Little lasting impact of the Paleocene-Eocene Thermal Maximum on shallow marine molluscan faunas.

Global warming, acidification, and oxygen stress at the Paleocene-Eocene Thermal Maximum (PETM) are associated with severe extinction in the deep sea and major biogeographic and ecologic changes in planktonic and terrestrial ecosystems, yet impacts on shallow marine macrofaunas are obscured by the incompleteness of shelf sections. We analyze mollusk assemblages bracketing (but not including) the PETM and find few notable lasting impacts on diversity, turnover, functional ecology, body size, or life history of important clades. Infaunal and chemosymbiotic taxa become more common, and body size and abundance drop in one clade, consistent with hypoxia-driven selection, but within-clade changes are not generalizable across taxa. While an unrecorded transient response is still possible, the long-term evolutionary impact is minimal. Adaptation to already-warm conditions and slow release of CO2 relative to the time scale of ocean mixing likely buffered the impact of PETM climate change on shelf faunas.

Effects of dams on downstream molluscan predator-prey interactions in the Colorado River estuary.

River systems worldwide have been modified for human use and the downstream ecological consequences are often poorly understood. In the Colorado River estuary, where upstream water diversions have limited freshwater input during the last century, mollusc remains from the last several hundred years suggest widespread ecological change. The once abundant clam Mulinia modesta has undergone population declines of approximately 94% and populations of predators relying on this species as a food source have probably declined, switched to alternative prey species or both. We distinguish between the first two hypotheses using a null model of predation preference to test whether M. modesta was preyed upon selectively by the naticid snail, Neverita reclusiana, along the estuary's past salinity gradient. To evaluate the third hypothesis, we estimate available prey biomass today and in the past, assuming prey were a limiting resource. Data on the frequency of drill holes-identifiable traces of naticid predation on prey shells-showed several species, including M. modesta, were preferred prey. Neverita reclusiana was probably able to switch prey. Available prey biomass also declined, suggesting the N. reclusiana population probably also declined. These results indicate a substantial change to the structure of the benthic food web. Given the global scale of water management, such changes have probably also occurred in many of the world's estuaries.

Abundance is not enough: the need for multiple lines of evidence in testing for ecological stability in the fossil record.

The fossil record is the only source of information on the long-term dynamics of species assemblages. Here we assess the degree of ecological stability of the epifaunal pterioid bivalve assemblage (EPBA), which is part of the Middle Devonian Hamilton fauna of New York--the type example of the pattern of coordinated stasis, in which long intervals of faunal persistence are terminated by turnover events induced by environmental change. Previous studies have used changes in abundance structure within specific biofacies as evidence for a lack of ecological stability of the Hamilton fauna. By comparing data on relative abundance, body size, and predation, indexed as the frequency of unsuccessful shell-crushing attacks, of the EPBA, we show that abundance structure varied through time, but body-size structure and predation pressure remained relatively stable. We suggest that the energetic set-up of the Hamilton fauna's food web was able to accommodate changes in species attributes, such as fluctuating prey abundances. Ecological redundancy in prey resources, adaptive foraging of shell-crushing predators (arising from predator behavioral or adaptive switching in prey selection in response to changing prey abundances), and allometric scaling of predator-prey interactions are discussed as potential stabilizing factors contributing to the persistence of the Hamilton fauna's EPBA. Our study underscores the value and importance of multiple lines of evidence in tests of ecological stability in the fossil record.

Minimal-memory bit-vector architecture for computational mathematical morphology using subspace projections.

Computational mathematical morphology (CMM) is a nonlinear filter representation particularly amenable to real-time image processing. A windowed, translation-invariant filter is represented by a set of less-than-or-equal decisions that are executed by a parallel arrangement of comparators. In the state-of-the-art implementation, each pixel value of a windowed observation is indexed into separate lookup tables to retrieve a set of bit vectors which are "anded" together to produce a bit vector with a unique nonzero bit. The position of that bit is used to look up a filter value in a table. The number of stored bit vectors is proportional to the number of image gray levels. An architecture for CMM is presented that uses a minimal number of bit vectors so that required memory is less sensitive to the number of gray levels. The number of pixels in the observation window is the dimension of the image space. In the proposed architecure, basis elements are projected to subspaces of the image space and only bit vectors unique to each subspace are stored. Each projection corresponds to a subspace partition. Filter memory is greatly reduced by using intermediate lookup tables to map observations to unique bit vectors. We investigate two possible projection strategies: A fixed, singleton architecture, in which each subspace is one dimension, and a minimal architecture, in which a large number of subspace projections are searched for, one with minimal memory. Insensitivity to the number of gray levels is demonstrated through simulated, random-image space tessellations. We also present memory savings in a digital photocopier application.

Bit vector architecture for computational mathematical morphology.

A real-time, compact architecture is presented for translation-invariant windowed nonlinear discrete operators represented in computational mathematical morphology. The architecture enables output values to be computed in a fixed number of operations and thus can be pipelined. Memory requirements for an operator are proportional to its basis size. An operator is implemented by three steps: 1) each component of a vector observation is used as an index into a table of bit vectors; 2) all retrieved bit vectors are "ANDed" together; and 3) the position of the first nonzero bit is used as an index to a table of output values. Computational mathematical morphology is described, the new architecture is illustrated through examples, and formal proofs are given. A modification of the basic architecture provides for increasing operators.