Snakes : Ecology and Conservation by Stephen J.(Author) Mullin

Author:Stephen J.(Author) Mullin [Mullin, Stephen J.(Author)]
Language: eng
Format: mobi
Published: 2012-07-11T10:06:25.314812+00:00

256 S. J. Beaupre and L. E. Douglas

Fig. 9.1. An explicit representation of the relationships among operative environments, time and mass-energy allocations, physiological responses, and population dynamics. Operative temperatures on the left simultaneously infl uence tandem behavioral-time and mass-energy budgets. Operative environments determine constraints on time and energy allocations as well as apportionments of available time to competing behaviors (foraging, moving, resting or in retreat, mate searching, mate handling, gestating, ecdysis, and thermoregulation) and available mass-energy to competing functions (maintenance, activity, growth, reproduction, and storage). Each behavior-time or mass-energy allocation decision carries with it the risk of mortality and a fi tness pay-off. Critical responses such as FMR and BCI provide insights regarding changes in time and mass-energy allocations. These variables refl ect environmental infl uences on the life history of the organism. A, activity (physical and biochemical); BCI, body condition index; E, ecdysis; F, foraging; FMR, fi eld metabolic rate; G, growth; GE, gestation; L, locomotion; M, maintenance; MH, mate handling; MS, mate search; NAE, net assimilated energy; R, reproduction; RR, resting or in retreat; S, storage; T, thermoregulation; T body tempera-b,

ture. (Adapted from Dunham et al. 1989; Dunham 1993; O’Connor et al. 2006) A more readily measured bioenergetic variable, body condition, can be easily obtained from routine measurements upon capture and recapture.

Recently, body condition has been identifi ed as a useful variable for monitoring and understanding organismal function in the context of conservation (Stevenson and Woods 2006). Like FMR, body condition integrates two important aspects of mass-energy allocation: growth and storage (see Fig. 9.1).

As such, rises and declines in body condition are direct indicators of the mass-energy status of individuals. When food resource conditions are poor, body condition is expected to decline; when food resources are abundant, body condition should improve. Physiological variables, such as body condition and FMR may be especially useful in understanding the responses of uncommon, cryptic, or long-lived, infrequently reproducing species to environmental change. Such species may be less amenable to traditional numerical population analysis.

Snakes as Indicators and Monitors of Ecosystem Properties 257

600

400

200

BCI

0

-200

-400

-600

1994 1996 1998 2000 2002 2004 2006

Year

Fig. 9.2. Body condition index (BCI) of four representative adult male radiotagged Timber Rattlesnakes monitored from 1995 to 2006 in Madison Co., Arkansas. These individuals were chosen because of the long time frames over which each was monitored.

As an example of the rapid response and potential utility of physiological monitoring, consider the long-term studies of a Timber Rattlesnake population that has been under study in northwest Arkansas since 1995 (Wills and Beaupre 2000; Beaupre and Zaidan 2001; Cundall and Beaupre 2001; Zaidan and Beaupre 2003; Browning et al. 2005; Beaupre 2008). During routine mark-recapture and radiotelemetry studies, captured snakes are weighed and measured (snout vent length, SVL). In some cases, radiotagged animals are measured multiple times per year, over several years. A body condition index (BCI) is derived for each capture event. We defi ne BCI as the deviation in actual mass from predicted mass based on a nonlinear regression relating body mass to SVL. The nonlinear regression is fi t to the population length-mass data set, in this case W eight(g) = 21.

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.