Ecological Release Research Articles

Ecological release and niche partitioning under stress: Lessons from dorvilleid polychaetes in sulfidic sediments at methane seeps

Organisms inhabiting methane seep sediments are exposed to stress in the form of high levels of hydrogen sulfide, which result mainly from sulfate reduction coupled to anaerobic methane oxidation. Dorvilleidae (Polychaeta) have successfully invaded this ecosystem, and multiple species in divergent genetic clades co-occur at high densities. At methane seeps in the NE Pacific off California and Oregon, the genera Ophryotrocha, Parougia and Exallopus are especially well represented. To test the hypothesis that dorvilleid coexistence is facilitated by niche partitioning through sulfide tolerance and trophic patterns, we examined dorvilleid species-specific patterns of occurrence and nutrition at methane seeps off Eel R. [ER] on the Californian continental slope and at Hydrate Ridge [HR] on the Oregon continental slope, and in two habitats (clam bed and microbial mat) characterized by lower and higher hydrogen sulfide levels, respectively. Microelectrode measurements of hydrogen sulfide enabled characterization of environmental sulfide levels for species sampled in background sediment cores and in colonization trays. Dorvilleids tolerated H2S levels from 10μM to over 2.6mM, with the majority of species inhabiting sediments with similar environmental H2S concentrations (median 85–100μM). Dorvilleid species richness was greater at HR than ER, but did not differ between clam bed and microbial mat habitats. Species distribution patterns reflected preferences for ER clam bed (lower sulfide levels), ER mat and HR clam bed (moderate sulfide levels), or HR mat (very high sulfide levels). Nutritional patterns, including trophic diversity and functional similarity, were examined using community stable isotope metrics based on δ15N and δ13C. Within each region, dorvilleid species exhibited multiple trophic strategies. Co-existing congeners typically exhibited distinct isotope signatures, suggesting trophic partitioning. Trophic diversity and δ15N range for whole assemblages (measured by Total Hull Area and Standard Elliptical Area using species averages) and functional redundancy or species packing (measured as distance to nearest neighbor) among species and individuals were generally higher at ER, where sulfide levels were lower than at HR. In contrast, average trophic diversity among individuals within a species was greater at HR than ER. In colonization experiments involving agar-based manipulations of sulfide in tray sediments that mimicked clam bed and mat conditions, dorvilleids comprised 68% and 48% of colonists at ER and HR, respectively. Dorvilleid species richness was higher in trays that were initially more sulfidic. However, habitat exerted stronger influence on the composition of colonizing dorvilleids than did sulfide additions. In the NE Pacific, regional, habitat and vertical (down-core) variation in hydrogen sulfide creates complex environmental heterogeneity at methane seeps, promoting high diversity of stress-tolerant taxa such as dorvilleid polychaetes.

Ecological release: swimming and diving behavior of an allopatric population of the Mediterranean water shrew

za Forest, eastern Poland. In contrast to sympatric Polish N. anomalus, allopatric Portuguese N. anomalus were more efficient in some swimming parameters (such as stroking frequency) and showed greater variation in diving profiles. Allopatric N. anomalus also were able to take food from deep water, a behavior that previously had been observed only in N. fodiens. Foraging success underwater, however, was much lower in allopatric N. anomalus than in N. fodiens. Our results suggest that in the absence of the dominant N. fodiens, allopatric N. anomalus can use 2 foraging modes: wading in shallow water (its primary foraging mode) and diving in deep water, thus extending its ecological niche.

Evolution of microhabitat association and morphology in a diverse group of cryptobenthic coral reef fishes (Teleostei: Gobiidae: Eviota)

Gobies (Teleostei: Gobiidae) are an extremely diverse and widely distributed group and are the second most species rich family of vertebrates. Ecological drivers are key to the evolutionary success of the Gobiidae. However, ecological and phylogenetic data are lacking for many diverse genera of gobies. Our study investigated the evolution of microhabitat association across the phylogeny of 18 species of dwarfgobies (genus Eviota), an abundant and diverse group of coral reef fishes. In addition, we also explore the evolution of pectoral fin-ray branching and sensory head pores to determine the relationship between morphological evolution and microhabitat shifts. Our results demonstrate that Eviota species switched multiple times from a facultative hard-coral association to inhabiting rubble or mixed sand/rubble habitat. We found no obvious relationship between microhabitat shifts and changes in pectoral fin-ray branching or reduction in sensory pores, with the latter character being highly homoplasious throughout the genus. The relative flexibility in coral-association in Eviota combined with the ability to move into non-coral habitats suggests a genetic capacity for ecological release in contrast to the strict obligate coral-dwelling relationship commonly observed in closely related coral gobies, thus promoting co-existence through fine scale niche partitioning. The variation in microhabitat association may facilitate opportunistic ecological speciation, and species persistence in the face of environmental change. This increased speciation opportunity, in concert with a high resilience to extinction, may explain the exceptionally high diversity seen in Eviota compared to related genera in the family.

Habitat associations of thermophilous butterflies are reduced despite climatic warming

Climate warming threatens the survival of species at their warm, trailing-edge range boundaries but also provides opportunities for the ecological release of populations at the cool, leading edges of their distributions. Thus, as the climate warms, leading-edge populations are expected to utilize an increased range of habitat types, leading to larger population sizes and range expansion. Here, we test the hypothesis that the habitat associations of British butterflies have expanded over three decades of climate warming. We characterize the habitat breadth of 27 southerly distributed species from 77 monitoring transects between 1977 and 2007 by considering changes in densities of butterflies across 11 habitat types. Contrary to expectation, we find that 20 of 27 (74%) butterfly species showed long-term contractions in their habitat associations, despite some short-term expansions in habitat breadth in warmer-than-usual years. Thus, we conclude that climatic warming has ameliorated habitat contractions caused by other environmental drivers to some extent, but that habitat degradation continues to be a major driver of reductions in habitat breadth and population density of butterflies.

Thesis abstract: Ecology and biogeography of island parasitoid faunas

ISSN 1948-6596 news and update thesis abstract Ecology and biogeography of island parasitoid faunas Ana M. C. Santos 1,2,3 PhD Thesis, Silwood Park Campus, Division of Biology, Imperial College London, UK Departamento de Ecologia, Instituto de Ciencias Biologicas, Universidade Federal de Goias, 74001-970 Goiânia, GO, Brazil; 2 Centro de Biologia Ambiental, Faculdade de Ciencias da Universidade de Lisboa, C2 5th Floor, 1749-016 Lisbon, Portugal; 3 Departamento de Biodiversidad y Biologia Evolutiva, Museo Nacional de Ciencias Naturales (CSIC), C/ Jose Gutierrez Abascal 2, 28006 Madrid, Spain ana.margarida.c.santos@googlemail.com; http://www.wix.com/guidasanto1/anamcsantos Abstract. Species on islands tend to use a wider range of resources than their mainland counterparts. In this thesis I investigated whether island parasitoid communities have proportionally more idiobiont spe- cies (which tend to have a wider host range; i.e. are more generalist) than their mainland source, and which factors determine island community structure. These questions were approached using data on the distribution of Ichneumonoidea species worldwide and data from a survey conducted in the Macaronesian islands and mainland. Prior to the global analyses, I assessed whether islands and archipelagos follow the same species–area relationship, and identified which islands have comparable inventories. Globally, is- lands have proportionally more idiobionts than continental areas, and the species pool for colonization is the most important determinant of island community structure. Specimens collected in the Macaronesian region were tentatively identified using a protocol based on host dissection and DNA barcoding. At this scale, mainland faunas have proportionally more koinobiont species and island communities have a greater proportion of idiobionts. Keywords: community structure, DNA barcoding, host-parasitoid interactions, host range, island biogeo- graphy, island species–area relationship, Macaronesia, species pool Islands constitute natural laboratories for the study of evolutionary and ecological processes because of their discrete and isolated nature, small size and simplified biotas. Island faunas, es- pecially those of oceanic islands, tend to be spe- cies-poor and disharmonic, meaning that there are often fewer species on an oceanic island than on a same-sized area of mainland, and that the structure of their communities is different from their continental counterparts (e.g. some trophic guilds can be absent from island communities). The phenomenon of ecological release, typical in many island populations, occurs when a species colonizing an island encounters a new environ- ment in which competitors and/or predators are missing (Whittaker and Fernandez-Palacios 2007). One of the consequences of this process is the expansion to empty or invasible niche space, lead- ing to niche expansion and/or niche shifts, with species from island assemblages often using a wider range of resources than their counterparts from the source mainland. Therefore it is not sur- prising that many oceanic islands have a high re- presentation of generalist species when compared to the mainland (e.g. Olesen and Valido 2003). In addition, some evidence suggests that generalist species may simply have an a priori advantage during the colonization process (Piechnik et al. Parasitoids are generally defined as insects whose larvae develop to adulthood by feeding in or on the body of an arthropod host, eventually causing its death (Quicke 1997; see more details of their biology in Santos & Quicke 2011). Parasi- toids are usually divided into two different groups that reflect different life-history strategies: koino- bionts, which allow the host to continue its devel- opment after oviposition of the parasitoid, and idiobionts, which do not (Askew and Shaw 1986). Many life-history traits appear to be correlated with this dichotomy (e.g. Hawkins 1994, Quicke 1997; see Table 1). Host range, i.e. the group of frontiers of biogeography 4.1, 2012 — © 2012 the authors; journal compilation © 2012 The International Biogeography Society

Graptoloid diversity and disparity became decoupled during the Ordovician mass extinction

The morphological study of extinct taxa allows for analysis of a diverse set of macroevolutionary hypotheses, including testing for change in the magnitude of morphological divergence, extinction selectivity on form, and the ecological context of radiations. Late Ordovician graptoloids experienced a phylogenetic bottleneck at the Hirnantian mass extinction (∼445 Ma), when a major clade of graptoloids was driven to extinction while another clade simultaneously radiated. In this study, we developed a dataset of 49 ecologically relevant characters for 183 species with which we tested two main hypotheses: (i) could the biased survival of one graptoloid clade over another have resulted from morphological selectivity alone and (ii) are the temporal patterns of morphological disparity and innovation during the recovery consistent with an interpretation as an adaptive radiation resulting from ecological release? We find that a general model of morphological selectivity has a low probability of producing the observed pattern of taxonomic selectivity. Contrary to predictions from theory on adaptive radiations and ecological speciation, changes in disparity and species richness are uncoupled. We also find that the early recovery is unexpectedly characterized by relatively low morphological disparity and innovation, despite also being an interval of elevated speciation. Because it is necessary to invoke factors other than ecology to explain the graptoloid recovery, more complex models may be needed to explain recovery dynamics after mass extinctions.

Of mice and mammoths: evaluations of causal explanations for body size evolution in insular mammals

AbstractAim We investigated the hypothesis that the insular body size of mammals results from selective forces whose influence varies with characteristics of the focal islands and the focal species, and with interactions among species (ecological displacement and release).Location Islands world‐wide.Methods We assembled data on the geographic characteristics (area, isolation, maximum elevation, latitude) and climate (annual averages and seasonality of temperature and precipitation) of islands, and on the ecological and morphological characteristics of focal species (number of mammalian competitors and predators, diet, body size of mainland reference populations) that were most relevant to our hypothesis (385 insular populations from 98 species of extant, non‐volant mammals across 248 islands). We used regression tree analyses to examine the hypothesized contextual importance of these factors in explaining variation in the insular body size of mammals.Results The results of regression tree analyses were consistent with predictions based on hypotheses of ecological release (more pronounced changes in body size on islands lacking mammalian competitors or predators), immigrant selection (more pronounced gigantism in small species inhabiting more isolated islands), thermoregulation and endurance during periods of climatic or environmental stress (more pronounced gigantism of small mammals on islands of higher latitudes or on those with colder and more seasonal climates), and resource subsidies (larger body size for mammals that utilize aquatic prey). The results, however, were not consistent with a prediction based on resource limitation and island area; that is, the insular body size of large mammals was not positively correlated with island area.Main conclusions These results support the hypothesis that the body size evolution of insular mammals is influenced by a combination of selective forces whose relative importance and nature of influence are contextual. While there may exist a theoretical optimal body size for mammals in general, the optimum for a particular insular population varies in a predictable manner with characteristics of the islands and the species, and with interactions among species. This study did, however, produce some unanticipated results that merit further study – patterns associated with Bergmann’s rule are amplified on islands, and the body size of small mammals appears to peak at intermediate and not maximum values of latitude and island isolation.

Ecological release in White Sands lizards.

Ecological opportunity is any change that allows populations to escape selection from competition and predation. After encountering ecological opportunity, populations may experience ecological release: enlarged population size, broadened resource use, and/or increased morphological variation. We identified ecological opportunity and tested for ecological release in three lizard colonists of White Sands, New Mexico (Sceloporus undulatus, Holbrookia maculata, and Aspidoscelis inornata). First, we provide evidence for ecological opportunity by demonstrating reduced species richness and abundance of potential competitors and predators at White Sands relative to nearby dark soils habitats. Second, we characterize ecological release at White Sands by demonstrating density compensation in the three White Sands lizard species and expanded resource use in White Sands S. undulatus. Contrary to predictions from ecological release models, we observed directional trait change but not increased trait variation in S. undulatus. Our results suggest that ecological opportunity and ecological release can be identified in natural populations, especially those that have recently colonized isolated ecosystems.

Elevated size and body condition and altered feeding ecology of the grouper Cephalopholis argus in non-native habitats

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 439:203-212 (2011) - DOI: https://doi.org/10.3354/meps09338 Elevated size and body condition and altered feeding ecology of the grouper Cephalopholis argus in non-native habitats Amanda L. Meyer1,2,*, Jan Dierking1,3,*,** 1Department of Zoology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA 2Present address: Pacific Reefs National Wildlife Complex, US Fish and Wildlife Service, Honolulu, Hawaii 96850, USA 3Present address: Leibniz Institute of Marine Sciences (IFM-GEOMAR), Evolutionary Ecology of Marine Fishes Group, 24105 Kiel, Germany *The 2 authors contributed equally to this study**Email: jdierking@ifm-geomar.de ABSTRACT: In 1956, the shallow-water grouper Cephalopholis argus was introduced from Moorea (French Polynesia), where grouper diversity (14 species) is high, to the Main Hawaiian Islands (MHI), where only 2 rare native deep-water groupers occur. In this non-native environment, the species has flourished and has become the dominant apex predator on many reefs. In the present study, a comparison of non-native populations of C. argus in the MHI with native populations in Moorea showed that mean total length (32.0 vs. 26.9 cm), mass (722 vs. 326 g), growth, and body condition were each significantly elevated in the MHI. In addition, while an ontogenetic shift towards larger prey occurred in both locations, it was faster and more consistent in Moorea than in the MHI. As a result, while small C. argus of comparable size in the 2 locations consumed similar-sized prey, large C. argus in Moorea consumed significantly longer and deeper-bodied prey than their counterparts in the MHI. This pattern was unrelated to the size distributions of available prey and may thus reflect stronger intra- and interspecific competition for small prey in Moorea. Although ecological release in a broader sense (i.e. a combination of predator release, parasite release, and competitive release) may play a role, the most direct explanation for the observed differences between C. argus in native habitats in Moorea (with many competing grouper species) and non-native habitats in the MHI (few competitors) would be competitive release (here used in the sense of benefits resulting from the reduction of interspecific competition). KEY WORDS: Competitive release · Ecological release · Interspecific competition · Niche shift · Invasive species · Peacock hind · Main Hawaiian Islands · Moorea (French Polynesia) Full text in pdf format PreviousNextCite this article as: Meyer AL, Dierking J (2011) Elevated size and body condition and altered feeding ecology of the grouper Cephalopholis argus in non-native habitats. Mar Ecol Prog Ser 439:203-212. https://doi.org/10.3354/meps09338 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 439. Online publication date: October 20, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

Avian succession along ecological gradients: Insight from species-poor and species-rich communities of Sylvia warblers

Abstract The mechanisms responsible for species replacement during ecological successions is a long-standing and open debate. In this study, we examined the distribution of the Sardinian warbler Sylvia melanocephala along two grassland-to-forest gradients, one in a high-diversity area (Albera-Aspres chain in Catalonia: eight Sylvia warbler species) and one in a low-diversity area (Mount Hymittos in Greece: four species). In Catalonia, distribution models suggested that the apparent exclusion of S. melanocephala from the open and forest ends of the gradient may be explained entirely by the preference of S. melanocephala for mid-successional shrublands. However, a joint analysis of both data sets revealed that: 1) S. melanocephala was more evenly distributed along the vegetation gradient in Greece, suggesting ecological release in the low-diversity area; and 2) a distribution model assuming interspecific competition (based on the distribution of Sylvia species showing a negative co-occurrence pattern with S. melanocephala) had a significantly higher predictive ability than a distribution model based on habitat variables alone. Our study supports the view that species turnover along ecological gradients generally results from a combination of intrinsic preferences and interspecific competition.

Evolution, insular restriction, and extinction of oceanic land crabs, exemplified by the loss of an endemic Geograpsus in the Hawaiian Islands.

Most oceanic islands harbor unusual and vulnerable biotas as a result of isolation. As many groups, including dominant competitors and predators, have not naturally reached remote islands, others were less constrained to evolve novel adaptations and invade adaptive zones occupied by other taxa on continents. Land crabs are an excellent example of such ecological release, and some crab lineages made the macro-evolutionary transition from sea to land on islands. Numerous land crabs are restricted to, although widespread among, oceanic islands, where they can be keystone species in coastal forests, occupying guilds filled by vertebrates on continents. In the remote Hawaiian Islands, land crabs are strikingly absent.Here we show that absence of land crabs in the Hawaiian Islands is the result of extinction, rather than dispersal limitation. Analysis of fossil remains from all major islands show that an endemic Geograpsus was abundant before human colonization, grew larger than any congener, and extended further inland and to higher elevation than other land crabs in Oceania.Land crabs are major predators of nesting sea birds, invertebrates and plants, affect seed dispersal, control litter decomposition, and are important in nutrient cycling; their removal can lead to large-scale shifts in ecological communities. Although the importance of land crabs is obvious on remote and relatively undisturbed islands, it is less apparent on others, likely because they are decimated by humans and introduced biota. The loss of Geograpsus and potentially other land crabs likely had profound consequences for Hawaiian ecosystems.

The decoupling of abundance and species richness in lizard communities

1. Patterns of species richness often correlate strongly with measures of energy. The more individuals hypothesis (MIH) proposes that this relationship is facilitated by greater resources supporting larger populations, which are less likely to become extinct. Hence, the MIH predicts that community abundance and species richness will be positively related. 2. Recently, Buckley & Jetz (2010, Journal of Animal Ecology, 79, 358-365) documented a decoupling of community abundance and species richness in lizard communities in south-west United States, such that richer communities did not contain more individuals. They predicted, as a consequence of the mechanisms driving the decoupling, a more even distribution of species abundances in species-rich communities, evidenced by a positive relationship between species evenness and species richness. 3. We found a similar decoupling of the relationship between abundance and species richness for lizard communities in semi-arid south-eastern Australia. However, we note that a positive relationship between evenness and richness is expected because of the nature of the indices used. We illustrate this mathematically and empirically using data from both sets of lizard communities. When we used a measure of evenness, which is robust to species richness, there was no relationship between evenness and richness in either data set. 4. For lizard communities in both Australia and the United States, species dominance decreased as species richness increased. Further, with the iterative removal of the first, second and third most dominant species from each community, the relationship between abundance and species richness became increasingly more positive. 5. Our data support the contention that species richness in lizard communities is not directly related to the number of individuals an environment can support. We propose an alternative hypothesis regarding how the decoupling of abundance and richness is accommodated; namely, an inverse relationship between species dominance and species richness, possibly because of ecological release.

Biogeography and morphological evolution in a Pacific island ant radiation

While insular radiations are documented for many terrestrial arthropods, few examples are known for eusocial insects. This study seeks to ascertain whether the spinescence observed among Fijian Pheidole ants was inherited from an oversea ancestor or is evidence of ecological release from interspecific competitors. We broaden our understanding of morphological convergence, insular radiation and Pacific biogeography by testing three hypotheses proposed previously for the Fijian Pheidole roosevelti group: (i) the group is monophyletic; (ii) spinescence is a plesiomorphic trait inherited from an overseas ancestor; and (iii) the group is closely related to spinescent New Guinean relatives. The analysis included the fragments of two mitochondrial genes (COI, cytb) and two nuclear genes (H3, EF1α-F2) from 66 taxa, including all members of the roosevelti group, representatives from the spinescent subgenus Pheidolacanthinus, Fijian congeners and widespread Pacific congeners. Our results yield new insights into the biogeographic history of Fiji, reveal a fascinating example of convergent evolution and serve as a novel example of ecological release occurring within an insular eusocial insect lineage. These findings recover the history of a presumably unremarkable ant species that colonized a remote oceanic archipelago in the Miocene (17-10 Ma) and radiated across the emerging islands into niche-space occupied elsewhere in the Pacific by distantly related spinescent congeners. We propose the radiation of Fijian Pheidole into spinescent morphotypes was the consequence of ecological opportunities afforded by the absence of competing ant lineages with conspicuous epigaeic foraging strategies.

Ecological opportunity and the origin of adaptive radiations

Ecological opportunity--through entry into a new environment, the origin of a key innovation or extinction of antagonists--is widely thought to link ecological population dynamics to evolutionary diversification. The population-level processes arising from ecological opportunity are well documented under the concept of ecological release. However, there is little consensus as to how these processes promote phenotypic diversification, rapid speciation and adaptive radiation. We propose that ecological opportunity could promote adaptive radiation by generating specific changes to the selective regimes acting on natural populations, both by relaxing effective stabilizing selection and by creating conditions that ultimately generate diversifying selection. We assess theoretical and empirical evidence for these effects of ecological opportunity and review emerging phylogenetic approaches that attempt to detect the signature of ecological opportunity across geological time. Finally, we evaluate the evidence for the evolutionary effects of ecological opportunity in the diversification of Caribbean Anolis lizards. Some of the processes that could link ecological opportunity to adaptive radiation are well documented, but others remain unsupported. We suggest that more study is required to characterize the form of natural selection acting on natural populations and to better describe the relationship between ecological opportunity and speciation rates.

Paradigm Shifts in Habitat Ecology of Threatened Newfoundland Martens

Abstract: We evaluated multiscale habitat selection by threatened Newfoundland (Canada) martens (Martes americana atrata) across landscapes composed of a range of habitat types to test the hypothesis that martens preferred mature (61–80‐yr‐old) and overmature (>80 yr) conifer stands. At both the landscape and stand scales, adult (≥1 yr) resident martens (n = 58, 92 yr‐specific home ranges) selected for, or used in proportion to availability, a broad range of habitat types, including recent cuts ≤ 5 yr old, regenerating forest <6.5 m, precommercially thinned stands, and mature and overmature forest. Marten home ranges were not dominated by mature and overmature forest; median availability of mature and overmature forest within individual home ranges was only 30% (range = 11–76%). Age distributions were not different among martens with high, intermediate, and low quantity of mature and overmature forest in their home range; our data do not indicate that martens inhabiting ranges with little mature and overmature forest were compromising fitness. Habitat selection by martens in Newfoundland was more generalized than has traditionally been inferred, and we suggest that inherent landscape fragmentation, in combination with absence of many predators and competitors (i.e., ecological release), caused the Newfoundland marten to evolve to use a more generalized habitat niche than many mainland populations of American martens. We recommend that landscapes suitable for marten not exceed >29% younger aged forest. Maintaining resident martens in landscapes where forest harvesting is occurring requires prescriptions that recognize the highly fragmented nature of the natural landscape, the prevalence of mature and overmature forest, younger forests, avoided landcover types, and human access.

Ecological release from interspecific competition leads to decoupled changes in population and individual niche width.

A species's niche width reflects a balance between the diversifying effects of intraspecific competition and the constraining effects of interspecific competition. This balance shifts when a species from a competitive environment invades a depauperate habitat where interspecific competition is reduced. The resulting ecological release permits population niche expansion, via increased individual niche widths and/or increased among-individual variation. We report an experimental test of the theory of ecological release in three-spine stickleback (Gasterosteus aculeatus). We factorially manipulated the presence or absence of two interspecific competitors: juvenile cut-throat trout (Oncorhynchus clarki) and prickly sculpin (Cottus asper). Consistent with the classic niche variation hypothesis, release from trout competition increased stickleback population niche width via increased among-individual variation, while individual niche widths remained unchanged. In contrast, release from sculpin competition had no effect on population niche width, because increased individual niche widths were offset by decreased between-individual variation. Our results confirm that ecological release from interspecific competition can lead to increases in niche width, and that these changes can occur on behavioural time scales. Importantly, we find that changes in population niche width are decoupled from changes in the niche widths of individuals within the population.

Dinoflagellate blooms in upwelling systems: Seeding, variability, and contrasts with diatom bloom behaviour

The influence of diatom bloom behaviour, dinoflagellate life cycles, propagule type and upwelling bloom cycles on the seeding of dinoflagellate blooms in eastern boundary current upwelling systems is evaluated. Winter–spring diatom bloom behaviour is contrasted with upwelling bloom behaviour because their phenology impacts dinoflagellate blooms. The winter–spring diatom bloom is usually sustained, whereas the classical upwelling diatom bloom occurs as a series of separate, recurrent mini-blooms intercalated by upwelling-relaxation periods, during which dinoflagellates often bloom. Four sequential wind-regulated phases characterize upwelling cycles, with each phase having different effects on diatom and dinoflagellate bloom behaviour: bloom “spin up”, bloom maximum, bloom “spin down”, and upwelling relaxation. The spin up – bloom maximum is the period of heightened diatom growth; the spin down – upwelling-relaxation phases are the periods when dinoflagellates often bloom. The duration, intensity and ratio of the upwelling and relaxation periods making up upwelling cycles determine the potential for dinoflagellate blooms to develop within a given upwelling cycle and prior to the subsequent “spin up” of upwelling that favours diatom blooms. Upwelling diatoms and meroplanktonic dinoflagellates have three types of propagules available to seed blooms: vegetative cells, resting cells and resting cysts. However, most upwelling dinoflagellates are holoplanktonic, which indicates that the capacity to form resting cysts is not an absolute requirement for growth and survival in upwelling systems. The long-term (decadal) gaps in bloom behaviour of Gymnodinium catenatum and Lingulodinium polyedrum, and the unpredictable bloom behaviour of dinoflagellates generally, are examined from the perspective of seeding strategies. Mismatches between observed and expected in situ bloom behaviour and resting cyst dynamics are common among upwelling dinoflagellates. This disassociation suggests unrecognized upwelling system factors that fall within the physical–chemical–biological domain are more important than life cycle in selecting dinoflagellates species having the survival-seeding strategies and ecophysiological adaptations required for growth in physically robust upwelling systems. It is conjectured that diatom life cycles, as a group, are geared towards exploiting seeding opportunities, whereas dinoflagellates have evolved life-cycle behaviour more attuned to survival. The role of ecological dormancy and ecological release from bloom inhibition underlying dinoflagellate bloom irregularity is considered. The expectation that the dinoflagellate species selected to bloom from among the common upwelling flora would be the same in all eastern boundary upwelling systems is not realized.

Explosive morphological diversification of spiny-finned teleost fishes in the aftermath of the end-Cretaceous extinction

The spiny-finned teleost fishes (Acanthomorpha) include nearly one-third of all living vertebrate species and assume a bewildering array of bodyplans, but the macroevolutionary assembly of modern acanthomorph biodiversity remains largely unexplored. Here, I reconstruct the trajectory of morphological diversification in this major radiation from its first appearance in the Late Cretaceous to the Miocene using a geometric morphometric database comprising more than 600 extinct species known from complete body fossils. The anatomical diversity (disparity) of acanthomorphs is low throughout the Cretaceous, increases sharply and significantly in the wake of the Cretaceous-Palaeogene (K-P) extinction, and shows little change throughout subsequent Cenozoic intervals. This pattern of morphological diversification appears robust to two potential biasing factors: the 'Lagerstätten effect', and the non-random segregation of rare and common taxa along phenotypic axes. Dissecting the trajectory of acanthomorph radiation along phylogenetic lines reveals that the abrupt post-extinction increase in disparity is driven largely by the proliferation of trophically diverse modern groups within Percomorpha, a spiny-fin subclade containing more than 15 000 living species and identified as showing a substantially elevated diversification rate relative to background vertebrate levels. A major component of the Palaeogene acanthomorph radiation reflects colonization of morphospace previously occupied by non-acanthomorph victims of the K-P. However, other aspects of morphological diversification cannot be explained by this simple ecological release model, suggesting that multiple factors contributed to the prolific anatomical radiation of acanthomorphs.

Functionally diverse reef-fish communities ameliorate coral disease.

Coral reefs, the most diverse of marine ecosystems, currently experience unprecedented levels of degradation. Diseases are now recognized as a major cause of mortality in reef-forming corals and are complicit in phase shifts of reef ecosystems to algal-dominated states worldwide. Even so, factors contributing to disease occurrence, spread, and impact remain poorly understood. Ecosystem resilience has been linked to the conservation of functional diversity, whereas overfishing reduces functional diversity through cascading, top-down effects. Hence, we tested the hypothesis that reefs with trophically diverse reef fish communities have less coral disease than overfished reefs. We surveyed reefs across the central Philippines, including well-managed marine protected areas (MPAs), and found that disease prevalence was significantly negatively correlated with fish taxonomic diversity. Further, MPAs had significantly higher fish diversity and less disease than unprotected areas. We subsequently investigated potential links between coral disease and the trophic components of fish diversity, finding that only the density of coral-feeding chaetodontid butterflyfishes, seldom targeted by fishers, was positively associated with disease prevalence. These previously uncharacterized results are supported by a second large-scale dataset from the Great Barrier Reef. We hypothesize that members of the charismatic reef-fish family Chaetodontidae are major vectors of coral disease by virtue of their trophic specialization on hard corals and their ecological release in overfished areas, particularly outside MPAs.

Do virus‐resistant plants pose a threat to non‐target ecosystems? II. Risk assessment of an Australian pathosystem using multi‐scale field experiments

AbstractIt has been widely argued that the acquisition of novel disease resistance genes by wild host populations following the release of novel pathogen‐resistant plants into agricultural systems could pose a significant threat to non‐target plant communities. However, predicting the magnitude of ecological release in wild plant populations following the removal of disease remains a major challenge. In this paper we report on the second phase of a tiered risk assessment designed to investigate the role of disease on host growth, survival, fecundity and fitness in a model pathosystem (the pasture species Trifolium repens infected with Clover yellow vein virus, ClYVV) and to assess the level of risk posed to at‐risk native plant communities in southeast Australia by newly developed genetically modified and conventionally bred virus‐resistant T. repens genotypes. Multi‐year field experiments conducted in woodland and grassland environments using host‐pathogen arrays derived from 14 ClYVV isolates and 21 T. repens genotypes indicate that viral infection reduces fecundity, growth and survival of wild T. repens plants but that the severity of these effects depends on host tolerance to infection, isolate aggressiveness and specific spatial and temporal environmental conditions. Demographic modelling showed that by reducing host survival and growth, ClYVV also limits the intrinsic population growth rate and niche size of wild T. repens populations. Given the significant fitness cost associated with viral infection we conclude that virus‐resistant T. repens genotypes may pose a threat to some high conservation‐value non‐target ecosystems in SE Australia. We also argue that long‐term, multi‐tiered experiments conducted in a range of controlled and non‐controlled environments are necessary to detect and accurately quantify risks associated with the release of disease‐resistant plants in general.