Non-additive and non-stationary properties in the spatial distribution of a large marine fish population

Density-independent and density-dependent variables both affect the spatial distributions of species. However, their effects are often separately addressed using different analytical techniques. We apply a spatially explicit regression framework that incorporates localized, interactive and threshold effects of both density-independent (water temperature) and density-dependent (population abundance) variables, to study the spatial distribution of a well-monitored flatfish population in the eastern Bering Sea. Results indicate that when population biomass was beyond a threshold a further increase in biomass-promoted habitat expansion in a non-additive fashion with water temperature. In contrast, during years of low population size, habitat occupancy was affected positively only by water temperature. These results reveal the spatial signature of intraspecific abundance distribution relationships as well as the non-additive and non-stationary responses of species spatial dynamics. Furthermore, these results underscore the importance of implementing analytical techniques that can simultaneously account for density-dependent and density-independent sources of variability when studying geographical distribution patterns.     

Invasive ecosystem engineers on soft sediment change the habitat preferences of native mayflies and their availability to predators

1. Dreissenid mussels (quagga mussels, Dreissena bugensis, and zebra mussels, D. polymorpha) are invasive species that function as ecosystem engineers in the Laurentian Great Lakes. Dreissena are increasingly abundant on silt, sand and other soft substrates; by altering benthic habitat, these mussels can alter benthic community structure. 2. We used laboratory mesocosm experiments to examine the effects of soft‐sediment Dreissena clusters on the habitat preference of Hexagenia, a native burrowing mayfly that is an important food source to fish. We conducted three experiments to test whether Hexagenia: (1) select for bare sediment, soft sediment covered with live Dreissena (added structure and food resources) or soft sediment with clusters made of empty Dreissena shells (added structure only), (2) prefer a specific density of live Dreissena on soft sediment and (3) select for or avoid sediment with an accumulation of empty Dreissena shells. 3. Contrary to initial expectations, we found that Hexagenia selected for sediment covered with live Dreissena clusters, followed by empty Dreissena shells clusters, and lastly what was previously thought to be the preferred habitat, bare sediment. Not only did Hexagenia prefer Dreissena‐covered sediment, but they also preferred high densities of Dreissena. 4. We also experimentally tested the effects of Dreissena‐covered soft sediment on the availability of Hexagenia to fish. We had three treatment levels representing three distinct habitat types: (1) bare sediment (no Dreissena) treatment in which water was turbid because of mayfly activity, (2) Dreissena‐covered sediment treatment in which water was clear because of Dreissena filtration and (3) Dreissena‐covered sediment with added turbidity. We found that in low light conditions, similar to many locations where both organisms are found to co‐occur, both yellow perch and round goby consumption of Hexagenia significantly decreased when Dreissena covered the bottom sediment. 5. These results suggest that by choosing Dreissena‐covered habitat, Hexagenia receive protection from fish predation in turbid/low light systems. However, protection from predation cannot be the only reason Hexagenia select Dreissena‐covered sediments, as Hexagenia selected for live clusters more often than empty clusters and may be a result of additional food resources.     

底栖生物影响下的潮滩微地貌演化数值模拟

潮滩是海岸带湿地的主要类型之一,其中分布的底栖生物对生态环境具有重要的调节作用。潮滩底栖微藻、泥沙与水动力之间存在相互作用,影响潮滩微地貌形态,明晰底栖生物对潮滩微地貌的演化机制至关重要。以黄河三角洲潮滩湿地为研究区,通过构建潮滩微地貌动力模型,探究底栖生物对微地貌格局演化的作用机制,分析底栖生物对微地貌系统稳定性的影响。结果表明(1)底栖微藻生长与泥沙扩散、水流再分配过程交互作用驱动下,潮滩上可形成底栖微藻覆盖的高丘与积水洼地交替分布的规则性微地貌斑图;(2)微地貌斑图的形成提高了潮滩生态系统初级生产力和泥沙淤积高度;(3)底栖微藻与泥沙、水流的交互作用使得潮滩微地貌系统对侵蚀扰动呈现非线性响应行为,系统存在临界点,且在一定侵蚀率范围内存在双稳态;(4)黄河口泥螺入侵使得微地貌系统抵抗侵蚀扰动能力减小,且系统稳定性随泥螺生物量的增加而降低。     

Fouling mussels (Dreissena spp.) colonize soft sediments in Lake Erie and facilitate benthic invertebrates

• 1 We conducted survey and transplant studies to determine whether colonization and residency on soft sediments by introduced, fouling mussels (Dreissena polymorpha and D. bugensis) were affected by physical disturbance, and whether Dreissena presence in turn influenced the diversity and population densities of other benthic invertebrates. Surveys revealed that colony density was typically higher at moderate depths than at shallower and greater ones. However, the largest, midsummer colonies and greatest coverage of sediments by mussels occurred at deeper sites.
• 2 Disturbance of transplanted colonies varied by depth and colony size, with deeper and larger colonies experiencing the lowest destruction rates. Colony destruction rate was positively correlated with current velocity adjacent to the lakebed.
• 3 Absence of mussel colonies at shallow sites was not determined by recruitment or substrate limitation, as recruit density was higher and sediment characteristics more suitable for postveliger settlement at shallow than at deeper sites. Rather, seasonal storms have much stronger effects in shallow than in deep water.
• 4 Mussel residency on soft sediment has profound effects on invertebrate biodiversity. Invertebrate species (taxon) richness and total abundance were positively correlated with mussel colony area. Mussel‐sediment habitat supported between 462 and 703% more taxa, and between 202 and 335% more individuals (exclusive of Dreissena) than adjacent soft‐sediment lacking mussels.
• 5 Results from this study illustrate that physical disturbance directly limits the distribution of mussels on soft sediments, and the diversity and abundance of other benthic invertebrates in consequence.

     

Relationship of Sponge Macrofauna with the Morphology of their Hosts in the North Aegean Sea

The associated macrofauna of four Aegean Sea sponge species (Agelas oroides, Petrosia ficiformis, Ircinia variabilis and Aplysina aerophoba) was compared. The total number of individuals and species was found to be related to sponge volume for all sponge species. The associated macrofaunal weight per individual on all sponge species was negatively correlated with sponge volume. Sponge complexity, as measured by sponge surface area to biomass ratio, was not a consistent predictor of associated macrofauna abundance or diversity. Sponge macrofauna species were not host specific and their relative abundances differed among sponge species.     

Habitat-specific predation susceptibilities of a littoral rotifer to two invertebrate predators

The rotifer Euchlanis dilatata lives associated with submerged vegetation in the littoral zone of freshwater lakes and ponds. I assessed habitat-specific predation susceptibilities for this rotifer in the presence of three aquatic macrophytes (Myriophyllum exalbescens, Elodea canadensis, and Ceratophyllum demersum) and two predators (damselfly nymphs — Enallagma carunculata; and cnidarians — Hydra). Rotifer survival was greatest on Myriophyllum in the presence of both predators. Conversely, the presence of the other macrophyte species actually increase rotifer suspectibility to predation by damselfly nymphs. I also manipulated plant structural complexity. As predicted, decreasing the relative complexity of each plant resulted in lower rotifer survival.     

Can Invasive Species Facilitate Native Species? Evidence of How, When, and Why These Impacts Occur

Although the predatory and competitive impacts of biological invasions are well documented, facilitation of native species by non-indigenous species is frequently overlooked. A search through recent ecological literature found that facilitative interactions between invasive and native species occur in a wide range of habitats, can have cascading effects across trophic levels, can re-structure communities, and can lead to evolutionary changes. These are critical findings that, until now, have been mostly absent from analyses of ecological impacts of biological invasions. Here I present evidence for several mechanisms that exemplify how exotic species can facilitate native species. These mechanisms include habitat modification, trophic subsidy, pollination, competitive release, and predatory release. Habitat modification is the most frequently documented mechanism, reflecting the drastic changes generated by the invasion of functionally novel habitat engineers. Further, I predict that facilitative impacts on native species will be most likely when invasive species provide a limiting resource, increase habitat complexity, functionally replace a native species, or ameliorate predation or competition. Finally, three types of facilitation (novel, substitutive, and indirect) define why exotic species can lead to facilitation of native species. It is evident that understanding biological invasions at the community and ecosystem levels will be more accurate if we integrate facilitative interactions into future ecological research. Since facilitative impacts of biological invasions can occur with native endangered species, and can have wide-ranging impacts, these results also have important implications for management, eradication, and restoration.Contribution Number 2293, Bodega Marine Laboratory, University of California at Davis.