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Prescribed Burning Affects a Measure of Fitness in Ctenus hibernalis (Araneae: Ctenidae) at Oak Mountain State Park, Shelby County, AL

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Fire-suppressed forests in Oak Mountain State Park (OMSP; Shelby County, AL) have undergone experimental prescribed burning as a means to restore the open canopy architecture and diverse understory characteristic of Pinus palustris (Longleaf Pine) communities. Populations of a ground-hunting spider, Ctenus hibernalis, in the forests of OMSP were studied in order to examine the effect of restoration efforts on populations of understory arthropods. Study sites included regions burned 1 year prior and 5 years prior, as well as a region that has experienced 2 decades of fire suppression. No individuals of C. hibernalis were found in the region burned 1 year prior. There was no significant difference in the total number of spiders in the fire-suppressed region and the region burned 5 years prior, although the body mass of the spiders in the region burned 5 years prior was significantly greater than those in the fire-suppressed region. These results suggest that increased resource availability related to prescribed burns leads to increased spider fitness.
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Southeastern Naturalist
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T.J. Cole and R.A. Hataway
2016 Vol. 15, No. X
SOUTHEASTERN NATURALIST
2016 15(X):00–00
Prescribed Burning Affects a Measure of Fitness in Ctenus
hibernalis (Araneae: Ctenidae) at Oak Mountain State Park,
Shelby County, AL
T. Jeffrey Cole1 and Robert A. Hataway1,*
Abstract - Fire-suppressed forests in Oak Mountain State Park (OMSP; Shelby County,
AL) have undergone experimental prescribed burning as a means to restore the open canopy
architecture and diverse understory characteristic of Pinus palustris (Longleaf Pine) com-
munities. Populations of a ground-hunting spider, Ctenus hibernalis, in the forests of OMSP
were studied in order to examine the effect of restoration efforts on populations of understo-
ry arthropods. Study sites included regions burned 1 year prior and 5 years prior, as well as
a region that has experienced 2 decades of re suppression. No individuals of C. hibernalis
were found in the region burned 1 year prior. There was no signicant difference in the total
number of spiders in the re-suppressed region and the region burned 5 years prior, although
the body mass of the spiders in the region burned 5 years prior was signicantly greater than
those in the re-suppressed region. These results suggest that increased resource availability
related to prescribed burns leads to increased spider tness.
Introduction
Pinus palustris Mill. (Longleaf Pine) ecosystems, historically the dominant
ecosystems in the southeastern United States, depend on frequent res to maintain
understory biodiversity and the open forest architecture that fosters Longleaf Pine
recruitment (Bruce and Bickford 1950). Following European colonization, particu-
larly in the 20th century, forest res were suppressed (Van Wagtendonk 2007). The
resulting accumulation of leaf litter and understory shrubs constrains Longleaf Pine
germination (Garren 1943). This additional fuel can cause res to be hotter when
they do occur (Youngblood et al. 2005). Recently, prescribed burning has become
a common practice in an attempt to restore the composition and structure of Long-
leaf Pine communities (Bradstock et al. 1998). Effective burns remove leaf litter,
downed logs, and competitive re-intolerant shrubs, opening the understory for the
growth of grasses and other light-dependent herbaceous vegetation (Beckage and
Stout 2000, Outcalt and Brockway 2010, Ware et al. 1993).
Forest-re suppression has dramatically altered forest ecosystems in the dwin-
dling montane Longleaf Pine woodlands across the southeastern United States
(Shumway et al. 2001). This change is especially evident in the largest state park
in Alabama, Oak Mountain State Park (OMSP, ~4047 ha [~10,000 ac]), Shelby
County, AL. Prescribed burning designed to simulate historical periodic forest res
and alleviate forest-re suppression has taken place in over 40.5 ha (100 ac) of
experimental forest plots in OMSP at various frequencies over the past decade.
1Department of Biological and Environmental Sciences, Samford University, 800 Lake-
shore Drive, Birmingham, AL 35229. *Corresponding author - rahatawa@samford.edu.
Manuscript Editor: Jason Cryan
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2016 Vol. 15, No. X
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Species diversity and population dynamics of ora and fauna within an ecosystem
can be used to monitor the progress of restoration efforts by comparing sites affected
by the prescribed burns to regions undergoing re suppression (Malumbres-Olarte et
al. 2013, Matthews and Spyreas 2010, Rey Benayas et al. 2009). Since faunal succes-
sion depends on complex variables other than vegetation return (e.g., ecological and
landscape composition, surrounding gene-pool structure, connectivity, and biotic
factors), studying the forest fauna is a more inclusive tool for monitoring restoration
than oristic surveys alone (Brudvig 2011, Grimbacher and Catterall 2007, Majer
2009). Arthropod communities are useful as indicators of community response to res-
toration measures because they are very sensitive to ecological changes due to their
short life cycles, rapid growth rates, and ubiquity (Brand 2006, Kremen et al. 1993).
A recent study conducted in a Piedmont forest in northern South Carolina, under
burning circumstances similar to OMSP, found that spider families were impacted
differently. Numbers of spiders were either not affected or quickly recovered after the
burn events (Vickers and Cullin 2014). However, research has not been conducted on
the population dynamics of an individual species.
Ground-hunting spiders, such as Ctenidae (wandering spiders), are common
arthropods studied in population ecology (Marc et al. 1999). They are suitable
organisms to monitor community responses to restoration due to their position as
generalized predators of soil arthropods. This aspect of their life history makes them
sensitive to changes in leaf-litter depth, grassy biomass, and shrub abundance (Uetz
and Unzicker 1975). Changes in the microhabitat affect the spiders’ food supply as
well as protective cover from predators (Wheater et al. 2000). Fire suppression sig-
nicantly reduces the amount of grasses in woodlands, thus depleting the preferred
open understory habitat for these spiders, which provides space for burrowing and
shelter from predators as well as a diverse array of prey organisms (Major et al. 2006,
Martin and Major 2001, Pinzon et al. 2013, Ryndock et al. 2012).
The ground-hunting spider Ctenus hibernalis Hentz is a generalist predator
endemic to the southeastern United States that has been collected primarily in
Alabama and can be found throughout OMSP (Bradley 2012, Peck 1981). With its
large home range, this species is an ideal candidate for monitoring the response of
predatory arthropods to restoration efforts.
The aim of this study was to monitor the density of 3 geographically distinct popu-
lations of C. hibernalis in OMSP. By comparing the population size and body mass of
C. hibernalis in 2 burn treatments of different frequencies and 1 re-suppressed site,
we hoped to gain insight as to whether the initiation of prescribed burning has been
successful in opening and restoring the microhabitat of this species.
Methods
We established three 10 m x 10 m quadrats in each of 3 burn treatment plots in
OMSP: plots that were burned 1 year prior (33.35763°N, 86.710452°W), 5 years
prior (33.36974°N, 86.691518°W), and in a plot that has undergone re suppres-
sion for at least the past 2 decades (33.35798°N, 86.70749°W), for 9 total quadrats.
Quadrats were located in the understory of south-facing slopes of predominantly
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T.J. Cole and R.A. Hataway
2016 Vol. 15, No. X
oak/hickory/Longleaf Pine forest at a similar elevation (~230 m). Quadrats within
a treatment plot were a minimum of 20 m apart. All sampling sites were at least
100 m from a road to prevent any edge effect that could inuence predation rate or
other parameters (Cady et al. 1980).
We collected Ctenus hibernalis individuals at night by spotlighting the reec-
tive tapetum within their eyes (Beccaloni 2009). We sampled each quadrat within
each site 5 times between the months of June and July 2014, at least 1 hour after
dark for 1 hour. This time period allowed for an exhaustive search of the entire
quadrat. Adults were hand collected and visually identied to species based on
morphological characteristics, counted, weighed, and released. We postponed
sampling if there was any precipitation within 24 hours prior to collecting. The
total number of individuals that were collected per quadrat in one hour of sampling
determined population densities.
At each sampling, we recorded National Weather Service weather data such as
temperature, average wind speed, moon phase, moon position, amount of recent
precipitation, humidity, and cloud cover to be used in multiple regression models
to account for confounding factors. We measured leaf-litter depth in all 9 quadrats
was measured in 9 places to compare leaf-litter removal between the regions.
All statistical analysis was conducted using R version 3.1.1 (R Core Team 2014)
statistical programming language. We used a Mann-Whitney U-test to detect dif-
ferences in spider abundance and spider biomass between the burn treatments. We
created multiple linear regression models using all environmental and human factors
as independent variables in the MuMIn package in R to predict total spiders caught,
and then evaluated the models using Akaike Information Criterion (AIC) techniques.
Finally, we regressed spider mass and total number of spiders caught against one an-
other to test for associations between individual size and population density.
Results
We collected a total of 315 individuals of Ctenus hibernalis in the re-sup-
pressed region and the region burned 5 years prior. The density of C. hibernalis in
the region burned 1 year prior was too small to be quantied, nding 0 spiders in the
quadrats and <5 outside of the quadrats. This region was removed from all subse-
quent analyses. There was no signicant difference in population density between
the plot that was burned 5 years prior and the re-suppressed region as determined
by a Mann-Whitney U-test. Of the 127 linear models, created using all environ-
mental and human factors, the model with the highest AIC score did not predict
population density (AIC = 210.58, weight = 0.10, P = 0.558). The mean ranks of
the number of individuals per 100 m2 quadrat of the burned and re-suppressed
region were 12.07 ± 6.44 SD and 12.27 ± 8.81 SD, respectively (n = 30, U = 104,
P = 0.7352, r = 0.064; Fig. 1A).
Spider masses were signicantly greater in the region burned 5 years prior than
in the re-suppressed region as determined by a Mann-Whitney U-test. The mean
ranks of the individual masses within the burned and re-suppressed region were
0.17 ± 0.12 g SD and 0.12 ± 0.09 g SD, respectively (n = 202, U = 3310, P < 0.0001,
Southeastern Naturalist
T.J. Cole and R.A. Hataway
2016 Vol. 15, No. X
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r = 0.30; Fig. 1B). There was no signicant relationship between the average mass
of spiders and total number of spiders caught per quadrat. This result suggests com-
petitiveness of large individuals does not inuence population density negatively.
Discussion
There was no significant difference in the total number of spiders in the fire-
suppressed region and the region burned 5 years prior, although the body mass
of the spiders in the region burned 5 years prior was significantly greater than
those in the fire-suppressed region. Spider mass is positively correlated with fe-
cundity and overall fitness (Nicholas et al. 2011, Skow and Jakob 2003). In our
study, the differences in spider mass between sites suggests that the individuals
living in the region that had been burned 5 years prior have higher fecundity and
overall potential individual fitness than individuals in the fire-suppressed region.
Additionally, the lack of correlation between individual masses and population
density supports the prediction that spiders in the region burned 5 years ago have
more available resources.
Figure 1. (A) Average in-
dividuals caught per 10-
m2 quadrat between treat-
ment regions. (B) Average
mass of spiders caught per
treatment region. Aster-
isks indicate signicance
(P < 0.001). Bars indicate
standard error.
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2016 Vol. 15, No. X
Previous studies on spider community changes in response to re restoration in
both the piedmont forest in northern South Carolina and the open oak woodlands
in northern Mississippi found changes in the community structure that varied
according to family, with open-habitat specialists’ abundance increasing with the
restoration of re regimes (Ryndock et al. 2012, Vickers and Cullin 2014). The
community in the South Carolina study had recovered 1 year after burning whereas
the data presented here, with no individuals being found, suggests that the region
that was burned 1 year prior has yet to recover from that burn. This difference could
perhaps be due to variation in the intensity of the burns.
Future experiments will be necessary to determine the relationship between
arthropod populations and understory vegetation in relation to the prescribed burn
regime. Despite the expectation that population densities in the burned region
would be greater than in the re-suppressed region, we were unable to detect a
signicant difference in population density among sites, except for the fact that no
spiders were found in the plot burned 1 year prior.
Acknowledgments
This research was supported by a REU grant from the NSF (REU award number
1327466). For providing helpful comments, we thank L.J. Davenport, Erynn Maynard, and
Mary Anne Sahawneh.
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Spiders are among the most diverse groups of terrestrial invertebrates, yet they are among the least studied and understood. This first comprehensive guide to all 68 spider families in North America beautifully illustrates 469 of the most commonly encountered species. Group keys enable identification by web type and other observable details, and species descriptions include identification tips, typical habitat, geographic distribution, and behavioral notes. A concise illustrated introduction to spider biology and anatomy explains spider relationships. This book is a critical resource for curious naturalists who want to understand this ubiquitous and ecologically critical component of our biosphere.
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We document the fire history and associated ecological changes of an old-growth forest stand in western Maryland, U.S.A. The study area is located on the side slopes of a ridge system (Savage Mountain). Twenty basal cross sections were obtained from old trees cut in 1986, which provided evidence of 42 fires from 1615 to 1958. Nine fires were recorded in the sample trees in the 17th century, 13 in the 18th century, 12 in the 19th century, and eight in the early to mid-20th century. However, there were no major fire years after 1930. The Weibull modal fire interval was 7.6 years. Oaks recruited consistently from the early 1600s to the early 1900s, but there was increased Acer rubrum L. and Betula lenta L. recruitment with fire suppression after 1930. Species recruitment patterns and long-term fire history reported in this study offer important direct support for the hypothesis that periodic fire played an important role in the historical development and perpetuation of oak forests of the mid-Atlantic region before and after European settlement.Les auteurs ont reconstitué l'historique des feux et les changements écologiques qui y sont associés dans un peuplement de vieille forêt situé dans l'Ouest du Maryland, aux États-Unis. L'aire d'étude est située sur les versants d'une chaîne de montagnes (Savage Mountain). Vingt sections radiales prélevées à la base de vieux arbres abattus en 1986 montrent que 42 feux sont survenus de 1615 à 1958. Neuf feux ont été notés dans les arbres échantillonnés au 17e siècle, 13 au 18e siècle, 12 au 19e siècle et huit du début à la moitié du 20e siècle. Cependant, il n'y a eu aucun feu important après 1930. L'intervalle modal entre les feux établi d'après la formule de Weibull est de 7,6 ans. Le recrutement des chênes a été constant du début des années 1600 au début des années 1900, mais il y a eu une augmentation dans le recrutement de Acer rubrum L. et de Betula lenta L. suite à la suppression des feux après 1930. Les patrons de recrutement des essences et l'historique des feux à long terme rapportés dans cette étude constituent un appui direct important à l'hypothèse selon laquelle la récurrence périodique des feux a joué un rôle important dans le développement historique et le maintien des forêts de chênes de la région mi-atlantique avant et après la colonisation par les Européens.[Traduit par la Rédaction]
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Fire suppression has altered the uplands of northern Mississippi (U.S.A.). Once blanketed by open oak woodlands, this region is now experiencing mesophytic tree invasion, canopy closure, reduced oak regeneration, and herbaceous understory loss. In an attempt to reestablish historical conditions, experimental restoration was initiated through thinning and burning treatments. Our study, part of a comprehensive monitoring effort, is the first to examine the impact of oak woodland restoration on the spider community and associated habitat structure. Samples measuring a variety of environmental variables and utilizing an array of spider collecting techniques were taken within four habitats located at the restoration site: fire‐suppressed forest, moderately treated forest, intensely treated forest, and old field. Two main conclusions resulted from this study. (1) Open‐habitat specialists responded positively to increased canopy openness regardless of the availability of herbaceous vegetation. (2) Woodland restoration increased spider diversity, perhaps through the formation of diverse habitat structure and/or by altering species dominance patterns. A rise in open‐habitat specialist diversity was observed as treatment intensity increased, with no compensatory reduction in the diversity of forest specialists. What remains to be seen is whether the continued transition to open woodland habitat will result in losses of forest specialist species. More aggressive overstory tree thinning is currently being administered to encourage the growth of herbaceous grasses and forbs, which will permit future tests of a hypothesized decline in forest specialists.
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The pholcid spider Holocnemus pluchei (Scopoli 1763) competes for food with conspecifics, and spiders reared on high food levels are generally larger. In this study, we examined whether larger female body size (as estimated by tibia-patella length) translated into increased reproductive success in the form of increased clutch size, clutch weight, and average egg weight. Larger spiders had more eggs and thus heavier clutches, but there was no relationship between maternal size and average egg weight. We also looked for a tradeoff between average egg weight and egg number, and we found a weak relationship in which average egg weight was highest for intermediate-sized clutches. Larger female body size thus translates into increased reproductive success in terms of egg number and clutch weight, but not weight of individual eggs.
Article
The ‘Natural Disturbance Paradigm’ for forest management seeks to meet conservation goals by modeling industrial harvest in fire-driven forest systems on patterns associated with wildfire. Fire suppression and increased forest harvesting may have detrimental effects on biodiversity, and therefore prescribed burning is suggested to retain legacies of wildfire not emulated under natural disturbance based approaches. The merits of this approach are being tested in the EMEND experiment in the Canadian boreal mixedwood forest. We compared responses of ground-dwelling spiders between sites subjected to prescribed post-harvest burning and retention harvest during three seasons during the first 7 years after disturbance. Overall, 38,661 adult spiders representing 190 species were collected. Estimated species richness was highest in undisturbed sites in all 3 years. Burning had the strongest negative effect on species richness 1–2 years after treatment; however, richness was higher in burns than in harvested sites 5–6 years postdisturbance. Species turnover was highest within controls but tended to increase over time between burned and harvested plots. Lower turnover in burned and harvested sites may reflect habitat homogenization by disturbance, suggesting a management and conservation challenge in relation to naturally disturbed and undisturbed areas. Species were grouped into disturbance-specialists, disturbance-tolerant, disturbance-generalists and generalists; 22 species were significant indicators for untreated sites, 18 for the burn and three for the harvest treatments. No major differences were observed in the spider fauna between harvested and burned areas within the first 6–7 years post-disturbance, and little evidence of recovery toward the pre-harvest fauna was evidenced. However, long term experiments may improve understanding of natural disturbance processes and improve management of boreal forests.
Article
Abstract The abundance of wolf spiders (Lycosidae) was measured across woodland–pasture boundaries in the wheat-belt of New South Wales, Australia, to determine the nature and magnitude of any edge effect. Spiders were collected by spotlighting along sample plots in woodlands located at distances of 5, 20, 35 and 200 m from the edge, and along sample plots in paddocks located at distances of 5 and 20 m from the edge. The wolf spider assemblage changed significantly across the edge, but the difference could be accounted for only by a change between the woodland and the paddock and not by any changes within the woodland at different distances from the edge. Ground cover (wolf spider microhabitat) changed significantly between the paddock and the woodland, but there were no consistent differences in microhabitat with distance from edge within either paddocks or woodlands. There was a significant correlation between an ordination of sites based on spider species abundance and an ordination based on microhabitat variables, suggesting that the wolf spider assemblage was responding to differences in microhabitat. Fine-scale selection of microhabitat by most wolf spider species was non-random, with most species preferring locations with grass cover, rather than more open locations. The present study indicates that wolf spiders are mostly unaffected by edge conditions at the woodland–paddock boundary. Accordingly, small and/or linear remnants with high edge-to-area ratios may constitute suitable faunal habitat for wolf spiders and perhaps other terrestrial arthropod species, despite the fact that this configuration is unsuitable for many vertebrate species.
Article
We studied the effect of burning frequency on the density and species richness of understory flowering stems in a Florida sandhill. Flowering stems were censused weekly for 54 weeks in six sites that had been burned one to six times in the previous 16 years. We concurrently measured overstory characteristics such as species composition, density and basal area. We used maximum likelihood and Akaike's Information Criterion to compare linear, quadratic, saturating, and null models of community response to repeating burning. We did not find a relationship between species richness, diversity or flowering stem density and fire frequency. Tree density was related to fire frequency and may represent an indirect pathway for fire effects on understory characteristics. While we found no support for the Intermediate Disturbance Hypothesis, an analysis of our experimental design indicated that we had low statistical power. We develop the hypothesis that a saturating model of response to fire best describes understory species richness in our system. We test this hypothesis using the most extensive published fire data set we are aware of and find support for a saturating model.