Ponce, Suzán and Francke population structure of




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Ponce, Suzán and Francke



POPULATION STRUCTURE OF CENTRUROIDES BALSASENSIS (SCORPIONES: BUTHIDAE) IN THE BALSAS DEPRESSION, MÉXICO.
Javier Ponce Saavedra1, Humberto Suzán-Azpiri2* And Oscar F. Francke 3
1= Laboratorio de Entomología “Sócrates Cisneros Paz”, Facultad de Biología, Universidad Michoacana de San Nicolás de Hidalgo, Edificio B4 2º. Piso, Ciudad Universitaria, Morelia, Mich. C.P. 58040, México.

2= Escuela de Biología, Universidad Autónoma de Querétaro, C.U. Cerro de las Campanas, s/n, Querétaro, Qro. C.P 76010, México.

3= Colección Nacional de Arácnidos, Instituto de Biología, Departamento de Zoología, Universidad Nacional Autónoma de México. Tercer Circuito Exterior sin número, Cuidad Universitaria Apartado Postal 70-153 Mexico D. F., 04510



*Correspondent: hsuzan@sunserver.uaq,mx



Abstract--The Balsas Depression in the state of Michoacán, México is a region with average diversity of scorpions. A bimonthly population survey of a recently described species of the genus Centruroides was conducted at two permanent sites. The sampling quadrats measured 400 m2. The relative abundance, sex ratio and population density of the dominant scorpion species in the zone, Centruroides balsasensis Ponce and Francke, were estimated using the simple capture-recapture method of Lincoln-Petersen. Some aspects of the surface activity of the individuals at the moment of capture were recorded. Densities varied through the year depending on season and food availability, between 0.023 individuals/m2 and 0.18 individuals/m2. The sex ratio fit the 1:1 expected, and the principal activity detected in the sampling nights was ambushing, mainly over stones or over bare soil. The average litter had 26.2 young, and the duration of the first three instars of development (216 days) suggest that this species requires at least two years to reach maturity.

Key words: Scorpions, Centruroides balsasensis, population structure, sex ratio, instars and scorpions.


Resumen -- La Depresión del Balsas en el Estado de Michoacán, México es una región con una amplia distribución de alacranes. Se llevó a cabo un monitoreo bimensual en poblaciones de una especie recientemente encontrada del género Centruroides en dos sitios permanentes de muestreo. Los cuadrantes muestreados tenían 400 m2. Se determinó la abundancia relativa, proporción de sexos y densidad poblacional de la especie de alacranes dominante en la zona, Centruroides balsasensis Ponce y Francke, por medio de el método simple de marca recaptura de Lincoln-Petersen. Se estudiaron algunos aspectos de la actividad aparente de los individuos al momento de ser capturados. Las densidades encontradas variaron entre 0.023 individuos /m2 y 0.18 individuos /m2 dependiendo de la disponibilidad de alimento y época del año. La proporción de sexos fue de 1:1 como se esperaba, y la principal actividad detectada en las noches de muestreo fue el asecho, sobre rocas y suelo desnudo. El promedio de escorpiones por camada fue de 26.2 y el tiempo de duración promedio de los tres primeros instares de desarrollo fue de 216 días, lo cual sugiere que esta especie requiere al menos de dos años para alcanzar la madurez.

Palabras clave: Alacranes, Centruroides balsasensis, estructura de poblaciones, proporción sexual, instares.

The genus Centruroides comprises scorpions of the family Buthidae which has several species with great biological and medical importance. In México, although this genus has the greatest medical importance of all scorpions, information regarding its biology is scarce and mainly related to taxonomic aspects (Moreno et al., 1998; Ponce and Beutelspacher, 2001). The incomplete knowledge of scorpion diversity and distributions often leads to the discovery of new species when faunistic surveys of scorpions are conducted in relatively well-known regions (Ponce, 2003). Specifically for the Balsas Depression (Balsas Basin) in the State of Michoacán, México, two new species where reported for the first time in 2003 (Ponce, 2003) One of them, a recently described species of the genus Centruroides, C. balsasensis Ponce and Francke, is the subject of this study.

Information about population structure and dynamics of scorpions in México is almost null. Density estimations detected in medical reports or taxonomic descriptions only mention them as “abundant” or “scarce”. Therefore, quantitative knowledge of densities and other demographic parameters become fundamental for the management of scorpions (Polis, 1990a). It is important to note that worldwide we have knowledge of basic population biology for only three scorpion species (Polis, 1990b).

Habitat micro-characterization is another important factor in the scorpion’s life history (Polis, 1990b; Benton, 2001; Lourenço, 1988; Lourenço and Cloudsley Thompson, 1999). Some species inhabit a wide array of habitats and geographical regions, while others have restricted distributions in specialized habitats (Francke, 1981; Polis, 1990a).

Species of the genus Centruroides are considered as opportunistic (Polis, 1990b) and tend to be active foragers with high motility (Stahnke, 1971). Therefore, the estimations of basic demographic parameters such as density must be accompanied by a characterization of the habitat used by the particular species.

Biomass is another factor to be considered in population analyses. The easiest way to estimate biomass is the multiplication of density times the average weight of individuals. However, differences in size and age must be considered (Polis, 1990b). Shorthouse (1971) and Marples and Shorthouse (1982 ) used the average weight as function of age groups to estimate biomass production of Urodacus yaschenkoi (Birula) (Scorpionidae: Urodacinae) in Australia; Bacon (1972) with Uroctonus mordax Thorell (Vaejovidae) in the United States, and Polis (1990b) for three species of the family Buthidae. Those estimations show that scorpions are among those terrestrial arthropods with highest biomass per hectare, ranking only below ants and termites.

The majority of tropical scorpions do not have well defined reproductive seasons (Benton, 2001), and the highest percentage of matings occur after the females have given birth (Benton, 2001). Scorpions are viviparous, and the size of the litter is apparently negatively correlated with the size of the young individuals (Francke, 1981; Brown, 2001).

The objectives of the present study are: a) to determine the relative importance of Centruroides balsasensis in two scorpion communities; b) to describe basic population parameters such as density, age structure, sex ratio and biomass for this species; c) and to describe the apparent activities and habitat use of the species.

Methods and Materials--Study areaThe Balsas Depression is a wide structural depression formed by the lowest parts of the Balsas River Watershed, located mainly in the state of Michoacán, México (Toledo and Ordóñez, 1993). Two contrasting sites with Centruroides balsasensis populations were selected in the lowest altitudinal region of the Balsas Depression. The first site, located on Turitzio mountain, in the municipality of Huetamo (18°31.69´N, 100°55.45´W, altitude: 450-550 m), is characterized by a hot and humid isothermal climate (with a mean monthly temperature of 28°C with a thermal variation of 5°C year-round), and a tropical deciduous forest dominated by arboreal trees of the genus Bursera (Rzedowski, 1978). The second population was located near the town of Churumuco (18°39.28´N, 101°39.28´ W, altitude: 370-500 m) in the municipality with the same name. This region is hotter and drier than Turitzio, with a mean monthly temperature of 30°C and variation of 5°C year-round, and a tropical deciduous forest dominated by columnar cacti such as Backembergia militaris and Stenocereus quevedonis (Guevara-Féfer, 1981).

Population structure-- Fieldwork was conducted in the years 2000-2001 with the populations of Centruroides balsasensis at the two selected sites. Population size and structure were determined for each site by bimonthly samplings and simple mark-recapture methods or Lincoln-Petersen methodology (Krebs, 2000). The sampling was conducted during clear nights with black light lamps (wavelength = 300 nm) that allow a 6-8 m vision (Sissom et al., 1990).

Sampling events for each site consisted of two consecutive fieldwork nights. On the first night we walked randomly in an area approximately 3 km2 to determine the scorpion community of each site. Two points were located at random and from those we installed two 400m2 quadrats where we marked (with acrylic fluorescent non-toxic paint) all C. balsasensis individuals with a sampling effort of 2 hrs/man. All individuals were marked on the mesosoma, and the following data were collected: maximum length, sex, time of capture, life stage (adult, juvenile) and apparent activity. On the second night all recaptured individuals were subjected to a second measurement. Collected data were used to determine population size, density estimates, sex ratios, life stage, and juvenile-adult proportions.

Population size was determined with the program Mark-Recapture of the Ecological Methodology (second edition) Book (Krebs, 2000).

Sex ratio was determined separately for adult and juvenile scorpions, considering if the animals were captured or recaptured. Sex ratio was tested with a non-parametrical concordance test using as a null hypothesis the 1:1 sex ratio reported for non-parthenogenic scorpions (Polis and Sissom, 1990).

The total length registered for each captured individual determined its life stage according to a growth factor calculated in laboratory specimens according to Francke and Sissom (1984), and by the determination of the instars necessary for scorpions to reach adult age (Francke, 1976). The estimated number of instars for C. balsasensis are seven immature plus one adult stage (Ponce, 2003), and the field estimations agree with laboratory observations on partial life histories (Ponce, 2003).

The assignation of field-captured and field-measured individuals to a given instar was made after measuring the total length of body for each individual and an estimation procedure based on the growth factor of 1.3 obtained for this species (Ponce, 2003) (Table 1). The knowledge of the actual measurement of newborn ( = first instar) and adult females (those carrying young on their backs) was fundamental in establishing the estimated instar sizes (Francke and Sissom, 1976). After each mark-recapture date, a group of scorpions were collected and preserved to be measured in the laboratory. This sample (n =192) was divided into groups according to the measure of the total body length: Adults, instar VII, instar VI and those from the instars V to I which were considered as "juveniles".

Fresh weight biomass estimations for the two populations were obtained by an average of individual weights obtained from a sample of 10 scorpions per site. The mark-recapture studies indicated a 62:38 ratio of adults: juveniles in Turitzio and 74:26 in Churumuco. The proportions obtained for both localities were averaged and then the fresh-weight biomass estimation was determined with 7 adults and 3 juveniles (instars IV and V) selected in the laboratory, and with the average individual weight we estimated the fresh weight of the scorpions in a particular date and place.

In order to estimate the average size of a litter we counted the number of newborn (first or second instar) carried by females detected in the field, and 13 female scorpions which gave birth under laboratory conditions (27°C  2 and relative humidity 55% 10%). Raising the newborn in the laboratory enabled us to measure growth (confirming the 1.3 growth rate at each molt used in the instar-size estimates above) and to estimate the average duration for the first four instars.

In each of the permanent sites an environmental data logger HOBO H8 (H08-004-02) collected temperature, relative humidity and light intensity data every six hours for one year.

Apparent activity and use of habitat-- For all the mark-recapture dates we registered the apparent activity of the scorpions captured in order to analyze behavioral population patterns. The basic activities (considered after Polis, 1990b) were: a) ambushing (stationary position with the metasoma and pedipalps upright, and the pedipalp chelae open); b) resting; c) walking; d) eating; e) in courtship (couples grasping by the pedipalps). For each scorpion we also recorded sex, habitat utilization and estimated age (juvenile or adult), according to the results of the assignation of instars to the scorpions previously measured in the laboratory.
Results-- Species and sexual proportions of the scorpion communities after all samplings in Churumuco and Turitzio indicated that Centruroides balsasensis was the dominant species for both sites (Figure 1). In Churumuco the relative abundance for all individuals, regardless of sex, was 64% for C. balsasensis, followed by Vaejovis aff. variegatus (31%), Vaejovis sp. (4.94%) and Diplocentrus sp. (0.62%). In Turitzio the numbers were 57% for C. balsasensis , followed by Vaejovis sp. (22%) and Vaejovis aff. variegatus (21%).

We marked a total of 259 C. balsasensis on the first night of sampling for both sites; and on the second night recorded 78 scorpions recaptured and 155 new captures in the 400m² quadrats. In Churumuco 177 scorpions were marked (49 recaptured), and in Turitzio 82 scorpions marked (29 scorpions recaptured). The number and proportion of adults to juveniles for each sampling date and locality are described in Table 2.The density of animals per quadrat for each sampling date are described in Table 3. In Churumuco the minimum density estimated was 17 scorpions per quadrat (0.04/m²) in July- August, and the maximum was of 73 per quadrat (0.18/m²) (Figure 2) in January- February. In Turitzio we obtained a minimum estimation of 7 scorpions per quadrat (0.02 /m²) in May-June, and a maximum estimation of 27 scorpions per quadrat (0.07/m²) in July-August (Figure 3). Densities obtained were lower than other species of the family Buthidae in the world (Table 4). Locally the densities in Turitzio were lower than Churumuco ( P <0.05) probably due to the climatic and vegetation differences between the localities, although both have deciduous dry forest, there are difference in the species composition and vegetal community structure as well as the annual precipitation and temperature (Ponce et al., 2004). The pattern of the population densities in Churumuco shows the maximum was observed in January-February, decreasing toward the rainy season and recovering during the last two months of this season (Figure 2); whereas in Turitzio we observe the pattern of the population densities decreasing in the dry season followed by a rapid upward response at the beginning of the rainy season (Figure 3). Therefore, densities seem to depend both on food availability and weather fluctuations.

The sex ratio for 535 individuals captured (or recaptured) in the quadrats indicated that the populations fit the expected sex ratio of 1:1 for both juveniles and adult scorpions (Table 5). In all the capture-recapture dates the same proportion was observed.

The recapture percentages for males, females and juveniles on 11 recapture dates were not significantly different (Wilcoxon/Kruskal-Wallis one-way test, χ2 = 0.172, d.f.= 2, P=0.92). However, at least some males were always recaptured the night following marking [= 31.8%, s.d. = 0.14, range 13% (1 of 8) to 57% (4 of 7)], which was not the case for females [= 34.8%, s.d. = 0.31, range 0% (0 of 7) to 100% (3 of 3)] or juveniles [= 36.5%, s.d. = 28.8, range 0% (0 of 1) to 100% (1 of 1)], suggesting some difference in displacement activity patterns. However, the analyzed sample sizes are very low and this aspect deserves further study.

Life stages were determined for 492 individuals captured or recaptured in the field. The adult/juvenile proportions in Churumuco fluctuate between 66% and 80% always with more adults than juveniles. These proportions were lower in Turitzio where they fluctuate between 54% and 75% (Table 2). After the instars were assigned to the 192 scorpions captured and measured in the laboratory, adults represented 60.4 % of the population, 22 % corresponded to instar VII, 10% to instar VI, and 7% to instar V or younger.

Adult and juveniles densities were variable in time. Adults increased between March and June, simultaneously with an instar VII decrease (Figure 4). In August and September the densities of instars VII densities increased considerably as a result of recruitment from instar VI, while adult densities decreased (Figure 4).

Cannibalism of juveniles by adults was observed only once, in January (the driest month of the year). Also, predation by C. balsasensis on Vaejovis sp. was observed in the field once, in Turitzio in August.

In the field, we observed mating events at different months of the year (March, June, August and December) and birth events (females with newborn scorpions of instar I on their back’s) were recorded in March, August and September; although the frequency of those events in each month were not recorded. However, the increase in adults noted in Churumuco in March and in Turitzio in June, suggest a higher reproductive activity between March and June, providing abundant prey for the pregnant females during the rainy months and better survival possibilities for the new litters (Figures 2, 3).

The low percentage of scorpions smaller than instar IV (7%), suggests a population structure dominated by adults and with a low reproductive (recruitment) rate; or younger scorpions are harder to detect because of their size and/or their activity is limited to avoid cannibalism. However, the variation between dates of capture was high, and could reflect a sampling bias to the easiest detectable sizes (larger).

Fresh-weight laboratory measurements (7 adults and 3 individuals of instars VII and VI; i. e., the proportion of adult to juveniles recorded in the field) indicated that average individual weight was 1.16 g (min = 0.267g; max = 2.107g). With the densities detected in each site and date, the biomass field estimations fluctuate between 0.174 kg/ha and 3.447 kg/ha (Table 6).

The average number of offspring was 26.18 (standard error of 1.336), with a minimum of 19 and maximum of 36 young scorpions per litter, from 13 births recorded in the laboratory. The births occurred between March and October, which closely matches the months where females with young were detected in the field (March through September).

We never detected iteroparity, and some of the females survived in the laboratory up to 14 months after the birth of newborns. With the individual observations of the young scorpions we determined the average duration of the first four instars: instar I or newborn the average time was 13 days (n = 7); instar II lasted 113.4 days (n = 5); instar III 90.7 days (n = 3) and instar IV 46 days (n = 1).



Apparent activity-- In both permanent observation sites we recorded the activity of 492 scorpions (including 78 recaptures and 155 new captures), and in adjacent sites we recorded the activity of other scorpions detected in the sampling nights; thus, a total of 512 scorpions provided us with a total of 1024 observations. According to the total body length measurements made in the field, we assigned age to “adults” and “juveniles” for data analysis. It was observed that juveniles represented 28% of the sightings; 40% were male adults and 32% female adults (Table 7).

The principal activity detected in the sampling nights was ambushing (50.39%), mainly on stones (20.89%) or on bare ground (31.05%); but shrubs (14.45%) and branches of trees (8.98%) were also common sites for ambushing and hunting (Table 7). When the scorpions were resting (44.1% of all activities recorded) we detected them under leaf litter (54.54%), beneath stones (34.54%), in dry wood stems (4.54%), and beneath the bark of trees (4.54%) and only 1.84% in other sites.

Activities of juvenile scorpions were dominated by ambushing (49.15%) walking over bare ground or leaf litter (34.74 %), and when resting (8.36%) the young scorpions were commonly detected on branches of herbaceous plants, but we never found them beneath the bark of trees (Table 7).

To analyze the surface activity we did specific mark-recapture studies with exact location records on a 20 x 20 m quadrat on consecutive nights in June, August and September 2001 at the Churumuco site. Out of 63 total marked individuals only 29 were recaptured the following night, even though the searches extended for up to 30 m away from the quadrats to look for “strays.” The shortest displacements recorded were by two juveniles which moved 0.39 and 0.41 m, respectively; and the furthest were by two males that moved 18.16 and 24.97 m, respectively. The average displacement for all recaptured individuals was 6.41 m (n=29), and Kruskal-Wallis analyses indicate no significant differences with respect to sex or age categories (χ2 = 2.052, d.f. = 2, P = 0.358), nor among the three sample periods (χ 2 = 2.156, d.f. = 2, P = 0.340).


Discussion-- The species composition and relative abundance of the dominant species for both localities studied (four species in Churumuco and three species in Turitzio) represented the most common pattern reported for scorpion communities in the world (Polis, 1990b). Species richness between three and seven species where reported for 68% of the communities, and situations where a dominant species comprised more than 40% of the individuals are also extremely common (more than 80%) (Polis, 1990b). However, communities with four species and a relative abundance for the dominant species between 60 and 80% (like Churumuco) were reported only once (Polis, 1990b).

The low density numbers for the region, compared with those of other parts of the world (Polis, 1990b), suggest that in extremely warm places without a marked winter season (like the Balsas Depression) food availability might be the key factor controlling densities and not weather fluctuations (McReynolds, 2004). However, our density estimates were obtained by single mark-recapture methods that could be influenced by the season of the year, foraging behavior, motility and the supposition that the population is closed (no demographic changes during the sampling period). Therefore, the sampling method could produce differences in density estimations. However, Yamashita (2004) used single mark-recapture for closed populations and the Jolly-Seber method for open populations and his results were similar (140 and 110 scorpions, respectively, for the study site).

Population structure reflected a 1:1 sex ratio for all the life stages, and data suggested a continuous and synchronic replacement of the instars through the year with generations overlapping.

The surface activity in Turitzio was greater in July-October and in Churumuco it was in August-October, closely matching the activity periods reported for C. vittatus in Arkansas and Texas (McReynolds, 2004; Yamashita, 2004); however, in Churumuco we observed another peak of activity in January.

In both localities reproductive activities throughout the year indicated similarities with other tropical species (Polis, 1990b), in contrast with temperate species that do have a marked temperature-related seasonality.

The duration of the first life stages (Instar I-IV) of 216 days suggest that C. balsasensis requires more than a year to reach sexual maturity. Similar results for other species were described by Francke and Sissom (1984).

Density estimations obtained for C. balsasensis were lower compared to other Buthidae species reported (Table 4). The highest value obtained for the region is lower than the lowest value reported for Centruroides exilicauda in Baja California or to the Centruroides margaritatus densities reported in Costa Rica (Polis, 1990b) and clearly lower than Leiurus quinquestriatus in Israel. However, densities seem high if we compare them with the values reported for Compsobuthus werneri judaicus (Birula) in Israel (Zinner y Amitai, 1969 in Polis, 1990b), Tityus fasciolatus in Brazil (Lourenςo 1978 in Polis, 1990b) and for Centruroides vittatus in Arkansas (Table 4).

The average body weight of Centruroides balsasensis calculated in our study (1.16 g/individual) and a biomass range between 0.174-3.447 kg/ha are consistent with those reported by Polis (1990b) for Centruroides margaritatus (Gervais) and Centruroides exilicauda (Wood)(1 g/individual and 2.0-5.0 kg/ha for the populations), but significantly lower than those of Leiurus quinquestriatus (Ehrenberg)(with a weight of 1.5 g/individual and a biomass of 16.5 kg/ha) (Polis 1990b). However, in order to validly compare biomass estimations we must know the biomass changes through the year, because of the changes in size and weight observed between the rainy and dry seasons of the year as a result of fluctuations in food availability (it is not known during which season the estimates were made for L. quinquestriatus and the other species previously reported).

Yamashita (2004) obtained individual weights for adults of Centruroides vittatus of 0.41g (males) and 0.49 g (females) using data of surveys made in March to November in Arkansas. This individual weight is clearly lower that any of the data published for other Buthidae species, and considerably lower than our data. This lower weight is also reflected in the low biomass registered per hectare that was of only 0.11 to 0.133 kg/ha, although the obtained density for this species was of 0.024 to 0.029 scorpions for square meter. In southern Texas the estimation for this species was of 0.074 individuals/m² (Brown et al., 2002).

Our surface-activity studies corroborate that Centruroides species are active foragers with high motility. Six recaptured juveniles, about 4 cm long, moved an average of 4.51 m overnight; 12 adult females, about 7-8 cm long, moved an average of 5.22 m overnight; and 11 adult males, also 7-8 cm long, moved an average of 8.75 m. There are no statistically significant differences in the distances moved by each group, but the sample sizes are small and the observed variation is wide. Further observations are necessary to test the hypotheses (a) that juveniles wander less to reduce the risk of predation, and (b) that males venture further in search of potential mates.


Acknowledgements

The authors are grateful to Rocío J. Moreno B, Erwin P. Miranda L., Leticia Escalante J., Marco A. Villaseñor R., Ramón Cancino M., Elvia Lemus O. and Erasto Hernández C. of the Universidad Michoacana for their support in the field work. We also thank to the Research Coordination of the Universidad Michoacana for their financial support for this work. Finally we are grateful for the diligent review of the manuscript provided by W. David Sissom.


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Toledo, V. M., and M. J. Ordóñez. 1993. The biodiversity scenario of México: A review of terrestrial habitats. In. Ramamoorthy T., R. Bye, A. Lot and J. Fa. Editors. Biological diversity of Mexico. Oxford Univ. Press. N.Y., pp 757-777.

Yamashita, T. 2004. Surface activity, biomass, and phenology of striped scorpion, Centruroides vittatus (Buthidae) in Arkansas. Euscorpius-Ocassional Publications in Scorpiology 17:25-33.

Table 1 -- Estimated values of total body length for the instars of Centruroides balsasensis according to the growth factor of 1.3. The max and min values were estimated using the confidence limits for each age group ( P <0.05).


(Newborns individuals or Instar I) Observed

Instar

Estimations of body length (mm)

Mean

Max.

Min.

Mean: 9.5

II

12.3

15.9

10.1

Max: 12.2

III

16.0

20.6

13.2

Min: 07.8

IV

20.8

26.8

17.1




V

27.0

34.8

22.3




VI

35.2

45.3

29.0




VII

45.7

58.9

37.6




Adult

59.4

76.6

48.9


Table 2—Proportion of adults and juveniles of Centruroides balsasensis per sampling date, quadrat and locality




Sampling date

Date




Adults

Juveniles

% Ad

% Juv




October (2000)

19

7

73.1

26.9

Locality:

January (2001)

22

19

53.7

46.3

Turitzio

March (2001)

20

17

54.1

45.9

(n = 153)

June (2001)

13

3

75.0

25.0




August (2001)

18

15

54.6

45.4




Subtotal

92 (60.1%)

61 (39.9%)




























Sampling date

Date




Adults

Juveniles

% Ad

% Juv




September (2000)

16

6

72.7

27.2

Locality:

November (2000)

47

18

72.3

27.6

Churumuco

January (2001)

92

33

73.6

26.4

(n = 339 )

March (2001)

39

10

79.5

20.4




June (2001)

27

7

79.4

20.5




September (2001)

29

15

65.9

34.0




Subtotal

250 (73.9%)

89 (26.1%)








Table 3-- Densities of Centruroides balsasensis per quadrat

Density estimated for quadrats of 400 m²

Locality and Date

Estimation

Confidence Limits

Lower

Upper

Churumuco. September (2000)

17.0

10

62.7

Turitzio.

October (2000)



18.2

11.6

51.5

Churumuco. November (2000)

37.4

26.5

81.7

Turitzio.

January (2001)



16.8

11.9

30.1

Churumuco.

January (2001)



72.7

53.9

112.3

Turitzio.

March (2001)



12.3

9.3

19.8

Churumuco.

March (2001)



35.5

24.1

66.6

Turitzio.

June (2001)



9.5

6.0

29.6

Churumuco.

June (2001)



26.4

16.6

65.1

Turitzio.

August (2001)



25.0

15.7

60.7

Churumuco.

September (2001)



43.6

25.9

115.4

Table 4-- Comparison of Centruroides balsasensis densities in the Balsas Depression with other Buthidae densities reported in literature.

SPECIES

DENSITY

(ind/m2)



GEOGRAPHIC

REGION


HABITAT

REFERENCE

Centruroides balsasensis Ponce and Francke

0.02-0.18

Balsas Depression, México

Tropical deciduous forest

This study

Centruroides margaritus (Gervais)

0.4

Costa Rica

Tropical low lands

Polis 1990b

Centruroides exilicauda (Wood)

0.2-0.5

Baja California (South)

Xerophytic shrubland

Polis 1990b

Centruroides vittatus (Say)

0.024-0.029

Pope County, Arkansas. USA

Rocky upland semi-forested area

Yamashita 2004

Centruroides vittatus (Say)

0.0736

West Texas

Desert

Brown et al. 2002

Compsobuthus werneri judaicus (Birula)

0.0017

Israel

Mediterranean

Zinner y Amitai 1969 In: Polis 1990b

Leiurus quinquestriatus (Hemprich and Ehrenberg)

1.12

Israel

Desert

Shulov y Levy 1978 In: Polis 1990b


Tityus fasciolatus Pessoa

0.0002

Brazil

Termite mounds

Lourenςo 1978 In: Polis 1990b

Table 5-- Sex ratios of Centruroides balsasensis in the Balsas Depression, Michoacán. (n = 380 adults and 155 juveniles). Null hypotheses are for a 1:1 male (M) to female (F) sex ratio.










Values

χ² calc.

Probability

Adults

Captured and marked

F=92: M=114

2.35

0.1253 n.s.




Recaptures

F=26: M=32

0.64

0.4308 n.s.




New captures

F=56: M=60

0.14

0.7103 n.s.















Juveniles

Captured and marked

F=31: M=43

2.28

0.1630 n.s.




Recaptures

F=26: M=32

0.4

0.4308 n.s.




New captures

F=10: M=13

0.14

0.5316 n.s.

Table 6 -- Estimated biomass per hectare of Centruroides balsasensis in the Balsas Depression, Michoacán. (Estimation based on 1.16 g per individual).




DATE / SITE

ESTIMATED (kg)

MINIMUM

(kg)


MAXIMUM (kg)

Churumuco. September (2000)

0.493

0.290

1.8183

Turitzio. October (2000)

0.5278

0.3364

1.4935

Churumuco. November (2000)

1.0846

0.7685

2.3693

Turitzio. January (2001)

0.4872

0.3451

0.8729

Churumuco. January (2001)

2.1083

1.5631

3.2567

Turitzio. March (2001)

0.3567

0.2697

0.5742

Churumuco. March (2001)

1.0295

0.6989

1.9314

Turitzio. June (2001)

0.2755

0.174

0.8584

Churumuco. June (2001)

0.7656

0.4814

1.8879

Turitzio. August (2001)

0.725

0.4553

1.7603

Churumuco. September (2001)

1.2644

0.7511

3.3466

Table 7 -- Apparent activity and use of habitat by Centruroides balsasensis at the Balsas Depression in Michoacán (total of observations n = 1024).


Activity


Adult fem.

Juvenile fem.

Adult males

Juvenile males

Total

Ambush

84

32

102

40

258

Walking

26

18

50

36

130

Eating

3

1

4

4

12

Courtship

1

0

1

0

2

Resting

37

14

49

10

110










Subtotal:

512

Use of habitat

















Beneath stones

12

4

22

0

38

Base of trees

10

1

10

2

23

On litter foliage

14

11

21

14

60

Stone cavity

3

0

0

0

3

Stem cavity

2

1

2

0

5

Beneath cortex

3

0

2

0

5

Between stones

1

1

6

1

9

Over brush

14

5

7

6

32

Over ground

36

22

65

23

146

Over stone

47

5

46

9

107

Over plant

3

4

2

1

10

Over branch

16

9

12

9

46

Over stump

2

0

2

0

4

Over stem

11

2

9

2

24













Subtotal:

512

Total

325

130

412

157

1024







Figure 1. Species and sexual proportions after all samplings for the scorpion communities of Churumuco (A) and Turitzio (B). (cesp= Centruroides balsasensis, vava=Vaejovis variegatus, vaci=Vaejovis cisnerosi, and disp=Diplocentrus sp.).


Figure 2. Temperature and precipitation fluctuations in a yearly basis and its correlation to densities detected in 2001 at Churumuco (hashed vertical lines indicate onset and termination of the rainy season).
Figure 3. Temperature and precipitation fluctuations in a yearly basis and its correlation to densities detected in 2001 at Turitzio (hashed vertical lines indicate the onset and termination of the rainy season).
Figure 4. Stage or instars proportion fluctuation in 2001 for Churumuco and Turitzio populations.


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