A Comparison on the Flight-Initiation Distance as Escape Response of Rhinella Marina from Two Sites in Laguna

A comparison on the Flight-Initiation Distance as escape response of Rhinella marina from two sites in Laguna- University of the Philippines Los Banos campus, Sta. Maria1 

Abarintos, Christine Hazel

Alvarez, Maria Lemie

Cleofe, Andrew

Leal, Tisha Nicole

Group 3 Sec. U-1L

November 21, 2018

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                     1A scientific paper submitted in partial fulfilment of the requirements in Zoology 122 laboratory under Prof. Eleanor Aurellado, 1st sem., 2018-2019.

ABSTRACT

        The Flight-Initiation Distance as an escape response of Rhinella marina from two sites, UPLB campus and Sta. Maria, Laguna, was determined. Twenty three samples from each site were studied.  To measure the FID, an initial distance of three meters was maintained before approaching the sample on a constant speed of 0.5 m/s. The final position of the researcher and the initial position of the sample was measured upon observing escape behaviour. Results showed that the area where samples were studied highly correlates the FID of the toads. Sta. Maria, a rural area in Laguna where human disturbance is less showed higher FID values than UPLB campus samples where human disturbance is expected to be high. It can be concluded that the human induced disturbance from each sites greatly affected the FID of the samples, such that higher human disturbance would result lower FID values due to species being less sensitive to disturbance. Moreover, the toads from UPLB are more habituated to the presence of humans.

INTRODUCTION

Optimal Escape Theory predicts that prey initiate escape attempts at a distance that maximizes the prey’s expected lifetime fitness after the encounter (Cooper and Frederick, 2007). Optimal escape theory was recently developed to predict Flight-Initiation Distance, which is the distance separating a prey from an approaching predator, based on effects of the prey’s initial fitness, predation risk, and costs of escaping on expected fitness after the encounter (Cooper and Frederick, 2007). These costs of escaping correspond to benefits that might be obtained by not fleeing but must be forgone to escape. The optimal escape model assumes that a prey has detected an approaching predator and does not flee immediately but monitors its approach (Cooper, 2008). Considering the effects of starting distance, which is the distance from prey when the predator begins to approach, let to recognition of a zone beyond which prey do not detect a predator or may detect it but not react because risk is at cackground level (Blumstein, 2003; Stankowich and Coss, 2006). In optimal escape theory, an encounter cannot begin beyond this distance. Prey can make more profitable escape decisions under the optimal escape model (Cooper and Frederick, 2007).

The optimal escape model has the advantages of permitting the prey to make better escape decisions, allowing the prey to accept being killed if benefits to lifetime fitness are large enough and being mathematically explicit (Cooper and Frederick, 2007). Because it is explicit, it can be modified to apply in situations not considered in its original form. Because effects of fleeing and not fleeing are specified and the prey's initial fitness is taken into account, optimal escape theory provides a conceptual framework for understanding how single factors that alter multiple traits relevant to escape in complex ways may alter escape decisions.

Flight initiation distance is predicted to increase as predation risk increases (Ydenberg and Dill, 1986; Cooper and Frederick, 2007). It decreases as opportunity cost, the loss of benefit that might be gained if the prey does not flee, increases. Other factors that affect escape decisions are the prey’s fitness at the beginning of the predator-prey encounter (initial fitness) and escape costs, which are costs due to energetic expenditure and risk of injury due to escape efforts.

Cane toads (Rhinella marina) are highly invasive anurans, native to South and Central America. Their invaded range extends through many tropical areas worldwide. When approached by garter snakes, toads crouch and usually become immobile; visual stimuli are required to elicit these responses. Toads contacted by the main trunk (body) of a snake usually remain immobile and thus undetected by the snake; toads contacted by the head of a snake usually respond by hopping away and crouching again. The survival rates of toads exhibiting the species-typical response (i.e., hopping when contacted by the head of a snake and remaining immobile when contacted by the body of a snake) are significantly higher than those that respond with the alternative behaviour (Muller, 2018).

As for human stimuli, one can approach to within a few feet of a green frog of bullfrog and make all sorts of noises without causing it to give any signs of uneasiness. Just as soon, however, as a quick movement is made by the observer the animal jumps (Courtis, 2018).

Location of origin has a significant effect in the anti-predator tactics of toads (Hudson, 2017). The anti-predatory response of toads involves a fight, which means exudation of toxins or a flight trade off (Cannon, 1929; Hudson 2017). It is more likely that toads from UPLB will display high reluctance score and poor running ability since these toads are typically experiencing disturbances brought by humans and anthropogenic activities in their habitat. It is also possible that these toads exude toxins because toads that are less willing to fly are more willing to exude toxins to display their preferred anti-predator tactic in which they think is most advantageous for them (Hudson, 2017). Toads from Santa Maria are expected to be a more reluctant runners and which occur more frequently at night near rice paddies, irrigation systems and in rivers which are relatively less disturbed and far from different anthropogenic activities.

Since Rhinella marina is an alien invasive species that thrives in a wide range of habitat, it is crucial to study how their physiological, morphological and behavioral traits which are the focus of this study, significantly affect their perpetuation and survival in the stages of their invasion process. Understanding the variety of responses of this species to avoid capture and evade detection through anti-predator tactics can give clarifications on how their escape behavior allows them to become successful invaders.