Robert I. Gara

Ecological Effects of a Chum Salmon (Oncorhynchus keta) Spawning Run in a Small Stream of the Pacific Northwest

ABSTRACT We studied effects of chum salmon spawning activities on nutrients, epilithic algae, and benthic insect communities in a small stream of Pacific Northwest. The reach with salmon spawning had greater concentrations of Kjeldahl-N, NH4+-N, and total soluble P than the reach without salmon. However, chlorophyll a concentration was lower in the reach with salmon. In particular, chlorophyll a concentration was significantly lower during salmon spawning. Three caddisfly genera and two stonefly genera collected from salmon carcasses fed on salmon flesh. The total insect density in containers baited with salmon flesh was significantly greater than in containers without salmon flesh, but the difference was insignificant for the total biomass. Orthocladiinae and Baetis sp. had significantly greater densities and biomasses in the containers with salmon flesh. These results support the notion that mass salmon spawning activities affect structure and dynamics of ecosystems.

The effect of a teak (Tectona grandis) plantation on the establishment of native species in an abandoned pasture in Costa Rica

Abstract Many tropical forest plantation projects, particularly those funded through governmental or development agencies are designed to provide secondary social or environmental benefits in addition to timber. The research reported here examined the ecological effects of establishing a teak (Tectona grandis) plantation on an abandoned pasture in southwestern Costa Rica. The 10-year-old plantation’s understory was evaluated using a nearby non-planted area as a baseline for potential local recruitment of native tree species. The native trees in the teak plantation were significantly less abundant, less diverse, and more restricted to the lower height classes than the trees in the abandoned pasture. Furthermore, trees with shrubby growth forms dominated the plantation’s understory, whereas larger species were more common in the unplanted abandoned pasture. Several aspects of teak’s biology may contribute to the species’ exclusion of native trees. The primary goal of nearly all forest plantations is the production of timber. However, for those managers secondarily interested in the goal of providing habitat for native forest species, teak appears to be a poor choice of crop tree.

Increased individual growth rate and community biomass of stream insects associated with salmon carcasses

We showed that salmon carcass tissue can increase the growth rate of individual caddisflies as well as increase the local biomass of the aquatic insect community in 3 major stream habitat types. Sixteen insect taxa were found on salmon carcasses. The 7 dominant taxa in terms of biomass all had greater biomass in containers baited with salmon flesh in all habitats sampled; however, only 5 showed a significant salmon effect at the Bonferroni adjusted α of 0.007. The larval growth of Ecclisomyia conspersa was significantly greater on salmon muscle tissue than on conditioned leaves. Asynarchus pacificus grew significantly better with a combination of salmon and conditioned leaves than with either conditioned leaves or salmon muscle tissue alone. Our findings contribute to the understanding of the transfer of marine nutrients between generations of salmonids via aquatic insects, which are important prey items of juvenile salmonids.

Monoterpenes in sitka spruce: Within tree and seasonal variation

Abstract The composition of oils from needles and cortex of Sitka spruce is unique. Cortex oil is essentially all monoterpene hydrocarbons, while needle oil may be up to 50% oxygenated monoterpenes. Very wide seasonal variations in composition occur in needle oil in young tissue. At bud burst, the oil is > 95% myrcene; this drops to about 40% at the end of summer. The oxygenated terpenes camphor and piperitone develop to about 20% each in concentration during the growing season.

Emission of ethanol and monoterpenes by fungal infected lodgepole pine trees

Abstract The boles of lodgepole pine trees (Pinus contorta murrayana) infected with heartwood decay fungi, emitted ethanol, a potential primary attractant for the mountain pine beetle (Dendroctonus ponderosae), at a higher rate (45.9 μg m−2 day−1) than uninfected trees (19.2 μg m−2 day−1) , on average. The average rate of emission of ethanol by the infected trees was not discernibly different from the average rate of emission of total monoterpenes (32.3 μg m−2 day−1) by these trees. However, the rate of emission of ethanol by uninfected trees exceeded that of total monoterpenes (6.8, μg m−2 day−1), on average. Decay fungi: Perenniporia subacida, Tyromyces sericeomollis and Phellinus pini, were identified in one or more of the decayed trees.

Effects of Chum Salmon Redd Excavation on Benthic Communities in a Stream in the Pacific Northwest

Abstract We studied effects of redd excavation by wild chum salmon Oncorhynchus keta on insect communities in a stream in the Pacific Northwest. During the salmon redd excavation, the total mean insect densities in the spawning reach decreased to 10.8–14.7% of their predisturbance values. Mean densities of the major taxa, mayflies Baetis spp. and Cinygmula spp., midges Orthocladiinae, stoneflies Paraperla spp., and black flies Simuliidae, in the spawning reach were 0.4–55.1% of the predisturbance values during redd excavation. Densities of these taxa in the spawning reach were 1.1–46.6% of densities in the nonspawning reach during salmon redd excavation. Twenty-nine days after redd excavation, the densities of Baetis spp., Orthocladiinae, and Simuliidae in the spawning reach exceeded the values of the same taxa in the nonspawning reach. Statistical analyses revealed that the presence or absence of spawning salmon was significantly associated with the distances (or dissimilarities) among stream insect comm...

Macroinvertebrate community dynamics: strong negative response to salmon redd construction and weak response to salmon-derived nutrient uptake

Abstract Densely spawning salmon (Oncorhynchus spp.) affect macroinvertebrates negatively through redd construction and positively through nutrients released during spawning and carcass decomposition. We investigated the long-term characteristics of this interaction by measuring density, biomass, and C and N sources in benthic macroinvertebrates over 1 y. Total macroinvertebrate community biomass decreased during spawning and redd construction. However, the percentage of macroinvertebrate biomass derived from salmon increased. The highest percentage (56%) and biomass (2.71 g/m2) of salmon-derived tissue in the macroinvertebrate community occurred 3 mo after spawning. Shredders accumulated the most salmon-derived biomass per individual; however, collector-filterers, scrapers, and predators accumulated the most salmon-derived biomass at the population level, a result that suggests multiple pathways of salmon nutrient acquisition. Salmon-derived macroinvertebrate biomass was never <22% of macroinvertebrate community biomass in the spawning reach, but 6 mo after spawning, no clear density or biomass differences were found between reaches with and without salmon. This pattern held true at all scales examined, from whole community to functional feeding group to individual taxa in prespawning samples from both years. These results suggest that increased macroinvertebrate production from the nutrient and energy subsidy from salmon was restricted to the recovery period following the disturbance of redd construction and might have been obscured by emergence and transfer to higher trophic levels.

Spatial and temporal distribution of coho salmon carcasses in a stream in the Pacific Northwest, USA

During two consecutive spawning seasons, the movement and distribution of naturally occurring coho salmon (Oncorhynchuskisutch) carcasses were monitored, and the effectiveness of large woody debris (LWD) in retaining carcasses in a stream was evaluated. In both seasons studied, the proportion of carcasses trapped by LWD increased as the season progressed. Densities of salmon carcasses were higher in slow waters such as stream edges and backwaters throughout the study periods. The average distance drifted by carcasses was 19.5 m in the first season and 32.1 m in the second season. These results support the notion that LWD contributes to retention of salmon carcasses and enhances availability of salmon-derived nutrients for organisms near salmon spawning grounds.

Aquatic insect assemblages associated with subalpine stream segment types in relict glaciated headwaters

Aquatic habitats and biotic assemblages in subalpine headwaters are sensitive to climate and human impacts. Understanding biotic responses to such perturbations and the contribution of high‐elevation headwaters to riverine biodiversity requires the assessment of assemblage composition among habitat types. We compared aquatic insect assemblages among headwater stream segment types in relict glaciated subalpine basins in Mt. Rainier National Park, Washington, USA. Aquatic insects were collected during summer and autumn in three headwater basins. In each basin, three different stream segment types were sampled: colluvial groundwater sources, alluvial lake inlets, and cascade‐bedrock lake outlets. Wards hierarchical cluster analysis revealed high β diversity in aquatic insect assemblages, and non‐metric multidimensional scaling indicated that spatial and temporal patterns in assemblage composition differed among headwater stream segment types. Aquatic insect assemblages showed more fidelity to stream segment types than to individual basins, and the principal environmental variables associated with assemblage structure were temperature and substrate. Indicator species analyses identified specific aquatic insects associated with each stream segment type. Several rare and potentially endemic aquatic insect taxa were present, including the recently described species, Lednia borealis (Baumann and Kondratieff). Our results indicate that aquatic insect assemblages in relict glaciated subalpine headwaters were strongly differentiated among stream segment types. These results illustrate the contribution of headwaters to riverine biodiversity and emphasise the importance of these habitats for monitoring biotic responses to climate change. Monitoring biotic assemblages in high‐elevation headwaters is needed to prevent the potential loss of unique and sensitive biota.

Aerial Arthropod Communities of Native and Invaded Forests, Robinson Crusoe Island, Chile

ABSTRACT Invasive species significantly contribute to biological change and threaten biodiversity, with a growing body of evidence that plant invasions affect higher trophic levels. We explored the relative importance of plant invasion and forest structure on aerial arthropod abundance, diversity, and composition on Robinson Crusoe Island, Chile. We used flight intercept traps to sample aerial arthropods within distinct canopy strata of native and invaded forests over 3-mo periods in 2006 and 2007. Arthropod abundance and diversity were higher in native than invaded forest, and arthropod communities were distinct between forest types. In both forest types, arthropod abundance was highest in the lower canopy, and canopy strata exhibited some differences in arthropod community composition. Several morphospecies were distinctly associated with each forest type. The strong differences in aerial arthropod communities associated with the invasion of native forest by non-native plants may affect other trophic levels, such as insectivorous birds. Steps to stop invasive plant spread and to restore native forest composition and structure are needed to safeguard the integrity of native communities, from plants to higher-level consumers.