The effect of food availability, female culture-density and photoperiod on ephippia production in Daphnia magna Straus (Crustacea: Cladocera)

1983 ◽  
Vol 13 (1) ◽  
pp. 37-46 ◽  
Author(s):  
GARY R. CARVALHO ◽  
ROGER N. HUGHES
1988 ◽  
Vol 66 (2) ◽  
pp. 543-549 ◽  
Author(s):  
Scott A. Wissinger

I conducted two types of laboratory experiments with larvae of the dragonflies Libellula lydia and L. luctuosa. In one experiment I varied the number of Daphnia magna fed daily to these larvae to determine the effect of food availability on growth and survivorship. The time spent in each instar decreased dramatically with increased food availability, but the number of molts did not vary and the size at each molt was only slightly affected. Mortality was low in all but the lowest feeding treatment, despite 2- to 5-fold differences in instar duration. These results suggest that the number and size of instars are determinate in these species, and that starvation is an unlikely cause of larval mortality in nature. In a second experiment I used naturally co-occurring size combinations of L. lydia and L. luctuosa to determine how inter-odonate predation varies as a function of larval size difference. For both intra- and inter-specific combinations, (i) little or no predation occurred between larvae similar in size, (ii) some predation always occurred when larvae differed by more than two instars, and (iii) the number of larvae consumed increased dramatically as a function of instar difference. The proportional difference between the labial (gape) width of the larger instar and the head width of the smaller instar was a good estimator of inter-odonate predation rates across all instar and species combinations. Together these results suggest that the effects of inter-odonate competition and predation can be disentangled in the field by manipulating the instar structure of experimental populations.


2015 ◽  
Vol 63 (1) ◽  
pp. 12 ◽  
Author(s):  
Alexandra M. Leslie ◽  
Mathew Stewart ◽  
Elizabeth Price ◽  
Adam J. Munn

Daily torpor, a short-term reduction in body temperature and metabolism, is an energy-saving strategy that has been interpreted as an adaptation to unpredictable resource availability. However, the effect of food-supply variability on torpor, separately from consistent food restriction, remains largely unexamined. In this study, we investigated the effect of unpredictable food availability on torpor in stripe-faced dunnarts (Sminthopsis macroura). After a control period of ad libitum feeding, dunnarts were offered 65% of their average daily ad libitum intake over 31 days, either as a constant restriction (i.e. as equal amount of food offered each day) or as an unpredictable schedule of feed offered, varied daily as 0%, 30%, 60%, 100% or 130% of ad libitum. Both feeding groups had increased torpor-bout occurrences (as a proportion of all dunnarts on a given day) and torpor-bout frequency (average number of bouts each day) when on a restricted diet compared with ad libitum feeding, but torpor frequency did not differ between the consistently restricted and unpredictably restricted groups. Most importantly, torpor occurrence and daily bout frequency by the unpredictably restricted group appeared to change in direct association with the amount of food offered on each day; torpor frequency was higher on days of low food availability. Our data do not support the interpretation that torpor is a response to unpredictable food availability per se, but rather that torpor allowed a rapid adjustment of energy expenditure to manage daily fluctuations in food availability.


Hydrobiologia ◽  
1994 ◽  
Vol 287 (2) ◽  
pp. 207-214 ◽  
Author(s):  
Fernando Martínez-Jerónimo ◽  
Rafael Villaseñor ◽  
Guillermo Rios ◽  
Félix Espinosa

River Systems ◽  
2001 ◽  
Vol 12 (2-4) ◽  
pp. 425-440 ◽  
Author(s):  
W. Reckendorfer ◽  
H. Keckeis ◽  
V. Tutu ◽  
G. Winkler ◽  
H. Zornig ◽  
...  

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