A meta-analysis of the freshwater trophic cascade.

The generality of the trophic cascade has been an intensely debated topic among ecologists. We conducted a meta-analysis of 54 separate enclosure and pond experiments that measured the response of the zooplankton and phytoplankton to zooplanktivorous fish treatments. These results provide unequivocal support for the trophic cascade hypothesis in freshwater food webs. Zooplanktivorous fish treatments resulted in reduced zooplankton biomass and increased phytoplankton biomass. The trophic cascade was weakly dampened at the level of the phytoplankton. However, the response of the phytoplankton to the trophic cascade was highly skewed, with very strong responses in slightly more than one-third of the cases and weak responses in the others.

Handbook of the freshwater fishes of India : giving the characteristic peculiarities of all the species at present known, and intended as a guide to students and district officers / By R. Beavan.

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Receipt signed by Daniel Marsh, 1756 December 10

Handwritten receipt signed by Daniel Marsh acknowledging payment by John Sale of scholarship funds.

Payment order for Daniel Marsh, 1761 February 16

Handwritten order to John Sale to pay scholarship funds to Deacon Daniel Marsh, signed by Thomas Foxcroft and Charles Chauncey

Receipt signed by Daniel Marsh, 1770 December 17

Handwritten receipt signed by Deacon Daniel Marsh acknowledging payment of scholarship funds by John Sale.

Mr. Marsh's catalogue, ca. 1764

A half-page handwritten list of books with the author's surname, title, and location in the old Harvard Library, signed "Mr. Marsh." The list includes the note, "Shuckford's Connection is charged to you." The document is undated but presumably was created following the Harvard Hall Fire of 1764 as part of the College's efforts to inventory volumes that were spared because they were checked out at the time of the fire. Many of the books are listed in a charging record for Thomas Marsh recorded in a Harvard library account book (UAIII 50.15.60, Volume 1, Box 95), including "Shuckford's connection" which was charged to Marsh on September 23, 1763.

Diary of Thomas Marsh, 1751

Diary kept in an interleaved almanac from 1751. Entries in the diary are brief and sporadic, recording events including travel, visitors, weather, sermons heard, holidays, illnesses and deaths. Occasional expenses are noted, including ones for hay, cider, bottles, shoes, and doctoring. A few dates of college events are noted, including the semi-annual Corporation meeting and Commencement. On the last page is a list of student names, presumably those tutored by Marsh.

Intraspecific Behavioural Diversity in a Freshwater Zooplankton: A study of the fitness consequences of vertical migration behaviour for distinct morphs of Daphnia pulicaria

The literature on niche separation and coexistence between species is large, but there is widespread variation in behavioural strategy between individuals of the same species that has received much less attention. Understanding what maintains this diversity is important because intraspecific behavioural diversity can affect population dynamics and community interactions. Multiple behavioural strategies can arise either as phenotype-dependent ‘conditional strategies’, where phenotypic variation causes individuals to adopt different strategies for optimizing fitness, or as internally-independent ‘alternative strategies’, where multiple fitness peaks exist for individuals and strategic ‘choice’ remains plastic. Though intraspecific variation in stable phenotypes is known to maintain intraspecific behavioural diversity through conditional strategies, when internal conditions are highly plastic or reversible, it is not clear whether individual behaviours are maintained as conditional strategies, or as alternative strategies of equal fitness. In this study, I combine an observational and experimental approach to identify the likely mechanisms maintaining behavioural diversity between hemoglobin-rich and hemoglobin-poor morphs in a natural population of Daphnia pulicaria. In Round Lake, individuals with low hemoglobin migrate daily from the hypolimnion to the epilimnion, whereas individuals with high hemoglobin remain in the hypolimnion. Using high-resolution depth and time sampling, I discovered behavioural diversity both within and among hemoglobin phenotypes. I tested the role of hemoglobin phenotype in maintaining behavioural diversity using automated migration robots that move individuals across the natural environmental gradients in the lake. By measuring the fitness of each morph undergoing either a natural migration behaviour, or the migration of the opposite morph, I found that the fitness of hemoglobin rich and poor morphs in their natural behaviour does not differ, but that Hb-rich individuals can obtain equal fitness from either behaviour, while Hb-poor morphs suffer substantial drops in survivorship in the alternate migration behaviour. Thus, migration behaviour in this system exists as a conditional strategy for some individuals, and as alternative strategies of equal fitness for others. The results of this study suggest that individual limits in the expression of highly flexible internal conditions can reinforce intraspecific behavioural diversity. Few studies have measured the fitness consequences of switching migration strategies and this study provides a rare example in the field.