Predator diversity enhances secondary production and decreases the likelihood of trophic cascades

We manipulated the diversity of top predators in a three trophic level marine food web. The food web included four top benthic marine fish predators (black goby, rock goby, sea scorpion and shore rockling), an intermediate trophic level of small fish, and a lower trophic level of benthic invertebrates. We kept predator density constant and monitored the response of the lower trophic levels. As top predator diversity increased, secondary production increased. We also observed that in the presence of the manipulated fish predators, the density of small gobiid fish (intermediate consumers) was suppressed, releasing certain groups of benthic invertebrates (caprellid amphipods, copepods, nematodes and spirorbid worms) from heavy intermediate predation pressure. We attribute the mechanism responsible for this trophic cascade to a trait-mediated indirect interaction, with the small gobiid fish changing their use of space in response to altered predator diversity. In the absence of top fish predators, a full-blown trophic cascade occurs. Therefore the diversity of predators reduces the likelihood of trophic cascades occurring and hence provides insurance against the loss of an important ecosystem function (i.e. secondary production).

Relación entre anchoveta y otros componentes del ecosistema

Se hipotetiza que la mortalidad por pesca ocasiona efectos ecosistémicos, no sólo sobre la anchoveta, sino también sobre otros componentes del ecosistema, tales como los depredadores tope. El objetivo es realizar simulaciones con un modelo ecotrófico multiespecífico cubriendo el decenio de los años 2000, cambiando la mortalidad por pesca y analizando las variaciones en la biomasa de anchoveta, aves guaneras y lobos marinos. Se usó el Índice de Oscilación Peruano (IOP) para incluir una mediación que afecte la vulnerabilidad de las presas de la anchoveta. Se comparó el ajuste de los datos observados, usando dos tipos de dieta para anchoveta (fitoplanctófaga y zooplanctófaga). Se realizaron proyecciones de la biomasa, cambiando la mortalidad por pesca de 0,0 a 1,4 año-1. Las simulaciones con la dieta zooplanctófaga, que eleva el nivel trófico de la anchoveta de 2,35 a 3,36, produjo un menor ajuste entre los datos observados y simulados. La relación inversa entre la mortalidad por pesca y la biomasa desovante de la anchoveta, mostró que mortalidades por pesca entre 0,8 y 1,4 año-1 estarían asociadas a una biomasa desovante mínima de anchoveta, tomando en consideración sus relaciones multiespecíficas. También se encontró una relación inversa entre la mortalidad por pesca y las poblaciones de aves guaneras y lobos marinos.

Food webs of Mediterranean coastal wetlands

En aquesta tesi doctoral s'han estudiat els efectes directes i indirectes de dos tipus d'espècies claus de la comunitat aquàtica dels aiguamolls de l'Empordà (aiguamolls costaners mediterranis amb una xarxa tròfica senzilla). S'han realitzat experiments al camp utilitzant microcosmos i mesocosmos i els resultats han estat analitzats mitjançant tres aproximacions: la taxonòmica, la funcional i la de mides. S'ha comprovat que en situacions amb absència de predadors i dominància d'una única espècie en el zooplàncton (en aquest cas Calanipeda aquaedulcis i Daphnia magna), la segregació del recurs entre els diferents estadis de desenvolupament de la mateixa espècie zooplanctònica és una estratègia per evitar la competència intraespecífica en condicions de limitació de recurs. Per altra banda, la presència de diferents top-predators a la comunitat aquàtica (en aquest cas la medusa Odessia maeotica i el peix Aphanius iberus) desencadena una cascada tròfica en el plàncton però amb efectes top-down diferents segons el top-predator.

Population Trends of a Mixed-Species Colony of Humboldt and Magellanic Penguins in Southern Chile after Establishing a Protected Area

Worldwide marine protected areas (MPAs) have been designated to protect marine resources, including top predators such as seabirds. There is no conclusive information on whether protected areas can improve population trends of seabirds when these are further exploited as tourist attractions, an activity that has increased in past decades. Humboldt Penguins (Spheniscus humboldti) and Magellanic Penguins (S. magellanicus) breed sympatrically on Puñihuil Islets, two small coastal islands off the west coast of Chiloé Island (41° S) in southern Chile that are subject to exploitation for tourism. Our goal was to compare the population size of the mixed colony of Humboldt and Magellanic Penguins before and after protection from unregulated tourism and freely roaming goats in 1997. For this purpose, two censuses were conducted in 2004 and 2008, and the numbers compared with those obtained in 1997 by other authors. The proportion of occupied, unoccupied, and collapsed/flooded burrows changed between years; there were 68% and 34% fewer collapsed burrows in 2004 and 2008, respectively, than in 1997. For the total number of burrows of both species, we counted 48% and 63% more burrows in 2004 and 2008, respectively, than in 1997. We counted 13% more burrows of Humboldt Penguins in 2008 than in 1997, and for Magellanic Penguins, we estimated a 64% increase in burrows in 2008. Presumably, this was as a result of habitat improvement attributable to the exclusion of tourists and the removal of goats from the islets. Although tourist visits to the islets are prohibited, tourism activities around the colonies are prevalent and need to be taken into account to promote appropriate management.

Description of diet of pelagic fish in the southwestern Atlantic, Brazil

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

STOMACH CONTENTS ANALYSIS of WHITE MARLIN (TETRAPTURUS ALBIDUS) CAUGHT OFF SOUTHERN and SOUTHEASTERN BRAZIL: A BAYESIAN ANALYSIS.

This study proposes to ascertain the importance of each alimentary category in the Tetrapturus albidus diet composition, as well as to propose the use of the Bayesian approach for analysis of these data. The stomachs were collected during fishing cruises carried out by the Santos-SP longliner from July 2007 to June 2008. For Bayesian model formulation, each alimentary item was clustered in four food categories as: teleost, cephalopod, crustaceans, and others. To estimate the proportion of each food category, the multinomial model with Dirichlet conjugate prior distribution was used. After the stomach contents analysis, 133 food items were identified, which belonged to 9 taxa. The most important food category is constituted by cephalopod molluscs, followed by teleost fishes. The food category comprised of crustaceans presents a low contribution and in this case it could be considered to be an accidental food item. The Bayesian approach means a distinct view in relation to traditional methods, as it permits one to incorporate information obtained from the literature. It should be useful to analyse great top predators, which are usually caught in small numbers.

Alien fishes in lakes of the Doce river basin (Brazil): Range, new occurrences and conservation of native communities

The present study shows the distribution of alien fish species in tropical lakes in the middle Doce river basin, southeastern Brazil, obtained from a rapid assessment program. The causes for their introductions were sport-fishing improvement in some specific lakes and aquaculture in the studied basin. Presently, these species have a wide distribution occurring in 41 of the 54 lakes studied, representing an actual threat to regional native fish community. The natural connection among lakes and streams during the rainy season and the dispersal mediated by local people are the main invasion agents for alien fishes. The success of these invaders is probably due to absence of pre-existing effective competitors or top-predators in the invaded communities. We consider that the eradication of alien fishes by means of the available management tools may be very difficult due to the large number of lakes invaded and to the wide spectrum of lake conditions and resources exploited by these alien species. We recommend the use of environmental education as a tool to stop the human-mediated dispersion of aliens and to improve conservation of native fish community in lakes where these alien species are not present yet. © 2004 Instituto de Ciências Biológicas - UFMG.

Ecologia da ictiofauna e análise ecossistêmica das áreas de influência direta da UHE Coaracy Nunes, Ferreira Gomes - AP

O reservatório da UHE Coaracy Nunes no rio Araguari esta localizado entre os municípios de Ferreira Gomes e Porto Grande no estado do Amapá-Brasil, distando 200 km do Oceano Atlântico. A usina Coaracy Nunes foi a primeira hidrelétrica a ser construída na Amazônia brasileira, tendo suas obras iniciadas em 1967. O rio Araguari e o principal rio do estado do Amapá e representa fonte de geração de renda através da pesca, atividades agropecuárias em sua várzea, navegação, mineração, geração de energia e lazer. O presente estudo teve por objetivo avaliar as alterações impostas pela construção do reservatório da UHE Coaracy Nunes, através das assembleias de peixes de quatro áreas de influencia direta desta usina. Para isso, no período de maio de 2009 a julho de 2010, foram realizadas coletas bimensais, de peixes, com redes de malhas padronizadas variando de 1,0 a 10,0 cm entre nos adjacentes e outras técnicas auxiliares. A partir destas coletas, no capitulo 1 foi verificado a composição, abundancia (CPUEn) e biomassa (CPUEp) relativas da ictiofauna, eficiência amostral (curva do coletor, curva de rarefação e Jacknife) e descritores ecológicos de comunidades (riqueza, diversidade, equitabilidade e dominância) das assembleias das quatro áreas. Foram efetuadas analises de variância (ANOVA: bifatorial), Kruskal-Wallis, teste-T e Mann-Whitney para verificar se havia diferenças significativas dos descritores entre as áreas e períodos sazonais. Estas análises foram corroboradas por analises multivariadas de agrupamento (cluster), ordenamento (MDS), Anosim e Simper. No capitulo 2, os estados ecológicos das quatro áreas foram verificados utilizando como indicadores: curvas espécie abundancia, curvas K-dominância e curvas ABC, assim como modelos espécie-abundancia serie geométrica, log serie, log normal e broken stick, e modelo de regressão linear de espectros de tamanho. No capitulo 3, a estrutura trófica foi estimada a partir da categorização das espécies de cada área em 5 guildas: piscívora, onívora, detritívora, carnívora e herbívora. A abundancia, biomassa e índices ecológicos destas guildas foram estimados e verificados suas variações espaço-temporais, por analises de variância (ANOVA: bifatorial e Kruskal-Wallis) e teste t. No capitulo 4, a dieta das espécies mais abundantes das assembleias de cada área foi verificada e suas variações espaço-temporais detectadas por analise de variância (ANOVA: bifatorial e Kruskal-Wallis). Também foram estimados a amplitude e sobreposição de nicho das espécies mais abundantes, assim como a existência de competição entre as espécies através de modelagem nula. No capitulo 5 foi realizada a avaliação ecossistêmica das quatro áreas através de modelos de fluxo de biomassa na rede trófica do ecossistema, usando como instrumento de modelação o software Ecopath. Essas análises tinham por objetivo descrever as variações dos atributos ecológicos que quantificam as propriedades de maturidade, estabilidade e resiliência ecossistêmica que pudessem refletir os estados ecológicos dessas áreas. O modelo incluiu compartimentos funcionais desde produtores primários ate predadores de topo. No geral, todas as análises indicaram sensíveis alterações na ictiofauna atribuídas a implantação da UHE Coaracy Nunes, que se refletem nos três níveis de organização: ecossistema, comunidade (assembleia) e guilda. Os resultados indicaram a captura de 1.977 peixes distribuídos em 2 classes, 9 ordens, 23 famílias, 73 gêneros e 108 espécies. As curvas de acumulação de espécies e curvas de rarefação individualizadas demonstraram que houve suficiência amostral nas áreas Reservatório e Lacustre. Os resultados mostraram que a área Jusante foi mais rica, diversa e equitativa em relação as demais e que a sazonalidade não influenciou na variação destes índices. A abundancia relativa (CPUEn) foi superior nas áreas Reservatório e Lacustre e a biomassa relativa (CPUEb) foi superior na área Jusante, não havendo diferenças sazonais para esses descritores em todas as áreas. As analises de agrupamento (cluster) e ordenamento (MDS) da ictiofauna permitiram identificar a formação de três assembleias distintas: Jusante, Montante e uma assembleia que compreende as áreas Reservatório e Lacustre, ratificando a similaridade dessas duas áreas. Os resultados das curvas whitakeplot, ABC e K-dominância, assim como o ajuste satisfatório do modelo broken stick e os padrões das curvas de espectro de tamanho para a assembleia da área a jusante indicam que esta área foi a mais equilibrada em termos ecológicos. Nas áreas Lacustre e Reservatório, os resultados tanto do ajuste ao modelo serie geométrica, quanto os resultados das curvas whitake-plot, ABC e K-dominância e o espectro de tamanho, assim como os resultados das curvas e ajustes ao modelo série e menor espectro de tamanho para a assembleia da área Reservatório, refletem que os peixes destas áreas, em sua maioria, são indivíduos pequenos com elevada dominância e baixa equitabilidade, caracterizando comunidades típicas de áreas impactadas. A estrutura trófica das assembleias de peixes das áreas represadas (Reservatório e Lacustre) foram formatadas em função do barramento do rio, que isolou e fragmentou o ambiente, determinando sua modificação física, impondo o estabelecimento de uma ictiofauna de espécies pré-adaptadas as condições ambientais de represamento, diferente, em parte, da estrutura da ictiofauna fluvial pre-barramento, destacando as piscívoras, onívoras e detritívoras, que foram as mais ricas e abundantes em função da disponibilidade, nas duas áreas, dos recursos alimentares de sua preferencia. Os resultados demonstraram que as dietas das assembleias de todas as áreas foram similares quanto ao predomínio do consumo de peixes e detritos, seguidos de alimento vegetal aloctone, revelando um padrão com poucos nichos amplos e uma concentração maior de espécies com nichos mais estreitos. Contudo, o padrão de baixa amplitude trófica foi evidenciado pelo predomínio da guilda piscívora, somada as guildas detritívora e herbívora. A sazonalidade pouco influenciou na alimentação da maioria das espécies em todas as áreas. Os padrões comparativos da dieta entre as áreas Montante e Jusante com as áreas Reservatório e Lacustre indicam que a maioria das espécies das áreas represadas pertenciam as guildas piscívora, onívora e detritívora antes do barramento do rio, que colonizaram estes ambientes, influenciadas, principalmente, pela abundancia dos recursos alimentares de suas preferencias e das condições físicas ambientais favoráveis. Interações competitivas foram evidenciadas pelos modelos nulos, sugerindo que a competição também foi um fator importante na estruturação das assembleias. Ecossistemicamente, os quatro modelos de fluxo de biomassa representam ecossistemas com elevada produção primaria oriunda da floresta riparia e algas filamentosas, que são utilizadas parcialmente. A cadeia trófica baseada em detrito apresentou ser mais importante que a que tem como base a produção primaria nas áreas Reservatório e Lacustre. A maioria dos fluxos ocorre nos compartimentos de níveis tróficos baixos. As propriedades ecossistêmicas da área Jusante indicam que este ambiente se encontra mais desenvolvido e maduro em relação aos outros, caracterizado por resiliência e entropia altas. As áreas represadas (Reservatório e Lacustre) apresentaram atributos ecossistêmicos que lhe conferiram características de menos resiliente e menos maduro que as áreas de rio. A área Montante apresentou um padrão intermediário de resiliência, estabilidade e maturidade. Esses resultados evidenciam que apos quarenta anos da construção da barragem do reservatório de Coaracy Nunes, a fragmentação do ambiente proporcionou alterações ecossistêmicas negativas, refletidas nas assembleias de peixes das áreas acima do barramento e na analise ecossistêmica, evidenciando que a área jusante apresenta características de ambiente em bom estado ecológico, com baixa alteração de origem antrópica e capaz de suportar distúrbios.

Interações tróficas entre espécies pelágicas do Atlântico Sudoeste: utilizando isótopos estáveis e inferência bayesiana

Pós-graduação em Ciências Biológicas (Zoologia) - IBRC

An Additional Baurusuchid from the Cretaceous of Brazil with Evidence of Interspecific Predation among Crocodyliformes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Use of chemical tracers in assessing the diet and foraging regions of eastern North Pacific killer whales

Top predators in the marine environment integrate chemical signals acquired from their prey that reflect both the species consumed and the regions from which the prey were taken. These chemical tracers—stable isotope ratios of carbon and nitrogen; persistent organic pollutant (POP) concentrations, patterns and ratios; and fatty acid profiles—were measured in blubber biopsy samples from North Pacific killer whales (Orcinus orca) (n = 84) and were used to provide further insight into their diet, particularly for the offshore group, about which little dietary information is available. The offshore killer whales were shown to consume prey species that were distinctly different from those of sympatric resident and transient killer whales. In addition, it was confirmed that the offshores forage as far south as California. Thus, these results provide evidence that the offshores belong to a third killer whale ecotype. Resident killer whale populations showed a gradient in stable isotope profiles from west (central Aleutians) to east (Gulf of Alaska) that, in part, can be attributed to a shift from off-shelf to continental shelf-based prey. Finally, stable isotope ratio results, supported by field observations, showed that the diet in spring and summer of eastern Aleutian Island transient killer whales is apparently not composed exclusively of Steller sea lions.

Use of chemical tracers in assessing the diet and foraging regions of eastern North Pacific killer whales

Top predators in the marine environment integrate chemical signals acquired from their prey that reflect both the species consumed and the regions from which the prey were taken. These chemical tracers—stable isotope ratios of carbon and nitrogen; persistent organic pollutant (POP) concentrations, patterns and ratios; and fatty acid profiles—were measured in blubber biopsy samples from North Pacific killer whales (Orcinus orca) (n = 84) and were used to provide further insight into their diet, particularly for the offshore group, about which little dietary information is available. The offshore killer whales were shown to consume prey species that were distinctly different from those of sympatric resident and transient killer whales. In addition, it was confirmed that the offshores forage as far south as California. Thus, these results provide evidence that the offshores belong to a third killer whale ecotype. Resident killer whale populations showed a gradient in stable isotope profiles from west (central Aleutians) to east (Gulf of Alaska) that, in part, can be attributed to a shift from off-shelf to continental shelf-based prey. Finally, stable isotope ratio results, supported by field observations, showed that the diet in spring and summer of eastern Aleutian Island transient killer whales is apparently not composed exclusively of Steller sea lions.

How deforestation pattern in the Amazon influences vertebrate richness and community composition

The effects of habitat configuration on species persistence are predicted to be most apparent when remaining habitat cover is below 30%. We tested this prediction by comparing vertebrate communities in 21 landscapes located in the southern Amazonia, including 7 control landscapes (similar to 100% of forest cover) and 14 fragmented landscapes (4 x 4 km). The fragmented landscapes retained similar proportions of forest (similar to 25%), but had contrasting configurations, resulting from two different deforestation patterns: the "fish-bone pattern" common in small properties, and the large-property pattern generally used by large ranchers. Vertebrates were surveyed in all landscapes in February-July 2009 with interviews (n = 150). We found a significant difference in reported species richness among the fish-bone, large-property, and control areas (mean = 29.3, 38.8 and 43.5 respectively). Control areas and large-properties tended to have a higher number of specialist species (mean = 13.7, and 11.7, respectively), when compared with the fish-bone pattern (5.1). Vertebrate community composition in the control and large-properties was more similar to one another than to those of the fish-bone landscapes. The number of fragments was the main factor affecting the persistence of species, being negatively associated with specialist species richness. Species richness was also positively related with the size of the largest fragment structurally connected to the studied landscapes (i.e., a regional scale effect). Our results demonstrated that the large-property pattern, which results in less fragmented landscapes, can maintain a more diverse community of large vertebrates, including top predators, which are considered fundamental for maintaining ecosystem integrity. These results support the hypothesis that landscape configuration contributes to the persistence and/or extirpation of species.

Eco-Evolutionary Spatial Dynamics. Rapid Evolution and Isolation Explain Food Web Persistence

One of the current challenges in evolutionary ecology is understanding the long-term persistence of contemporary-evolving predator–prey interactions across space and time. To address this, we developed an extension of a multi-locus, multi-trait eco-evolutionary individual-based model that incorporates several interacting species in explicit landscapes. We simulated eco-evolutionary dynamics of multiple species food webs with different degrees of connectance across soil-moisture islands. A broad set of parameter combinations led to the local extinction of species, but some species persisted, and this was associated with (1) high connectance and omnivory and (2) ongoing evolution, due to multi-trait genetic variability of the embedded species. Furthermore, persistence was highest at intermediate island distances, likely because of a balance between predation-induced extinction (strongest at short island distances) and the coupling of island diversity by top predators, which by travelling among islands exert global top-down control of biodiversity. In the simulations with high genetic variation, we also found widespread trait evolutionary changes indicative of eco-evolutionary dynamics. We discuss how the ever-increasing computing power and high-resolution data availability will soon allow researchers to start bridging the in vivo–in silico gap.

(Table 1) Lipid content and organohalogen contaminant concentration in captive sledge dogs (Canis familiaris) and wild female polar bears (Ursus maritimus) from Greenland

The limited knowledge and/or the inability to control physiological condition parameters that influence the fate of organohalogen contaminants (OHCs) has been the foremost confounding aspect in monitoring programs and health risk assessments of wild top predators in the Arctic such as the polar bear (Ursus maritimus). In the present comparative study, we used a potential surrogate Canoidea species for the East Greenland polar bear, the captive sledge dog (Canis familiaris), to investigate some factors that may influence the bioaccumulation and biotransformation of major chlorinated and brominated OHCs in adipose tissue and blood (plasma) of control (fed commercial pork fat) and exposed (fed West Greenland minke whale (Balaenoptera acutorostrata) blubber) adult female sledge dogs. Furthermore, we compared the patterns and concentrations of OHCs and their known or suggested hydroxylated (OH) metabolites (e.g., OH-PCBs) in sledge dogs with those in adipose tissue and blood (plasma) of East Greenland adult female polar bears, and blubber of their main prey species, the ringed seal (Pusa hispida). The two-year feeding regime conducted with sledge dogs led to marked differences in overall adipose tissue (and plasma) OHC residue accumulation between the control and exposed groups. Characteristic prey-to-predator OHC bioaccumulation dynamics for major PCB and PBDE congeners (patterns and concentrations) and biotransformation capacity with respect to PCB metabolite formation and OH-PCB retention distinguished, to some extent, captive sledge dogs and wild polar bears. Based on the present findings, we conclude that the use of surrogate species in toxicological investigations for species in the Canoidea family should be done with great caution, although they remain essential in the context of contaminants research with sensitive arctic top carnivore species such as the polar bear.