Gulf Stream warm core rings: phytoplankton in two fall rings of different ages

Warm core ring (WCR) 82-H was sampled in September–October(1982) as a Gulf Stream meander pinched off and became a ring.It is compared with the 3-month-old WCR 81-D, visited September–October(1981). Although the rings have different histories, their phytoplanktonassemblages share some characteristics. Using cluster analysesbased on quantitative group counts, a station from one ringoccasionally clusters most closely with a station from the otherring, showing a similar balance of organisms. The younger ringat the time of sampling, WCR 82-H, had lower diversity, fewershelf species, and greater consistency between stations, exceptfor a high level of Oscillatoria in the meander before the ringpinched off. Interaction with slope water was seen principallyat the ring margin. WCR 81-D, on the other hand, showed a greatdeal of structure, and immediate dilutions with slope waterand the Gulf Stream were apparent, with higher diversity beforeand a week after such interactions. The upper water column ofwarm core rings, although showing evidence of physical mixing,can exhibit stratification of species, even after a storm.     

Resource and habitat sharing by the stoplight parrotfish,Sparisoma viride, a Caribbean reef herbivore

Synopsis We compare the vertical distribution, substrate preferences, grazing behaviour and social interactions of the stoplight parrotfish,Sparisoma viride, with that of other scarids at a fringing reef off Bonaire (Netherlands Antilles). Earlier reports thatS. viride only displays territorial behaviour against conspecifics are confirmed by the non-aggressive nature of this parrotfish and the low time expenditure on interactions with other herbivores. The vertical distribution ofS. viride is largely identical to that of several other scarids, acanthurids and pomacentrids, whose ranges may completely coincide withS. viride territories. Comparison of the substrate use of the five most common scarids inside a singleS. viride territory yields no evidence of food partitioning. We suggest that the lack of interspecific territorial behaviour inS. viride is explained by the inability to economically defend a territory against all potential food competitors. Factors that may favour territory sharing between herbivores are fine-scale resource partitioning and shared defence, both of which would reduce the costs of territorial life. However, more detailed investigation of herbivore food selection is required before definite conclusions can be drawn.     

Stream noise,habitat filtering,and the phenotypic and phylogenetic structure of Neotropical anuran assemblages

The structure of assemblages may be determined by interspecific interactions or environmental factors (e.g. competition and habitat filtering). Since communication between conspecific and heterospecific affects fitness of individuals, habitat characteristics that prevent communication could determine habitat use and co-occurrence of species. However, at present there are few studies, most with birds, testing the relationship between sensory ecology and community ecology. Abiotic noise on streams could impede the detection and decoding of auditory signals by receivers through a process named auditory masking. Therefore, we tested the role of abiotic noise on streams as a habitat characteristic influencing the phenotypic and phylogenetic structure of Neotropical anuran assemblages. We tested this hypothesis using data of male body size, call frequency, calling place (alongside and away from streams), and phylogenetic relationship of 110 and 38 anuran species at regional and local scale, respectively. After we found quantitative evidence suggesting that call frequency and body size are conserved phenotypic traits, we found that assemblages alongside streams exhibit both phenotypic and phylogenetic clustering, while assemblages away from streams exhibit both phenotypic and phylogenetic overdispersion. These results offer quantitative evidence suggesting a role of noise on streams promoting a process of habitat filtering and affecting the structure of anuran assemblages alongside streams both at Neotropical and local scale. This is the first study using modern phylogenetic comparative metrics for covering potential causes of phenotypic and phylogenetic structure of anuran assemblages, and one of the few testing a link between community ecology and the evolutionary biology of acoustic communication to understand the processes mediating species co-occurrence in vertebrates.     

Survival, growth, and escape from herbivory are determined by habitat and herbivore species for three Australian woodland plants

To understand how plant communities are structured by herbivory it is essential to investigate the roles of different herbivores and the responses of a variety of plant species in different habitats. We examined the effects of mammalian herbivores on survival and growth of transplanted seedlings of two native trees (Eucalyptus albens and Callitris glaucophylla), and one native grass (Themeda australis) in white box (E. albens) woodlands in eastern Australia over 3 years. Herbivores were manipulated using four fencing treatments that successively excluded livestock, macropods, and rabbits from woodland and grassland (cleared pasture). Survival was highest in the absence of mammalian herbivores and in woodlands, and patterns differed among plant species. Survival of T. australis was low, especially in grasslands, and mortality by overgrowth was common in ungrazed treatments. All plant species were taller in fenced plots, and differences between treatments were greater in grassland. Rabbits and livestock had the greatest influence on C. glaucophylla, while T. australis and E. albens were most affected by livestock and macropods. We used field data to parameterize stage-classified matrix models to predict escape from herbivory (escape height >100 cm) for tree species. Reduced herbivory increased the proportion of individuals reaching escape height after 15 years. Rate of escape was greater in grassland, and this faster growth appeared to counteract much of the negative impact of herbivores. While T. australis was unable to escape herbivory, larger, ungrazed individuals were more likely to flower and therefore contribute to the maintenance of the population. Our results show that habitat and herbivore species strongly influence the effect of herbivory on vegetation.     

Resource complementation and the response of an insect herbivore to habitat area and fragmentation

Few studies have disentangled the effects of the area and fragmentation of a focal habitat type on species that use multiple habitat types within a landscape. We experimentally investigated the effects of habitat area, habitat fragmentation, and matrix composition on the movement and distribution of Melanoplus femurrubrum. Adults of this grasshopper feed preferentially on grasses, but oviposit almost exclusively in soil dominated by forbs. We compared population densities among plots that were made to vary in the area and fragmentation of clover habitat and composition of the matrix (grass or bare ground) within which clover habitat was embedded. In addition, a mark-recapture survey was conducted to examine effects of habitat area, fragmentation, and matrix composition on loss of individuals from a plot’s clover habitat and movement between clover subplots within plots. Overall densities of adult M. femurrubrum (averaged over clover and matrix) were 2.2× higher in plots where the matrix was composed of grass as compared to bare ground, and 1.8× higher in plots with 64 compared to 16 m² of clover habitat. Overall densities of nymphs were also positively influenced by greater clover area, but were unaffected by matrix composition. Within focal clover habitat embedded in grass matrix, adult densities were 2.1× higher in small clover subplots than large clover subplots. We conclude that the grass matrix had a positive effect on adult densities, but not nymph densities, because grass and forb-dominated habitats likely provide complementary resources only for adults. The aggregation of adults on small clover subplots within grass matrix was mainly attributed to a greater rate of emigration loss per unit area. In addition, this study emphasizes that a species’ response to changes in the area of a focal habitat type can depend significantly on the availability of complementary resources in the surrounding landscape. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Gulf sturgeon summer habitat use and fall migration in the Pascagoula River, Mississippi, USA

The locations and habitat features of freshwater holding areas and the timing of fall migration are undocumented for Gulf sturgeon in the Pascagoula River drainage, Mississippi. Our objectives were to identify and characterize holding areas for Gulf sturgeon (Acipenser oxyrinchus desotoi), document their summer and fall movement patterns, and determine migration cues. To do this we captured, radio‐tagged, and monitored movement of Gulf sturgeon in the Pascagoula River drainage and analyzed these data using geographic information systems. From May to November Gulf sturgeon congregate in a holding area in the lower portion of the Pascagoula River and Big Black Creek [river kilometers (rkm) 57–68] and near Cumbest Bluff (rkm 40), before they return to the Gulf of Mexico. While in the holding area, Gulf sturgeon were typically found in deep locations, either in or downstream from river bends. As found in other rivers, Gulf sturgeon in the Pascagoula River showed little movement within the holding area and often stayed within a single river bend; although we observed local movements by some individuals (under 10 rkm). In the Pascagoula River, Gulf sturgeon initiated their migration out of fresh water from late‐September to mid‐October, coincident with shorter day length, falling water temperature (mean = 23.7°C, range 21–26°C), and elevated river flow. Our work demonstrates that the lower Pascagoula River serves as a vital area for Gulf sturgeon.     

Landscape context outweighs local habitat quality in its effects on herbivore dispersal and distribution

Past studies with spatially structured herbivore populations have emphasized the primacy of intrinsic factors (e.g., patch quality), patch geometry (e.g., patch size and isolation), and more recently landscape context (e.g., matrix composition) in affecting local population abundance and dispersal rate. However, few studies have examined the relative importance of each factor, or how they might interact to affect herbivore abundance or dispersal. Here, we performed a factorial field experiment to examine the independent and interactive effects of patch quality (plant biomass, leaf protein, leaf phenolics) and matrix composition [mudflat or non-host grass (Bromus inermis)] on planthopper (Prokelisia crocea) emigration from host-plant patches (prairie cordgrass, Spartina pectinata). In addition, a field survey was conducted to examine the relative importance of patch quality, geography, and matrix composition on planthopper occupancy and density. In the experiment, we found that rates of emigration from low and intermediate quality patches were, on average, 21% percent higher for patches embedded in brome than mudflat. In contrast, the emigration rate was unaffected by matrix composition in nutrient-rich patches. Within matrix types, plant quality had little effect on emigration. In the survey, planthopper density and the patch occupancy rate of planthoppers increased nonadditively with increasing patch size and the percentage of the surrounding matrix composed of mudflat. This study suggests that landscape-level factors, such as the matrix, may be more important than factors intrinsic to the patches.     

Divergence in host use ability of a marine herbivore from two habitat types

We studied ecological divergence of host use ability in a generalist marine herbivore living in two distinct host plant assemblages. We collected Idotea balthica isopods from three populations dominated by the brown alga Fucus vesiculosus and three dominated by the seagrass Zostera marina. In two reciprocal common garden feeding experiments for adult and laboratory‐born juvenile isopods, we found that isopods from both assemblages performed better with their sympatric dominant host species than did isopods allopatric to this host. This indicates parallel divergence of populations according to the sympatric host plant assemblage. Furthermore, initial body size and body size‐dependent mortality differed between populations from the two assemblages. In nature, this may result in lower fitness of immigrants compared with that of residents and consequently reinforce divergence of the populations. Finally, we discuss how phenotypic plasticity and maternal and random effects may associate with the results.     

Stream inflow and predation risk affect littoral habitat selection by benthic fish

1. We examined small, fishless headwater streams to determine whether transport of macroinvertebrates into the littoral zone of an oligotrophic lake augmented food availability for Cottus asper, an abundant predatory fish in our study system. We sampled fish and macroinvertebrates during the recruitment and growth season of 2 years, either monthly (2004) or bi‐monthly (2005), to observe whether stream inputs increased prey availability and whether variation in total macroinvertebrate biomass was tracked by fish. 2. Observations from eight headwater streams indicated that streams did not increase the total macroinvertebrate biomass in the shallow littoral zone at stream inflows, relative to adjacent plots without stream inputs (controls). The taxonomic composition of stream macroinvertebrates drifting toward the lake differed from that in the littoral lake benthos itself, although there was no evidence of any species change in the composition of the littoral benthos brought about by stream inputs. 3. Although streams made no measurable contribution to the biomass or taxonomic composition of the littoral macroinvertebrate benthos, there was substantial temporal variation in biomass among the eight sites for each of the (n = 7) sample periods during which observations were made. Variation in total biomass was primarily a function of bottom slope and benthic substrata in the lake habitats. Dominant taxonomic groups were Baetidae, Ephemerellidae (two genera), Leptophlebiidae, Chironomidae (three subfamilies) and Perlodidae, although we did not determine the specific substratum affinities of each taxon. 4. Mixed effects linear models identified a significant interaction between macroinvertebrate biomass and plot type (stream inflow vs. control) associated with fish abundance. Across the observed range of macroinvertebrate biomass, fish showed a significant preference for stream inflows, but more closely tracked food availability in the controls. For young‐of‐the‐year (YOY), a negative effect of temperature was also included in the model, and we observed lower temperatures at stream inflows. However, abundance of predatory adults affected habitat selection for YOY. Lake‐bottom slope also accounted for variation in abundance in both fish models. 5. Our results suggest that the effect of fishless headwater streams on downstream fish may not always be through direct delivery of food. In this study system, fish preferred stream inflow plots, but this preference interacted with macroinvertebrate biomass in a manner that was difficult to explain. For YOY, predation risk was related to the preference for stream inflows, although the specific factor that mitigates predation risk remains poorly understood.     

Non-native regal demoiselle,Neopomacentrus cyanomos,presence, abundance,and habitat factors in the North-Central Gulf of Mexico

Remotely operated vehicle (ROV) surveys were conducted at reef sites in the northern Gulf of Mexico (nGOM) during 2018–2019. Artificial (AR?=?63) and natural (NR?=?139) reefs were located in a 2?×?10⁵ km² area south of Mobile, AL to Destin, FL at depths of 13–75 m. We observed a total of 5371 damselfishes (Family: Pomacentridae) belonging to eight taxa. The non-native regal demoiselle (regal), Neopomacentrus cyanomos, was present at 30.2% of ARs but only 1.4% of NRs with densities ranging from 0.19 to 18.11 fish per 100 m². Regals were most dense at shallow ARs, comprising 53% of the damselfish community, and least dense at deeper reefs comprising?<?1% of observed damselfishes. Results from generalized linear mixed models (GLMMs) indicated the interaction among reef type, complexity, relief, and depth had a significant effect on regal density but that reef type (36%) and the interaction between reef type and depth (25%) explained the greatest proportions of variance in the data (partial η²) while the interaction among all four main effects explained only a small amount (2%). Our data indicate regals prefer shallow artificial structures with low complexity but can occupy deeper reefs, including NRs, despite less-favorable conditions. Our data document the persistence of regals in the nGOM and identify habitat factors that are significantly related to their presence and density in the region. However, the dynamics controlling their distribution are still uncertain and potential negative impacts on native reef fish communities remain unclear.

     

Seasonal shifts in habitat selection of a large herbivore and the influence of human activity

Failure to recognize factors contributing to variation in habitat models like resource selection functions (RSFs) can affect their application for projecting probabilities of occurrence, and thereby limit their relevance for conservation and management. We compared seasonal RSFs (2006–2008) for 16 adult female moose (Alces alces) with home ranges located in western Algonquin Provincial Park (APP), Ontario, Canada, to those of 14 adult females located in provincial Wildlife Management Unit (WMU) 49, 40 km west of the protected area. Wildlife and habitat management practices differed between regions: hunting was higher in WMU 49 compared to APP, and APP preserved large tracts of old growth forest rarely found in WMU 49. Seasonal RSFs projected expected similarities in moose resource use between regions (e.g., responses to wetlands and stands of eastern hemlock, Tsuga canadensis [in winter]); however, we also observed differences consistent with the hypothesis that animals, through effects of hunting, would shift habitat use seasonally and in response to roads. We further observed evidence of functional responses in habitat selection due to underlying differences in forestry practices (e.g., responses to stands of old-growth hemlock forest). Given the close proximity and shared biogeographic region between study areas, we believe that observed spatial dynamics in RSFs were ultimately reflective of divergent management strategies between areas and ensuing differences in predation and hunting mortality risk, and functional habitat.     

Synergistic effects of an extreme weather event and habitat fragmentation on a specialised insect herbivore

Habitat fragmentation is considered to be one of the main causes of population decline and species extinction worldwide. Furthermore, habitat fragmentation can decrease the ability of populations to resist and to recover from environmental disturbances such as extreme weather events, which are expected to occur at an increasing rate as a result of climate change. In this study, we investigated how calcareous grassland fragmentation affected the impact of the climatically extreme summer of 2003 on egg deposition rates, population size variation and survival of the blue butterfly Cupido minimus, a specialist herbivore of Anthyllis vulneraria. Immediately after the 2003 summer heat wave, populations of the host plant declined in size; this was paralleled with decreases in population size of the herbivore and altered egg deposition rates. In 2006 at the end of the monitoring period, however, most A. vulneraria populations had recovered and only one population went extinct. In contrast, several butterfly populations had gone extinct between 2003 and 2006. Extinction probability was significantly related to initial population size, with small populations having a higher risk of extinction than large populations. These results support the prediction that species of higher trophic levels are more susceptible to extinction due to habitat fragmentation and severe disturbances.     

Enhanced fitness and greater herbivore resistance: implications for dandelion invasion in an alpine habitat

Several hypotheses have been proposed to explain the defense strategies of invasive plants in new ranges. In the absence of specialist herbivores, it is believed that invasive plants may allocate fewer resources to resistance and more to growth and reproduction, thus increasing tolerance to damage in the invasive genotypes. In order to test these predictions, we compared both performance (growth and reproduction) and defense strategies (tolerance and resistance) of two populations of Taraxacum officinale, one from the native range in the French Alps, and one from the introduced range in the Chilean Andes. Individuals from the introduced population demonstrated improved reproductive traits relative to those from the native population, although there was no discernible difference in biomass accumulation. Additionally, reduced tolerance was evident in the case of the former; whereas fitness traits of native plants were unaffected by damage, invasive plants reduced growth and seed output by 25 and 30% respectively following damage treatments. Increases in levels of phenols and anthocyanins, produced as a defense response to herbivory, were observed in introduced plants. Our results suggest that reallocation of resources to reproduction may be an important factor favouring invasive success of T. officinale in Chile, and that a higher investment in chemical resistance traits in this population may also be a factor in this regard.     

Entry of migrating American eel leptocephali into the Gulf Stream system

Abundance, size and depth distributions of American eel(Anguilla rostrata) leptocephali collected in four transects across the Florida Current between the Straits of Florida and Cape Hatteras, North Carolina, were examined in order to assess the relative importance of two migration routes into the Gulf Stream system. A nine-fold increase in the abundance and an increase in the mean length of leptocephali collected in the Florida Current north of the Straits of Florida indicate that most leptocephali enter the Gulf Stream system directly from the Sargasso Sea rather than by a more southern route through the Bahama Islands. Leptocephali were concentrated in the upper 140 m at night and upper 350 m during the day. Wide vertical ranges in daytime collections precluded more refined estimation of vertical distribution. The collection of eight small leptocephali (11 to 17 mm total length) in the western Caribbean Sea is discussed in relation to the origin of leptocephali taken in the Straits of Florida.     

Macroalgal susceptibility to grazing by herbivore fish Siganus spp. at Gulf of Mannar reef,Indian Ocean

Environmental Biology of Fishes - Enhancing the herbivore fish stock is envisaged as a mitigation tool to reverse the macroalgal dominance in a coral reef environment. However, identifying the key...     

Individual-based spatially-explicit model of an herbivore and its resource: the effect of habitat reduction and fragmentation

We present an individual-based, spatially-explicit model of the dynamics of a small mammal and its resource. The life histories of each individual animal are modeled separately. The individuals can have the status of residents or wanderers and belong to behaviorally differing groups of juveniles or adults and males or females. Their territory defending and monogamous behavior is taken into consideration. The resource, green vegetation, grows depending on seasonal climatic characteristics and is diminished due to the herbivore's grazing. Other specifics such as a varying personal energetic level due to feeding and starvation of the individuals, mating preferences, avoidance of competitors, dispersal of juveniles, as a result of site overgrazing, etc., are included in the model. We determined model parameters from real data for the species Microtus ochrogaster (prairie vole). The simulations are done for a case of an enclosed habitat without predators or other species competitors. The goal of the study is to find the relation between size of habitat and population persistence. The experiments with the model show the populations go extinct due to severe overgrazing, but that the length of population persistence depends on the area of the habitat as well as on the presence of fragmentation. Additionally, the total population size of the vole population obtained during the simulations exhibits yearly fluctuations as well as multi-yearly peaks of fluctuations. This dynamics is similar to the one observed in prairie vole field studies.     

Density dependent and temporal variability in habitat selection by a large herbivore; an experimental approach

Both density dependent and density independent processes such as climate affect population dynamics in large herbivores. Understanding herbivore foraging patterns is essential to identify the underlying mechanisms behind variation in vital rates. However, very little is known about how animals vary their selection of habitat temporally, alone or in interaction with density during summer. At the foraging scale, we tested using a fully replicated experiment whether domestic sheep Ovis aries stocked at high (80  per  km²) and low (25  per  km²) densities (spatial contrasts) varied their habitat selection temporally over a four year period. We predicted reduced selection of high productivity vegetation types with increasing density, and that seasonal and annual variation in climate would affect this density dependent selection pattern by increasing competition for high quality habitats in late grazing season and in years with poor vegetation development and over time related to vegetation responses to grazing. As predicted from the Ideal free distribution model, selection of high productivity habitat decreased at high density. There was also a marked temporal variation in habitat selection. Selection of the most productive vegetation types declined towards the end of each grazing season, but increased over years both at low and high sheep density. There was only weak evidence for interactions, as selection ratio of highly productive habitats tended to increase more over years at low density as compared to high density. Limited interactive effects of density and annual variation on habitat selection during summer may explain why similar interactions in vital rates have rarely been reported for summer seasons. Our results are consistent with the view that variation in habitat selection is a central mechanism for climate and density related variation in vital rates.