Predation of cassowary dispersed seeds: is the cassowary an effective disperser?

Integrative Zoology 2011; 6: 168-177                                                       doi: 10.1111/j.1749-4877.2011.00242.x


Predation of cassowary dispersed seeds: is the cassowary an
effective disperser?

CSIRO-Sustainable Ecosystems, Tropical Forest Research Centre, Atherton, Queensland, Australia

   Post-dispersal predation is a potentially significant modifier of the distribution of recruiting plants and an often
   unmeasured determinant of the effectiveness of a frugivore’s dispersal service. In the wet tropical forests of Austra-
   lia and New Guinea, the cassowary provides a large volume, long distance dispersal service incorporating benefi-
   cial gut processing; however, the resultant clumped deposition might expose seeds to elevated mortality. We exam-
   ined the contribution of post-dispersal seed predation to cassowary dispersal effectiveness by monitoring the fate
   of 11 species in southern cassowary (Casuarius casuarius johnsonii Linnaeus) droppings over a period of 1 year.
   Across all species, the rate of predation and removal was relatively slow. After 1 month, 70% of seeds remained
   intact and outwardly viable, while the number fell to 38% after 1 year. The proportion of seeds remaining intact in
   droppings varied considerably between species: soft-seeded and large-seeded species were more likely to escape
   removal and predation. Importantly, across all species, seeds in droppings were no more likely to be predated than
   those left undispersed under the parent tree. We speculate that seed predating and scatter-hoarding rodents are
   responsible for the vast majority of predation and removal from droppings and that the few seeds which undergo
   secondary dispersal survive to germination. Our findings reinforce the conclusion that the cassowary is an impor-
   tant seed disperser; however, dispersal effectiveness for particular plant species can be reduced by massive post-
   dispersal seed mortality.
   Key words: Australia, Casuarius casuarius, disperser effectiveness, secondary dispersal, seed shadow.

INTRODUCTION                                                     ment. Dispersal and disperser effectiveness traditionally in-
                                                                 corporate both quantity and quality components of seed dis-
   Seed dispersal is a fundamental process in the dynamics       persal (Schupp 1993). The quantity component is concerned
of tropical forests. For fleshy-fruited plants, dispersal is     with the number of seeds dispersed while the quality com-
largely a product of the foraging patterns of frugivores and     ponent deals with the treatment of the seed by dispersers,
the associated movement and deposition of the seeds.             seed deposition, and the consequences for subsequent sur-
However, for effective or realized dispersal to occur, a seed    vival and germination. As germination rarely occurs imme-
must survive to germination and, ultimately, to establish-       diately after deposition, the processes that act upon a seed
                                                                 after initial dispersal make a critical contribution to dispersal
                                                                 and disperser effectiveness.
                                                                    Pre-dispersal and post-dispersal predation have a mas-
Correspondence: Matt Bradford, CSIRO, PO Box 780 Atherton,
                                                                 sive influence on the probability of a seed surviving to
Qld, 4883, Australia.
                                                                 germination. Evidence suggests that seed predators de-

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Predation of cassowary dispersed seeds

stroy the majority of seeds in many plant communities             moval (Andresen & Levey 2004; Russo 2005), largely
around the world (e.g. Janzen 1971; Blate et al. 1998;            because of the relative ease with which individual versus
Vander Wall 2001). High levels of post-dispersal preda-           large clumps of seeds are detected by a predator or
tion might counter any perceived benefits of dispersal,           disperser. Although deposition pattern might have an
such as movement away from a parent, handling effects             effect, other factors, such as availability of other seeds,
and deposition pattern (Traveset et al. 2007) or improved         will influence the strength of this effect (McConkey 2005).
location (Harper 1977; Schupp 2007).                                 Three species of cassowary reside in the closed forests
   The extent of seed predation experienced by a plant is         of northern Australia and New Guinea. All of these spe-
determined by a range of extrinsic and intrinsic factors.         cies are fruit specialists and are considered important as
Primary extrinsic determinants of the level of predation          seed dispersers. The relatively long gut passage time and
experienced include predator type present and predator            ability to move large distances in search of food result in
densities (Donatti et al. 2009). Both of these factors are        large dispersal distances for plants in its diet (Mack 1995;
determined by habitat type (Osunkoya 1994) and other              Westcott et al. 2005). Despite the cassowary’s relatively
environmental variables at a site (e.g. Lord & Kelly 1999;        gentle gut processing of seeds, it has been shown to alter
Zelikova et al. 2008). The type of predators present also         the germination success of individual seeds of some plant
determines whether dispersed seeds are most likely to be          species (Lamothe et al. 1990; Webber & Woodrow 2005;
predated or secondarily dispersed (Harrington et al. 1997;        Bradford & Westcott 2010). Across a broad spectrum of
Seufert et al. 2010). Although secondary dispersal will           fruit and seed types, however, cassowary gut passage has
generally result in little significant change in dispersal        no net effect on probabilities of survival or germination
distances (e.g. Forget 1990; Theimer 2001), it might or           (Bradford & Westcott 2010).
might not result in improved survival for seeds (Schupp              Although cassowary gut-passage has little effect on
1988; Willson 1988).                                              individual seed germination, cassowaries deposit seeds
   Intrinsic determinants of seed fate include seed size and      in large clumps that might contain thousands of seeds.
morphology. We might expect that the larger the reward            This deposition pattern, along with surrounding fecal
offered by a seed, the greater the probability that it would be   material, can reduce seed germination success for some
subject to secondary dispersal or predation. This would sug-      species (Bradford & Westcott 2010). Furthermore, it is
gest that large seeds would be favored by secondary dis-          possible that deposition in large clumps with fecal mate-
persers and predators (Forget et al. 1998; Theimer 2003).         rial might result in a greater signal to potential predators
Large seeds can be predated upon by all predator sizes, but       and, therefore, might influence seed predation rates.
are limited to being secondarily dispersed by larger animals.     Currently, there is no information on seed survival through
However, small seeds are easily moved by a greater range          to germination in clumped cassowary droppings. In this
of animals, including invertebrates (Levey & Byrne 1993;          paper, we investigate whether the beneficial effects of large
Andresen 2001). Seed fate, however, is likely to be at least      volume, long distance dispersal and gut processing are
partly dependent on energy and nutritive values of the seed       outweighed by any negative effect of seed predation and
(Vander Wall 2001; Briones-Salas et al. 2006). For some           removal of cassowary dispersed seeds.
traits, it is easier to generalize. For example, hard-seeded         Specifically, our study examines the dispersal effec-
species generally have an induced dormancy (Hopkins &             tiveness of the southern cassowary (Casuarius casuarius
Graham 1987) and, consequently, must persist longer at a          johnsonii Linnaeus) in the Wet Tropics of Australia. In
site than soft-seeded species before germination occurs.          northern Australia, the species consumes large amounts
Therefore, hard-seeded species are generally exposed to seed      of fruit from a wide range of species (Westcott et al. 2005),
mortality factors for longer periods.                             including a high proportion of large-seeded species
   Rates of post-dispersal predation and secondary dis-           (Bradford et al. 2008). We quantify the probability that a
persal are also potentially influenced by the deposition          seed will be predated or secondarily dispersed from cas-
pattern of the disperser (Kwit et al. 2007). Some dispers-        sowary droppings before germination and compare these
ers scatter seeds, either by depositing seeds individually        results to those for single seeds below, or adjacent to, par-
as they move or in a manner that results in the seeds set-        ent trees. Using previously published studies, we specu-
tling individually (e.g. from a height such that dung is          late on the vectors responsible for predation and second-
dispersed as it falls). Others leave large clumps of seeds        ary dispersal of the seeds in the Wet Tropics of Australia.
surrounded by fecal material. These contrasting patterns          Although we conclude cassowary dispersal to be effective,
might result in different probabilities of predation and re-      when predation and secondary dispersal are considered,

© 2011 ISZS, Blackwell Publishing and IOZ/CAS                                                                               169
M.G. Bradford and D.A. Westcott

we predict that effective dispersal kernels (sensu Schupp                  mately 10 km2. The trails, which are little more than in-
1993) will differ significantly from our current understand-               distinct tracks, are unlikely to influence predator behavior.
ing of cassowary-produced dispersal kernels (Westcott et                   Droppings were chosen for monitoring if they showed no
al. 2005; Dennis & Westcott 2007).                                         outward signs of disturbance, predation or seed removal.
                                                                           The fruit, endocarps or seeds (henceforth referred to as
MATERIALS AND METHODS                                                      seeds) were identified and counted with minimal distur-
                                                                           bance to the dropping. Seeds were monitored each month
Study site and species                                                     and assessed as either: (i) intact and viable; (ii) predated;
                                                                           (iii) removed; (iv) rotted; or (v) germinated. Seeds with
    We conducted the study in intact rainforest in                         the endocarp penetrated by either vertebrate or inverte-
Wooroonooran National Park, on the eastern edge of the                     brate predators and rendered unviable were recorded as
Atherton Tablelands, North Queensland, Australia (17°22’S,                 predated. Predated seeds were left in the dropping. Ger-
145°45’E). The study area ranges from 600 to 700 m in                      minated seeds were left in the droppings and for the analy-
altitude. Dominant forest types are complex mesophyll vine                 sis were considered to be intact until the end of the study.
forest on basalt and simple notophyll vine forest on metamor-
                                                                               All species were monitored for 12 months, with the
phics. The southern cassowary (Casuarius casuarius
                                                                           exception of Castanospora alphandii (F.Muell.) F.Muell.,
johnsonii) is a large flightless bird, residing in northern Aus-
                                                                           which was monitored for 6 months due to its late fruiting
tralia and the southern lowlands of New Guinea. In Australia,
                                                                           in the study.
it primarily occurs between Townsville and Cooktown, with
additional populations on Cape York. It is a resident of closed                To identify any influence of seed characteristics on pre-
forest but is known to use adjacent seasonally inundated                   dation and removal, we documented each species’ seed
swamps, woodland, mangroves and agricultural land.                         hardness, seed size and residual flesh adhering to the seed
                                                                           after gut passage. Seed hardness was scored using the
Experimental procedure                                                     categories of Blate et al. (1998): soft, able to be punc-
   Between March 1998 and July 2000, we located re-                        tured by a fingernail; firm, able to be penetrated by a knife;
cently deposited (less than 7-day-old) intact cassowary                    and hard, not able to be penetrated by a knife. Seed size
droppings on, and adjacent to, lightly used research trails                was scored as large (>8 mL volume), medium (1–8 mL)
within the study area. The network of trails was approxi-                  and small (
Predation of cassowary dispersed seeds

   Only large and medium-seeded species were monitored             To aid in relocating the fruit, a 10 cm length of dental
in our study. Residual flesh was scored as either all flesh     floss was glued to the fruit, and a plastic tag was inserted
stripped or minimal flesh stripped and was assessed by          into the soil 10 cm from the fruit. The single fruits were
one author (MB) to ensure consistency.                          revisited monthly and the fate of each was assessed in the
   Four species commonly found in both cassowary drop-          same manner as the seeds in the droppings. Fruit moved
pings and as fruiting trees in the area, Aceratium doggrellii   but still with the dental floss attached and those located
C.T.White, Acmena divaricata Merr. and L.M.Perry,               within 20 cm of the original placement were considered
Elaeocarpus grandis F.Muell. and Prunus turneriana (F.          to be present. The control treatments were monitored for
M.Bailey) Kalkman, were chosen to assess the fate of            6 months.
seeds in 2 control treatments. The control treatments were:
(1) single undispersed fruits located under the canopy of       Data analysis
parent trees, and (2) single fruits placed beyond the canopy       Only droppings that were dominated by 1 species (see
of parent trees. For control 1, fruiting trees of the 4 spe-    Bradford et al. 2008) were used in the analysis. In addition,
cies were chosen and ripe fallen fruits were haphazardly        droppings were considered only if they had more than 10
located and marked in situ (see below) under the canopy.        seeds of the dominant species. This limited the number of
Fruit of the same species within a 20 cm radius were            droppings to 38 (Table 1). Because at each time period,
removed. For control 2, fruits were placed at distances of      including the final time period, seeds could be predated,
10, 20, 30, 40 and 50 m from the edge of the projected          removed, rotted, germinated or intact, we used survival
canopy of each control tree at each of the cardinal com-        analysis to test for the effect of seed traits and control
pass directions. Fruits from the control treatments were        treatments, and for relationships between traits or treat-
not placed within 100 m of another conspecific fruiting         ments and survival time. Survival analysis is appropriate
tree. Difficulties in locating fruiting trees or fruit during   in circumstances where the dependent variable represents
the study limited us to 2 trees of each species and we aimed    time to a terminal event (e.g. time to seed mortality), but
for 20 fruits in each control treatment per tree. However       where not all experimental subjects will achieve that event
for A. divaricata and A. doggrellii, this was not possible      in the timeframe of the experiment, that failure is still of
due to low fruit numbers or the presence of other conspe-       interest (Statsoft 2005). For example, in the present study,
cific fruiting trees immediately adjacent. Species attributes   some seeds were still alive, either as seeds or seedlings,
and treatment details are provided in Table 1.                  after 12 months, when the study had to be terminated.
                                                                Predated, removed and rotted seeds were coded as com-

Figure 1 Mean proportion (±1 SE) of
seeds remaining intact (, Y left axis)
and cumulative mean proportion (±1 SE)
of seeds predated (), removed () and
rotted () across all species (Y right

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M.G. Bradford and D.A. Westcott

plete (i.e. dead), whereas germinated and intact seeds were          were removed, and 3.5% rotted. Figures 2 and 3 show the
coded as censored (i.e. still alive at the end of the experiment).   percentage of seeds intact, predated, removed and rotted
To test for differences between the categories of seed traits,       for each species. For the 11 species, total germination
we used Cox’s F-test, and to test for an effect of time on           reached 14.8% by 12 months.
the relationship between survival time and a trait, we used
proportional hazard regression. This method makes no                 Fate in droppings: effect of seed traits
assumptions about the underlying hazard rate distribution                The 4 soft-seeded species attained maximum germination
but rather assumes that this is a function of the dependent          within 2 months, with total germination values of: Beilschmiedia
variables (Statsoft 2005). The model for the hazard of the           oligandra L.S.Sm. (100%), Diploglottis bracteata Leenh
ith individual under a given treatment is estimated as               (100%), C. alphandii (64%) and Cryptocarya oblata F.M.Bailey
Hi(t) = h0(t)*exp( *z1), where h0(t) is the baseline hazard          (68%). The only firm-seeded species (A. divaricata) attained
when independent variables equal zero, t is the respective           maximum germination after 6 months, with a total germination
survival time and z is the vector of individual cases. To            of 63%. Calophyllum costatum F.M.Bailey was the only hard-
reduce the effect of the small number of droppings for               seeded species to show germination (2% at 2 months).
some species, comparisons within seed traits were under-             Consequently, there was an effect of seed hardness on survival
taken on the basis of seed hardness, size and residual flesh         (Cox’s F(358,2914) = 3.64, P < 0.001) with soft-seeded and firm-
categories, and not by species.                                      seeded species remaining intact longer than hard-seeded
                                                                     species. Figures 2 and 3 show the fate of seeds in the 3 seed
RESULTS                                                              hardness categories. Seed size and residual flesh also showed
                                                                     a significant effect on survival, with larger seeds remaining
Fate in droppings: across species                                    intact longer (Cox’s F(218,3054) = 2.63, P < 0.001) and defleshed
                                                                     seeds remaining intact longer (Cox’s F(1854,1418) = 1.75,
   The 11 species used in the analysis are presented in              P < 0.001). The effect of these traits on survival was related
Table 1 along with seed attributes and details of treatments.        to time (χ2 = 252.7, df = 3, P < 0.001). Parameter estima-
From an initial 2342 seeds present in 38 droppings, the              tion indicated that this relationship was significant for
mean proportion of intact (germinated and ungerminated)              each trait (hardness: â = –0.82, exp(â) = 0.44, Standard
seeds was 70% after 1 month and 38.5% at the end of the              error (SE)(â) = 0.10, Wald statistic = 72.22, P < 0.001; size:
study period (Fig. 1). After 12 months, a mean of 23.4%              â = 0.34, exp(â) = 1.41, SE(â) = 0.11, Wald statistic = 8.9,
of seeds were predated and left in the droppings, 34.6%              P = 0.003; defleshing: â = 0.21, exp(â) = 0.1.22, SE(â) = 0.05,

Figure 2 Fate of soft-seeded and firm-
seeded species in cassowary droppings after
30, 180 and 360 days. Fates are intact ( ),
predated ( ), removed ( ) and rotted ( ).
d = number of droppings, n = number of
seeds. Seeds germinated are considered to
be still intact regardless of their fate after
germination. Castanospora alphandii
seeds were only monitored for 180 days.

172                                                                                  © 2011 ISZS, Blackwell Publishing and IOZ/CAS
Predation of cassowary dispersed seeds

Wald statistic = 15.26, P < 0.001). It should be noted that        that the cassowary is an effective seed disperser. Across the
soft-seeded and firm-seeded species in our study are sig-          11 species tested, 38% of seeds were left intact in the drop-
nificantly larger than hard-seeded species (t = –2.88, df = 9,     pings after 1 year, with 15% of these having germinated.
P = 0.018). Despite this, these effects remain significant even    Two species, E. grandis and P. turneriana, showed little or
when included together in the proportional hazard regres-          no survival to 1 month, with interim observations suggest-
sion analysis.                                                     ing that these seeds probably did not survive intact more
                                                                   than a few nights. Rates of seed predation and removal might
Comparison of droppings and controls                               vary with forest type, altitude and season. For example, while
    For the 4 control species combined, the proportion of in-      we recorded complete and rapid predation of E. grandis
tact seeds remained higher in droppings than in the controls       seeds, Stocker and Irvine (1983) report seedlings of the same
at all time periods (Fig. 4); however, this was not a signifi-     species emerging from an old cassowary dropping. Most
cant difference (χ2 = 0.03, df = 1, P = 0.86). The 4 species       importantly, only 1 of the 4 species for which control com-
individually showed varied treatment effects in the number         parisons were available, P. turneriana, experienced higher
of seeds surviving (i.e. intact or germinated). None of the        predation levels in droppings than in undispersed seeds or
seeds of E. grandis remained intact in either the control treat-   those dispersed adjacent to parent trees. In addition, seeds
ment or in droppings for 1 month. Seeds of A. doggrellii           consumed and deposited by the cassowary will generally be
showed no difference in survival between controls and              dispersed further from the parent than if dispersed by other
droppings ( = 0.05, exp( ) = 1.05, SE( ) = 0.16, χ2 = 0.1,         animal vectors (Westcott & Dennis 2007), with generally
df = 1, P = 0.76). Seeds of A. divaricata ( = 1.03, exp( )         positive effects on germination success (Bradford & Westcott
= 2.81, SE( ) = 0.21, χ2 = 25.76, df = 1, P < 0.001) survived      2010). For large-seeded species, the absence of other ani-
longer in droppings than both controls, while seeds of             mals capable of dispersing and internally processing their
P. turneriana survived longer under and away from the par-         seeds in Australia means that cassowary dispersal, no mat-
ent than in droppings ( = –0.39, exp( ) = 0.68, SE( ) = 0.10,      ter how effective, will be beneficial.
χ2 = 15.3, df = 1, P < 0.001).                                        Our study shows that the clumped nature of cassowary
                                                                   seed deposition has no detrimental effect on seed survival.
                                                                   The small number of replicate trees achieved in this study
DISCUSSION                                                         means that these results alone should not be considered
   Despite sometimes significant levels of predation expe-         as conclusive. However, the concordance with other stud-
rienced by seeds in cassowary droppings, our work shows            ies from the region documenting comparable rates of single

Figure 3 Fate of hard-seeded species in
cassowary droppings after 30, 180 and 360
days. Fates are intact ( ), predated ( ),
removed ( ), and rotted ( ). d = number
of droppings, n = number of seeds. Seeds
germinated are considered to be still intact
regardless of their fate after germination.

© 2011 ISZS, Blackwell Publishing and IOZ/CAS                                                                                173
M.G. Bradford and D.A. Westcott

seed removal (Osunkoya 1994; Harrington et al. 1997)           et al. 1997; Thiemer 2001; Dennis et al. 2004) have shown
supports our conclusion. This result is not dissimilar to      that a large proportion of the seed removal and predation in
other studies where high densities of dispersed seeds are      the study area is due to the actions of scatter-hoarding and
found, such as in clumped deposition by large dispersers       predatory mammals. Although there are possibly 5 species
(e.g. Pizo & Simao 2001; Andresen 2002) or the deposi-         of ground dwelling mammals able to consume high propor-
tion of seeds at latrines (Fragoso 1997). This result might    tions of fruit and seeds in the region (Dennis 2003), the white-
be negated in some cases by the effect of seed clumping        tailed rat (Uromys caudimaculatus Krefft) is likely respon-
on germination success, which is generally seen as a nega-     sible for the largest proportion of the predation and seed
tive for the cassowary (Bradford & Westcott 2010) and          removal from the droppings. The species is common
other frugivores (Travaset et al. 2007). Similarly, germi-     (Laurance & Grant 1994; Harrington et al. 1997) and is
nation in clumps might ultimately lead to reduced root         known to inflict high rates of mortality on the seeds of nu-
and shoot development due to competition at later stages       merous rainforest species (Harrington et al. 1997; Theimer
of growth (Pizo & Simao 2001) or increase the attraction       2001). Although the white-tailed rat is probably responsible
to herbivores and pathogens.                                   for the bulk of predation and seed removal, other rodents,
   There are few published studies on post-dispersal preda-    feral pigs, musky rat-kangaroos, litter disturbance by ground
tion and secondary dispersal in the wet tropical forests of    foraging birds and abiotic factors, such as gravity and over-
Australia and certainly there is an absence of work on cas-    land water movement, probably also contribute to a lesser
sowary dispersed seeds. However, we can speculate on the       extent.
agents of seed removal and mortality. Coprophagy is some-          For effective or realized dispersal to occur, a seed must
times practiced by cassowaries immediately after deposi-       remain intact and viable until germination and then
tion (Mack & Druliner 2003; M. Bradford, pers. observ.)        establishment. In comparison with soft-seeded species, spe-
but was not considered in our study because we began moni-     cies with a hard seed coat or endocarp were generally more
toring the droppings 1–7 days after deposition. Webber and     heavily predated or removed by the end of 12 months, a
Woodrow (2005) report a high incidence of mortality of a       period generally shorter than their time to germinate (Table
soft-seeded species, Ryparosa sp. nov. 1, in cassowary drop-   1; Figs 2 and 3). Exceptions were Halfordia kendack
pings due to fruit flies. We did not document insect damage    (Montrouz.) Guillaumin, the seeds of which rotted, and
to our seeds; however, we assume it was insignificant, as a    Elaeocarpus ruminatus F.Muell., the seeds of which prob-
large proportion of our soft-seeded species survived to        ably avoided heavy predation because of their small size.
germination. Previous studies (Osunkoya 1994; Harrington       This rate and magnitude of loss is comparable to other stud-

Figure 4 Mean proportion of seeds
(±1 SE) remaining intact in droppings
( ), singly under parent trees ( ) and sin-
gly beyond the canopy of parent trees ( )
for the species Aceratium doggrellii,
Acmena divaricata, Elaeocarpus grandis
and Prunus turneriana combined.

174                                                                           © 2011 ISZS, Blackwell Publishing and IOZ/CAS
Predation of cassowary dispersed seeds

ies involving hard-seeded species in Australian wet tropical      remains undispersed close to the parent. This result sug-
forests (Osunkoya 1994; Harrington et al. 1997; Thiemer           gests that any Janzen-Connell effects (Janzen 1970;
2001). Considered alone, this suggests that hard-seeded fruit     Connell 1971) that are likely to come into play do so after
are disadvantaged by cassowary deposition; however, pre-          the seed stage and during the establishment phase.
dation and removal rates from droppings were similar or           Consequently, the cassowary must be considered an ef-
lower than for undispersed seeds (Fig. 4). In contrast, the       fective disperser as the long distance and large volume
soft and firm seeds remained relatively intact throughout         movement of seeds combined with a generally positive
the study, before and after germination. Before germination,      gut processing effect negate any detrimental effect that a
seeds without mechanical defenses tend to be targeted by          clumped deposition pattern might have on seed germina-
invertebrate predators (e.g. Sharma & Amritphale 2008;            tion and seedling survival. Due to high seed mortality for
Kupruwicsi & Garcia-Robledo 2010) and are generally less          particular species, our results also show that the incorpo-
preferred by vertebrate predators due to chemical defenses        ration of predation and secondary dispersal of deposited
(Blate et al. 1998; Grant-Hoffman & Barboza 2010) or lower        seeds is essential in the generation of effective, or realized,
nutritional content (Vander Wall 2001). Post-germination,         dispersal kernels.
the altered chemical and nutritive state and functional mor-
phology of cotyledons will largely determine if the cotyle-
dons and seedling is predated. All soft-seeded species in our
study exhibit hypogeal germination, resulting in cotyledons         This study was undertaken as part of the Rainforest
being less nutritious and more redundant for seedling sur-        CRC and conducted under CSIRO Animal Ethics Approval
vival with time. Although differential patterns of fruiting       OB15/12 and Queensland Department of Environment
and predator satiation might influence relative removal rates,    Scientific Purposes Permit FO/001071/96/SAB. Earlier
the low predation of soft-seeded species seen in our study is     versions of this paper were improved by Helen Murphy
the result of minimal enforced dormancy in soft-seeded spe-       and Graham Harrington (CSIRO). Pierre-Michel Forget
cies (Hopkins & Graham 1987), resulting in short times to         (Museum National d’Histoire Naturelle, Brunoy) and 3
germination and reduced exposure to post-dispersal seed           anonymous reviewers greatly improved the manuscript.
predation. The fact that cassowary gut passage results in
increased germination success for softer seeds (Bradford &        REFERENCES
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similar probability of survival to germination than if it           Austral Ecology 35, 325–33.

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© 2011 ISZS, Blackwell Publishing and IOZ/CAS                                                                              177
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