Author: Elizalde-Arellano, Cynthia
Date published: October 1, 2012
Most terrestrial mammals are known to maintain their activity within a relatively specific area, commonly referred to as the home range, or if defended, the territory (Burt, 1943). Though the home range can change seasonally and over the lifetime of the animal, it is the area where animals spend most of their time and make their daily movements for foraging and other fitness related activities. General patterns regarding the size and use of this area are that larger mammals have larger home ranges and travel longer distances than small mammals (McNab, 1963; Schmidt-Nielsen, 1984). Within a given species, however, there is often a high amount of variability in the size of home ranges, the amount they travel per day within the area, and the timing of these periods of activity (McNab, 1963; Gompper and Gitdeman, 1991). Common factors that seem to contribute to this variation are the sex of individuals, their age, time of year, habitat type, food type, prey density, and lastly latitude of occurrence (Harestad and Bunnell, 1979).
Among the different trophic groups, members of the order Carnivora seem to have a high amount of latitudinal variability within species. The general pattern appears to be smaller home range sizes in lower, more equatorial latitudes, which has been explained by the variation of quantities of food resources with latitude (Gittleman and Harvey, 1982; Gompper and Gittleman, 1991). Within this group, the bobcat (Lynx rufus) appears to be one of the more variable.
Bobcats are widely distributed latitudinally (Lariviére and Walton, 1997; Sunquist and Sunquist, 2002; Hansen, 2007) and show ample geographic differences not only in their home range size but also in their daily movements (daily travel distance and speed), and activity patterns within United States (McCord and Cardoza, 1982; Lariviére and Walton, 1997; Hansen, 2007).
Daily travel distances ranged from 1 .1 to 4.9 km in Montana and Oregon and 6.2 to 9.9 km in South Carolina. (Buie et a?, 1979; Knowles, 1985; Witmer and DeCalesta, 1986; Sunquist and Sunquist, 2002). In all instances, males traveled longer distances (6.2 km ±1.5 se) than females (3.8 km ± 1.4 se) based on data in Lariviére and Walton (1997). The average speed bobcats travel appears to be higher in the north (Illinois: 0.601 km/h for males and 0.30 km/h for females) than the south (Louisiana: males; 0.36 to 0.45 km/h and females; 0.19 to 0.22 km/h; (Hall and Newsom, 1976; Woolf and Nielsen, 2002). In all areas there were differences in speed of travel between the sexes.
Home range sizes of bobcats are highly variable even within the same geographical region, e.g., 0.6 to 95 km2 in California and 13 to 201 km2 in Minnesota (McCord and Cardoza, 1982), making latitudinal comparisons difficult. Females appear to have smaller home ranges than males and in most studies female ranges do not overlap (Bailey, 1974; Lariviére and Walton, 1997; Hansen, 2007). Conversely, male home ranges will overlap with females and other males (Lariviére and Walton, 1997).
The activity pattern of bobcats suggests they are mainly crepuscular predators, being most active before and after sunset and sunrise with their lowest activity at midday hours (Lariviére and Walton, 1997; Sunquist and Sunquist, 2002; Chamberlain et al, 2003). In northern areas in winter, bobcats are more active during daytime hours, whereas in more southern areas where daytime temperatures are higher than 26 C, bobcats are mainly nocturnal (Sunquist and Sunquist, 2002).
Though these studies have added significandy to our understanding of geographical and latitudinal differences in home range and activity characteristics of bobcats, most studies have been conducted in more northern areas of their range. Though bobcats have been studied as far south as southern New Mexico (Harrison, 2010), they extend further southward to the central-southern part of Mexico (Hall, 1981; McCord and Cardoza, 1982). Although data exist on a variety of aspects of bobcats from this region (Delibes et al, 1986; Delibes and Hiraldo, 1987; Romero, 1993; Delibes et al, 1997; Jiménez et al, 1997; Chávez and Ceballos, 1998; Moreno-Valdéz, 1998; Pacheco et al, 1999-2000; Aranda et ai, 2002; Burton et al, 2003; Romero and Ceballos, 2004; Barcenas and Medellin, 2007; RodriguezMartinez et al, 2007) across this vast range, we have no information on how or if home range and activity characteristics vary from more northern populations. Having data on home range and activity characteristics from this more southern region would help fill the gap in our knowledge on this species and provide a valuable comparison regarding possible latitudinal variation in these parameters.
To fill the gap in our data on bobcats from more southern regions of their range and provide data for comparisons with more northern populations, we investigated the home range size, daily travel distances, and activity patterns of bobcats in mid-northern Mexico. In particular we conducted our study in the central part of the Chihuahuan Desert (Fig. 1 ) . Our objective was to estimate home range size, daily activity patterns, and daily travel distances, then compare those data with data from more northern populations. In addition, we regressed our data witìi those of odier studies against latitude of the study sites to test if there was any support for predictable latitudinal changes in these parameters. The results of these comparisons and regression analyses should help increase our understanding of how and possibly why these home range and activity characteristics vary over the range of bobcats.
This study was conducted at the Mapimi Biosphere Reserve (MBR), (26°1G-27°00'?, 103°23'-104°07'W) in the Chihuahuan desert. The Reserve is 342,388 ha in size and is in the states of Durango, Coahuila and Chihuahua in Mexico (Fig. 1). The climate is hot and semiarid, with a mean annual temperature of 1 1 C in winter and 28 C in summer. Mean annual precipitation is 264 mm, with a rainy season from Jul. to Sep. when 71% of the rainfall occurs (Cornet, 1988). The area is surrounded by mountains that reach 1400 m above sea level, but most of the terrain in the Reserve is flat. The dominant vegetation types are creosote bush (Larrea tridentata), mesquite (Prosopis glandulosa), prickly-pear cacti (Opuntia rastrera), agave (Agave rastrera), and tobosa grass (Pleuraphis mutica; Montaña, 1988). Mapimi is a Man and Biosphere (MAB) site and as such the wildlife, including bobcats are protected from hunting. There is extensive cattle grazing on the Reserve, but overall human use is low.
Between 2006 and 2008, we trapped eight adult bobcats (four females and four males) with no. 2 victor soft catch leg-hold traps, following guidelines for the use of wild mammals for scientific research (Gannon et al, 2007) and with the authorization of Secretaria de Medio Ambiente y Recursos Naturales (SEMARNAT, no. permission 04008). Each animal was immobilized with a mixture of ketamine and xylazine hydrochlorides (Beltrán and Tewes, 1995), measured, weighed, sexed, ear-marked, and radiocollared. We used model Lotek GPS 3300s radiocollars with, temperature sensor, and a 9 wk timed drop-off. Collars were programmed (software Lotek wireless ver. VI. 970) to estimate animal coordinates every half hour at night (1900 to 0800 h) and every hour during the day (0800 to 1900 h). Temperature sensors provided ambient temperature (C) every 5 min, but we only used temperatures recorded for when time locations were recorded. After the collars fell off we recovered them with the use of a portable three elements yagi antenna (Wildlife Materials) and a VHF receiver (TR4 Telonics).
MOVEMENTS AND HOME RANGE SIZE
For each animal we obtained more than 2000 pairs of X.YUTM coordinates, equivalent to 63 blocks of 24 h each. Because of the open nature of the area, periods of lost fixes never exceeded more than 9% of the total data sets. These data were arranged in a spreadsheet data base, distances traveled (km) between two consecutive coordinate points were estimated using the Pythagorean Theorem. We then summed appropriate distances over the Urne intervals desired. Speed of travel (km/h) was estimated using distances traveled between two consecutive coordinates divided by the time that it took the animals to travel that distance.
To estimate home range size, we superimposed all localizations obtained for each bobcat (previously eliminating outliers) on a satellite image (LANDSAT ETM + Mar. 2003) in ArcView GIS (ver 3.2) and calculated their size with the Minimum Convex Polygon method included in the menu of Home Range tools of Arc View GIS (ver 3.2).
All distances at the same hour of every 24 h period were arranged in columns of a worksheet for all 63 d (rows) for each bobcat. We then obtained total distance traveled per each day by summing up each row and then averaging (±se, ? = 63 d) the data of the column for each bobcat. For each hour, distance traveled a given hour for an animal was the mean (±se) of the appropriate columns. This provided us an estimate of travel speed for each hour block. Traveled distances during the day (0600 to 1700 h) and night (1800 to 0530 h) periods were sums within each row across the appropriate columns (e.g., 0600 to 1700 h). Again, for each animal, the 63 estimates of daily or nightly travel were averaged. For statistical comparisons, we only used these means of the 63 d for all data to avoid pseudoreplication. To estimate distances traveled in wet and dry seasons, data from bobcats captured and radiocollared from Jan. tojun. (n = 4) were considered as the dry season, and data from different bobcats captured and radiocollared from Jul. to Dec. (n = 4) were considered as the wet season.
DISTANCE TRAVELED AND AMBIENT TEMPERATURE
To test if there is a correlation between distance traveled and ambient temperature (C) , mean temperature of each hour of the day was obtained from the collars of four different bobcats equipped with that function, two trapped in the dry season (Mar.-May) and two in the wet season (Jun.-Aug. and Oct.-Dec). Temperatures were plotted against mean travel distances for each hour of a 24 h period. Average temperature of each month in Mapimi were compared with other places where bobcats were studied.
DATA FROM LITERATURE
To compare our data with other published data, we reviewed 42 articles (Table 1) where data of daily traveled distances (total, for each sex, for night and day periods), speed, home range sizes (total and for each sex), or activity patterns were clearly provided.
Distances and velocities traveled daily among bobcats within our study were compared among individuals with a one-way ANOVA. Distances and daily travel speeds between sexes and between wet and dry seasons were compared with a two group ¿test design. Mean distances traveled in day-night periods were compared with a non-parametric Wilcoxon signed rank test for non-independent tracking data. A simple correlation was used to investigate the relationship between activity patterns and environmental temperature. The statistically significant rejection level was ? < 0.05 (Zar, 1984).
To compare the data of our study with other publications, we calculated a mean value with data obtained from the literature for the following criteria, daily travel distances, speed, home range sizes, and activity patterns. We dien compared the mean value of our study with those from die literature using a one sample Kest (Zar, 1984). To test if there was any latitudinal pattern in home range size we conducted a simple linear regression where home range size estimates of each study were regressed against latitudinal distance from the Equator as obtained from Google Earth® images. We did not have sufficient data on daily travel distance or daily travel speeds to conduct similar analyses.
MOVEMENTS AND HOME RANGE SIZE
Mean distances traveled daily by bobcats varied from 1.9 to 8.9 km and averaged 4.8 ± 0.72 km. One female (F3) traveled the longest daily distance of 27.8 km. The outlier data of this female were excluded from analyses. When compared to otfier studies, our results did not differ (Table 1).
When grouped by sex, the mean daily distance of females and males (n = 4, 5.9 ± 1.04 km and ? = 4, 3.6 ± 0.67 km, respectively) did not statistically differ (t = 1.860, 6 d.f., ? = 0.112). Distances traveled by males were not statistically different from data reported in odTer studies of bobcats (Table 1 ) , but the distances traveled by females were statistically different from other studies (Table 1). This difference is notable because most other studies reported males traveling significandy more than females (Fig. 2A).
All bobcats traveled significandy longer distances at night (3.4 ± 0.51, ? = 8) than during the daytime (1.4 ± 0.28, ? = 8, ? = 2.521, ? = 0.012, Fig. 2B). When compared to other studies our results did not differ (Table 1).
Distances traveled by bobcats during the dry season (Feb. to Jun.) tended to be shorter than during the wet season (Oct. to Jan.), 3.7 km ± 1.5, than vs. 5.8 ± 2.1 km but were not statistically different (i = 1.545, 6 d.f., ? = 0.173). We did not find comparable data in other studies regarding this type of seasonal activity of bobcats because traditionally seasons in more northern areas were divided differently tiian in Mapimi. In a comparison between spring/ summer and autumn/winter in Idaho (Bailey, 1974), bobcats traveled longer distances than 1.6 km more often in spring/ summer and distances from 0 to 1.6 km in autumn/winter. However, we cannot make direct comparisons between our seasonal divisions and these because of the differences in how seasons were divided.
Mean speed of bobcats was 0.3 ± 0.04 km/h and ranged from 0.01 to 1.6 km/h. Female travel rates tended to be higher (0.3 km/h ± 0.06, ? = 4) than males (0.2 km/h ± 0.04, n = 3) but were not statistically different (t = 0.969, 5 d.f., ? = 0.377). Mean speeds estimated for females and males in Mapimi are similar to others reported in different areas of United States (Table 1).
Average home range size for bobcats in Mapimi was 25.9 km2 ± 3.72, ? = 8. This size is not statistically different from the mean obtained from the literature in northern latitudes in United States (Table 1). The average size of the home ranges between sexes in Mapimi was not statistically different, females: 27.1 km2 ± 6.41, ? = 4 and males: 24.7 km2 ± 4.74, ? = 4. Home range sizes of females do not differ from their counterparts for other study areas found in the literature, but the home range size of males did (t = 2.954, 28 d.f., ? = 0.006; Table 1).
For the regression of home range size against latitude, we had sufficient cross-study data from 35 studies (Fig. 3A). When we regressed home-range size estimates there was a significant (P < 0.001) positive relationship (Fig. 3B). However, the variance explained by the regression was only 29%. When arranged with increasing latitude (Fig. 3B), the amount of variation in the data can be seen and it can be noted that our estimate of home range size was greater than for studies of similar latitude.
Over the 24 h period, the lowest average distance traveled per hour for males and females combined was between 1300 to 1600 h (Fig. 4A). During this time the average hourly distance traveled was 0.06 ± 0.007 km, ? = 7. After 1600 h, activity increased and peaked at around 2100 h. From 2200 to 2400 activity decreased and from 2400 to 0400 h activity remained relatively constant at an average of 0.1 5 ± 0.002 km (n = 7). Bobcats increase their activity and showed a peak around 0700 h and then gradually declined again into the day (Fig. 4A). Females and males showed distinct differences in their patterns of activity. First, females peaked in activity sooner than males in the evening (1800-1900 h vs. 2000-2100 h) and later in the morning (0900-1 100 h vs. 0600-0700 h; Fig. 4A). Females also remained more active during most of the night than males (Fig. 4A). Periods of high and low activity of bobcats in Mapimi occur at similar or the same hours to most of those previously reported, indicating a mainly crepuscular pattern (Fig. 4B). The differences between studies are the time bobcats remain active and the length of time they are active, e.g., in Mapimi and South Carolina (Fig. 4B, studies 1 and 5) bobcats are active for longer periods of time in contrast with the ones of Alabama and Illinois (studies 4 and 6). Also, in Mapimi, bobcats seemed to have the shortest low activity period at midday in comparison to northern areas, even in a locality in New Mexico within die Chihuahuan Desert (Fig. 4B). The distances bobcats traveled in each period of time mentioned by McCord and Cardoza (1982) are higher than die ones we found in Mapimi. However, because theirs was just one sample, we could not make a statistical comparison.
Activity patterns of dry and wet seasons appeared similar to the general pattern previously described. Bobcats in the wet season traveled longer distances dian the ones in dry season. There are two main activity peaks, one from 1800 to 2300 h and the other from 0600 to 1 100 h, and one period with minimum activity from 1300 to 1600 h (Fig. 5). As was the case with daily distance traveled between wet and dry seasons, we did not find data regarding this type of seasonal differences in activity of bobcats to compare with the activity pattern of the seasons in Mapimi.
DISTANCE TRAVELED AND AMBIENT TEMPERATURE
Mean ambient temperature of the microhabitat that bobcats inhabit in Mapimi was from 28.0 C at 1100 h with a maximum of 34.2 C at 1700 h and decreased to 25 C at 2100 h. At night, the temperature was from 23.3 C at 2200 h to the lowest of 17.3 C at 0700 h (Fig. 6A). Activity levels of bobcats increased when temperature decreased between 1900 and 2000 h. After this period, activity of bobcats was constant and increased again into the morning until noon, when the temperature was again high and the activity of bobcats was the lowest. Environmental temperature and activity were significantly but negatively correlated (r = 0.506, ? = 24, ? < 0.05; Fig. 6B).
We did not find similar data of this relationship between distance traveled and temperature in other studies to statistically compare with our results, but we compared the average temperatures of low and high activity periods in Mapimi with the ones from more northern areas where activity patterns were recorded. In all studies, low activity periods corresponded to higher environmental temperatures and high activity periods corresponded to lower temperatures (Fig. 7) .
HOME RANGE SIZE AND MOVEMENTS
Home range size is one of the most studied ecological characteristics of bobcats and its size varies widely across tiheir geographic range (Lariviére and Walton, 1997; Hansen, 2007). One of the consistent observations made is that male home ranges are up to twice the size of those of females (Bailey, 1974; Kitchings and Story, 1984; Litvaiüs et al., 1986). In contrast to these previous studies, we found that in Mapimi males and females did not differ significantly in their home range sizes. The consequences of these results relative to the proposed explanations for differences between the sexes is unclear at this urne. It has been suggested that the difference between genders is a response to habitat quality. Though Conner et al. (2001) dismissed this idea, it may require re-analysis considering the differences in habitat quality between our study area and more northern ones. It also has been mentioned that females use their home range more intensively than males (Sunquist andSunquist, 2002).
With the GPS location schedule we used, it was possible to analyze intensity of home range use by our study animals to test ÜTis hypothesis; however, we did not included it because it was not one of the objectives of this current analysis. Litvaitis et al. (1986) showed that home range size was correlated with bobcat mass and males had a 28% greater energy requirement than females if reproductive costs are ignored. However, this energetic difference may not be enough to explain the extent of the differences found in home range sizes. The relationship of energetic needs and size of the home range is under further study in Mapimi and may provide further tests of this hypothesis. Also, it is possible that our limited sample size of four each of males and females did not allow us to detect differences between sexes. However, because of the large number of relocations per animal (>2000) we compared to other studies, our data set should include the more accurate estimates of home range size. It is more possible that home range estimates of other studies, based usually on less than 100 relocations, had more biased estimates. As more GPS studies of bobcats are conducted, we should be able to clarify if the number of relocations per animal affects comparisons of male and female home range sizes.
In addition to home range size, it is also widely accepted that males travel further and at higher velocities than females on a daily basis (Sunquist and Sunquist, 2002; Hansen, 2007). Again, our data contradict both of these trends in that we found no statistical difference between sexes, with females averaging slightly more traveling than males. In fact, females in Mapimi traveled longer distances than they do in northern areas, which had not been recorded before and it was an adult resident female that traveled the longest distance recorded (27.8 km in one day) . This was also the longest distance traveled by a resident female bobcat yet to be recorded (Larivière and Walton, 1997) . We also found no difference in travel speeds, although females tended to travel at higher speeds than males. Again, though limited sample sizes, the accuracy and higher frequency of GPS relocations of our study provides a much more detailed analysis of travel distances and speeds than possible in the past.
The one area where we did find differences between males and females was in their activity over the 24 h period. Females in Mapimi were active for longer periods than males, starting their activities earlier at sunset, and finishing them later after sunrise. They also maintained higher levels of activity throughout the night. These differences in timing and levels of activity actually contributed to longer distances females traveled each day compared to males and possibly explain why female home ranges were not smaller than those of males. Why females would show these differences in activity patterns is unclear at this time. Possibly the longer periods and higher levels of activity may be related to increased energy demands when females have kittens. The finding that in general bobcats had higher levels of activity during the night in the wet season (reproductive season for bobcats) than the dry season supports this idea. However, we did not have sufficient data or knowledge on reproductive status of females to specifically test this hypothesis.
Apart from the gender differences previously noted, in general we found that most of the characteristics of bobcats in Chihuahuan Desert in Mexico showed no differences with those recorded in northern areas. Bobcats in our study area traveled the same total daily distance, at similar velocities, and were active at similar times as their more northern populations. The only difference we found was that male home range sizes in our study area were smaller than the average for all other sites. Alternatively, female and combined home range sizes did not differ with other studies.
Although we did not find significant differences between our home range estimates and other studies, our regression analysis did support a latitudinal decreasing trend. However, there was a high amount of variability and many home range estimates did not fit the trend. This included our home range estimate that was a factor of 10 times larger than estimates from similar latitudes. The high amount of variability, including within the same studies, indicates that other factors than those related to latitude are affecting home range size in bobcats. For example, the idea of smaller home range sizes in lower latitudes is related to the perception that more equatorial ecosystems are more productive (Gompper and Gitleman, 1991). Given our study area was a relatively low-productive hot desert, this general trend of productivity and latitude is not consistent and may explain why our estimates were higher than more productive ecosystems in the southern U.S. If home range size is related to ecosystem productivity, regardless of latitude, this hypothesis could be tested by comparing home range sizes of bobcats with measures of ecosystem productivity. The fact that our home range estimate was smaller than those of Harrison (2010) from another Chihuahuan Desert site in New Mexico, indicates that productivity alone may not be the only explanatory factor. Perhaps a multiple regression analysis with latitude, primary productivity, and possibly rainfall as independent factors might help identify which, if any, of these factors contribute to home range size in bobcats.
Relative to the timing of activity, even in the more extreme temperature conditions in Mapimi, bobcats showed similar crepuscular activity patterns in more northern areas (Buie et al., 1979; Miller and Speake, 1979; Witmer and DeCalesta, 1986). This similarity indicates that extreme conditions, regardless of geographic location, would force bobcats to adjust the timing of their movements. As with distance traveled, the timing of activity also is probably related to changes in energetic needs, prey abundance and behavior, environmental conditions, or other possible changes affecting a bobcat's hunting strategies.
In summary, our results provide the first detailed analysis of home range size, daily travel distances, and activity patterns of bobcats from the more southern part of their range in the Chihuahuan Desert, Mexico. Most data demonstrated these behaviors of bobcats in this hot desert environment do not differ in general from those in more northern populations. Other data indicated particular differences in this population that did not follow the general patterns described for the species in previous literature. As we learn more about bobcat behavior across its large geographic range, we may more fully understand which factors, e.g., prey type, energetic demands, habitat type, environmental conditions, etc., affect this species behavior and possibly survival.
Acknowledgments. - This study is part of the Ph.D. studies of CEA, Doctorado en Ciencias Biológicas y de la Salud, Universidad Autonoma Metropolitana. It was funded by Consejo Nacional de Ciencia y Tecnología (CONACyT), Fondo Mixto for Durango State (Project no. DGO-2006-C01-4383) to LH. CONACyT provided two Ph.D. grants, one to C. Elizalde-Arellano (no. 167852), and one to J. C. LópezVidal (no. 167853). The authors wish to thank the many undergraduate students for their field assistance in bobcat trapping and recovering GPS collars. We specially want to thank Karina GrajalesTamm, Lupita Diaz, Efrain Rodriguez, Antonio Guerra, Francisco and Tina Herrera for their special support during different activities related with this project. We give thanks also to the Instituto de Ecología A.C., Durango Regional Center and Xalapa Center for their logistics assistance and for providing the accommodations at the Mapimi Field Laboratory. We are grateful to Dr. Leslie Carraway and three anonymous referees for their valuable comments that improved this manuscript.
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SUBMITTED 12 JULY 2011 ACCEPTED 2 MARCH 2012
Doctorado en Ciencias Biológicas y de la Salud, Universidad Autónoma Metropolitana, Calzada del Hueso no. 1100,
Col Villa Quietud, Coyoacán 04960, México DI'.
JUAN CARLOS LÓPEZ-VIDAL
Laboratorio de Cordados Terrestres, Departamento de Zoología, Escuela Naaonal de Ciencias Biológicas, IPN.
Carpio y Plan de Ayala s/n, Col. Santo Tomás 11340, México Dß.
LUCINA HERNÁNDEZ2 and JOHN W. LAUNDRÉ3
Instituto de Ecología, A.C, Xalapa, Veracruz 91070, Mexico
FERNANDO A. CERVANTES
Departamento de Zoología, Instituto de Biología, Universidad Nacional Autónoma de México,
Coyoacán 04510, México D.F.
Laboratorio de Etologia. Dpto. Producción Agrícola y Animal. Universidad Autónoma Metropolitana, Xochimilco.
Cali, del Hueso 1100, Col. Villa Quietud 04960, México D.F.
1 Corresponding author's present address: Laboratorio de Cordados Terrestres, Departamento de Zoología, Escuela Nacional de Ciencias Biológicas, IPN. Carpio y Plan de Ayala s/n, Col. Santo Tomás, 11340, México D.F.; Telephone/FAX: (5255) 5729-6000 ext. 62421; e-mail: email@example.com
2 Present address: Rice Creek Field Station, Department of Biological Sciences, 225a Snygg Hall, SUNY Oswego, Oswego, New York 13126; Telephone: (315) 312-3633
3 Present address: Department of Biological Sciences, 126 Snygg Hall, SUNY Oswego, Oswego, New York 13126; Telephone: (315) 312-3633