Vegetation cover at the water surface best explains seed retention in open channels

An open channel is a channel where water flows with free water. In open channels, such as rivers (natural channels), channel parameters are very irregular. Damming the channel is a transition that serves to determine the height of the water surface along the channel, on this issue the author examines how water flows when through open channel with v-notch, rectangular and trapezoidal shapes in a stream. Based on the test results on 35° valve angle variations, the increase debit from the v-notch debit leads to a rectangular-notch debit of 23.63% and the largest decrease in debit from the rectangular notch to trapezodial-notch is 48.38%. In the valve angle variation 40°, the largest increase in debit between the v-notch discharge towards a rectangular-notch discharge of 18.64% and the decrease in the largest debit from rectangular-notch to trapezodial-notch at 45.31%. In the valve angle variation 45° the largest increase debit between the v-notch debit towards a rectangular-notch debit is 18.64% and the largest decrease debit from the rectangular notch to trapezodial-notch debit is 46.15%.

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Factors affecting escape behavior of Iberian green frogs (Rana perezi)

Canadian Journal of Zoology ◽

10.1139/z05-114 ◽

2005 ◽

Vol 83 (9) ◽

pp. 1189-1194 ◽

Cited By ~ 35

Author(s):

José Martín ◽

Juán José Luque-Larena ◽

Pilar López

Keyword(s):

Body Size ◽

Predation Risk ◽

Vegetation Cover ◽

Escape Response ◽

Water Surface ◽

Escape Behavior ◽

Theoretical Models ◽

Factors Affecting ◽

Approach Distance ◽

Rana Perezi

Theoretical models and empirical evidence suggest that prey should not flee immediately upon detecting an approaching predator, but instead should adjust their escape response to minimize the costs of flight. Similarly, after deciding to escape, animals should tend to adjust the magnitude and characteristics of their escape response according to the perceived level of predation risk. Although these hypotheses have been tested in some prey types, it remains for their applicability to a wider range of taxa to be ascertained and for a larger variety of microhabitat and environmental conditions to be considered. We simulated predator approaches to Iberian green frogs (Rana perezi Seoane, 1885) in the field. Frogs were approached while they were foraging alone at the edge of water, and they escaped by jumping into the water. Results showed that escape decisions of frogs are influenced by microhabitat variables and body size. Both the approach distance allowed to the predator and the distance jumped by the frogs in response to the approach were positively correlated with the initial distance of the frog from the water's edge; they were also dependent on vegetation cover at the edge of and in the water. Small frogs appeared to rely on crypsis more than large frogs and allowed shorter predator approach distances. They also remained still on the water surface after jumping more often than large frogs. We conclude that such flexibility in the escape response may allow frogs to reduce predation risk without incurring excessive costs.

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