1. Feeding Niche Differentiation between Two Species of Blastoid Echinoderms
Ryan FitzGerald Morgan
Tarleton State University
Abstract
Methods
Morphofeature
D. batheri (68)
D. delta (365)
t-test result
Average Height / /
2.4935E-18
Average Width / /
1.8898E-13
Ambulacral Length / /
1.096E-17
Ambulacral Width / /
9.9832E-07
Deltoid Length / /
3.2145E-10
Radio-deltoid Width / /
1.7342E-10
Radial Length / /
1.7361E-16
Conclusions
Deltoblastus batheri and Deltoblastus delta are common blastoid echinoderm species within the Permian deposits of Timor. Biological needs dictate that resource partitioning will naturally evolve out of intraspecific competition when there is significant overlap in use of a finite resource; however, this differentiation and resultant competitive exclusion is difficult to observe among fossil faunas. Pristine preservation of Deltoblastus species allows for fine-detail landmark measurement, and this data has been used to test whether significant differences exist between these closely related species. Thin plate spline analysis aids in visualizing the key differences between these latently dissimilar species.
Measurements of D. batheri and D. delta were taken of select theca points using digital calipers, demonstrated in Figure 2. Care was used to ensure accuracy of measurements, and all specimen identifications and associated information were noted. Averages of these measured data are shown in Figure 3.
Study of these two closely related species reveals changes in the ambulacra region to be the greatest difference, despite an overall significant difference among all traits measured. These changes on contemporaneous species are interpreted as the following:
D. batheri and D. delta are two extremely similar species in all respects excepting significant changes in the upper ambulacra region.
Thin plate spline analysis shows notable changes in the size and placement of the ambulacra, but limited changes to other parts of the theca.
Being contemporaneous geographically would place these species in direct competition.
Ambulacra differentiation would impact food gathering capability, and the large changes observed signify food niche differentiation, lessening competition.
Figure 1. Coated specimen photographs of Deltoblastus batheri (left) and Deltoblastus delta (right)
Genus
Species
ID #
Series
Locale
Province
Drawer
Deltoblastus
delta
e59742
Sonnebait
Basleo
Amanoebang
60A34
e59201
Neoetpantoekak
e59732
e59182
Soempak
e30752
Faoet Ao
60A33
e59734
e59736
e59809
Soem Peh
e30962
Kioemoko
e59185
e59184
e30969
Materials
Figure 3. Average measurements with variance and t-test results. Note low p-values for all compared characters.
While many of the Deltoblastus species could have been used, this study focused on Deltoblastus batheri and Deltoblastus delta, as these two species commonly occur together in large numbers (Figure 1). In addition, these two species are readily available in many major museum collections, making the results of this analysis particularly pertinent and easily tested for validity. Specimens for this analysis came from the British Museum of Natural History, London (NMUK). These included 68 specimens of Deltoblastus batheri and 365 specimens of Deltoblastus delta, chosen for their completeness and lack of damage.
Results
Analysis of D. batheri and D. delta demonstrated significant difference exists between the two closely related species among all measured parameters (Figure 4). The largest variances were in the upper half of the theca, and were most influential on the dimensions of the ambulacra. Thin plate spline analysis comparing these two species aids in visualizing these differences, and the changes in upper ambulacra exposure are very evident (Figure 5).
Introduction
Niche differentiation is the process by which competing populations use the environment differently in a way which allows both to coexist. While observed commonly in the Recent, this process is challenging to observe and quantify in the fossil record. Particular challenges are the lack of well constrained chronologies and continuous, or near-continuous, deposition and preservation of the fossils in question. Deltoblastus, with many species, pristine preservation, contemporaneous species, and limited geographic and chronostratigraphic extent, presents an ideal platform for observing niche differentiation in the fossil record.
Figure 2. Sample table of data collected for each specimen measured in NMUK collections.
References
FAY, R. O Deltoblastus, A new Permian blastoid from Timor. Oklahoma Geology Notes, Oklahoma Geological Survey, 21,
HAMMER, Ø. AND HARPER, D. A. T Paleontological Data Analysis. Wiley-Blackwell, Boston, Massachusetts, 368 pp.
HAMMER, Ø., HARPER, D.A.T., RYAN, P.D PAST: Paleontological statistics software package for education and data analysis. Palaeontologia Electronica 4(1): 9 pp.
Following measurement, a t-test was performed to ensure these measurements were significantly different (Figure 4). These absolute measurements were then converted into landmark data. These data were loaded into the statistical program PAST, where thin plate splines were produced (Figure 5).
Figure 5. Thin plate spline analysis results for converted landmark data. Blue= little change, Red= high degree of change. Red region corresponds to upper theca ambulacral region.
Figure 2. Generalized diagram of a blastoid, showing major measurement locations.
Contact
Ryan F Morgan;
Department of Chemistry, Geosciences, and Physics
Box T-0540, Tarleton State University
Stephenville, TX 76402