Thesis Defense
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Thesis Defense

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My thesis defense in 2007; it has changed since then.

My thesis defense in 2007; it has changed since then.

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Thesis Defense Thesis Defense Presentation Transcript

  • SNAKE COMMUNITY ECOLOGY WITHIN THE FLINT HILLS NATIONAL WILDLIFE REFUGE By: Bryan Maher Emporia State University, Department of Biological Sciences, 1200 Commercial Street, Emporia, KS 66801
  • Chapter 1: Snake Assemblage Related to the Vegetation Structure on Native Prairies
    • Introduction
    • Midwest – grasslands: millions of acres  scattered remnants
    • Anthropogenic disturbance: conversion to agricultural crops, rangeland, & residential development
    • Enhances natural differences among patches within heterogeneous landscape
    • Profound effect on plant & animal communities
    • Introduction
    • Habitat selection/presence & absence studied widely
    • Assemblages = species populations (immigrated or already present) within a patch
    • Influenced by environment, interaction with other species, & properties associated with assemblage groupings
    • Natural history important to determine appropriate scales to investigate
    • Introduction
    • Heterogeneity effects community assemblage/structure by increasing species richness
    • Vegetation structure diversity, climate, diversity of microhabitat, morphological, & behavioral traits
    • Habitat selection by any species depends on structural features of the patch or surrounding areas  must be suitable for reproductive purposes
    • Available forage, den/nest sites, predators, competitors, etc.
    • Introduction
    • Few conservation efforts focus on prairie amphibians & reptiles…much to learn about snake habitat selection in Midwest
    • Why study snakes?
    • - specific habitat requirements for daily activities
    • - great for ecological research
    • Numbers are declining…must focus on identifying & protecting critical habitat
    • Identify distinct patterns that may exist between snake assemblages & vegetation structure within native prairie patches
    • Account for differences that may exist between study sites using local vegetation composition
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  • Drift Fence Arrays Within Each Site
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  • • Biomark PIT tags inserted on left lateral, about 5 cm from cloaca • Scale-clipped ventral scales on juvenile snakes • Pocket Reader to identify unique number codes
    • Vegetation Sampling
    • 5-cm by 100-cm pole to measure height of visibility (Robel et al. 1970)
    • 1-m ² quadrat to determine % bare ground, woody vegetation, forbs, and grasses
    • ArcView 3.3 to select random coordinates from the native patches…used GPS device to find random points
    • Took three fixed samples between arms of each array at all sites x 2
    • Data Analysis
    • Bray-Curtis measure of dissimilarity with LNMDS ordination to find clusters
    • Simpson’s Index of Diversity for abundance patterns and species richness for each site
    • Randomized block to determine significant differences for species diversity between site and year
    • Randomized block to determine significant differences for vegetation composition between site and year
    • Results
    • Prairie consisted of warm-season grasses: Big bluestem ( Andropogon gerardii ) , little bluestem ( Andropogon scoparium ), Indian grass ( Sorghastrum nutans ) and switchgrass ( Panicum virgatum ); and various forbs
    • 13 snake species (brownsnake, copperhead, gartersnake, kingsnake, massasauga, racer, ratsnake, ribbonsnake, ringneck snake, and watersnake) in 29,268 trap nights
    • Few recaptures ( Thamnophis sirtalis parietalis )
  • Total number of unique individuals by species captured at the Blackbird, Fitch Hill, Garner Lane, and Slead sites from June 2004 to November 2004 at FHNWR, Kansas. 221 54 33 39 95 Total 101 19 17 17 48 Thamnophis sirtalis parietalis 39 12 2 2 23 Thamnophis proximus 2 1 0 0 1 Thamnophis radix 0 0 0 0 0 Storeria dekayi texana 3 0 1 2 0 Sistrurus catenatus tergeminus 0 0 0 0 0 Nerodia r. rhombifer 4 0 1 0 3 Nerodia e. transversa 0 0 0 0 0 Lampropeltis g.holbrooki 2 1 0 0 1 Lampropeltis c. calligaster 8 3 2 2 1 Elaphe o. obsoleta 1 1 0 0 0 Diadophis punctatus arnyi 59 15 10 16 18 Coluber constrictor flaviventris 2 2 0 0 0 Agkistrodon contortrix Total Slead Garner Fitch Blackbird Species
  • Total number of unique individuals by species captured at the Blackbird, Fitch Hill, Garner Lane, and Slead sites from April 2005 to November 2005 at FHNWR, Kansas. 179 70 29 24 56 Total 73 35 9 8 21 Thamnophis sirtalis parietalis 17 3 2 4 8 Thamnophis proximus 1 1 0 0 0 Thamnophis radix 1 0 0 0 1 Storeria dekayi texana 3 0 2 1 0 Sistrurus catenatus tergeminus 1 0 0 0 1 Nerodia r. rhombifer 1 1 0 0 0 Nerodia e. transversa 1 1 0 0 0 Lampropeltis g.holbrooki 1 1 0 0 0 Lampropeltis c. calligaster 3 1 1 0 1 Elaphe o. obsoleta 0 0 0 0 0 Diadophis punctatus arnyi 72 22 15 11 24 Coluber constrictor flaviventris 5 5 0 0 0 Agkistrodon contortrix Total Slead Garner Fitch Blackbird Species
  • Total number of unique individuals captured each month from June 2004 to November 2005 for Yellow-bellied Racers, Red-sided Gartersnakes, and Western Ribbonsnakes within the Blackbird, Slead, Fitch Hill, and Garner Lane sites at FHNWR, Kansas.
  • Total number of unique individuals captured from June 2004 to November 2005 for Massasauga Rattlesnakes and Osage Copperheads within the Blackbird, Slead, Fitch Hill, and Garner Lane sites at FHNWR, Kansas.
  • LNMDS depicting the clustering affect of similar communities on each array for all sites from June 2004 to November 2004 at FHNWR, Kansas.
  • LNMDS depicting the clustering affect of similar communities on each array for all sites from April 2005 to November 2005 at FHNWR, Kansas.
  • LNMDS depicting the clustering affect of similar communities on each array for all sites from June 2004 to November 2005 at FHNWR, Kansas.
    • Results
    • No significant difference for snake diversity between all sites (F = 2.207, P = 0.266) or between years (F = 1.42, P = 0.319)
    • Significant difference between year (F = 46.84, P = 0.006) for the average height of visibility through the flora
  • Paired T-test indicating significant differences in grass cover from June 2004 to November 2005 on several sites at FHNWR, Kansas. 0.7826 0.285 8 0.0230 Blackbird 0.0334 -2.564 8 0.0232 Slead 0.0042 3.962 8 0.0219 Garner Lane 0.0189 2.931 8 0.0156 Fitch Hill P-value t Stat df Variance Site
  • Paired T-test indicating significant differences in forb cover from June 2004 to November 2005 on several sites at FHNWR, Kansas. 0.716 0.377 8 0.0198 Garner Lane 0.016 -3.039 8 0.0043 Blackbird 0.012 3.231 8 0.3833 Slead 0.035 2.525 8 0.0148 Fitch Hill P-value t Stat df Variance Site
  • LNMDS of Bray-Curtis dissimilarities depicting changes in the vegetation composition from June 2004 to November 2004 at the FHNWR, Kansas.
    • Discussion
    • Controlled spring burns in 2004 vs. uncontrolled burns in 2005 on several sites
    • Spring flood in 2005 restricted access to several sites
    • Species utilizing multiple habitat patches
    • Individuals learned to avoid traps
    • Longer sampling period = higher census
    • Discussion
    • Trend of increased richness with increased heterogeneity
    • Species richness increased as plant richness increased, then decreased when warm-season grasses dominated
    • Decrease activity as thatch layer increases
    • As vegetative cover increased, plant diversity decreased creating lower quality habitat
    • Snake populations depend upon lushness of ground vegetation & environmental conditions
    • Discussion
    • The Garner Lane & Fitch Hill sites indicated the lack of plant cover may repel species
    • The amount of plant cover instead of vegetation type has been shown to influence habitat preference
    • Discussion
    • Vegetation structure within a patch is important, but so are habitat features around a patch
    • Over-wintering den sites and rookeries (pregnancy rocks) very important features
    • Some patches may not be utilized if not in close proximity to hibernaculum, even though it has suitable features
    • Management Implications
    • Improved conservation efforts that focus on expanding upon national wildlife refuge system
    • Certain biogeographical principles apply: distance from main species pool, and area
    • Link landscape on multiple scales: within refuge and outside refuge
    • Most importantly: educate the public!!!
  • Chapter 2: Abundance Patterns for Coluber constrictor flaviventris , Thamnophis proximus , and Thamnophis sirtalis parietalis at the Flint Hills National Wildlife Refuge
    • Introduction
    • Anthropogenic disturbance has not only had profound effect on plant animal communities, but with ecological interactions as well.
    • Population and community level caused by which species are present, which habitat they occupy, and the type of forage available.
    • Species populations within a patch are limited by suitable conditions or resources, size, proximity of other patches, length of time the patch is habitable, and the rate of population growth.
    • Anthropogenic disturbances enhances natural differences within a population.
    • Introduction
    • Reptiles and amphibians constantly interact with their physical environment.
    • - pursuing prey, vocalizing, defending territory, thermoregulation and breeding
    • Indicators of changing environmental conditions.
    • Introduction
    • Investigating the abundance patterns of several species within a stable community can help identify conditions within a habitat patch which species prefer, and to determine the distribution and abundance of similar patches where a species would be expected to occur.
    • The presence of diverse prey items can influence whether enough individuals to form a population will inhabit a patch.
    • Kansas snake species such as yellow-bellied racers ( Coluber constrictor flaviventris ) and red-sided gartersnakes ( Thamnophis sirtalis parietalis ) prey mostly on small rodents or amphibians.
    • Introduction
    • Social interactions may be just as important as prey availability
    • In New Hampshire, social interactions between racers and gartersnakes influenced activity patterns and body size
    • Individuals that could not compete (small body size or less active) were forced to occupy lower quality habitat (lower veg. height, more bare ground, & lower plant diversity)
    • Predation can cause smaller species/individuals to occupy marginal quality habitat (juveniles moving from natal areas )
    • Introduction
    • What interactions or factors influence these species’ abundance patterns?
    • Recapture rates would be low and the abundance of the most frequently captured species to not vary from site to site
    • The larger of the two species would suppress the smaller species’ abundance.
    • Adult body size for both species would be comparable
    • Data Analysis
    • Randomized block to determine significant differences for species between site and year
    • Randomized block to determine significant difference for prey species between site and year
    • Collapsed ANOVA to determine significant site effects for snake species
    • Collapsed ANOVA to determine significant site effects for prey species; Least Squared Means to detect abundance patterns within each site for species
    • Fisher’s Least-Significant Difference Test to determine significant differences within populations between sites
    • Results
    • 400 unique individuals from 13 snake species; 29,268 trapnights
    • The three most abundant species accounted for 90 percent of unique individuals captured: 44 % Thamnophis s. parietalis, 33 % Coluber c. flaviventris , and 14 % Thamnophis proximus
    • Prey items regurgitated include: Sigmodon hispidus, adult Microtus ochrogaster, grasshoppers , juvenile and adult Rana blairi, and Acris crepitans blanchardi
    • 87% of Rana blairi captured were on Blackbird and Slead sites; 59% of Sigmodon hispidus were captured on the Garner Lane site
    • Results
    • The number of unique individuals for Thamnophis s. parietalis (F = 4.12, P = 0.048) and Thamnophis proximus (F = 18.45, P = 0.00059) and Sigmodon hispidus (F = 8.63, P = 0.0068) were significantly different by site
    • Thamnophis s. parietalis population on Blackbird was significantly different from the Fitch Hill ( P = 0.018) and the Garner Lane ( P = 0.022) sites; Coluber c. flaviventris population on Blackbird also was significantly different from the Fitch Hill ( P = 0.027) and the Garner Lane ( P = 0.027) sites
  • Fisher’s Least-Significant-Difference Test with pairwise comparison probabilities 1.000000 0.113227 0.092513 0.322731 Slead 1.000000 0.898448 0.022073 Garner Lane 1.000000 0.018036 Fitch Hill 1.000000 Blackbird Slead Garner Lane Fitch Hill Blackbird Thamnophis sirtalis parietalis
  • Fisher’s Least-Significant-Difference Test with pairwise comparison probabilities 1.000000 0.120181 0.120181 0.370555 Slead 1.000000 1.000000 0.027585 Garner Lane 1.000000 0.027585 Fitch Hill 1.000000 Blackbird Slead Garner Lane Fitch Hill Blackbird Coluber constrictor flaviventris
  • Fisher’s Least-Significant-Difference Test with pairwise comparison probabilities 1.000000 0.018308 0.039207 0.006106 Slead 1.000000 0.635687 0.000161 Garner Lane 1.000000 0.000273 Fitch Hill 1.000000 Blackbird Slead Garner Lane Fitch Hill Blackbird Thamnophis proximus
  • Least Squares Means from Collapsed ANOVA analysis indicating a similar abundance pattern for three snake species and one amphibian species at the FHNWR, Kansas. T. proximus C. c. flaviventris T. s. parietalis
    • Discussion
    • Yellow-bellied racers suppress smaller-bodied species population .
    • September 2004 smaller Thamnophis sirtalis parietalis individuals were present when Coluber constrictor flaviventris individuals were absent.
    • First-years moving from lower quality habitat to fill void in higher quality habitat.
    • Could be last individuals to reach hibernaculum  avoiding predation and competition.
    • Discussion
    • Grassland snakes utilize wide variety of prey items.
    • In the past, these snakes followed trends of rodent prey.
    • Population would decline as species diversity declined (grass replaced forbs & woody vegetation replaced grass).
    • Overgrazed pastures and cultivated fields support fewer species  Fitch Hill and Garner Lane.
    • Discussion
    • Blackbird and Slead exhibited larger populations due to proximity to wetlands  2005 flood could have reduced those populations
    • Juvenile Thamnophis s. parietalis prefer mesic, lowland habitats
    • Flood forced smaller individuals to upland habitats which were inhabited by larger individuals  increased predation and competition.
    • Interactions in 2004 much different than 2005
    • Discussion
    • Breeding activities influences abundance patterns
    • Physiological characteristics also influence abundance patterns by determining habitat use (thermoregulation & activity)
    • Individuals shift home ranges depending on thermodynamics and active foraging
    • Feasible that individuals compete for habitat with abundant prey, why not compete for habitat with suitable thermodynamics?
    • Ecological research is complex; therefore, difficult to pin down one factor within a natural environment that solely influences snake assemblage patterns…too many factors that could all contribute!
    • ACKNOWLEDGMENTS
    • I would like to thank my committee members (L. Sievert, B. Thomas, G. Sievert, and T. Menard) for their comments on each draft of my thesis. My deepest gratitude for the financial support from the Harold Durst Graduate Research Award Committee and Emporia State University Department of Biological Sciences. The generous support of the United States Fish and Wildlife Service (USFWS) and the Flint Hills National Wildlife Refuge (FHNWR) for allowing me to set up trapping arrays. I was also like to thank G. Smith, and D. Zelmer for their comments on earlier drafts of my thesis. J. Campbell, B. Smart, C. Dobbs, L. Simpson, K. Jackson, J. Phillis, A. Parsons, W. Dunn, and K. Shepherd for their assistance in the field. The support and love of my family and friends.
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