sábado, 6 de octubre de 2012

Prey and prey-age preference by the Iberian wolf Canis lupus signatus in a multiple-prey ecosystem. Isabel Barja. (2009)

Foto de Javier Muñoz Gutiérrez. En: fotonatura.org/
In many regions of the Iberian Peninsula, wild ungulates have disappeared and wolves Canis lupus often depend on garbage dumps and domestic animals. This paper represents an example of wild ungulate preferences of the Iberian wolf Canis lupus signatus in an environment with no human-wildlife conflicts, because wolves rarely predate on livestock. I studied the patterns of prey selection by the Iberian wolf during May 1998-October 2002 in northwestern Spain, in an area which supports a diverse community of wild ungulates and in which also domestic ungulates are present. My analysis of 593 wolf scats showed that wild ungulates were consumed preferentially over other prey (i.e. domestic ungulates, carnivores and lagomorphs). Roe deer Capreolus capreolus was the most important prey species followed by red deer Cervus elaphus and wild boar Sus scrofa. Domestic ungulates were poorly represented in the wolf diet. Predation frequencies of domestic and wild ungulates varied seasonally and between years. The consumption of roe deer and wild boar increased during the birthing season, probably because of the higher vulnerability of newly born animals; wolves predate mainly on juvenile roe deer and wild boar.

Most studies on the feeding ecology of the wolf Canis lupus have been conducted in North America. In Europe, there have been various studies on wolf diet, some of which showed wild ungulates as the wolf’s main prey. However, the feeding habits of Iberian wolves Canis lupus signatus have received little attention and the studies performed have shown that the species’ food habits are highly variable depending on the areas in which the species occurs. In many regions of the Iberian Peninsula, domestic ungulates are of importance, whereas in other areas, the most relevant prey is wild ungulates. However, the former studies were fundamentally descriptive, and usually only included data corresponding to one year. It is not known, therefore, whether and how wolf feeding habits change over time. Furthermore, the information contained data, which did not study the age of the selected prey. The trophic ecology of the Iberian wolf, therefore, remains largely unknown. The aim of my study was to test the hypothesis that the Iberian wolf is an opportunist species. To test this hypothesis, I predicted that: 1) the wolf consumes the most abundant prey species and also food which is easier to acquire (i.e. domestic ungulates, carrion and garbage), 2) the consumption of prey species varies throughout the year according to prey vul nerability, so wolves will prey on the individuals and species easier to capture, and 3) for an opportunist species, in a multiple-prey ecosystem and with high food availability, trophic specialisation should not be observed over time.
Material and methods
Figure 1. Location of the study area in the Iberian Peninsula.
My study was conducted in the Macizo Central Ourensano in Galicia (northwestern Spain), a mountainous area that includes the Montes do Invernadeiro Natural Park (Fig. 1). The study area, which covers 120 km2 and is part of a larger continuous area (45,829 km2) […] The human population density in the study area is one of the lowest in the region (0.8 habitants/km2).

Scat analysis and collection
Both prey and prey-age preferences of the Iberian wolf were assessed from scats collected systematically every 45 days during May 1998-October 2002. Scats were collected by surveying roads and firebreaks in the study area. Faecal marking sites (mainly crossroads) were also included in the search, because the probability of defecation in these places is greater. […]The date of collection and age of all scats were registered. Maps with a grid of 1 km2 cells (Universal Transverse Mercator,UTM) were used to record the scat position. […] Analysis of scats followed standard procedures. […]

Prey and biomass estimation
The linear regression model used for ingested prey was y=0.0731+0.00406x (R2=0.84, F=42.4, df=1,8, P=0.0002; derived from Table 1 in Ruehe et al. 2003), where y is the biomass ingested (in kg) per collected scat, and x the average consumed mass (in kg)of an individual of each prey type.
To estimate the ingested biomass of domestic and wild ungulates (i.e. roe deer Capreolus capreolus, red deer Cervus elaphus, wild boar, sheep Ovis aries and goat Capra aegagrus), the relative proportions of the two age classes ( juvenile and adult) were taken into account (Table 1). However, to calculate the ingested biomass of fallow deer Dama dama and mouflon Ovis orientalis, the average mass for the two age classes was used, because it was impossible to assess the relative age of the consumed individuals. For carnivores and lagomorphs, the ingested biomass was calculated considering only the mass of adults.
To determine the densities of wild ungulates (i.e. roe deer, red deer and wild boar) in the study area, observations of all species were registered along four transects whose total length was 82 km. […] Goats and sheep are maintained in an intensive system (700 individuals) in the study area, where as cows Bos Taurus and horses Equus caballus are in an extensive system (86 individuals). All domestic and wild ungulates were potentially available to wolves all year around.

Table 1. Composition of Iberian wolf diet during May 1998 - October 2002 based on 508 scats. The ingested biomass (a in kg) was calculated using body masses only for adults. The birds (b) were not included in the linear regression model, because only mammals
were included in the feeding trials. These results were estimated on the basis of the consumed prey mass of an individual prey, which represents x in the biomass equation. The prey mean mass (c in kg) was obtained from Urios 1995, Llaneza et al. 1996, Blanco 1998 and Mateos-Quesada 2002.
Data analysis
I used a hierarchical log-linear analysis (Backward method) to investigate the effects of season and year simultaneously on the consumption of domestic and wild ungulates. […]

Figure 2. Percentage (frequency of occurrence) of two domestic
and three wild ungulate species in the Iberian wolf diet per year.
The Shannon diversity index (H') and dominance index (D) are
calculated per year. In 1998: N=74, in 1999: N=146, in 2000:
N=96, 2001: N=78 and in 2002: N=94.
General remarks
A total of 593 scats were used for dietary analysis. A fraction (10.9%) of the scats consisted of a combination of soil, plants and undetermined matter; 6.2% of the scats contained soil and 9.4% contained B. sylvaticum, but none of these items were considered to be food. The majority (98.5%) of the analysed scats contained remains of just one prey species, and only 1.5% contained remains of two prey species. Prey species were identified in 87.3% of the scats collected. In terms of biomass, the types of food identified in the analysed scats were wild ungulates (87.1% including roe deer, wild boar, red deer, fallow deer and mouflon), domestic ungulates (11.3% including goat and sheep), carnivores (1.1% including dog Canis familiaris, cat Felis catus and badger Meles meles) and lagomorphs (0.5% rabbit Oryctolagus cuniculus). […]

Figure 3. Percentage (frequency of occurrence) of two domestic
and three wild ungulate species consumed per season. The percentage
of occurrence for each prey species is based on the total
number of scats found per season.
Annual and seasonal patterns
Roe deer was the main prey taken in all years (Fig. 2). In 2001, the lowest dietary diversity and the highest dominance were found, taking into account the following prey species: roe deer, red deer, wild boar, goat and sheep. The highest diversity and the lowest dominance values corresponded to 1998 (see Fig. 2). Roe deer was the prey species that was consumed most often in all seasons (Fig. 3), but especially during summer (52.0%; frequency of occurrence) and spring (26.2%). The consumption of wild boar was greater in spring (37.1%) and autumn (31.0%) than in summer (19.8%) and winter (12.1%). The highest consumption of red deer occurred in spring (37.4%), followed by autumn (28.1%), winter (26.9%) and summer (7.6%). The consumption of domestic ungulates (sheep and goats) also showed seasonal variation, with consumption significantly higher in spring (50.0%) and summer (23.8%) than during autumn and winter. […]

Prey-age preferences
Analysis of bone remains allowed the identification of prey species in 85 of the 119 scats in which they were found. Of the scats, 69.4% contained bone remains of roe deer, while 27.0% contained wild boar bones, 2.4% goat/sheep bones and 1.2% red deer bones. Wolves selected juveniles from roe deer and wild boar populations: 74.1% of roe deer and 82.6% of wild boar whose age was determined were juveniles (<1 year old).

The wolves studied fed mainly on wild ungulates, while domestic ungulates and other preys (carnivores, lagomorphs and birds) were taken occasionally. In my study, the consumption rate of wild and domestic ungulates did not depend on their availability. […]The presence of livestock remains in wolf scats implies scavenging behaviour, because no attacks on livestock were reported during my study. Furthermore, in a zone of the study area (Montes do Invernadeiro Natural Park), horses and cows were kept in an extensive system, but there was no indication that wolves preyed on them (neither on adults nor on young). […]
The scarce consumption of livestock species in the study area could be correlated with the high abundance, richness and diversity of wild ungulates […] However, predation on domestic ungulates may remain high if livestock is locally abundant and the methods of livestock raising are inappropriate, i.e. the livestock is left unguarded in the countryside. In some regions of the Iberian Peninsula with high human population densities and scarce wild preys, wolves take livestock, carrion and even garbage […]

The trophic position of the wolf in the study area is closer to a facultative specialist than to an opportunist species, because a facultative specialist may change from a key food item when other profitable prey is available. Furthermore, it is important to emphasise that the predation upon roe deer in the study area could depend on local feeding specialisation of the studied wolves.
The study of wolf populations inhabiting areas which are only a little altered by men, and with a high availability of wild ungulates and low human population densities, provides very valuable information on the wolf diet under conditions of low human interference. Understanding the factors related to wolf prey preferences in areas where different potential prey species coexist is of great use in reducing the number of attacks on livestock. In areas with low wild ungulate densities, and where wolves therefore prey on domestic ungulates, reinforcement of wild prey numbers, surveillance of livestock and limitation of the access to carrion would force wolves to specialise in the consumption of wild prey and to transmit this behaviour to their offspring. This would help minimise the conflicts between wolves and humans, which without doubt would help to guarantee the long-term conservation of the species.

Prey and prey-age preference by the Iberian wolf Canis lupus signatus in a multiple-prey ecosystem. Isabel Barja. (2009)  http://bit.ly/PI5wja Wildl. Biol. 15: 147-154 (2009) (Publicado en internet por http://www.wildlifebiology.com/ )


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