Effect of rodents on acorn dispersal and survival of the Liaodong oakWord格式文档下载.docx

1、revised 26 March 2002;accepted 13 May 2002.;Available online 8 August 2002. AbstractWe used a new method of labeling seeds with small pieces of coded tin-tags to investigate the effect of rodent on the seed fate of Liaodong oak （Quercus liaotungensis） in a mountainous area （4000N, 11530E） of Beijing

2、, China. In the fall of 1999 and 2000, a total of 1994 and 660 acorns were released and then seed loss was checked. Both sides of the 50m wide transect were extensively checked to locate the tagged seeds or their fragments. The results indicated that Apodemus speciosus, Rattus confucianus and A. agr

3、arius were potential Liaodong oak acorn predators. Nearly all acorns were consumed by small rodents within 10 days after acorn placement, demonstrating that seed predation was very heavy and that rodent predation contributes to the poor seed regeneration of the oak. The dispersal distances of most s

4、eeds were within 20m. The dispersal distance of the buried seeds was the longest and it was in favor of seed survival and seedling recruitment. Rodents preferred to eat tagged seeds under dense shrub. This is mostly related to predation risk in different micro-environments. Rodents tended to bury th

5、e tagged seeds under dense shrub. This burial place of rodent does not favor the seedling recruitment of the oak. The rodents preferred to move seeds to the horizontal and down directions of a slope and this tendency would save energy for rodents. The seeding regeneration rate of tagged acorns were

6、very low in 2 years. Rodent predation is the causative factor of low regeneration of Liaodong oak in the study region.Author Keywords: Liaodong oak （Quercus liaotungensis）; Rodent; Seed dispersal; Seed survival; RegenerationArticle Outline1. Introduction2. Methods2.1. Study site 2.2. Key rodent spec

7、ies affecting seeds disappearance 2.3. Seed-marking-releasing experiment 2.4. Statistics3. Results3.1. Key rodent species affecting the disappearance of oak acorns 3.2. The fate of acorns in situ 3.3. The fate of acorns dispersed 3.4. Dispersal distance 3.5. Micro-environment of the dispersed acorns

8、 or their preserved fragments 3.6. Dispersal slope-directions 3.7. Cache size 3.8. Seed survival4. Discussion4.1. Species affecting acorn disappearance and recruitment 4.2. Seed predation 4.3. Dispersal 4.4. Survival of the tagged seedsAcknowledgementsReferencesThe propagules of plants are exposed t

9、o high risk of attack by natural predators such as insects, vertebrates and fungi （Janzen, 1970）. Seed mortality due to predation by animals may affect plant fitness, population structure and dynamics, community structure and maintenance of species diversity （ Janzen; Grubb; Clark; Schupp; Schupp an

10、d Willson）. In forest ecosystems, rodents are recognized as an important factor affecting acorn fate （ Shaw and Shaw; Kanazawa and Nishikata, 1976; Kikuzawa, 1988; Herrera, 1995）. In most situations, a large proportion of dispersed acorns by rodents are consumed, hence very few acorns are able to be

11、come seedlings （ Sork; Miyaki and Herrera）. However, rodents can also disperse some acorns and bury a few of them. Seed dispersal is recognized as key phase affecting plant regeneration, species survival and distribution （ Howe and Smallwood, 1982）. Seed dispersal affects fitness of parent and offsp

12、ring plants through its effects on seed density, the dispersal distance from the parent tree, and the habitat where seeds arrive. Differences in dispersal may influence early seed and seedling survival by affecting incidence of predation or attack by pathogens, the habitat to which seeds are dispers

13、ed, as well as the types of plants with which the developing plant will compete （ Schupp; Jordano and Willson）.Although seed dispersal by animals is one of the most important mechanisms in the ecology and evolution of mutualistic systems （Bronstein, 1994）, we still have very limited knowledge about

14、seed dispersal systems. One of the reasons why research progress is slow is the difficulty in tracking the fate of all the seeds that are dispersed （ Sork, 1984）. A disadvantage of present techniques is that tagged seeds are not distinguishable from each other. Zhang and Wang （2001a） developed a new

15、 method of labeling seeds with small pieces of tin-tags. The tin-tagged seeds are coded and then identified easily from each other. This method makes it possible to determine the distribution of individual seeds dispersed by animals and the ultimate fates of those seeds.Quercus liaotungensis is one

16、of the common climax tree species in warm temperate broad-leaved deciduous forests in northern China and Q. liaotungensis forests are typical vegetation in the mountains of Beijing （Chen, 1992）. Because of extensive human disturbances, primary Liaodong oak forests no long exist and only small patche

17、s of secondary Liaodong oak forests or shrubs are scattered among shrubs or grasses （ Chen, 1997）. The acorn of Q. liaotungensis is ovoid, 0.91.8cm wide, 1.42.3cm long and 0.63.4g in mass （Wang and Ma, 2001）. The oaks （Quercus sp.） can be grouped into two subgenera which are White oak （WO） （Lepidoba

18、lanus） and Red oak （RO） （Erythrobalanus）. Liaodong oak （Q. liaotungensis） belongs to the WO. Since Liaodong oak acorns are nutritious, they are excellent food resources for small mammals and birds, especially for small rodents （Wang et al., 1999）. The natural regeneration of Quercus is lacking in th

19、e field in many woodlands （Cho and Boerner, 1991）. The regeneration mainly depends on the sprout and the growth of the coppices is bad. In the study region, the natural seeding regeneration rate of Liaodong oak is less than 0.1% （Zhang, unpublished）. It is very hard to see the seedlings of Liaodong

20、oak even after the acorn mast-year. Previous studies showed that rodents eat and disperse a large part of Quercus acorns in temperate forests （Shaw; Kikuzawa and Iida）. So it is necessary to understand effect of rodents on acorn dispersal and survival of the Liaodong oak for improving its natural re

21、generation.The purpose of this study was to investigate the effect of rodents on the fate of Liaodong oak acorns. Specially, we addressed the following subjects: （1） acorns fate in situ; （2） dispersed acorns fate; （3） dispersal distance and patterns of the tagged seeds; （4） micro-environments where

22、seeds are dispersed or buried; （5） survival of the tagged seeds.2.1. Study siteThe experiment was carried out in a mountainous area near Liyuanling Village, Mentougou District, Beijing, China. The study site is located at a latitude and longitude of 4030E, about 120km northwest of Beijing City. This

23、 area belongs to Dongling Mountain Region, with a warm temperate continental monsoon climate. In the study area, the ecosystem has been greatly destroyed due to extensive cutting and goat grazing for almost a century. Oak （Q. Liaotungensis）, wild walnut （Juglans mandshurica）, wild apricot （Prunus ar

24、meniaca）, Vitex negundo and Prunus davidiana are common shrubs. Under shrublands, Elymus excelsus, Poa spp., Elsholtzia stauntoni are common grasses. Larch （Larix principis-rupprechtii） and China pine （Pinus tabulaeformis） have been planted in small areas by a local forestation farm. In the study re

25、gion, the production of Liaodong oak acorn was very low in 1999 and nearly no sound and mature acorns were found. In contrast, the abundance of acorn reached its mast-year in 2000. The rodent densities in 2 years did not show obvious difference （trap success 3.125% in 1999; 2.95% in 2000）.2.2. Key r

26、odent species affecting seeds disappearanceOn 29 October 2000, wooden snare kill-traps were baited with fresh and ripe Liaodong oak acorns to determine the small rodents that were potentially removing acorns. In order to minimize the trapping effect on the rodent population in the plot where acorns

27、were released, the trapping plot was about 400m away from the seed-releasing transect but in the same slope. Four transects were selected. Twenty-five trap stations with an interval of 5m were set along each of the four transects for two consecutive nights. To compare the food preference of differen

28、t animals for Liaodong oak acorns, two traps were set side by side at each trap station at the same time. One trap baited with a Liaodong oak acorn, and another baited with a fresh peanut （a routine bait）. Traps were checked everyday and the captured rodents were recorded. We repeated this experimen

29、t on 5 November 2000.2.3. Seed-marking-releasing experimentOn 2030 September 1999 and 2000, intact and fresh Liaodong oak acorns were collected for seed-marking-releasing experiment. To prevent destruction of the kernel inside, tiny holes were pierced with a needle in the gap between the seed coat a

30、nd the kernel at the wider side of the acorns. Small, light tin-tags, 4cm long and 1cm wide were connected with a thin steel wire 3cm long. The tags were coded by using a sharp metal-pen. The tin-tagged seeds are easy to find after being dispersed by rodents. If seeds are buried in the soil by roden

31、ts, the tin-tags are left on the surface of the ground. Prior preliminary studies showed the metal-tagged seeds would be removed as readily as unmarked seeds. Thus the experimental treatment yields realistic results on the movement pattern of oak acorns.In the study area, a 220m transect was selected for seed-releasing and 22 plots were located 10m apart along this transect. A metal sign was hung near each plot to identify the plots. To identify the realistic results of seeds loss, we selected the plots where very few seeds of