalihinol A were isolated and purified from the marine sponge Acanthella cavernosa (Dendy). The results indicated that both compounds inhibited the growth of bacteria isolated from the natural environment whereas kalihinol A suppressed larval settlement of a major fouling polychaete, Hydroides elegans with an EC50 of 0.5 microg ml(-1). Kalihinol A was incorporated in Phytagel that was exposed to the bacterial consortia in natural seawater for biofilm formation. Biofilms that developed on the Phytagel surfaces were analysed for bacterial abundance and bacterial species composition using a DNA fingerprinting technique, terminal restriction fragment length polymorphism (T-RFLP). The results showed that kalihinol A only slightly reduced bacterial abundance (t-test, p = 0.0497), but modified the bacterial species composition of the biofilms. Inhibition of H. elegans larval settlement was observed when biofilms developed under the influence of kalihinol A were exposed to larvae, suggesting that compounds like kalihinol A from the sponge A. cavernosa may change bacterial community composition on the sponge surface, which in turn, modulates larval settlement of fouling organisms.     

Speciation and extinction drive the appearance of directional range size evolution in phylogenies and the fossil record

While the geographic range of a species is a fundamental unit of macroecology and a leading predictor of extinction risk, the evolutionary dynamics of species' ranges remain poorly understood. Based on statistical associations between range size and species age, many studies have claimed support for general models of range evolution in which the area occupied by a species varies predictably over the course of its life. Such claims have been made using both paleontological data and molecular estimates of the age of extant species. However, using a stochastic model, we show that the appearance of trends in range size with species' age can arise even when range sizes have evolved at random through time. This occurs because the samples of species used in existing studies are likely to be biased with respect to range size: for example, only those species that happened to have large or expanding ranges are likely to survive to the present, while extinct species will tend to be those whose ranges, by chance, declined through time. We compared the relationship between the age and range size of species arising under our stochastic model to those observed across 1,269 species of extant birds and mammals and 140 species of extinct Cenozoic marine mollusks. We find that the stochastic model is able to generate the full spectrum of empirical age-area relationships, implying that such trends cannot be simply interpreted as evidence for models of directional range size evolution. Our results therefore challenge the theory that species undergo predictable phases of geographic expansion and contraction through time.