Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

Citation classic - optimal foraging - a selective review of theory and tests

Ocean-going ships carry, as ballast, seawater that is taken on in port and released at subsequent ports of call. Plankton samples from Japanese ballast water released in Oregon contained 367 taxa. Most taxa with a planktonic phase in their life cycle were found in ballast water, as were all major marine habitat and trophic groups. Transport of entire coastal planktonic assemblages across oceanic barriers to similar habitats renders bays, estuaries, and inland waters among the most threatened ecosystems in the world. Presence of taxonomically difficult or inconspicuous taxa in these samples suggests that ballast water invasions are already pervasive.

https://science.sciencemag.org/content/sci/261/5117/78.full.pdf

Ecological Roulette: The Global Transport of Nonindigenous Marine Organisms

W. C. Allee brought attention to the possibility of a positive relationship between aspects of fitness and population size over fifty years ago. This phenomenon, frequently termed the Allee effect, has been the focus of increased interest over the past two decades in the light of concerns over conservation and the problems of rarity. Use of the term suffers from the absence of a clear definition however, with the result that Allee effects are frequently thought to involve only a narrow range of phenomena and are often overlooked altogether. We propose a definition for the effect and attempt to resolve the major issues underlying the confusion surrounding this term.

/pdf/what-is-the-allee-effect-2335v5pk8a.pdf

What Is the Allee Effect

1. Freshwater systems are losing biodiversity at a rapid rate, yet we know little about the functional role of most of this biodiversity. The ecosystem roles of freshwater burrowing bivalves have been particularly understudied. Here we summarize what is known about the functional role of burrowing bivalves in the orders Unionoida and Veneroida in lakes and streams globally.

2. Bivalves filter phytoplankton, bacteria and particulate organic matter from the water column. Corbicula and sphaeriids also remove organic matter from the sediment by deposit feeding, as may some unionids. Filtration rate varies with bivalve species and size, temperature, particle size and concentration, and flow regime.

3. Bivalves affect nutrient dynamics in freshwater systems, through excretion as well as biodeposition of faeces and pseudofaeces. Excretion rates are both size and species dependent, are influenced by reproductive stage, and vary greatly with temperature and food availability.

4. Bioturbation of sediments through bivalve movements increases sediment water and oxygen content and releases nutrients from the sediment to the water column. The physical presence of bivalve shells creates habitat for epiphytic and epizoic organisms, and stabilizes sediment and provides refugia for benthic fauna. Biodeposition of faeces and pseudofaeces can alter the composition of benthic communities.

5. There is conflicting evidence concerning the role of resource limitation in structuring bivalve communities. Control by bivalves of primary production is most likely when their biomass is large relative to the water volume and where hydrologic residence time is long. Future studies should consider exactly what bivalves feed upon, whether feeding varies seasonally and with habitat, and whether significant overlap in diet occurs. In particular, we need a clearer picture of the importance of suspension versus deposit feeding and the potential advantages and tradeoffs between these two feeding modes.

6. In North America, native burrowing bivalves (Unionidae) are declining at a catastrophic rate. This significant loss of benthic biomass, coupled with the invasion of an exotic burrowing bivalve (Corbicula), may result in large alterations of ecosystem processes and functions.

The functional role of burrowing bivalves in freshwater ecosystems

T h ~ r t y years ago Thorson (1966 Neth J Sea Res 3 267-293) calculated that juvenile mortallty in manne bivalves could exceed 98 6 % Subsequently juvenile mortality rates have been assumed to be high and to influence the evolution of life history traits However there have been no attempts to establish whether high luvenile mortality IS common or to determine if lnterspecific trends in l uven~ le mortality exist To address t h ~ s Issue we revlewed 30 studies of age-specif~c mortality among bivalves, gastropods, barnacles ascid~ans, bryozoans and echinoderms High juvenile mortality is widespread among benthic marlne Invertebrates with 20 of the 30 s t u d ~ e s reporting levels of luven ~ l e mortal~ty > 9 0 % Mortal~ty is part~cularly h ~ g h during the first moments of luvenile life and can exceed 30% during the f~ r s t day Pool~ng surv~vorship data from all species revealed a general trend with survivorsh~p decreasing exponentially during the first days or weeks of juvenile life until by the age of 4 mo, virtually all cohorts were reduced to <20% of their ~nit ial numbers ~nortality remained low thereafter We suggest that extreme vulnerability at the onset of luvenile life is a shared t r a ~ t hat is largely responsible for the surv~vorship trend Natural variation within this trend would be largely due to variation in intensity of mortality factors Predation and desiccation are well-documented causes of juvenile mortality, but the current lack of data on factors such as ultraviolet radiation, diseases and lnternal causes (energy depletion developmental and physiological defects) precludes a ranking of factors as se lec t~ve pressures Methods used to quantify juvenile mortality vary cons~derably in the level of resolution they can achieve wth in the early luvenile perlod Studies of early juvenile mortality should ideally monitor the fate of individuals from the onset of luvenile l ~ f e using sampling intervals 51 d Mapping and imaging techniques can provide accurate results for sess~le organisms, whereas mark and recapture can be effective for motile animals w ~ t h l ~ m ~ t e d dispersal Early juvenile mortahty has been shown to influence population abundance and distnbution as well as community structure Juvenile mortality is also expected to be an important determinant of age at matunty, but only among species ma tu r~ng within 4 mo of postlarval l ~ f e since mortality remalns low after the age of 4 mo A compilation of data on age at first reproduction In 92 species revealed a b~modal grouping of species 22% of species matunng within 45 d after beg inn~ng luvenile life and 60% maturlng after at least 1 yr The influence of luven~le mortality on age at inaturlty will d~ f fe r substantially among these 2 groups and will therefore not be equal or directly comparable among all species Given the magnitude of early juvenile mortality and the similarities in mortality patterns across diverse taxa and habitats a better understanding of early ]uvenile mortality should help researchers to understand how population parameters are regulated and help elucidate the s~gnificance of traits that characterize populations and specles

/pdf/juvenile-mortality-in-benthic-marine-invertebrates-3a05welxea.pdf

Juvenile mortality in benthic marine invertebrates

Marine invertebrate larvae swim by using cilia or muscles, or a combination of these. The effectiveness of cilia as locomotory organelles diminishes with increasing body size above 1 mm. Thus, larv...

Locomotion of marine invertebrate larvae: a review

Many organisms reproduce by releasing gametes into the environment. How- ever, very little is known about what proportion of released eggs become fertilized. We examined the influence of spawning group size, degree of aggregation, position within an aggregation, and water flow, on in situ fertilization in the sea urchin Strongylocentrotus franciscanus. This study was conducted at a depth of 9 m on the west coast of Vancouver Island, British Columbia, Canada. Males were simulated by syringes filled with sperm; females were simulated by sperm-permeable containers filled with eggs. Individuals were placed 0.5 or 2.0 m apart within a 2 x 2 or 4 x 4 (group size of 4 or 16 individuals) experimental array. The results indicate that group size, degree of aggregation, position within a spawning group, and water flow all affect fertilization success. Fertilization success ranged from 0 to 82%. Increases in group size and aggregation, decreases in flow velocity, and central and downstream positions within an aggregation all lead to increases in fertil- ization success. Thus, individual reproductive performance is dependent on, and highly sensitive to, population parameters and environmental conditions.

https://www.jstor.org/stable/info/1938736

How Distribution and Abundance Influence Fertilization Success in the Sea Urchin Strongylocentotus Franciscanus

Determining fertilization success of free spawning organisms in the field requires knowledge of how eggs and sperm interact under varying encounter fre- quencies and durations. In the laboratory, we investigated the relative influence of sperm concentration, egg con- centration, sperm-egg contact time, and sperm age on fer- tilization in the sea urchin Strongylocentrotus francis- canus. Our results indicated that sperm concentration, sperm-egg contact time, sperm age, and individual vari- ability were sequentially the most important factors in- fluencing fertilization success. Egg concentration was not significant over the range tested. A theoretical model of fertilization (Vogel-Czihak-Chang-Wolf model) was used to estimate the two rate constants of fertilization kinetics: the rate constant of sperm-egg encounter and rate constant of fertilization. This model explained 9 1% of the variation in fertilization success, provided estimates of the rate con- stants involved in fertilization, and indicated the propor- tion (3%) of sperm-egg contacts that result in fertilization. Estimates of sperm swimming velocity and egg diameter were used to independently calculate the rate of sperm- egg encounter and confirm the predictions of the model. This model also predicts the non-significant effect of egg concentration on fertilization success found empirically.

/pdf/kinetics-of-fertilization-in-the-sea-urchin-3b9vkoa2aq.pdf

Kinetics of Fertilization in the Sea Urchin Strongylocentrotus franciscanus: Interaction of Gamete Dilution, Age, and Contact Time.

Drifting and dispersal of small bivalves and gastropods with direct development

In nature, the marine bryozoan, Bugula pacifica, is consistently the ‘loser’ when competing for space with the compound ascidian, Diplosoma macdonaldi. We provide laboratory evidence to show that Bugula larvae will delay settling in either ‘Diplosoma-conditioned water’ or an alcohol Diplosoma extract. It is reasoned that the delay response is elicited by an inhibitory factor released continually from Diplosoma. This response is reversible, non-pathological, and species specific. The possible ecological significance of larval avoidance behavior in this and other communities is discussed.

Fu-Shiang Chia

Papers

Locomotion of marine invertebrate larvae: a review

How Distribution and Abundance Influence Fertilization Success in the Sea Urchin Strongylocentotus Franciscanus

Kinetics of Fertilization in the Sea Urchin Strongylocentrotus franciscanus: Interaction of Gamete Dilution, Age, and Contact Time.

Drifting and dispersal of small bivalves and gastropods with direct development

Laboratory evidence for delay of larval settlement in response to a dominant competitor