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Estimating biomass of berries consumed by gray wolves

DOI:10.1002/wsb.730
Authors:
Thomas Gable at University of Minnesota Twin Cities
Thomas Gable
Steve Windels at National Park Service
Steve Windels
John G. Bruggink
John G. Bruggink
John G. Bruggink
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Abstract

Gray wolves (Canis lupus) consume berries and other wild fruits seasonally when available or abundant. However, a method to convert percent frequency of occurrence or percent volume of berries in wolf scats to percent biomass has not yet been developed. We used estimates of the average number of blueberry (Vaccinium spp.) seeds in 10 individual wolf scats collected in and adjacent to Voyageurs National Park, Minnesota, USA, along with published values of the number of seeds per blueberry and blueberry masses to estimate that a wolf scat containing only berries equated to an average of 0.468 kg of berries consumed. We recommend using this berry conversion factor (0.468 kg/scat) to convert the percent frequency of occurrence or percent volume of berries and other wild fruits to percent biomass when estimating wolf diets from scats.
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Tools and Technology
Estimating Biomass of Berries Consumed by
Gray Wolves
THOMAS D. GABLE,
1
Northern Michigan University, Department of Biology, 1401 Presque Isle Avenue, Marquette, MI 49855, USA
STEVE K. WINDELS, Voyageurs National Park, 360 Highway 11 E, International Falls, MN 56649, USA
JOHN G. BRUGGINK, Northern Michigan University, Department of Biology, 1401 Presque Isle Avenue, Marquette, MI 49855, USA
ABSTRACT Gray wolves (Canis lupus) consume berries and other wild fruits seasonally when available or
abundant. However, a method to convert percent frequency of occurrence or percent volume of berries in wolf
scats to percent biomass has not yet been developed. We used estimates of the average number of blueberry
(Vaccinium spp.) seeds in 10 individual wolf scats collected in and adjacent to Voyageurs National Park,
Minnesota, USA, along with published values of the number of seeds per blueberry and blueberry masses to
estimate that a wolf scat containing only berries equated to an average of 0.468 kg of berries consumed.
We recommend using this berry conversion factor (0.468 kg/scat) to convert the percent frequency of
occurrence or percent volume of berries and other wild fruits to percent biomass when estimating wolf diets
from scats. Ó2017 The Wildlife Society.
KEY WORDS Canis lupus, correction factor, fruits, scat analysis, wolf diet.
Wolves (Canis lupus) are carnivorous mammals that feed
primarily on ungulates and other prey species such as beavers
(Castor spp.) or hares (Lepus spp.; Newsome et al. 2016).
Wolves are opportunists, however, and will take advantage of
other food sources such as human garbage, flightless molting
birds, and spawning salmon (Oncorhynchus spp.) when
available (Szepanski et al. 1999, Peterson and Ciucci
2003, Wiebe et al. 2009). Wolves also consume fruits
such as wild blueberries (Vaccinium spp.) and raspberries
(Rubus spp.) when these fruits are abundant. In areas where
berry consumption occurs, berries typically constitute a
minor (<10% frequency) portion of the summer diet
(Messier and Cr^ete 1985). However, in some areas, berries
can be a significant summer food item for wolves. Berries
(primarily blueberries) constituted 10–30% (frequency) of
the diet of wolves from 1 June to 15 September in southern
Quebec, Canada (Tremblay et al. 2001). Similarly, vegeta-
tion (primarily berries) occurred in 52% of scats collected at
home sites in July and 20% of scats collected on trails in
August and September in north-central Minnesota, USA
(Fuller 1989). In Voyageurs National Park, Minnesota,
berries constituted 30–50% (volume) of wolf diets in July and
August 2015 (T. D. Gable, personal observation). Though
berries can be an important summer food for wolves in boreal
systems, the percent biomass of wolf diets composed of
berries is largely unknown.
Percent frequency of occurrence or percent volume of a
particular species in wolf scats does not always equate to
percent biomass consumed of that species because smaller
prey have a larger proportion of indigestible material than
larger prey. The following equation (Weaver 1993) has been
used to correct for this bias and convert percent frequency of
occurrence or percent volume of mammalian prey to percent
biomass:
^
Y¼0:439 þ0:008 Xð1Þ
where Xis the average live mass of a prey species and ^
Yis the
prey mass per scat. The biomass of each prey species in the
wolf diet is determined by multiplying the prey mass per scat
by the proportion (based on volume or frequency) of that
species in the diet. The percent biomass of each prey species
is determined by dividing the biomass value of each prey
species by the summation of all biomass consumed and
multiplying by 100.
However, Weaver’s equation is not applicable to nonmam-
malian food items. Diet correction factors are generally
determined by feeding captive animals a known mass (or
volume) of food and measuring the mass (or volume) of fecal
material produced (e.g., Hewitt and Robbins 1996) or
counting the number of collectible scats produced (e.g., Floyd
et al. 1978). Such work has not been done for wolves and
berries, and digestibility of soft fruits by wolves is unknown.
Therefore, a method to convert percent frequency of
occurrence or percent volume of berries in wolf diets to
percent biomass of berries consumed needs to be developed to
better understand the contribution of berries and other fruits to
the diet of wolves. Wild fruits contain seeds that cannot be
digested by wolves; therefore, the biomass of ingestedfruits can
be estimated based on the number of seeds that pass in fecal
material. Thus, our objective was to develop a conversion factor
to convert the percent frequency of occurrence or percent
volume of berries in wolf diet to percent biomass by estimating
Received: 25 July 2016; Accepted: 27 November 2016
1
E-mail: thomasd.gable@gmail.com
Wildlife Society Bulletin; DOI: 10.1002/wsb.730
Gable et al. Estimating Berry Consumption by Wolves 1
the mass of blueberries consumed to produce one scat. Use of
this conversion factor should reduce overestimation of the
percent biomass of mammalianprey species in wolf diets where
berry consumption is high.
METHODS
As part of a larger study of wolf diets in and around
Voyageurs National Park, Minnesota (488300N, 938000W),
we collected 557 wolf scats during July–August 2015 from 3
wolf packs with 1 wolf/pack fitted with a Global
Positioning System (GPS) collar. Scats were collected on
trails and logging roads, at home sites, and at clusters of GPS
locations. We transferred individual scats to nylon stockings
and sterilized them by boiling in water for >45 min. We then
washed the scats in a washing machine and allowed them to
air dry for >12 hr (Gable 2016).
To estimate the biomass of berries consumed, we randomly
selected 10 out of 46 scats that contained only blueberries.
We spread the contents of each cleaned scat over an 8 8-cm
grid so that the seeds were uniformly distributed across each
grid cell. We then counted the number of seeds in one
randomly selected grid cell. We estimated the total number
of seeds in each scat by multiplying the number of seeds
counted in one grid cell by the total number of grid cells (64),
and then calculating an average number of seeds per scat. We
estimated the number of blueberries consumed by dividing
the average number of seeds per scat by the average number
of seeds per blueberry (14.6 seeds/berry; based on 12 seeds/
berry [Vander Kloet and Hill 1994] and 17.2 seeds/berry
[Usui et al. 2005]). This value was multiplied by the average
mass of a wild blueberry (0.335 g/berry; based on 0.300
[Welch et al. 1997] and 0.369 g [Usui et al. 1994]) to produce
an estimate of the mean biomass of blueberries (the berry
conversion factor) consumed per scat. Although we think
that the estimates derived from the literature represent a
broader sample of wild blueberries from across a larger
geographical region, we wanted to evaluate how the mean
mass of wild blueberries derived from Welch et al. (1997) and
Usui et al. (1994) compared with those in our study area. To
do so, we collected 2,000 individual blueberries from one
location in our study site and divided by the total mass of the
berries to derive an estimate of mass/berry.
RESULTS
We counted an average of 31993 (SD, range ¼209–477)
seeds/grid cell in the 10 scats examined, which was an average of
20,415 5,938 (SD, range ¼13,372–30,508) seeds per scat.
Our minimum estimateof the biomass of blueberries consumed
by wolves was 0.356kg/scat based on 17.2 seeds/berry (Usui
et al. 2005) and 0.300g/berry (Welch et al. 1997). Our
maximum estimate was 0.628 kg/scat based on 12 seeds/berry
(Vander Kloet and Hill 1994) and 0.369 g/berry (Usui et al.
1994). Using combined averages of 14.6 seeds/berry and
0.335 g/berry, we estimated the berry conversion factor, which
is the mean biomass of blueberries consumed per scat, to be
0.468 0.136 kg/scat (SD, range ¼0.306–0.699 kg/scat). Our
estimate of mass of wild blueberries in our study area was
0.329 g/berry.
DISCUSSION
We recommend using our conversion factor of 0.468 kg/
scat (prey mass per scat) to estimate the percent biomass
of berries in wolf diet from percent frequency of
occurrence or percent volume in wolf scats. For scats
that are only partially composed of berries, the results can
be scaled to the volumetric proportion of the scat that is
berries (e.g., 50% of scat volume consisting of blueberries
¼0.234 kg blueberries consumed). The estimated mass of
a blueberry (0.329 g) in our study area was similar to the
combined mean mass (0.335 g) that we used from
literature values, though we acknowledge the limitations
of this simple evaluation. Future studies that use our
method could be improved by deriving local estimates of
berry mass.
The contribution of berries relative to mammalian prey in
summer wolf-diet biomass can now be examined because
the prey mass per scat of both berries (using the berry
conversion factor) and mammalian prey (using Weaver’s
[1993]equation) can be determined. However, percent
biomass in the diet should not be confused with the energy
derived from a prey source. For example, wild blueberries
contain 0.51 kcal/g of energy, whereas ungulate prey
contains 1.87 kcal/g (Usui et al. 1994, Peterson and Ciucci
2003). Wolves almost certainly cannot digest berries as
efficiently as they can digest ungulate prey (Litvaitis and
Mautz 1976). However, even if digestibility of berries is
low, great abundance of berries on the landscape might
make berries an important food source because berries can
be acquired with little energy expenditure in the summer
months when availability of mammalian prey is low
(Tremblay et al. 2001).
In systems where berry consumption is high, use of the
berry conversion factor could help reduce overestimation of
the consumption of mammalian prey. Our conversion factor
is most appropriately applied to gray wolves that consume
blueberries. However, our conversion factor can also be
applied to other fruits of similar size and digestibility (e.g.,
raspberries) that wolves may eat, because each scat should
represent the same amount of food consumed. We caution
against extrapolating our results to other canids because our
results are based on individual wolf scats, which are larger
than those of other canids. Thus, using the berry conversion
factor for other canids would overestimate the biomass of
berries consumed. Further, differences in the digestibility of
berries by wolves and other canids are largely unknown and
as a result, the mass of scat produced per berry consumed by
other canids will likely be different from wolves. Additional
research may improve the accuracy and precision of our
berry conversion factor, especially for use in other regions
where the types of soft fruits consumed by wolves may be
different.
ACKNOWLEDGMENTS
We thank W. Severud and S. Barber-Meyer for reviewing an
earlier version of this manuscript and providing helpful
suggestions. We thank Voyageurs National Park and
2 Wildlife Society Bulletin 9999()
Northern Michigan University for funding and logistical
support.
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Associate Editor: Glenn.
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Allerdings sind solche Fälle selten, und es ist schwierig in der freien Natur, ein bestimmtes Individuum sicher zu identifizieren und zu töten. Nicht-letale Herdenschutzmaßnahmen sind im Vergleich zu letalen Maßnahmen deutlich besser geeignet, eine nachhaltige Reduktion der Schäden zu erreichen. Der einzige Weg, um in Koexistenz mit Wölfen eine dauerhafte Reduktion von Schäden an Nutztieren zu erreichen, ist die fachgerechte Umsetzung von Herdenschutzmaßnahmen in breiter Fläche. Übergriffe auf Nutztiere lassen sich zwar auch dadurch nicht vollständig verhindern, sie können jedoch durch korrekt angewandte Herdenschutzmaßnahmen deutlich reduziert werden. Das Wissen, wie Schäden an Weidetieren durch Herdenschutzmaßnahmen verringert werden können, ist auch in Deutschland vorhanden. Viele Tierhaltende haben hier inzwischen ein hohes Maß an Fachkompetenz entwickelt. Die Erfahrung aus den vergangenen 20 Jahren zeigt allerdings auch, dass die Auszahlung von Fördergeldern für Herdenschutzmittel allein nicht ausreicht, um die Anzahl der Übergriffe deutlich zu senken. Es muss auch gewährleistet werden, dass die fachliche Expertise für die korrekte Anwendung und Wartung zur Verfügung steht. Vor allem in Gebieten mit Prädations-Hotspots sollte aktiv auf die Tierhaltenden zugegangen werden und sollten die Gründe für die vermehrten Übergriffe analysiert und abgestellt werden. Bisher fehlen aus Deutschland Daten zur Funktionstüchtigkeit der geförderten und im Einsatz befindlichen Schutzmaßnahmen. Solche Daten sind notwendig, um zu verstehen, warum trotz steigender Präventionsausgaben die Nutztierschäden teilweise auch in Gebieten mit jahrelanger Wolfspräsenz nicht zurückgehen. Sie sind zudem die Grundlage für wissenschaftliche Studien zu möglichen Unterschieden in der Wirksamkeit verschiedener Herdenschutzmethoden. Daten zur Funktionstüchtigkeit von geförderten Herdenschutzmaßnahmen sollten zumindest stichprobenartig gesammelt werden, unabhängig davon, ob es in dem jeweiligen Gebiet Wolfsübergriffe gibt. Neben der Untersuchung der rein technischen Aspekte des Herdenschutzes ist es ebenso wichtig herauszufinden, wie die Akzeptanz gegenüber Herdenschutzmaßnahmen bei den Tierhaltenden verbessert und deren Eigenmotivation erhöht werden kann. Hierfür sind Daten zur Umsetzbarkeit und Akzeptanz der eingesetzten Herdenschutzmaßnahmen erforderlich. Nutztierhaltende sollten schon in die Konzeption entsprechender Studien mit eingebunden werden, um sicherzustellen, dass die Fragen untersucht werden, deren Beantwortung für sie am dringendsten ist. Der Weg von einem emotionsbasierten zu einem evidenzbasierten Wolfsmanagement führt über wissenschaftlich robuste Daten und Analysen. Entsprechende Untersuchungen sind nur in enger Zusammenarbeit zwischen Weidetierhaltung und Wissenschaft möglich. Basierend auf der Fachkompetenz und den praktischen Erfahrungen der Weidetierhaltenden kann die Wissenschaft helfen, die Herdenschutzmaßnahmen zu identifizieren und weiterzuentwickeln, die Nutztierübergriffe am effektivsten reduzieren. Summary As the wolf population grows, the number of attacks on livestock in Germany also increases from year to year. Agriculture, nature conservation and politics agree on one point: that wolf attacks on livestock should be reduced sustainably. However, there are differing views on how this goal can best be achieved. In the public debate, calls for simplified shooting of wolves or general hunting are becoming louder and louder. The assumption is that such measures could sustainably reduce livestock damage caused by wolves. Before wildlife management measures are applied, clear objectives are needed. The first question, therefore, must be: What is the primary objective of the management measure? Based on scientific evidence, it must be evaluated in advance whether the measures under consideration are suitable for achieving the objective. This is mandatory if the measures include the killing of sentient animals, particularly if they are strictly protected. Criteria for evaluating if the objective was reached are needed in order to be able to verify how effective the selected management measures are when applied. In this chapter, we address the question of which management measures are suitable, based on current knowledge, to achieve the goal of sustainably reducing wolf attacks on livestock. We first explain why wolves kill livestock and whether there is a relationship between the number of wolves and the amount of livestock damage. To do this, we examine, among other things, data on wolf attacks on livestock in Germany. Based on an extensive literature review, we analyse whether the following management measures are suitable to sustainably reduce wolf attacks on livestock: 1) a general hunting of wolves, 2) the selective removal of individual wolves causing damage, and 3) non-lethal livestock protection methods. Finally, we present recommendations for evidence-based and solution-oriented wolf management with respect to wolf-livestock conflict. In Germany, as wolf territories increase, attacks on sheep and goats also increase. However, the magnitude of the increase differs considerably among the federal states. Individual federal states achieve very different levels of damage with the same number of wolf territories. This suggests that the extent of damage is not solely determined by the number of wolves. We suspect that the differences in damage levels are mainly due to the different implementation of livestock protection measures in the individual federal states. The results of the literature review regarding the effectiveness of lethal and non-lethal management measures to protect livestock clearly show that general hunting of wolves does not reduce livestock damage. There is no scientific evidence that hunting significantly and sustainably reduces damage, unless the wolf population is drastically reduced or completely eradicated. This is not possible in Germany and in the European Union under the current legal situation. In contrast to an undifferentiated hunting of the wolf, the targeted shooting of individual animals can be effective if they are actually individuals that have learned to overcome recommended functional livestock protection measures. However, such cases are rare and it is difficult in the field to safely identify and kill a specific individual. Non-lethal livestock protection measures are much better at achieving sustained reductions in damage compared to lethal measures. The only way to achieve a lasting reduction of damage to livestock in coexistence with wolves is the professional implementation of livestock protection measures on a broad scale. Non-lethal livestock protection measures do not completely prevent attacks on livestock. However, if correctly applied they can significantly reduce wolf caused damages on livestock. The knowledge of how to reduce livestock depredation by wolves through herd protection measures is also available in Germany. Many livestock farmers have developed a high level of expertise in this field. However, experience from the past 20 years also shows that the funding of livestock protection measures alone is not enough to significantly reduce the number of wolf attacks. It is also necessary to ensure that technical expertise is available for proper application and maintenance of the measures. Especially in areas with predation hotspots, livestock owners should be actively approached and the reasons for increased attacks analysed and remedied. To date, there is a lack of data from Germany on the functionality of funded and applied protection measures. Such data are necessary to understand why, despite increasing prevention expenditures, livestock damage has not decreased in some cases, even in areas where wolves have been present for years. Moreover, such data are the basis for scientific studies on possible differences in the effectiveness of different livestock protection methods. Data on the functionality of funded protection measures should be collected at least on a random basis, regardless of whether there are wolf attacks in the respective area. In addition to investigating the purely technical aspects of herd protection, it is equally important to find out how the acceptance towards livestock protection measures can be improved among livestock owners and how their self-motivation can be increased. This requires data on the feasibility and acceptance of the applied protection measures. Livestock keepers should be involved already in the conception of appropriate studies to ensure that the investigations will answer the most urgent questions for them. The path from emotion-based to evidence-based wolf management is through scientifically robust data and analysis. Appropriate research is only possible through close collaboration between livestock owners and science. Based on the expertise and practical experience of farmers, science can help identify and improve the livestock protection measures that most effectively reduce wolf attacks on livestock.
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Do wolves hunt freshwater fish in spring as a food source?
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Full-text available
  • Mar 2018
In April–May 2017 we documented GPS-collared wolves (V034 and V046) from the same pack in northern Minnesota responding to a spring fish (northern pike and presumably white suckers) run, which to our knowledge is the first description of wolves outside of a coastal marine environment using fish as a seasonal food source. During this period, we opportunistically observed V046 hunting and consuming fish along a single creek, and documented a substantial number of wolf-killed fish in this area. We estimated V034 and V046 spent 43–63% of their daily time budget from mid-April to mid-May hunting and consuming fish at the same creek. Based on visual observation and the concentration of GPS locations, it appears the wolves targeted shallow, narrow areas along the creek to capture fish. Although short-term responses to alternate foods, such as fish, can be infrequent and challenging to document, they provide valuable insight to the flexibility of wolf hunting and foraging behavior.
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Food habits of the world's grey wolves
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Full-text available
Grey wolves Canis lupus have been studied extensively, but there has been no detailed review of the species' feeding ecology, despite growing debate about how to conserve wolf populations while limiting their impacts on wild or domestic ungulates. Here, we assess the extent to which the grey wolf diet varies among and within North America, Europe, and Asia. We derived dietary data from searches of published literature. We grouped studies based on their bioregional location. We compared grey wolf diet among locations using non-metric multidimensional scaling and analysis of similarity. We assessed whether increased human impacts are associated with decreased grey wolf dietary diversity. Finally, using studies from southern Europe, we assessed whether the importance of wild ungulates in grey wolf diet has increased over time, coincident with a decline in domestic species in grey wolf diet over time. We compiled dietary data from 177 studies incorporating 94607 scat and stomach samples. Grey wolf diet was dominated by large (240-650 kg) and medium-sized (23-130 kg) wild ungulates, but variation in the percentages of wild ungulates consumed, along with variation in the percentages of domestic and smaller prey species consumed, contributed to the dietary differences found among and within continents. We found no evidence that grey wolf dietary diversity varies globally, although the results from southern Europe suggest that grey wolves may switch their diets away from domestic species if more wild ungulates are available. The diversity of prey consumed by grey wolves shows that the species is capable of surviving dramatic anthropogenic upheaval. However, there is an urgent need to increase our understanding of grey wolf foraging ecology in human-dominated landscapes, in order to determine whether restoration of depleted prey populations, coupled with effective damage-prevention measures, will reduce human-wolf conflicts.
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Population dynamics of wolves in northcentral Minnesota
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Full-text available
  • Jan 1989
During September 1980-December 1986, 81 radio-collared wolves (Canis lupus) were monitored in and near the 839-km2 Bearville Study Area )BSA) in north-central Minnesota. Each year winter-territory size averaged 78-153 km2; no territories had road densities >0.72 km/km2. From zero to 30% of radiomarked pup, yearling, or adult wolves left their territories each month. Pups left natal packs during January-March and older wolves left frequently during September-April. Wolves temporarily leaving territories moved 5-105 km away and were absent 3-118 days; up to 6 exploratory moves were made prior to dispersal. Dispersing wolves traveled 5-100 km away during periods of 1-265 days. One disperser joined and established pack, but 16 others formed new packs. Annual dispersal rates were about 0.17 for adults, 0.49 for yearlings, and 0.10 for pups. Each year mean pack size ranged from 5-9 in November/December to 4-6 in March. Annual wolf density (including 16% lone wolves) ranged from 39-59 wolves/1,000 km2 in November-December and 29-40 wolves/1,000 km2 in March. Annual immigration was 7%. The observed mean annual finite rate of increase was 1.02, and annual rates of increase were correlated with mean number of pups per pack in November. Litters averaged 6.6 pups at birth and 3.2 pups by mid-November, at which time pups made up 46% of pack members. Annual survival of radio-marked wolves >5 months old was 0.64. Despite legal protection, 80% of identified wolf mortality was human caused (30% shot, 12% snared, 11% hit by vehicles, 6% killed by government trappers, and 21% kill by humans in some undetermined manner); 10% of wolves that died were killed by other wolves. During sample periods in 2 winters, wolves were located twice daily to estimate predation rates on white-tailed deer (Odocoileus virginianus). Estimated minimum kill rates during January-February (x = 21 days/kill/wolf) did not differ between winters with differing snow depths. Winter consumption averaged 2.0 kg deer/wolf/day (6% body wt/day). Scat analyses indicated deer were the primary prey in winter and spring, but beaver (Castor canadensis) were an important secondary prey (20-47% of items in scats) during April-May. Neonatal deer fawns occurred in 25-60% of scats during June-July whereas the occurrence of beaver declined markedly. Overall, deer provided 79-98% of biomass consumed each month. Adult wolves consumed an estimated 19/year, of which 11 were fawns. A review of North American studies indicates that wolf numbers are directly related to ungulate biomass. Where deer are primary prey, territory size is related to deer density. Per capita biomass availability likely affects pup survival, the major factor in wolf population growth. Annual rates of increase of exploited populations vary directly with mortality rates, and harvest exceeding 28% of the winter population often result in declines. Management decisions concerning wolf and ungulate density and ungulate harvest by humans can be made using equations that incorporate estimate of wolf density, annual ungulated kill per wolf, ungulate densities, potential rate of increase for ungulates, and harvest.
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Pollination and Breeding System of Lowbush Blueberries, Vaccinium angustifolium Ait. and V. myrtilloides Michx. (Ericacaeae), in the Boreal Forest
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Breeding systems and pollination requirements of two wild lowbush blueberries, Vaccinium angustifolium and V. myrtilloides, in the Canadian boreal forest in the Chapleau Crown Game Preserve, Ontario, were tested. Fruit production, size and seediness were significantly higher in samples exposed to natural pollination than in those cross- or self-pollinated by hand. There were no significant differences among artificial treatments (variously hand-pollinated and bagged) except when cross-pollination (xenogamy) was done by insect pins. In V. angustifolium, the density of flowering varied with forest age (canopy closure). It was most in open areas and least in the sites with the most mature forest. Although fruit-set and seediness varied among forest habitats of different ages, there were no significant differences between sites in forests of different ages. Thus, pollination seems to be similarly effective no matter the age of the forest. In both species, fruit-set in 1992, which had severe June frosts, was markedly poorer than that in 1993 when the flowers suffered little frost damage. The combined number of complete and incomplete seeds from the fruit among the breeding and pollination systems tested were similar; however, the ratio of complete seeds to total seeds was greater from cross-pollinated than from self-pollinated flowers. Our observations indicate that there is little natural fruit-set without insect-mediated cross-pollination and that cross-pollination provides much better fruit and seed-set than does self-pollination.
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Estimating grizzly bear food habits from fecal analysis
Article
  • Jan 1996
We fed 27 different food items to captive grizzly bears (Ursus arctos) to investigate the need for correction factors (CF's) when estimating grizzly bear food habits from fecal residue. The amount of food necessary to produce 1 ml of fecal residue ranged from 0.16 to 40.8 g dry matter, suggesting that uncorrected fecal analysis are rarely equivalent to food habits. We propose CF's that relate the volume of residue in the feces to the mass of dry matter ingested. The ranges of these CF's were 0.16-0.35 for vegetation, 0.51-1.84 for berries, 0.35-1.40 for roots, 0.91-1.25 for insects, 1.54 for pine nuts, 1.54-12.5 for mammals, and 40.8 for fish. The CF for large mammals depends upon how much skin, hair, bones, or other poorly digested components are consumed.
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Constraints On Frugivory By Bears
Article
Bears consuming wild fruits for fall energy accumulation are constrained by several factors, including intake rate, the physiological capacity of the gastrointestinal tract, and the metabolic efficiency of gain in body mass. We measured these relationships through foraging and feeding trials using captive and wild black bears (Ursus americanus) and grizzly bears (Ursus arctos). Four fruit types covering a range of sizes and clustering were offered to captive bears to determine the effect of density, size, and presentation on intake rate. Intake rate (in grams per minute) and bite rates (in bites per minute) increased curvilinearly with increasing fruit density in singly spaced fruits. Maximum intakes ranged from 30 g/min for 0.5-g berries to >200 g/min for 4.2-g fruits. The highest bite rates were obtained during the initial encounter with each patch as bears consumed all visually apparent fruits on the surface. Bite rates quickly dropped by 15-20% as foraging continued within the patch. Maximum bite rates were not depressed until initial fruit density fell to <50 berries/M3. Maximum daily fresh fruit intake for the captive bears averaged 34 ± 6% (mean ± 1 SD) of body mass. The dry-matter digestibility of wild fruits, particularly preferred species, was as high as 72%. While large captive bears could gain body mass very rapidly when given fruit ad libitum, foraging efficiencies increasingly constrained growth rates of wild bears >100 kg. We concluded that large bears, such as grizzlies, must depend on plants that permit large bite sizes or high bite rates through fruit clustering and bush configuration that reduce leaf-to-fruit ratios.
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Refining the Equation for Interpreting Prey Occurrence in Gray Wolf Scats
Article
  • Jul 1993
The degree to which relative frequencies of large ungulates in wolf scats represent the proportion of prey consumed is unknown. Thus, I fed mule deer (Odocoileus hemionus), elk (Cervus elaphus), and moose (Alces alces) carcasses to 3 captive gray wolves (Canis lupis; hereafter referred to as wolves) to refine interpretation of prey occurrence in wolf scats. The mass (kg) of prey per collectable scat (Y) increased as the body mass of prey (X) increased (r2=0.96). The slope of the linear regression (b = 0.008) differed (P < 0.001) from that of Floyd et al. (1978) (b = 0.020), but not from that of Traves (1983) (b = 0.011) (P = 0.13). I recommend using an equation (Y = 0.439 + 0.008X) derived from combined studies that spans prey sizes from snowshoe hare (Lepus americanus) to adult moose and is robust to variable field conditions. Maximum bias of up to 50% using frequency of occurrence (percentage of scats) occurs when 1 very small (e.g., beaver [Castor canadensis]) and 1 very large (e.g., adult moose) prey make up 20-80% of the scats. Previous studies that have extrapolated from the Floyd et al. (1978) equation for interpreting occurrence of adult elk and moose in wolf scats may have overestimated relative numbers and biomass of these large cervids by up to 18%.
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Relating Wolf Scat Content to Prey Consumed
Article
  • Jul 1978
In 9 trials, captive wolves (Canis lupus) were fed prey varying in size from snowshoe hares (Lepus americanus) to adult deer (Odocoileus virginianus), and the resulting scats were counted. Field-collectible scats were distinguished from liquid, noncollectible stools. In collectible scats, the remains of small prey occurred in greater proportion relative to the prey's weight, and in lesser proportion relative to the prey's numbers, than did the remains of larger prey. A regression equation with an excellent fit to the data (r2 = 0.97) was derived to estimate the weight of prey eaten per collectible scat for any prey. With this information and average prey weights, the relative numbers of different prey eaten also can be calculated.
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