Untangling ecotone diversity hypotheses: Spider communities within a forest-meadow interface - UC Natural ...
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
Untangling ecotone diversity hypotheses:
Spider communities within a forest-meadow interface
Melissa Grim1, Jagger Joyner1, Christina Nakhla2, Bautista Tobias3
1
University of California, Santa Barbara; 2University of California, Riverside;
3
University of California, San Diego
ABSTRACT
Edge effects are important and understudied in ecology. Spiders exhibit a diverse array
of predatory strategies which depend on habitat structure and abiotic environmental
factors, making them an important study taxon in edge habitats. In this study, we
evaluated the relationship between spider family richness, abundance, and diversity
with a forest-meadow interface in the Coast Range of California. We expected to
observe a difference in response to edge effects depending on the functional guild of
spiders, active hunters or web-weavers. We found that web-weavers were more
common in forest interiors while hunter abundance did not differ by habitat. However,
no difference in diversity was found between habitats. Overall, this study shows that
spiders do respond to edge effects and suggests that future research into edge effects
should look explicitly at the underlying environmental factors contributing to these
patterns.
Keywords: spiders, ecotones, edge effect, biodiversity
INTRODUCTION forest habitats may create intermediate
environments or microhabitats which
Biodiversity plays a crucial role in increase the biodiversity and abundance of
maintaining ecosystem dynamics and has specialist taxa (Meiners et al. 2000, Stašiov
been a focus of research in recent years. et al. 2021).
Biodiversity can vary greatly between While it has been hypothesized that edges
habitats, making the transitional edge maintain higher biodiversity than adjacent
between habitat types an area of interest. habitats (Senft 2009), this may not be the
This buffer zone, known as the ecotone, is case in forest-grassland interfaces (Turton
subject to changes that impact the habitat and Duff 1992, Harper 1995, Baldissera et
as a whole. Edge effects describe the shift in al. 2004) This lack of consensus suggests
species composition, vegetative structure, that further study of forest edge effects and
and ecosystem processes across an underlying environmental factors would be
ecotone, and can impact the abundance of value.
and distribution of species (Murcia 1995).
The ecotone or edge between open and
|
CEC Research https://doi.org/10.21973/N3D951 Spring 2021 Vol. 5, Issue 3 1/6
Spiders in particular present an METHODS
interesting study taxon given their roles as
invertebrate predators. Spiders vary in their 2. 1 Study Site
predatory strategies and preference of
habitat structure. They are highly abundant Research was conducted from May 6–9,
throughout most ecosystems, making them 2021, at Angelo Coast Range Reserve in
ideal for examining the effects of habitat Mendocino County, California. The reserve
transitions. Additionally, spiders have is located in the upper basin of the South
strong potential as bioindicators (Pearce Fork Eel River. Angelo has a Mediterranean
and Venier 2006). climate, with average summer highs of 30°C
Spider families can be separated into two and winters below freezing, and average
functional guilds based on their predation annual precipitation of 215.6 cm. In this
strategy: sit-and-wait (web-weaving) or study we looked at the edges between four
active hunting. Web-weaving spiders meadows and adjacent mixed coniferous
depend strongly on habitat structure for forests. Meadows primarily consist of
scaffolding to build webs (Robinson 1981, European grasses and forbs, with adjacent
Uetz 1991, Rodrigues et al. 2014), while forests of Douglas Fir, manzanita, madrone,
active hunters do not and instead are and oak species. the four meadows used in
limited more by temperature and moisture this study are Lower Walker Meadow,
(Downie et al. 1996). These functional Walker Meadow, White House Meadow,
guilds depend on different environmental and South Meadow.
factors, but both occupy a similar place in
2.2 Data Collection
the food web. How the two guilds respond
differently to biotic and abiotic factors may Three belt transects (30 m x 2 m) were
help to explain why previous studies have placed parallel to the east edge of each
reached contradictory conclusions when meadow with a 30-meter buffer between
looking at ecotone diversity. transects (Fig. 1). The edge was defined by
The goal of this study was to evaluate the furthest tree within the meadow and
differences in family richness, diversity, and was used when measuring the 30-meter
abundance of spider communities along buffers between the meadow, edge, and
four forest-meadow edges in Angelo Coast forest transects. Where terrain was
Range Reserve. We hypothesized that web inaccessible, transects were shifted north to
building spiders would be most abundant in the nearest accessible location.
forest interiors where there would be more
vegetative scaffolding, while family diversity
would be greatest in the intermediate edge
habitat. Conversely, since hunting spiders
are less dependent on scaffolding, we
hypothesized that both abundance and
diversity would be greatest in the edge
habitat.
|
CEC Research https://doi.org/10.21973/N3D951 Spring 2021 Vol. 5, Issue 3 2/6
on abundance of live spiders, webs, and
individual families at a transect.
RESULTS
Overall, 15 families were identified
between meadow, edge, and forest
habitats. There was no difference in family
richness between habitats (n = 4, F = 0.512,
p = 0.623). The combined abundance of live
Figure 1: Transect placement in South Meadow. The spiders and webs was greatest in forests,
first tree protruding into the meadow was used to
with no difference in abundance between
define edge. A 30 m x 2 m belt transect was set up
within each habitat type, with a 30 m buffer meadows and edges (n = 4, F = 12.758, p =
between transects. 0.007, Fig. 2). Web-weaver abundance was
greater in forests than meadows and edges,
Living spiders and individual webs were which were not significantly different (n = 4,
recorded along each transect, identified to F = 15.445, p = 0.004, Fig. 2). No difference
family level, and sorted into web-building or was found in the abundance of hunting
hunting guilds. We limited observation time families between habitat types (n = 4, F =
to 45 minutes per transect. Additionally, 2.956, p = 0.128, Fig. 2). Scaffolding index,
vegetation scaffolding index, which substrate type, and vegetative cover were
describes the amount of structural found to have no effect on family richness
vegetation available to web-builders, was or abundance.
recorded at two random points on each
transect based on methods by Miyashita et
al. (2004). Substrate and vegetative cover
were recorded in a 0.25 m2 quadrat at 0 m,
15 m, and 30 m, alternating sides along the
transect.
2.3 Statistical Analysis
All data analysis was completed using
RStudio version 1.3.1093 and JMP version
15. We used ANOVA tests were performed
to assess differences in live spider, spider
Figure 2: Abundance of spider guilds. Abundance of
web, and total spider abundance between web-weaver and hunter guilds the in meadow, edge,
habitats, using site as a random effect. and forest habitats. Web weavers were significantly
Shannon diversity index was calculated for more abundant in forests (n = 4, F = 12.758, p =
each transect and compared across 0.007), but no difference in hunter abundance was
habitats. We also tested the predictive found between habitat types (n = 4, F = 2.956, p =
0.128).
power of vegetative index and quadrat data
|
CEC Research https://doi.org/10.21973/N3D951 Spring 2021 Vol. 5, Issue 3 3/6The Shannon diversity index showed a
marginal trend, with meadows more
diverse than edge and forest (n = 4, F =
3.958, p = 0.080). The dominant family in
meadow and edge habitats was Theridiidae
(tangle-web weavers), and the dominant
family in forests was Linyphiidae (sheet-web
weavers) (Fig. 3, Table 1).
Figure 3: Rank abundance of the meadow, edge and
forest habitats. Abundance of spider webs and live
hunting spiders was averaged for all transects and
ranked from most to least abundant. Individual
family ranks can be found in Table 1.
Table 1: Average abundance of spider families. Ranks indicate most abundant family within meadow, edge, and
forest habitats, and correspond to Figure 3.
|
CEC Research https://doi.org/10.21973/N3D951 Spring 2021 Vol. 5, Issue 3 4/6DISCUSSION interior forest and meadow provide ideal
scaffolding for both of these families, but
This study investigated the differences in Agelenidae is better able to take advantage
spider family composition between of the tall grasses and thatch found in
meadow, edge, and forest habitats. We meadows. This complicates the hypothesis
hypothesized that hunting spiders would be that ecotones have increased diversity by
more abundant and diverse in the edge providing an intermediate habitat (Meiners
habitat. We found that there was no et al. 2000). In the case that organisms have
difference in hunting spider abundance or distinct structural habitat preferences, the
diversity across all three habitats. In other ecotone may not provide the necessary
words, edge effect did not impact hunting resources as demonstrated by two different
guild spiders. web types.
For web-weaving spiders, we expected to Future studies could improve several
see the greatest abundance of families aspects of our experimental design and
within the forest interior where we methods. We recommend taking more
predicted vegetation scaffolding index to be thorough measurements of substrate and
greatest. While we did find web-building vegetative ground cover in order to better
families to be most abundant in the forest quantify the impacts of these
interior, we found no difference in environmental factors on spider
vegetation scaffolding availability between communities. Additionally, we would
habitats. However, our measurements of recommend taking note of abiotic factors
scaffolding did not match our observations, such as temperature and relative humidity,
which indicates that our methods may have both of which influence microclimates.
been ineffective for the study system. Previous work has found that microclimates
Additionally, we expected family diversity and vegetation cover alter the activity of
to be the greatest in the edge. Instead, we spiders, including hunting and weaving
found that total family diversity was similar (Downie et. al 1996). The observation of
across all habitats, but marginally greater in microclimate differences within the three
meadows than both edge and forest habitats in our study may have been useful
habitats. in understanding the effects of abiotic
When analyzing family level abundance factors on spider community composition
across habitats we found that Linyphiidae and potential reasons for an increased
were the most abundant family within the diversity in the ecotone. Overall,
forest interior (Table 1). Agelenidae had a understanding the interaction between
similar abundance in both the interior abiotic and biotic factors within
forest and meadow. This difference may be microhabitats is important when
due to the specific requirements for each considering the impacts of ecotones on taxa
family; for example, Linyphiidae require a such as spiders. When analyzing edge
clearing to establish a sheet web, whereas effects, future studies should more broadly
Agelenidae construct more dense and consider the impacts of microclimates in
robust funnel webs closer to the ground and across ecotones.
within dense vegetation (Rojas 2011). The
|
CEC Research https://doi.org/10.21973/N3D951 Spring 2021 Vol. 5, Issue 3 5/6ACKNOWLEDGMENTS Pearce, J. L., and L. A. Venier. 2006. The use of
ground beetles (Coleoptera: Carabidae) and
We would like to acknowledge our spiders (Araneae) as bioindicators of sustainable
forest management: a review. Ecological
amazing teaching assistant, Robert Blenk indicators 6:780–793.
for all his guidance throughout the course.
We would also like to thank Mary Power, Robinson, J. V. 1981. The effect of architectural
Blake Suttle, and Kirsten Hill for their advice variation in habitat on a spider community: An
and guiding words. This work was experimental field study. Ecology 62:73–80.
performed at the University of California’s Rodrigues, E. N. L., M. D. S. Mendonça, and L. E.
Angelo Coast Range Reserve, Costa-Schmidt. 2014. Spider diversity responds
doi:10.21973/N3R94R. strongly to edge effects but weakly to vegetation
structure in riparian forests of Southern Brazil.
REFERENCES Arthropod-Plant Interactions 8:123–133.
Baldissera, R., G. Ganade, and S. B. Fontoura. 2004. Rojas, A. 2011. Sheet-web construction by
Web spider community response along an edge Melpomene sp. (Araneae: Agelenidae). The
between pasture and Araucaria forest. Biological Journal of Arachnology 39:189–193.
Conservation 118:403–409.
Senft, A. R. 2009. Species diversity patterns at
Downie, I. S., J. C. Coulson, and J. E. Butterfield. ecotones. Thesis, University of North Carolina at
1996. Distribution and dynamics of surface- Chapel Hill.
dwelling spiders across a pasture-plantation
ecotone. Ecography 19:29–40. Stašiov, S., V. Kubovčík, M. Čiliak, A. Diviaková, I.
Lukáčik, and M. Dovciak. 2021. Harvestmen
Greenstone, M. H. 1984. Determinants of web spider (Opiliones) community structure varies across
species diversity: Vegetation structural diversity forest-meadow ecotones in a biodiverse karst
vs. prey availability. Oecologia 62:299–304. region. Biodiversity and Conservation 30:1101–
1117.
Harper, K. A. 1995. Effect of expanding clones of
Gaylussacia baccata (black huckleberry) on Suttle, K. B., M. A. Thomsen, and M. E. Power. 2007.
species composition in sandplain grassland on Species interactions reverse grassland responses
Nantucket Island, Massachusetts. Bulletin of the to changing climate. Science 315:640–642.
Torrey Botanical Club 122:124.
Turton, S. M., and G. A. Duff. 1992. Light
Miyashita, T., M. Takada, and A. Shimazaki. 2004. environments and floristic composition across an
Indirect effects of herbivory by deer reduce open forest-rainforest boundary in northeastern
abundance and species richness of web spiders. Queensland. Austral Ecology 17:415–423.
Ecoscience 11:74–79.
Uetz, G. 1991. Habitat structure and spider foraging.
Meiners, S. J., S. N. Handel, and S. T. A. Pickett. 2000. In: Bell S.S., McCoy E.D, Mushinsky H.R. (eds.)
Tree seedling establishment under insect Habitat structure. Population and Community
herbivory: edge effects and inter-annual variation. Biology Series, Vol. 8, pp. 325–348. Springer, New
Plant Ecology 151:161–170. York, New York.
Murcia, C. 1995. Edge effects in fragmented forests:
implications for conservation. Trends in Ecology &
Evolution 10:58–62.
|
CEC Research https://doi.org/10.21973/N3D951 Spring 2021 Vol. 5, Issue 3 6/6You can also read
