Predation, Production, Communities, and Food Webs Posters
Presiding: E Marti, Centre d'Estudis Avancats de Blanes (CSIC); C Hoagstrom, South Dakota State University
NB33Q-01 1330h
Impacts of Size Structure on Intraguild Predation in Pond Communities
Size structure, the degree to which individuals in a population vary in size, can greatly influence the dynamics of intraguild predation (IGP) within ecological communities. I manipulated the degree of size structure within assemblages of IG predators and IG prey to examine impacts on the direction and intensity of IGP in communities of larval dragonflies and larval water beetles. In pond enclosure studies, Pachydiplax longipennis (IG prey) mortality was lower when exposed to size structured assemblages of Anax junius (IG predator) than when exposed to only large A. junius at the same density. Effects of size-structured assemblages of A. junius on shared prey, Ischnura verticalis, were similar to the effects each size class alone at the same density. Separate experiments with Dytiscid water beetle larvae as IG predators and size-structured assemblages of A. junius as IG prey suggest that IG prey size structure plays only a limited role in mediating shared prey survival. These experiments highlight the importance of size structure as a characteristic that may promote the coexistence of predators in IGP systems.
NB33Q-02 1330h
Herbivore Recolonization Rate Influences Light and Nutrient Effects on Algal Based Stream Ecosystems
The dynamics of algal based ecosystems are influenced by both resource availability and herbivory. Following a disturbance, the relative importance of top down versus bottom up regulation of algal dynamics in a particular system depends on both herbivore immigration rates and local resource availabilities. The effects of herbivore recolonization and resource availability on the recovery dynamics of algal ecosystems following a disturbance were investigated during two field experiments conducted in 24 in situ stream channels in Convict Creek, California. In each experiment, light and nutrients were cross-classified in a 6x2 factorial design, with 2 replicates per treatment. Initial algal and invertebrate densities were low. Using upstream drift nets of different mesh sizes, herbivore immigration was restricted in one experiment and unrestricted in a second experiment. The relative importance of herbivore versus resource regulation of algae was influenced by herbivore immigration. When immigration was restricted, as might occur following a severe disturbance, algae were more closely regulated by resource availability. In contrast, when herbivore immigration was not restricted, algae were regulated by both resource availability and herbivory. Finally, the effects of light and nutrients on algae were interactive when immigration was restricted, but not when immigration was unrestricted.
NB33Q-03 1330h
Effects of habitat structure and risk of cannibalism on life-history traits of red swamp crayfish (Procambarus clarki)
The effects of habitat structure on predator-prey interactions and intra-guild predation have been well studied in a number of ecological and laboratory systems. How intraspecific interactions among members of cannibalistic species are affected by habitat structure has received less attention. We measured the impacts of habitat structure on interspecific aggression, cannibalism, and life-history traits of Procambarus clarki. Crayfish were randomly assigned to structured or simple habitats. Structured habitats consisted of aquaria with four ceramic fire bricks each with three circular holes for shelter; simple habitats lacked shelters. We hypothesized that habitat structure would lead to decreased injury frequency, increased molting frequency, greater survival, and higher reproductive output in crayfish. Reproductive output did not differ between treatments, but juvenile survival was higher in the structured habitat. Molting was more frequent in the structured habitat. In sharp contrast to predictions, survival was lower in the structured habitat. We concluded the increased mortality in the structured habitat was due to the high degree of exposure to cannibalism and aggression among the crayfish immediately following molting.
NB33Q-04 1330h
Scathophagid fly Larvae as Predators of Neophylax rickeri (Trichoptera: Uenoidae) egg Masses
We examined the predator-prey interaction of an undescribed predator (Diptera: Scathophagidae) on egg masses of Neophylax rickeri (Trichoptera: Uenoidae). Over a two-year period, we regularly surveyed 14 riffles within a 200-m reach of Redwood Creek and Webb Creek (Marin County, California). In Webb Creek, scathophagid predators were absent despite the abundance of N. rickeri egg masses. However, in Redwood Creek scathophagid predators were found within 11% (n=1594 egg masses) of the N. rickeri egg masses collected. N. rickeri egg masses were more frequently found clustered in aggregations (86%) than singly (14%), and scathophagid predators were more frequently found within N. rickeri egg mass aggregations (23% infestation rate) than in singly deposited egg masses (5%). Scathophagid predators exhibited a bivoltine life cycle with an increase in abundance after the first winter rains (November/December) and again in late spring (May/June). The abundance of predator larvae in the winter coincided with the peak oviposition period of N. rickeri, but in the late spring when N. rickeri egg masses were absent, the predator fed on egg masses of several other trichopteran (Brachycentridae) and dipteran (Ceratopogonidae, Chironomidae) species.
NB33Q-05 1330h
The Effects of Amphibian Extirpations on Foodweb Structure and Function in Panamanian Highland Streams.
Amphibian populations are declining globally in uplands. Stream-dwelling tadpoles are potentially important herbivores, and their loss is expected to cause significant changes in structure and function of lotic ecosystems. This study is part of a collaborative effort to measure changes in trophic structure associated with amphibian extirpations. We used stable isotopes to elucidate trends in Panamanian highland streams at two locations, El Cope and Fortuna, which are differentially affected by the declines. Generally, the nitrogen source in the Fortuna stream, where amphibians have already declined, is primarily atmospheric, whereas it is more recycled in El Cope where tadpoles are still abundant. FBOM is an important food resource in El Cope, and because of the recycled N from tadpole feces, the delta N15 values of the periphyton are higher in the pools than in the riffles in El Cope. Generally, the delta N15 signal of similar trophic groups is lower at Fortuna than at El Cope. The delta N15 signals also tend to fall with increased rainfall. Leaf packs are apparently under-utilized in these systems. Results allow for an assessment of trophic structure in highland neotropical streams and suggest that stream-breeding anuran extirpations may alter nutrient cycling and energy flow.
NB33Q-06 1330h
Do Brook Trout and Mottled Sculpin Cause Trophic Cascades in Appalachian Streams?
The ability of fish to cause trophic cascades varies. The strength of the cascade may change depending on the foraging mode of the fish or interactions among coexisting fish species. We investigated the ability of brook trout (Salvelinus fontinalis) and mottled sculpin (Cottus bairdi) to cause trophic cascades individually and in tandem. Artificial channels (2.1m long and 38.5cm in diameter) constructed from PVC pipe were positioned in a stream to create enclosures. The channels were arranged in a randomized complete block design with blocks of four channels located in four different reaches. In each block channels were randomly assigned to one of the following treatments: (1) control (no fish added) (2) sculpin only (3) trout only (4) both sculpin and trout. We measured changes in invertebrate density, algal biomass, and leaf pack colonization and breakdown rate after three weeks. Compared to controls, algal biomass in channels with sculpin doubled. When trout were present alone or with sculpin, algal biomass was not significantly different from control channels. Our results suggest that sculpin and trout differ in their ability to cause trophic cascades, and that the effects of sculpin on lower trophic levels change when trout are present.
NB33Q-07 1330h
Benthic Diatoms of an Alpine Stream/Lake Network in Switzerland
We compared the benthic diatom composition of lakes, and lake inlet and outlet streams in a high elevation catchment (~2600 m a.s.l.). The catchment was separated in a southern and northern basin with different water sources. Streams in both basins flowed through a series of small lakes before converging into a lake with a primary outlet. The south basin had lower water temperatures and 2× higher nitrate-N levels (up to 300 Μg/L) while the north basin had 2-4× higher levels of particulate-P, particulate-N, and particulate organic matter. 143 and 109 diatom species was identified in streams and lakes, respectively, with a similar number of species found in each basin. PCA showed a clear separation between basins. Of the 10 most common species, Psammothidium helveticum, Achnanthes helvetica var. minor, Achnanthes marginulata, Achnanthes subatomoides, and Diatoma mesodon were more abundant in south basin, whereas Achnanthidium minutissimum, Aulacoseira alpigena and Luticola goeppertiana were more abundant in the north. In general, lake outlet assemblages were similar to respective downstream lake inlet assemblages. Composition shifted along each basins longitudinal flow path. The spatial patterns in species composition reflected the hierarchical interaction of landscape features (geology, hydrology) on longitudinal gradients (lake position) in the stream/lake network.
NB33Q-08 1330h
The All Taxa Biodiversity Inventory of Algae in the Great Smoky Mountains National Park, with a Focus on the Acidophilic Diatom, Eunotia Ehrenberg
Since the late 1990's, the National Park Service and Discover Life In America have taken on the ambitious task of completing an All Taxa Biodiversity Inventory in the Great Smoky Mountains National Park (GSMNP). As one of the most species-rich areas in the temperate zone, GSMNP is considered a hot spot of biological diversity and has been designated as an International Biosphere Reserve. Previous research has suggested that the algal diversity is high in the GSMNP and many species are new, endemic, or restricted in range. To date, 67 species new to science and 163 taxa new to the park have been reported. An update of new species and new park findings will be presented. In particular, the GSMNP supports a diverse community of the acidophilic diatom Eunotia Ehr., both in terms of number of species and geographical distribution. Eunotia species can flourish in the park because of aquatic and aerial habitats that are 5-10X more acidic than normal, in combination with the presence of a complex geology and range of altitudes. An image-rich documentation of the Eunotia will be presented, including both light microscope and scanning electron micrographs that show the diversity, distribution and the variability in morphology.
NB33Q-09 1330h
Importance of Riverine Energy Sources in Puerto Rican Estuaries
Studies conducted in temperate, deltaic systems suggest that freshwater energy sources contribute little to estuarine food webs. In contrast, small, riverine estuaries draining mountainous tropical islands may be more dependent on freshwater energy sources than temperate deltaic systems, due to differences in landscape characteristics. We used two methods to evaluate the importance of freshwater energy sources to fishes in two Puerto Rican estuaries. We used stable isotopes (C, N, S) to evaluate the relative importance of freshwater organic matter, estuarine primary producers, and mangroves to fishes and other estuarine macroconsumers. We also analyzed gut contents of fishes collected for stable isotope analyses. Preliminary carbon isotope data suggest that local production of phytoplankton and benthic microalgae provides the primary organic matter source for estuarine fishes. These results, however, appear inconsistent with gut content analyses which contained few benthic organisms. Gut contents of omnivorous fishes were dominated by pelagic larval fishes and larvae of amphidromous freshwater shrimps (found in estuarine pelagic littoral zones). Sulfur isotope data will further distinguish between primary producers supporting these estuarine food webs and may explain discrepancies between carbon isotopes and gut contents. This study emphasizes the importance of using multiple methods for ecosystem level food web analyses.
NB33Q-10 1330h
Marine Derived Nutrients (MDN) in Riverine Ecosystems: Developing Monitoring Tools for Tracking MDN in Alaska Watersheds
The objective of this study is to measure marine derived nutrient (MDN) presence and effects in stream and riparian habitats on the southern Kenai Peninsula, Alaska. Year 1 approach was to link stream chemistry, marine isotope signatures, and lipid measures along a gradient from headwaters to mouth in watersheds with and without spawning salmon (i.e., N.F. Anchor River and Happy Creek, respectively). The N.F. Anchor River received 13,000 kg of chinook (Oncorhynchus tshawytscha) and 2000 kg of coho (O. kisutch) biomass in 2004. Contrary to our hypothesis, NH4 concentrations were not related to salmon escapement, possibly due to rapid uptake in this apparently phosphorus-rich system. Dolly Varden char (Salvelinus malma), horsetail (Equisetum sp.), and macroinvertebrates collected in spawning reaches showed enriched 15N values relative to an upstream reference and Happy Valley Creek. Biota also showed a general trend toward 15N enrichment along a gradient from headwaters to mouth for both streams, suggesting that trophic complexity increased with stream size regardless of spawning salmon presence. In years 2 and 3 we will expand this study across replicate salmon and non-salmon watersheds and integrate with related studies develop a broader regional understanding of MDN effects in watersheds.
NB33Q-11 1330h
Vertical movements and colonisation patterns of stream invertebrates within the riverbed in a NW Italian stream
There is a growing interest in the vertical dimension of streams. We examined vertical movements and colonisation patterns of stream macroinvertebrates within the substratum in the Caramagna Creek (NW Italy) We sampled the macrobenthos at three levels (0-5 cm, 5-10 cm, 10-15 cm) below the streambed using 56 artificial substrata (5x5x15 cm baskets filled with clean substratum). Traps from 1 to 28 were covered with a nylon net (mesh width 265 m) except for the apex, allowing access exclusively from the top (T traps). Traps from 29 to 56 were covered with the same net, but in this case the only access was from the bottom (B traps). After 14, 28, 42 and 56 days, fourteen traps (seven T and seven B) were removed. Community richness and density considerably increased over time in both traps. Forty-one taxa colonised the riverbed traps, with significant differences between T and B traps. This study provides data about the presence of interesting vertical movements within the first layer of the riverbed, underlining the existence of patterns and preferential movement direction among macroinvertebrate taxa. The interstitial zone is an important habitat, playing an key role for the functioning of the entire lotic ecosystem.
NB33Q-12 1330h
Life History Variation in Invading Applesnails (Pomacea canaliculata) May Pose Ecological Threats to Wetlands
In native habitats, channeled applesnails (Pomacea canaliculata) graze periphyton. However, casual observations from introduced populations suggest these invaders show variation in feeding ecology, predator response and life history strategies. Attempts to predict this consumer influence on ecosystem function suffer from a lack of basic data. We tested how salinity affected snail mortality. Both adults and hatchlings tolerated salinity levels up to 8 ppt. Adult feeding on lettuce increased significantly at 8 ppt compared to 0 ppt (p = 0.002), while hatchling consumption of algae did not vary (p = 0.284). To see how these consumers responded to predators from the invaded ecosystem, we tested behavioural responses to predatory cues from fish, turtles, crayfish and adult applesnails. Results indicated that fish and crayfish prompted similar predator-avoidance behaviors in hatchlings (p's < 0.05) and that hatchling response changed over time. Consumption rates of juvenile redear sunfish did not vary (x2, p > 0.05) between native (ramshorn) and exotic applesnails, whereas adult fish consumed more applesnails (x2, p < 0.001). Our current efforts focus on examining if predator presence or macrophyte choice alters applesnail feeding rates. Research providing insight into the basic ecology of applesnails can foster management efforts at the ecosystem scale.
http://www.southwestern.edu/~marfurtr
NB33Q-13 1330h
Influence of Coarse Woody Debris and Particulate Organic Matter on Density and Biomass of the Crayfish Procambarus versutus
We estimated the density and growth of several populations of the crayfish Procambarus versutus (Cambaridae) in small sandy-bottom streams within the Southeastern Coastal Plain, at Fort Benning, Georgia. Study streams had varying levels of coarse woody debris (CWD, 4-13% of stream bottom surface) and benthic particulate organic matter (>2cm, BPOM, 1-5% of substrate). Limited work has been done to assess if CWD or BPOM, primary habitat and food resources, respectively, influence crayfish population dynamics, despite the high bioenergetic importance of crayfish in many streams. Mean monthly densities were highest in the stream with the highest %CWD and %BPOM compared with other streams; however, monthly biomass was not always highest in the high-density, high-%CWD/BPOM stream. Instead, the intermediate-%CWD stream typically had the highest crayfish biomass. This disparity may be explained by differential food quality among streams and omnivory. Benthic macroinvertebrate density and biomass both were highest in the intermediate-%CWD/POM stream, and higher macroinvertebrate biomass may have compensated for lower BPOM abundance in crayfish diets, and thus provide a better food resource for P. versutus. We are currently using stable isotope data from crayfish and potential food resources among streams to test this hypothesis.
NB33Q-14 1330h
Organic Seston Dynamics in Upland Neotropical Streams: Implications for Amphibian Declines
Organic seston represents food for filter feeders and a mechanism for downstream transport of energy and nutrients. As part of a study assessing the ecological impacts of stream-breeding anuran extirpations, we examined seston dynamics in 2 stream reaches with tadpoles (El Cope) and 2 without (Fortuna) in the Panamanian uplands. All reaches are high gradient with annual average discharge ranging from 46-102 L/s. Samples were collected multiple times per month at various discharges, sieved into fine (<754Μm, >98Μm) and very fine (<98Μm, >1.6Μm) fractions, and processed to estimate ash-free dry mass (AFDM), total C, and total N. Average annual concentrations ranged from 0.52- 2.51 mg/L (fine) and 2.04-3.14 mg/L (very fine), and total export ranged from 0.27-7,981 mg/s across all streams. On average, very fine particles comprised 78% of export from El Cope sites and 61% from Fortuna streams. Average total N export ranged from 5.32-30.53 mg/s in El Cope sites and 1.71-6.04 mg/s at Fortuna. Average particle quality (C/N) in El Cope streams was higher (7.6) than Fortuna streams (11.5). Lower export of very fine particles and lower seston quality in Fortuna streams suggests the loss of tadpoles may influence seston dynamics and quality in these systems.
NB33Q-15 1330h
Baetid mayflies are very messy eaters: evidence from field experiments in a tropical stream, Ilha Grande, RJ, Brazil
Mayflies may play an important role in periphyton dynamics. In previous field exclusion experiments, we had found that baetid mayflies (Americabaetis sp. and Cloeodes sp.) had a strong negative impact on periphyton. In this study we quantified the contributions of mayfly consumptive and non-consumptive effects on periphyton in the absence of shrimp. We carried out five field experiments: an egestion rate experiment to quantify periphyton consumed by mayflies and four shrimp exclusion experiments using electricity to exclude shrimps from natural substrate to estimate total removal of periphyton by mayflies. By comparing total removal with estimated ingestion, we estimated non-consumptive loss. We starved mayflies for 0, 3 and 6 h and assumed that periphyton egested would be replaced by ingestion at the same time. We found that, after 3h, 52.8% of the initial amount of periphyton in the mayfly alimentary canal was lost due to egestion, and 77.9% after 6h. During shrimp absence mayflies accumulated over control level and significantly reduced periphyton. Estimated ingestion was 2 to 23% of the periphyton depletion, thus mayfly non-consumptive periphyton removal contributed 98 to 77% of all periphyton lost inside electrified areas. Our results suggest that mayfly have strong negative non-consumptive effects on periphyton.
NB33Q-16 1330h
Changes in Benthic Invertebrate Communities During the Introduction of Zebra Mussels Into an Impounded Michigan River
Zebra mussels (Dreissena polymorpha, ZM) were introduced into the Croton impoundment on the Muskegon River, MI, sometime during the late 1990s, and subsequently colonized downstream. We evaluated changes in invertebrate communities in the Muskegon River during ZM colonization. ZM were not found in benthic samples collected during 1998-1999 but densities reached 12,000 m-2 and 26,000 m-2 in 2000 and 2001 respectively, immediately below the Croton impoundment. ZM densities remained relatively low (<70 m-2) at sites 1.75 km and 8.75 km downstream. Total arthropod densities increased from 1998-99 to 2001. Trichoptera densities declined at all sites in 2000 but recovered in 2001. The relative abundance of Hyropsychidae varied between 1998-99 and 2001 at each sample site. Cheumatopsyche sp. increased significantly below Croton dam occupying spaces within and below ZM clumps, but declined at downstream sites following introduction of ZM. Chironomidae were uncommon in 1998-99 samples but were numerically dominant in 2000 and 2001 averaging 16525 m-2 over both years. Data from 2003 indicated that ZM remove 32% of suspended Chl. a in the first 500 m below Croton Dam. Thus, ZM may affect benthic invertebrate communities in impounded river systems by redistributing particulate organic matter within the system.
NB33Q-17 1330h
Population genetic structure of the crayfish,Orconectes juvenilis, in central Kentucky
Orconectes juvenilis is distributed throughout the Kentucky River basin and surrounding drainages. Little is known about the patterns of gene flow between populations of this species, but such information is critical for understanding patterns of diversification in the genus and in conservation planning for the group. We assessed sequence-level variation in the 16S region of mitochondrial DNA within and among fourteen populations of O. juvenilis. We also compared these data to sequences collected from two populations of O. cristavarius and one population of O. rusticus, two closely related species. The geographic distribution of haplotypes and patterns of mtDNA polymorphism are consistent with current isolation among some populations and suggest recent population growth, perhaps associated with geographic expansion. The data also suggest gene flow between morphologically divergent populations of O. juvenilis and O. cristavarius.
NB33Q-18 1330h
HABSEED: a Simple Spatially Explicit Meta-Populations Model Using Remote Sensing Derived Habitat Quality Data
The HABSEED model uses remote sensing derived NPP as a surrogate for habitat quality as the driving mechanism for population growth and local seed dispersal. The model has been applied to the Sahel region of Africa. Results show that the functional response of plants to habitat quality alters population distribution. Plants more tolerant of medium quality habitat have greater distributions to the North while plants requiring only the best habitat are limited to the South. For all functional response types, increased seed production results in diminishing returns. Functional response types have been related to life history tradeoffs and r-K strategies based on the results. Results are compared to remote sensing derived vegetation land cover.
NB33Q-19 1330h
The Effect of Zebra Mussels on Algal Community Structure in an Impounded River System
The zebra mussel, Dreissena polymorpha, invaded the Great Lakes Region in the mid 1980's, and subsequently colonized inland lakes and coastal river systems through secondary invasions. The Muskegon River below Croton Dam was colonized by zebra mussels in 2000 following their introduction into Croton impoundment in the late 1990's. No zebra mussels were found below Croton Dam in 1999 but had increased to 25,000 m-2 by 2001. We examined the affect of zebra mussels on epilithic periphyton communities by comparing plots that were and were not colonized by zebra mussels. Chlorophyll a increased in both treatments over time but was significantly higher in control plots than in zebra mussel plots. The concentration of chlorophyll a in the control plots increased from 14 ægcm-2 to 26 ægcm-2 and the concentration in the zebra mussel plots started at 12 ægcm-2, peaked at 19 ægcm-2, and then decreased to 15 ægcm-2 over a 6 week period. In a related experiment using artificial streams, chlorophyll a increased with increasing zebra mussel density, but differences were not significant. The different trends observed between the two experiments may be explained in part by arthropod invertebrates associated with zebra mussel populations.