This study explores how varying patterns of connectivity between spatially fragmented habitats affects species richness. Pond microcosms were set up with networks of bottles connected by tubing in either evenly or unevenly connected patterns. Samples from the bottles were analyzed and species counted over time. Initial results found that networks with a higher number of bottles and even connectivity between bottles sustained higher levels of species richness on average. Further replicates are needed to solidify these findings and better understand how connectivity patterns impact community dynamics in spatially fragmented ecosystems.

1. THE EFFECT OF VARIABLE CONNECTIVITY ON RICHNESS IN
SPATIALLY FRAGMENTED POND MICROCOSMS
Heather M. David, Dr. Kurt E. Anderson
Department of Biology, University of California in Riverside
ABSTRACT
INTRODUCTION
Food webs are fragmented across landscapes in nature. An understanding of how
changing patterns of connectivity affects the persistence and dynamics of interacting
species is limited. Theory predicts that specific patterns of spatial connectivity can
influence richness and dynamics in food webs, but this has not been tested empirically.
Protist microcosms are used to manipulate connections among food webs in a laboratory
setting, simulating natural community dynamics. Microcosms in the laboratory have
shown to reproduce wild ecosystem community dynamics. Microcosm samples are being
collected from ponds in University of California at Riverside’s Botanical Gardens and
Agricultural Operations Facility. They are added to networks of 175 milliliter bottles
which are connected in various patterns by flexible tubing. The effect of connectivity on
richness is explored by varying the number of bottles per network and varying the number
of connections per bottle. In evenly connected networks, circle shaped networks of bottles
have the same number of connections between them, each containing two connections per
bottle. In uneven networks, a network of bottles will have variable numbers of
connections to other bottles with a more random pattern. The networks of bottles with
uneven connections are expected to support greater food web richness and the converse is
expected with evenly connected networks. This study attempts to inform ecological
theory by demonstrating how richness is affected by network size and level of connectivity
variability.
Figure 2: The protist Tetrahymena hunts E. coli in this photo illustration, which
features a microscope image of Tetrahymena. Credit: University at Buffalo
METHODS RESULTS
ACKNOWLEDGEMENTS
“Thank you” to the entities pictured below, Dr. Kurt E. Anderson, Sean Hayes, Ashkaan Fahimipour,
Maria Franco-Aguilar, the UC Riverside CAMP program, HSI-STEM, and UC LEADS, the Student
Veterans Association as well as the Anderson Lab and my Family for their support.
CITATIONS
Organisms collected in the wild were transferred to lab microcosms, samples were then
analyzed for novel species and added to networks of bottles connected by tubing in patterns of
either uneven connections (U9 and U5) or regular connections (R9 and R5). The specific
patterns were chosen based on previously published studies showing greatest richness in
similar spatial arrangements (Holland & Hastings 2008).
EVEN:
•9 bottles (R9)
•5 bottles (R5)
Two Connections
Per Bottle
UNEVEN:
•9 bottles (U9)
•5 bottles (U5)
Random
Connections Per
Bottle
Ecosystems in nature are spatially fragmented but are connected in various ways
(Levin 1992). Ponds in particular are spatially isolated habitats connected by
dispersal. At the base of the pond ecosystem food web are protists, diatoms, bacteria,
rotifers, and arthropods. Many studies have been done on multi-trophic interactions
using these types of ecosystems however, information is scarce regarding how
movement among habitats influences their interaction dynamics, despite being a large
part of the ecosystem (Amarasekare 2006). Theory predicts different patterns of
connections can lead to different richness (Holland & Hastings 2008) therefore,
richness is expected to result from variability among bottles, allowing species-rich
bottles to “rescue” species-poor ones. This project attempts to identify the organisms
living in these pond ecosystems and how habitat connectivity patterns affect them.
Tubing was 14 centimeters in length and each
bottle was inoculated with 75 mL of medium
composed of 1400 mL of deionized water, a
protist food pellet and 0.14 grams of powdered
reptile vitamins which was autoclaved to
prevent contamination. Ten drops from each
bottle were regularly aliquoted and the
number of species seen per 20 mL drop was
recorded. Regular one milliliter fluid
exchanges with fresh medium kept waste to a
minimum.
Levin, S.A. (1992). The problem of pattern and scale in ecology. Ecology 73 (6): 1943-
1976.
Amarasekare, P. (2006). Productivity, dispersal and the coexistence of intraguild
predators and prey. Journal of Theoretical Biology 243 (2006): 121-133.
Holyoak, M. (2000). Habitat Subdivision Causes Changes in Food Web Structure.
Ecology Letters 3: 509 - 515.
Holland, M. D., & Hastings, A. (2008, October 19). Strong effect of dispersal network
structure on ecological dynamics. Nature , pp. 792-794.
METHODS
RESULTS/DISCUSSION
CONCLUSION
In addition to being the foundation of pond ecosystems, studies of organism
interactions at the microscopic level, mirror those at macroscopic levels. An analogy to
these bottle arrays would be land bridges over freeways which connect fragmented
landscapes, or a river whose seasonal flooding creates isolated ponds when the waters
recede. Both contribute to dispersal at random times which sustain the diversity of life
within each mostly isolated community. It was expected that diversity and species
richness can be sustained at higher levels when augmented with species dispersal keeping
greater variability. Overall stability from asynchrony however, is proving to be elusive.
Larger, more random networks are theoretically expected to be harder to synchronize but
initially this seems to be not true.
PARTIAL LIST OF SPECIES IDENTIFIED IN POND SAMPLES
Euglena sp. Scenedesmus sp. Euplotes sp. Volvox sp.
Spirostomum sp. Urostyla sp. Blepharisma sp. Tetrahymena sp.
Paramecium sp. Cyclidium sp. Pleurosigma sp. Halteria sp.
Tubes with mesh covers filled with water and two wheat seeds were
secured into wood blocks strapped to bricks for weight. They were then
inserted into ponds and left for a week to be colonized by wild pond
organisms. The mesh size was small enough to exclude larger arthropod
invertebrate predators to preserve richness but large enough to permit
microorganism diversity.
Data from the sampling period are shown
in these graphs. The average number of
species per bottle in each array are presented
with associated standard deviations. Data
collected suggests that greater richness is
sustained using a higher number of bottles
per network and an even connection among
bottles. Using temporal blocking, more
replicates of this experiment will be run to
solidify these findings.
0
2
4
6
8
10
12
14
16
18
20
C1 C2 U9 U5 R9 R5
NumberofObservedSpecies
Treatment
Time Richness Table
Maximum Observed Richness Time-averaged Richness
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
J-31
A-3
A-4
A-5
A-6
A-7
A-10
A-11
A-12
A-14
A-17
A-19
A-20
A-21
A-24
A-26
A-28
S-4
S-9
S-11
S-16
CoefficientofVariation
Date
Array Variability
R5 R9 U5 U9
Figure 9: Variability of each bottle over time.
Figure 8: Average richness and max richness observed over time by bottle.
Figure 5: Four arrays of differing connectivity.
Figure 6: Prepping bottles. Figure 7: The arrays.
Figure 3: Sample collection tubes. Figure 4: Sample collecting.
At the right is a graph of the overall array
variability per array, per date. The regularly
connected array with nine bottles seems to have
the greatest variability which coincides with the
results in the richness table showing greater
richness, mostly disproving the third hypothesis.
The first and second hypothesis clearly cannot
be disproved with this study and the null is
disproved. Further replicates might reveal a
stronger connection between evenly connected
bottles, microcosm variability, and richness
sustainment.
Figure 10: Ciliate Protist 100x
Figure 14: Rotifer 100xFigure 12: Cyclops 100x
Figure 11: Diatom 100x
Figure 13: Bacteria 400x
Table 1: Species Identification List.
Ho: Richness unaffected by spatial arrangement.
H1: Interconnected bottles have greater richness than disconnected.
H2: More bottles foster greater richness than less bottles.
H3: Unevenly connected bottles foster greater richness than uniform
connections.
Figure 1: Sample collection.