Komodo Dragons (Varanus komodoensis)

[Paleosuchus]

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Here is some research on the prey preferences and niche segregation in sizes classes:

Ecological allometries and niche use dynamics across Komodo dragon ontogeny
Abstract
Ontogenetic allometries in ecological habits and
niche use are key responses by which individuals maximize
lifetime fitness. Moreover, such allometries have significant
implications for how individuals influence population and
community dynamics. Here, we examined how body size variation
in Komodo dragons (Varanus komodoensis) influenced
ecological allometries in their: (1) prey size preference, (2)
daily movement rates, (3) home range area, and (4) subsequent
niche use across ontogeny. With increased body mass,
Komodo dragons increased prey size with a dramatic switch
from small (≤10 kg) to large prey (≥50 kg) in lizards heavier
than 20 kg. Rates of foraging movement were described by a
non-linear concave down response with lizard increasing
hourly movement rates up until ∼20 kg body mass before
decreasing daily movement suggesting reduced foraging effort
in larger lizards. In contrast, home range area exhibited a
sigmoid response with increased body mass. Intrapopulation
ecological niche use and overlap were also strongly structured
by body size. Thus, ontogenetic allometries suggest Komodo
dragon’s transition from a highly active foraging mode
exploiting small prey through to a less active sit and wait
feeding strategy focused on killing large ungulates. Further,
our results suggest that as body size increases across ontogeny,
the Komodo dragon exhibited marked ontogenetic niche shifts
that enabled it to function as an entire vertebrate predator guild
by exploiting prey across multiple trophic levels.

"Between December 2002 and April 2015, we collected regurgitated
stomach contents (N= 52) and direct observations of
prey kills (N= 25) from Komodo dragons (with known identity
and body mass) across field sites during routine trapping
and telemetry studies (∼1100 field days). Production of
vomited prey items was an induced response to normal trapping
activities, and stomach flushing was not needed. All prey
items collected were identified to species level in situ. Prey
items were categorized into four prey size classes (<0.1, 0.1–
1, 1–5 and ≥50 kg). These size categories were deemed ecologically
appropriate as they reflected the natural and the
somewhat discontinuous body size categories representative
of prey species occupying terrestrial habitats in Komodo
National Park (Auffenberg 1981). Here, insects and small reptiles
comprised the smallest prey body size class, followed by
snakes, rodents and birds in the 0.1–1 kg prey class, next
juvenile ungulates and palm civets (Paradoxurus hermaphroditus) 
dominated the 1–5 kg prey size class, and
adult ungulates comprised the heaviest prey body mass class
(≥50 kg). To assign prey to their respective size class, intact
whole prey was weighted to the nearest gram using a digital
hanging scale. For dietary records that comprised the partial
prey remains large ungulates (i.e. Rusa deer and pigs) that
could not be fully consumed, we inferred prey mass from
the dentition class or using the diameter of long bones to
assign ungulates into juveniles or adults, following methods
described by Auffenberg (1981)."

" body size-related niche use and overlap
To consider ontogenetic difference in niche requirements, we
categorized Komodo dragons into four body mass classes
(<1 kg [hatchlings to small juveniles], 1–10 kg [large juveniles],
10–25 kg [sub-adult to small adults], >25 kg [large
adults]) that reflected key life stages differences in this species
(Auffenberg 1981; Imansyah et al. 2008; Laver et al. 2012).
To qualify the size-related differences in niche use, we compiled
data on four important measures of habitat use:

• Forest strata use: Here, we used radiotracking observations
  (N= 1200) of Komodo dragons that recorded their
  forest strata use determined by the height that individuals
  were observed above the ground. Effectively, the main
  point of this was to elucidate the relative use of terrestrial
  and arboreal forest strata by the different size classes.
• Vegetation community use: Body size could impose different
  requirement on habitat use reflected in how lizards
  use or occupy different vegetation communities. On
  Komodo Island within our study area, there are four key
  vegetation communities that Komodo dragons could utilize.
  Here, we recorded by way of visual inspection the
  specific type of vegetation composition found associated
  with each individual lizard’s positional fix recorded during
  telemetry study. Each fix location was then assigned
  to one of four vegetation types represented by: (1) Closed
  monsoon forest, (2) Deciduous monsoon forest, (3)
  Savannah woodland and (4) Savanna grassland.
  These four vegetation communities are typical of our
  study area (Auffenberg 1981). Given their different structural
  properties (e.g. closed to open canopy) and plant
  species compositions, they are expected to provide a basis
  for variation in habitat resources that could be differentially
  utilized by Komodo dragon size classes. Closed
  monsoon forest was restricted to hilltops (>500 m above
  sea level (ASL)) and some permanent watercourses. Here,
  the canopy is closed and dominated by trees not typically
  found at lower elevations (primarily Terminalia
  zollingeri, Podocarpus neriifolia and Ficus orupacea;
  Auffenberg 1981). Deciduous monsoon forest is restricted
  to coastal valley floors abutting significantly elevated hills
  (which receive precipitation, providing runoff to the valley
  floors). Deciduous monsoon forest consists of deciduous
  fire-resistant trees, primarily Tamarindus indica,
  Sterculia foetida, Jatropha curcas and Cladogynos
  orientalis. The canopy of deciduous monsoon forest is
  partially closed, and the understory is either open or dominated
  by perennial shrubs. In areas that receive little runoff
  or precipitation, monsoon forest is displaced by savannah
  woodland and/or savannah grassland. The canopy of
  savannah woodland is open, and the dominant trees are
  Borassus flabellifer, Zizyphus jujube and T. indica
  (Auffenberg 1981). Savannah grassland and the understory
  of savannah woodland are both composed of medium
  and tall grasses.
• Elevational occupancy: Elevational gradients are an important
  source of habitat variation that could influence
  size-specific requirements of individuals. To evaluate if
  different size classes of Komodo dragons preferred different
  habitat elevations, we recorded the elevation at each
  individual’s radio telemetry fix.
• Diet: Komodo dragons through body size effects and habitat
  use consume different types and diversity of prey species
  (Auffenberg 1981). Here, using 1200 dietary records
  from our own (regurgitated stomach contents) and published
  data (scat analyses from Auffenberg 1981), we categorized
  the frequency and breath of diet utilized by each
  of the four lizard size classes. Here, dietary records were
  classified into 8 prey categories: (1) Rusa deer (Rusa
  timorensis, 5–70 kg), (2) wild pigs (Sus scrofa, 2–
  50 kg), (3) rodents (e.g. Rattus rattus 0.1 kg), (4) palm
  civets (Paradoxurus hermaphroditus, <5 kg), (5) snakes
  [e.g. rat snake (Elaphe subradiata), whip snake
  (Dendrelaphis pictus) <1 kg], (6) insects [e.g. grasshoppers
  and beetle, <10 g], (7) lizards [e.g. skinks
  (Sphenomorphus florense) and geckos (Gecko gecko,Hemidactylus spp., <100 g] and (8) birds + eggs [e.g.
  orange-footed scrubfowl (Megapodius reinwartii) and
  Junglefowl (Gallus varius), <1 kg]. We used general
  prey categories to highlight coarse dietary preferences
  given that we compared diet across four classes
  of lizard body size that precluded more fine
  scale investigation of prey species composition with
  lizard body size."
  

"Increased lizard body mass was significantly correlated with
ingestion of larger prey body mass categories (GAM:
EDF = 5.30; F = 59.45; P < 0.001, R2
(adj) = 0.84; Fig. 2a).
Juvenile lizards selected smaller and lighter prey (e.g. supplementary
material), but as lizards increased in size, they increased
their preference for larger prey. This transition
seemed relatively abrupt with preference of large lizards
(>20 kg) contained only the largest prey mass class
(e.g. including adult Rusa deer estimated to weight
more than 50 kg).
Using telemetry, we monitored dragons for a mean period
of 151.7 ± 31.9 days resulting in 2108 movement data points.
Dragon hourly movement rates varied significantly with lizard
body mass (GAMM: EDF = 3.89; F1, 2106= 37.35; P< 0.001,
R2
(adj)= 0.12; Fig. 2b). There was a clear non-linear pattern
with hourly movement rates increasing in Komodo dragons
between the body mass ranges of 1.4–20 kg. Above this
movement rates asymptote and then decreased in largest
individuals.
A mean number of 286 ± 77 location fixes was recorded
among individuals. The minimum number of fixes required
to assess home range size was determined by plotting the
cumulative home range size per number of fixes recorded until
the home range reaches an asymptote. In this study, the average
minimum fixes needed to determine home range was 82.7
± 6.5 fixes. Home range area (1.71–1178.54 ha estimated from
95 % Kernel analysis) exhibited a significant non-linear increase
with body size (GAM: EDF = 2.79; F1,19 = 24.41;
P < 0.001, R2
(adj) = 0.62; Fig. 2c). Home range areas appeared
small and relatively invariant in area until lizards
exceeded 20 kg body mass. Above this mass, Komodo
dragon home range substantially increased with the large
adult male animals."

*This image is copyright of its original author

"The effects of body size on prey size preferences were
clearly evident with small lizards that preferentially consumed
small prey, whilst large adults targeted large ungulate prey. Rather than a continuous increase for larger prey with increased
lizard body size, there was body size-dependent
threshold effect at which Komodo dragons ceased
consumption of small prey and preferentially switched entirely
to killing large prey. Similar thresholds of prey size
switching appear common in interspecific comparisons of
mammalian predators. In carnivores, a body mass threshold
of ∼20 kg is advocated as the body mass threshold at
which predators switch from hunting small prey to
targeting large prey (Carbone et al. 1999; Ray and
Sunquist 2001). Our study also suggested that there were
distinct transitions in lizard prey preferences at ∼20 kg.
Our results support the notion that large ontogenetic
changes in body mass necessitate abrupt change in prey
size to optimize energy flux between energy expenditure
and intake (Carbone et al. 2007). Importantly, many other
functional processes would be associated with body size
that could further delimit the threshold at which Komodo
dragons switch to killing large ungulate prey. In particular,
larger lizards being heavier and stronger could better
dispatch larger prey items with increased gape size, bite
force and physical attack strength (Auffenberg 1981;
Pianka and Vitt 2003; McCurry et al. 2015)."
Link to study Reply