Andrew R. Beet

ON LUMPING SPECIES IN FOOD WEBS

Species in community food webs are commonly aggregated or lumped on the basis of overlap in predators and prey. This note reports an unexpected result of lumping species in observed food webs and simulated food webs. The main result is that it is much easier to lump species in observed webs than in simulated webs. The reason is that there is much more overlap in predators and prey for species in observed webs than in simulated webs. This points to a fundamental deficiency in web assembly models that assume a random distribution of links.

Natural and unnatural oil slicks in the Gulf of Mexico

Abstract When wind speeds are 2–10 m s−1, reflective contrasts in the ocean surface make oil slicks visible to synthetic aperture radar (SAR) under all sky conditions. Neural network analysis of satellite SAR images quantified the magnitude and distribution of surface oil in the Gulf of Mexico from persistent, natural seeps and from the Deepwater Horizon (DWH) discharge. This analysis identified 914 natural oil seep zones across the entire Gulf of Mexico in pre‐2010 data. Their ∼0.1 µm slicks covered an aggregated average of 775 km2. Assuming an average volume of 77.5 m3 over an 8–24 h lifespan per oil slick, the floating oil indicates a surface flux of 2.5–9.4 × 104 m3 yr−1. Oil from natural slicks was regionally concentrated: 68%, 25%, 7%, and <1% of the total was observed in the NW, SW, NE, and SE Gulf, respectively. This reflects differences in basin history and hydrocarbon generation. SAR images from 2010 showed that the 87 day DWH discharge produced a surface‐oil footprint fundamentally different from background seepage, with an average ocean area of 11,200 km2 (SD 5028) and a volume of 22,600 m3 (SD 5411). Peak magnitudes of oil were detected during equivalent, ∼14 day intervals around 23 May and 18 June, when wind speeds remained <5 m s−1. Over this interval, aggregated volume of floating oil decreased by 21%; area covered increased by 49% (p < 0.1), potentially altering its ecological impact. The most likely causes were increased applications of dispersant and surface burning operations.

Marine protected areas in 'nonlinear' ecosystems.

The very large changes observed within marine communities, owing to excessive harvesting, have been attributed to switches between alternative stable states. Correspondingly large reductions in overall fishing effort are usually difficult to implement. For such ‘nonlinear’ ecosystems, introducing large marine protected areas, with low to zero harvesting, but without reduction in overall fishing effort, can give a marked increase in total yield of the depleted stocks. These increases, however, are still less than can be achieved by reducing fishing effort.

Patterns in abundance and growth of juvenile lobster, Homarus americanus

The combined effort of assessing abundance and measuring the time between settlement and recruitment is fundamental to forecasting future recruitment to the lobster fishery. This study represents the first monthly year-round sampling for abundance and in situ growth of juvenile lobster, Homarus americanus. Juvenile lobsters for repeated mark-recapture surveys were tagged in situ, so disturbance to the animals was minimal. From direct measurements of tagged individuals, lobsters up to 17 mm CL were estimated to be within their first two growing seasons. Some juveniles in the study area were recaptured up to four years later, indicating use of this nursery habitat for the first four to five years of benthic life. The purpose of sampling year-round was to detect patterns in abundance and identify the optimal time of year for sampling designed to determine trends in abundance. The relative abundances of young-of-the-year and later juvenile lobsters incorporated significant seasonal cycles (P 0.05), indicating no overall increase or decrease in abundance from 1993 to 1999. Year-round monthly sampling of the lobster population is producing valuable information on patterns in abundance and individual growth rates.

The human health effects of Florida Red Tide (FRT) blooms: An expanded analysis

Human respiratory and digestive illnesses can be caused by exposures to brevetoxins from blooms of the marine alga Karenia brevis, also known as Florida red tide (FRT). K. brevis requires macro-nutrients to grow; although the sources of these nutrients have not been resolved completely, they are thought to originate both naturally and anthropogenically. The latter sources comprise atmospheric depositions, industrial effluents, land runoffs, or submerged groundwater discharges. To date, there has been only limited research on the extent of human health risks and economic impacts due to FRT. We hypothesized that FRT blooms were associated with increases in the numbers of emergency room visits and hospital inpatient admissions for both respiratory and digestive illnesses. We sought to estimate these relationships and to calculate the costs of associated adverse health impacts. We developed environmental exposure-response models to test the effects of FRT blooms on human health, using data from diverse sources. We estimated the FRT bloom-associated illness costs, using extant data and parameters from the literature. When controlling for resident population, a proxy for tourism, and seasonal and annual effects, we found that increases in respiratory and digestive illnesses can be explained by FRT blooms. Specifically, FRT blooms were associated with human health and economic effects in older cohorts (≥55 years of age) in six southwest Florida counties. Annual costs of illness ranged from

On an Early Result on Stability and Complexity

60,000 to

On Uncertain Sightings and Inference about Extinction

700,000 annually, but these costs could exceed

Testing for Shifts in the Vertical Distribution of Plankton Using a Robust Kolmogorov-Smirnov Like Statistic

1.0 million per year for severe, long-lasting FRT blooms, such as the one that occurred during 2005. Assuming that the average annual illness costs of FRT blooms persist into the future, using a discount rate of 3%, the capitalized costs of future illnesses would range between

A test for a shift in the boundary of the geographical range of a species

2 and 24 million.

Testing for a shift in a species boundary

In a recent paper, Solow and Beet (1998) showed that the links in observed community food webs are not randomly distributed. Instead, these webs appear to be lumpy in the sense of being composed of relatively tightly connected compartments, with relatively loose connections between compartments. In light of this finding, the question naturally arises as to why food webs have this structure. One possibility is that lumpiness contributes to the stability of the underlying dynamic predator-prey system. The relationship between the size and structure of an ecosystem and its stability and other dynamical properties has been a central issue in ecology for 120 yr (May 1974; Pimm 1982; Logofet 1993). In an early, widely cited, and much imitated contribution, Gardner and Ashby (1970) performed a simulation experiment of the way in which species number and connectance affects the probability of stability under a random food-web model. Referring to the results of this study, which are described in more detail later, and to related work by McMurtrie (1975), May (1972) pointed out that strictly compartmentalized food webs in which the links are confined to unconnected blocks of species are more stable than those in which the links are more uniformly distributed throughout the web. This could explain the structural features of observed food webs found by Solow and Beet (1998). However, in a