Global warming and flowering times in Thoreau's Concord: a community perspective

As a result of climate change, many plants are now flowering measurably earlier than they did in the past. However, some species' flowering times have changed much more than others. Data at the community level can clarify the variation in flowering responses to climate change. In order to determine how North American species' flowering times respond to climate, we analyzed a series of previously unstudied records of the dates of first flowering for over 500 plant taxa in Concord, Massachusetts, USA. These records began with six years of observations by the famous naturalist Henry David Thoreau from 1852 to 1858, continued with 16 years of observations by the botanist Alfred Hosmer in 1878 and 1888-1902, and concluded with our own observations in 2004, 2005, and 2006. From 1852 through 2006, Concord warmed by 2.4 degrees C due to global climate change and urbanization. Using a subset of 43 common species, we determined that plants are now flowering seven days earlier on average than they did in Thoreau's times. Plant flowering times were most correlated with mean temperatures in the one or two months just before flowering and were also correlated with January temperatures. Summer-flowering species showed more interannual variation in flowering time than did spring-flowering species, but the flowering times of spring-flowering species correlated more strongly to mean monthly temperatures. In many cases, such as within the genera Betula and Solidago, closely related, co-occurring species responded to climate very differently from one another. The differences in flowering responses to warming could affect relationships in plant communities as warming continues. Common St. John's wort (Hypericum perforatum) and highbush blueberry (Vaccinium corymbosum) are particularly responsive to changes in climate, are common across much of the United States, and could serve as indicators of biological responses to climate change. We discuss the need for researchers to be aware, when using data sets involving multiple observers, of how varying methodologies, sample sizes, and sampling intensities affect the results. Finally, we emphasize the importance of using historical observations, like those of Thoreau and Hosmer, as sources of long-term data and to increase public awareness of biological responses to climate change.     

Managing plant population spread: prediction and analysis using a simple model

Models can be used to direct the management of population spread for the control of invasives or to encourage species of conservation value. Analytical models are attractive because of their theoretical basis and limited data requirements, but there is concern that their simplicity may limit their practical utility. We address the applied use of simple models in a study of a declining annual herb, Rhinanthus minor. We parameterized a population-spread model using field data on demography and dispersal for four management systems: grazed only (GR), hay-cut once (H1), hay-cut twice (H2), and hay-cut with autumn grazing (HG). Within a replicated experiment we measured spread rates of introduced R. minor populations over eight years. The modeled and measured spread rates were very similar in terms of both patterns of management effects and absolute values, so that in both cases HG > H2, H1 > GR. The treatments affected both dispersal and demography (establishment and survival) and so we used decomposition approaches to analyze the major causes of differences in population spread. Increased dispersal under hay-cutting was more important than demographic changes and accounted for approximately 70% of the differences in spread rate between the hay-cut and grazed-only treatments. Furthermore, management effects on the tail of the dispersal curve were by far the most critical in governing spread. This study suggests that simple models can be used to inform practical conservation management, and we demonstrate straightforward uses of our model to predict the impacts of different management strategies. While simple models can give accurate projections, we emphasize that they must be parameterized with high-quality data gathered at the appropriate spatial scale.     

The influence of contrasting life history traits and oceanic processes on genetic structuring of rabbitfish populations Siganus argenteus and Siganus fuscescens along the eastern Philippine coasts

Genetic variability and structuring of rabbitfish populations with contrasting life histories, Siganus argenteus and Siganus fuscescens were determined using allozyme analysis. A total of 13–14 polymorphic loci were examined from samples collected in 2002 and 2003 from eight reefs representing 25 populations north (Kuroshio Current) and south (Mindanao Current) of the bifurcation of the North Equatorial Current along the eastern Philippine coast. S. fuscescens populations (H _OBS = 0.085) showed higher heterozygosity than S. argenteus (H _OBS = 0.053), consistent with predictions of the neutral theory for demersal egg spawners compared to pelagic egg spawners. The generally lower genetic variability of Kuroshio populations may be due to greater environmental disturbance affecting larval mortality and recruitment success. There was no significant overall population genetic structuring for S. argenteus (F _ST = 0.01485, P > 0.05) compared to S. fuscescens (F _ST = 0.03275, P < 0.05). The latter species showed highly significant genetic structuring among Kuroshio and Mindanao Current populations in both 2002 and 2003 (F _CT = 0.08120, P < 0.05; F _CT = 0.07500, P < 0.05, respectively), as well as among populations within regions. This conforms to expectations of correlations between observed population genetic structure and life history features related to dispersal potential and gene flow. However, there were significant temporal (i.e., 2002 vs. 2003 samples) genetic variations for both S. fuscescens (F _CT = 0.08542, P < 0.05) and S. argenteus (F _CT = 0.06330, P < 0.05), which may reflect interannual variability in recruitment success. Differences in population spatial genetic patterns between the two reef fish species suggest that broad scale physical factors (e.g. NEC bifurcation) and regional environmental perturbations (e.g. incidence of typhoons) affect population genetic structure of sympatric congeneric species with different life histories differently. Finer scale ecological processes, which affect larval dispersal and recruitment (e.g., local hydrographic features, distribution of habitats), particularly in the Mindanao Current region, exert more influence on structuring populations of S. fuscescens.     

Endogenous swimming rhythms underlying the spawning migration of the blue crab, Callinectes sapidus: ontogeny and variation with ambient tidal regime

Spawning female blue crabs, Callinectes sapidus, use ebb-tide transport (ETT) to migrate seaward. In estuaries with semi-diurnal tides, ETT in ovigerous blue crabs is driven by a circatidal rhythm in vertical swimming in which crabs ascend into the water column during ebb tide. The ontogeny of this rhythm was examined by monitoring swimming behavior of females before the pubertal molt, females that had recently undergone the molt but had not yet produced a clutch of eggs, and ovigerous females from an estuary with strong semi-diurnal tides. To assess variation in swimming rhythms with ambient tidal regime, swimming rhythms of ovigerous females from semi-diurnal (Beaufort, North Carolina), diurnal (St. Andrew Bay, Florida), and non-tidal (South River, North Carolina) estuaries were compared. Experiments were conducted during the summers of 2006–2008. Female crabs prior to oviposition had variable endogenous swimming rhythms (circadian, circatidal, or circalunidian). Ovigerous females from estuaries with semi-diurnal and diurnal tides had pronounced circatidal or circalunidian rhythms with swimming during the time of ambient ebb tide. Swimming rhythms of several ovigerous crabs switched between circatidal and circalunidian during the ~5-day observation period. Ovigerous crabs from a non-tidal estuary had a circadian rhythm with vertical swimming around the time of sunset. These results suggest that, while endogenous swimming rhythms are present in some female blue crabs prior to oviposition, rapid seaward movement via ETT in tidal estuaries begins following oviposition of the first clutch of eggs.     

Sampling animal association networks with the gambit of the group

Ecologists increasingly use network theory to examine animal association patterns. The gambit of the group (GoG) is a simple and useful assumption for accumulating the data necessary for a network analysis. The gambit of the group implies that each animal in a group is associating with every other individual in that group. Sampling is an important issue for networks in wild populations collected assuming GoG. Due to time, effort, and resource constraints and the difficulty of tracking animals, sampled data are usually a subset of the actual network. Ecologists often use association indexes to calculate the frequency of associations between individuals. These indexes are often transformed by applying a filter to produce a binary network. We explore GoG sampling using model networks. We examine assortment at the level of the group by a single dichotomous trait, along with many other network measures, to examine the effect of different sampling regimes, and choice of filter on the accuracy and precision with which measures are estimated. We find strong support for the use of weighted, rather than filtered, network measures and show that different filters have different effects depending on the nature of the sampling. We make several practical recommendations for ecologists planning GoG sampling.     

Biosecurity threats: the design of surveillance systems,based on power and risk

We consider the problem of designing a surveillance system to detect a broad range of invasive species across a heterogeneous sampling frame. We present a model to detect a range of invertebrate invasives whilst addressing the challenges of multiple data sources, stratifying for differential risk, managing labour costs and providing sufficient power of detection. We determine the number of detection devices required and their allocation across the landscape within limiting resource constraints. The resulting plan will lead to reduced financial and ecological costs and an optimal surveillance system.     

A stage-structured, Aedes albopictus population model

Aedes albopictus has been the fastest spreading invasive animal species in the world from the mid-1980s until the mid-2000s. In areas it infests, it disrupts native mosquito ecology and can potentially vector up to 21 viruses. To better understand the population dynamics of this species, we created a temperature dependent population model. A stage-structured model was chosen to allow each life-stage to have different temperature dependent mortality and development rates, and each stage was modeled with an ordinary differential equation. Model parameters and distributions were based upon literature values. Initially, a basic model was constructed. This model then had parameters that were forced based upon daily average temperatures. Several criteria were used to evaluate the model, including a comparison to field data from Lubbock, TX. In a stochastic version of the model, a 95% confidence limit contained 70.7% of the field data points. Based upon these results, we feel reasonably confident that we have captured the role of temperature in driving the population dynamics of Ae. albopictus.     

Drivers of inter-year variability of plant production and decomposers across contrasting island ecosystems

Despite the likely importance of inter-year dynamics of plant production and consumer biota for driving community- and ecosystem-level processes, very few studies have explored how and why these dynamics vary across contrasting ecosystems. We utilized a well-characterized system of 30 lake islands in the boreal forest zone of northern Sweden across which soil fertility and productivity vary considerably, with larger islands being more fertile and productive than smaller ones. In this system we assessed the inter-year dynamics of several measures of plant production and the soil microbial community (primary consumers in the decomposer food web) for each of nine years, and soil microfaunal groups (secondary and tertiary consumers) for each of six of those years. We found that, for measures of plant production and each of the three consumer trophic levels, inter-year dynamics were strongly affected by island size. Further, many variables were strongly affected by island size (and thus bottom-up regulation by soil fertility and resources) in some years, but not in other years, most likely due to inter-year variation in climatic conditions. For each of the plant and microbial variables for which we had nine years of data, we also determined the inter-year coefficient of variation (CV), an inverse measure of stability. We found that CVs of some measures of plant productivity were greater on large islands, whereas those of other measures were greater on smaller islands; CVs of microbial variables were unresponsive to island size. We also found that the effects of island size on the temporal dynamics of some variables were related to inter-year variability of macroclimatic variables. As such, our results show that the inter-year dynamics of both plant productivity and decomposer biota across each of three trophic levels, as well as the inter-year stability of plant productivity, differ greatly across contrasting ecosystems, with potentially important but largely overlooked implications for community and ecosystem processes.     

Catastrophe and the life span of coral reefs

A strong earthquake in the western Caribbean in 2009 had a catastrophic impact on uncemented, unconsolidated coral reefs in the central sector of the shelf lagoon of the Belizean barrier reef. In a set of 21 reef sites that had been observed prior to the earthquake, the benthic assemblages of 10 were eradicated, and one was partially damaged, by avalanching of their slopes. Ecological dynamics that had played out over the previous 23 years, including the mass mortalities of two sequentially dominant coral species and a large increase in the cover of an encrusting sponge, were instantaneously rendered moot in the areas of catastrophic reef-slope failure. Because these prior dynamics also determined the benthic composition and resilience of adjacent sections of reef that remained intact, the history of disturbance prior to the earthquake will strongly influence decadal-scale recovery in the failed areas. Geological analysis of the reef framework yielded a minimum return time of 2000-4000 years for this type of high-amplitude event. Anthropogenic degradation of ecosystems must be viewed against the backdrop of long-period, natural catastrophes, such as the impact of strong earthquakes on uncemented, lagoonal reefs.     

Geologic processes influence the effects of mining on aquatic ecosystems

Geologic processes strongly influence water and sediment quality in aquatic ecosystems but rarely are geologic principles incorporated into routine biomonitoring studies. We test if elevated concentrations of metals in water and sediment are restricted to streams downstream of mines or areas that may discharge mine wastes. We surveyed 198 catchments classified as "historically mined" or "unmined," and based on mineral-deposit criteria, to determine whether water and sediment quality were influenced by naturally occurring mineralized rock, by historical mining, or by a combination of both. By accounting for different geologic sources of metals to the environment, we were able to distinguish aquatic ecosystems limited by metals derived from natural processes from those due to mining. Elevated concentrations of metals in water and sediment were not restricted to mined catchments; depauperate aquatic communities were found in unmined catchments. The type and intensity of hydrothermal alteration and the mineral deposit type were important determinants of water and sediment quality as well as the aquatic community in both mined and unmined catchments. This study distinguished the effects of different rock types and geologic sources of metals on ecosystems by incorporating basic geologic processes into reference and baseline site selection, resulting in a refined assessment. Our results indicate that biomonitoring studies should account for natural sources of metals in some geologic environments as contributors to the effect of mines on aquatic ecosystems, recognizing that in mining-impacted drainages there may have been high pre-mining background metal concentrations.