Structure and Function of the Zooplankton Community of Mirror Lake, New Hampshire

An intensive study of the zooplankton community of Mirror Lake, New Hampshire, was undertaken over a 3-yr period. Our objectives in the lake study have included measurements of a number of attributes of the zooplankton community that integrate structure and function at the ecosystem level; among these are dispersion, biomass, productivity, respiration, and nutrient cycling. Eight species of rotifers and 3 species of cladocerans were successfully cultured. Generation time for planktonic rotifers was -8-10 days (170C). The effect of higher food levels on rotifers was to shorten generation time and to increase brood size. In cladocerans, high food levels caused an increase in length and brood size . A curvilinear relationship existed between zooplankton community respiration and temperature in Mirror Lake. Mean monthly zooplankton community respiration ranged from 96.0 kg C/ha/mo in June of 1969 to a low of 20.5 kg C/ha/mo in April of 1970. Over a 3-yr period, respiration was 79.9% of assimilation. The 0 to 4.5-m strata (;epilimnion) contributed 68.5% and 46.5% of the annual zooplankton production and biomass. Zooplankton community production ranged from 22.3 kg C/ha/yr to 29.3 kg C/ha/yr with a 3-yr mean of 25.2 kg C/ha/yr. The annual zooplankton biomass ranged from 1.4 to 2.6 kg C/ha with a 3-yr mean of 2.0 kg C/ha. A linear relationship was found to exist between net phytoplankton and zooplankton production in various lakes of the world. Ecological efficiency apparently increases with the trophic status of the lake. It is recommended that the term ecological efficiency be refined to include both autochthonous and allochthonous inputs of reduced carbon into the lake. Rotifers assume a major role in intrasystem nutrient cycling and energy transfer within the lake ecosystem. Of the total amount of P incorporated into the organic matter of zooplankton community each year, 33.5% is assimilated in rotifer tissue. The annual turnover rate of P by rotifers is 30.9 and is high compared to crustaceans (10.1). Copepods comprise 55.4% of the total zooplankton biomass. However, the copepods, with their slow growth over an entire year, represent only 19.3% of the zooplankton production, while rotifers account for 39.8% of the zooplankton production annually in Mirror Lake. Also, evidence is presented that rotifers play a major role in energy transfer in lakes of varying trophic status (oligotrophic to eutrophic)

Limnological measures related to climate change in the Hubbard Brook Valley, USA

Long-term monitoring within the Hubbard Brook Valley revealed changes in many climate and limnological variables known to affect the structure and function of aquatic ecosystems. The Hubbard Brook Valley is located in the White Mountains of New Hampshire, USA, and is the site of integrated, long-term ecological, biogeochemical, and hydrological studies. Mean annual temperatures in 2 headwater streams on south-facing slopes of the Hubbard Brook Valley declined ~2 °C from 1966 to 1983 and then showed a small (~1 °C) and variable increase thereafter. No significant change in temperature was observed in 3 north-facing, headwater streams. Reliable records of ice-in and ice-out have been maintained since 1968 for Mirror Lake at the base of the Hubbard Brook Valley. The duration of ice cover on Mirror Lake has declined since 1968 at a significant rate of about −0.475 d/yr as a result of earlier ice-out (0.203 d/yr) rather than later ice-in dates. Since about 1996 the duration of ice cover has become much more variable with a nonsignificant change in ice cover duration. Evaluating how various temperature-sensitive components of aquatic ecosystems in the Hubbard Brook Valley change (amount and timing) in the future will be important to developing a better understanding of limnological responses to climate change

Linking Scales in Stream Ecology

The hierarchical structure of natural systems can be useful in designing ecological studies that are informative at multiple spatial scales. Although stream systems have long been recognized as having a hierarchical spatial structure, there is a need for more empirical research that exploits this structure to generate an understanding of population biology, community ecology, and species-ecosystem linkages across spatial scales. We review studies that link pattern and process across multiple scales of stream-habitat organization, highlighting the insight derived from this multiscale approach and the role that mechanistic hypotheses play in its successful application. We also describe afrontier in stream research that relies on this multiscale approach: assessing the consequences and mechanisms of ecological processes occurring at the network scale. Broader use of this approach will advance many goals in applied stream ecology, including the design of reserves to protect stream biodiversity and the conservation of freshwater resources and services

Hurricane Hugo: Damage to a Tropical Rain Forest in Puerto Rico

Hurricane Hugo of September 1989 caused severe damage to the rain forest in the north-east corner of Puerto Rico. We assessed the severity of damage distributed in space, species, and size-classes of trees in the Bisley Watersheds of the Luquillo Experimental Forest. We analyzed pre- and post-hurricane data for vegetation from transects established in 1987 and 1988. The severity of damage was significantly greater in valleys than on ridges and slopes. All the species except Dacryodes excelsa, Sloanea berteriana, and Guarea guidonia showed 100% severe damage. Large trees (\u3e 70 cm DBH) were highly susceptible to hurricane damage, but there was no clear pattern in the small size-classes. D. excelsa (tabonuco) was the most resistant to damage by the hurricane. Tabonuco which has extensive root-grafts and root anchorage to bedrock and subsurficial rocks, apparently can survive frequent hurricanes and continue as a dominant species in this montane tropical rain forest. The high frequency of hurricanes, which can override other ecological and topographic factors, may largely determine the overall spatial pattern of species in this rain forest

Linking Direct and Indirect Data on Dispersal: Isolation by Slope in a Headwater Stream Salamander

There is growing recognition of the need to incorporate information on movement behavior in landscape-scale studies of dispersal. One way to do this is by using indirect indices of dispersal (e.g., genetic differentiation) to test predictions derived from direct data on movement behavior. Mark–recapture studies documented upstream-biased movement in the salamander Gyrinophilus porphyriticus (Plethodontidae). Based on this information, we hypothesized that gene flow in G. porphyriticus is affected by the slope of the stream. Specifically, because the energy required for upstream dispersal is positively related to slope, we predicted gene flow to be negatively related to change in elevation between sampling sites. Using amplified DNA fragment length polymorphisms among tissue samples from paired sites in nine streams in the Hubbard Brook Watershed, New Hampshire, USA, we found that genetic distances between downstream and upstream sites were positively related to change in elevation over standardized 1-km distances. This pattern of isolation by slope elucidates controls on population connectivity in stream networks and underscores the potential for specific behaviors to affect the genetic structure of species at the landscape scale. More broadly, our results show the value of combining direct data on movement behavior and indirect indices to assess patterns and consequences of dispersal in spatially complex ecosystems

Linking Direct and Indirect Data on Dispersal: Isolation by Slope in a Headwater Stream Salamander

There is growing recognition of the need to incorporate information on movement behavior in landscape-scale studies of dispersal. One way to do this is by using indirect indices of dispersal (e.g., genetic differentiation) to test predictions derived from direct data on movement behavior. Mark–recapture studies documented upstream-biased movement in the salamander Gyrinophilus porphyriticus (Plethodontidae). Based on this information, we hypothesized that gene flow in G. porphyriticus is affected by the slope of the stream. Specifically, because the energy required for upstream dispersal is positively related to slope, we predicted gene flow to be negatively related to change in elevation between sampling sites. Using amplified DNA fragment length polymorphisms among tissue samples from paired sites in nine streams in the Hubbard Brook Watershed, New Hampshire, USA, we found that genetic distances between downstream and upstream sites were positively related to change in elevation over standardized 1-km distances. This pattern of isolation by slope elucidates controls on population connectivity in stream networks and underscores the potential for specific behaviors to affect the genetic structure of species at the landscape scale. More broadly, our results show the value of combining direct data on movement behavior and indirect indices to assess patterns and consequences of dispersal in spatially complex ecosystems

Dissolution of wollastonite during the experimental manipulation of Hubbard Brook Watershed 1

Powdered and pelletized wollastonite (CaSiO 3 ) was applied to an 11.8 ha forested watershed at the Hubbard Brook Experimental Forest (HBEF) in northern New Hampshire, U.S.A. during October of 1999. The dissolution of wollastonite was studied using watershed solute mass balances, and a 87 Sr/ 86 Sr isotopic tracer. The wollastonite ( 87 Sr/ 86 Sr = 0.70554) that was deposited directly into the stream channel began to dissolve immediately, resulting in marked increases in stream water Ca concentrations and decreases in the 87 Sr/ 86 Sr ratios from pre-application values of 0.872 mg/L and 0.72032 to values of ∼2.6 mg/L and 0.71818 respectively. After one calendar year, 401 kg of the initial 631 kg of wollastonite applied to the stream channel was exported as stream dissolved load, and 230 kg remained within the stream channel as residual CaSiO 3 and/or adsorbed on streambed exchange sites. Using previously established values for streambed Ca exchange capacity at the HBEF, the dissolution rate for wollastonite was found to be consistent with dissolution rates measured in laboratory experiments. Initially, Ca was released from the mineral lattice faster than Si, resulting in the development of a Ca-depleted leached layer on mineral grains. The degree of preferential Ca release decreased with time and reached stoichiometric proportions after ∼6 months. Using Sr as a proxy for Ca, the Ca from wollastonite dissolution can be accurately tracked as it is transported through the aquatic and terrestrial ecosystems of this watershed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42477/1/10533_2004_Article_5118334.pd

Comment: Cultural eutrophication of natural lakes in the United States is real and widespread

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An empirical assessment and comparison of species-based and habitat-based surrogates: a case study of forest vertebrates and large old trees

A holy grail of conservation is to find simple but reliable measures of environmental change to guide management. For example, particular species or particular habitat attributes are often used as proxies for the abundance or diversity of a subset of other taxa. However, the efficacy of such kinds of species-based surrogates and habitat-based surrogates is rarely assessed, nor are different kinds of surrogates compared in terms of their relative effectiveness. We use 30-year datasets on arboreal marsupials and vegetation structure to quantify the effectiveness of: (1) the abundance of a particular species of arboreal marsupial as a species-based surrogate for other arboreal marsupial taxa, (2) hollow-bearing tree abundance as a habitat-based surrogate for arboreal marsupial abundance, and (3) a combination of species- and habitat-based surrogates. We also quantify the robustness of species-based and habitat-based surrogates over time. We then use the same approach to model overall species richness of arboreal marsupials. We show that a species-based surrogate can appear to be a valid surrogate until a habitat-based surrogate is co-examined, after which the effectiveness of the former is lost. The addition of a species-based surrogate to a habitat-based surrogate made little difference in explaining arboreal marsupial abundance, but altered the co-occurrence relationship between species. Hence, there was limited value in simultaneously using a combination of kinds of surrogates. The habitat-based surrogate also generally performed significantly better and was easier and less costly to gather than the species-based surrogate. We found that over 30 years of study, the relationships which underpinned the habitat-based surrogate generally remained positive but variable over time. Our work highlights why it is important to compare the effectiveness of different broad classes of surrogates and identify situations when either species- or habitat-based surrogates are likely to be superior.This study has been funded by the Australian Research Council, Parks Victoria, the Department of Sustainability and Environment (and its predecessor departments), Melbourne Water, the Earthwatch Institute, the Thomas Foundation and Lindenmayer’s personal funds