4.1 The contrasting relationship between HR and EE
Our findings confirm the hypothesis grazers increased energy investment
in foraging results in a lower harvest rate from available resources
(Fig. 3), when herbivores optimize their harvest rate, akin to
time-minimizing grazers that prioritize high energy gain within shorter
handling times (Bergman et al., 2001a; Hazen et al., 2015), they also
demonstrate a preference for energy efficiency. This is exemplified by
the foraging behaviors of wood bison, which balance residence time and
patch quality for efficient energy utilization (Bergman et al., 2001).
The novelty of our study lies in illustrating that grazers’ foraging
strategies encompass not only a preference for harvest rate efficiency
but also for optimizing energy expenditure.
The observed as the harvest rate increase a more pronounced decrease in
energy expenditure in larger herbivores compared to smaller ones (Fig.
3). Despite the lack of significant size-related differences in harvest
rates among grazers, larger sheep demonstrate notably higher energy
consumption during foraging than their smaller counterparts, ODBA does
not directly measure variation in physiological performance “capacity”
but rather the combination of intrinsic physiological constraints and
behavioral decisions made in a dynamic environment (Payne et al., 2016),
likely due to their overall posture and activity patterns (Chimienti et
al., 2020; Halsey et al., 2011). Furthermore, the impact of energy
expenditure on harvest rate is markedly greater in larger sheep,
implying that smaller sheep exhibit higher foraging efficiency (Fig. 4).
This conclusion is drawn from observable differences in harvest rate and
energy costs, highlighting behavioral distinctions in foraging
efficiency. Although, our study did not delve into physiological aspects
such as digestive efficiency in grazers, where higher basal metabolic
rates might lead to increased energy consumption and thus reduced
foraging efficiency (Nagy, 2005; White et al., 2009). Regarding the
differences of biting behaviors in response to resources conditions
larger herbivore due to their capacity for larger bite sizes, generally
consume more food (Spalinger and Hobbs, 1992; Wilmshurst et al., 2000).
However, smaller grazers exhibit a higher relative consumption compared
to their larger counterparts in low-biomass grasslands. Smaller animals
have shown greater proficiency in maintaining high food intake in
environments where resources are limited or dispersed (Fortin, 2006).
This efficiency is particularly notable in low productivity or patchy
environments, where smaller herbivores can sustain higher food intake
levels more effectively than larger herbivores (Fortin, 2006). This
finding underscores the adaptive foraging strategies of smaller
herbivores in resource-scarce ecosystems.