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Analysis of the Relationship between Small Mammal Distribution and Seed Depredation at a
Flood Plain in Plymouth, New Hampshire
Cassandra Saikin
Abstract
Habitat selection and behavior by small mammals are often dictated by the need to satisfy
their needs for food, shelter, and reproduction. Studies show that foraging is influenced by
predation, resource availability, and inter- and intraspecific competition and these factors often
influence one another. The goal of our study was to analyze the relationship between the small
mammal population distribution and abundance along with seed depredation in the ecotone,
forest, and field microhabitats of the flood plain in Plymouth, New Hampshire. The use of 10
artificial foraging stations in each microhabitat (for a total of 30) and three Sherman traps at each
station (for a total of 90) allowed us to measure seed depredation over the course of a week as
well as the relative abundance of each location. There was a significant relationship between
foraging and location and the day foraging took place, but there was no interaction between
location and day. Peromyscus species (nocturnal) and the eastern chipmunk (diurnal) were the
most abundant species and were found primarily in the ecotone and forest habitats. Our study
corroborates with similar studies performed in Israel, Chile, and Argentina – that small mammal
residents prefer to forage in sheltered habitats as opposed to open areas, which ultimately
provide greatest energy gain by providing more resources and reducing the threat of predation.
Introduction
Understanding how animals use their habitat can provide insight as to how these
organisms satisfy their needs for food, shelter, and reproduction (Anderson 1991, cited by Bos
and Carthew, 2003). How individuals satisfy these needs is generally influenced by habitat
configuration, predation, and resource availability (Brinkerhoff et al, 2005). Foraging is an
important mechanism for obtaining food (Kelt et al, 2004), and the foraging behavior of
organisms living in a particular environment is dictated by biotic factors, including predation and
intra-/interspecific competition, as well as other physiological constraints (Yunger et al, 2002).
Predation influences a species’ behavioral, population, and community ecology (Longland and
Price, 1991; Brown et al, 1994; Kotler et al, 1994b; Abramsky et al, 1997; Lima, 1998, all cited
by Abramsky et al, 2002) by inducing mortality on competing prey populations and by altering
intensity of competition between prey species (Hughes et al, 1994). Kelt, et al (2004) explains
that some abiotic factors, including season, lunar phase, microhabitat, and thermal regime, have
differential effects on predation and competition depending on the environment (Kotler, 1984;
Brown 1988; Brown et al, 1988, 1994b; Mitchell and Brown, 1990; Kotler et al, 1993; Hughes et
al, 1994; Meyer and Valone, 1999).
Each species is different and not every species selects habitats in the same fashion; some
species’ behavior is more of a result of competition intra- or interspecifically, while others’
behavior is dictated more by predation. Ranking of habitats is different between species because
of their varying fitness needs (Price and Waser, 1985). According to Price and Waser (1985),
optimality theory states that coexisting species will develop microhabitat preferences for those
that provide the best level of fitness for a particular species. Fitness is measured by two factors:
rate of resource harvest and predation risk (Price and Waser, 1985). Competitive exclusion
between species also results in habitat partitioning. For example, competitive exclusion between
gerbils Octodon (the more dominant diurnal species) and Phyllotis (a nocturnal species) results
in Phyllotis foraging in more open than in sheltered habitats because of resource depletion by
Octodon (Kelt et al, 2004). Hughes et al (1994) explains that competitive coexistence is possible
when the risk of predation on competing species results in habitat partitioning (Caswell, 1978;
Sih, 1980; Hanski, 1983; Werner et al, 1983).
Foraging animals need to obtain sufficient nutrients while also avoiding predators and
competing with other granivores or omnivores for the same resources (Kelt et al, 2004).
Abramsky, et al. (2002) explains the concept of adaptive foraging, where foragers learn to
perceive the environment (Stephens and Krebs, 1986), rank microhabitats in terms of safety and
resources (Kotler and Blaustein, 1995), and use trade-offs between food and safety (Abrahams
and Dill, 1989). Price and Waser (1985) suggest that because different habitats may vary in their
predator population and abundance, animals develop a sense of predation risk for certain areas.
In areas where predation risk is higher, foragers make energy trade-offs in deciding where and
what to food to select (Lima and Dill, 1990, cited by Taraborelli et al, 2003). For example,
animals will carry food to sheltered sites to avoid prolonged exposure and select food size that
allows them to eat quickly in open areas or carry back bigger items to protected areas
(Taraborelli et al, 2003). Many small mammals respond to cues of predation intensity, including
the presence of a predator (Kotler et al, 1992; Abramsky et al, 1997, 1998) and moonlight
(Lockard and Owing, 1974; Kotler, 1984a,b; Kotler et al, 1993, 1994a, all cited by Abramsky, et
al, 2002). In a study conducted by Hughes, et al (1994), which analyzed the behavior of Namib
Desert gerbils, the researchers found that the gerbils exposed themselves less on moonlit nights
when the risk of predation was higher. These gerbils also avoided open areas, where there was
greater exposure to predators. Another study conducted by Kelt, et al. (2004) found that small
mammals foraged at a greater rate under a new moon as well as under the cover of shrubs,
further reducing the risk of predation. Many small mammals will select the safer habitat that
reduces the risk of predation (Kotler et al, 1993; Brown et al, 1994; Abramsky et al, 1996, 1997,
all cited by Abramsky et al, 2002).
Many small mammals, including Peromyscus species (Wolf and Batzli, 2002), are
granivores. Studies using artificial seed trays at foraging stations can uncover seed predation
habits of small mammals by quantifying the amount of seeds depredated in different
habitats/conditions (Hughes et al, 1994). Having a known density of seeds at each station,
researchers can measure the seed depredation across each habitat (Kelt et al, 2004). Foraging
patterns are typically identified using giving-up densities (GUD), which is the level at which an
individual stops foraging at a particular site (Brown, 1988; Kotler et al, 1991; Brown et al, 1992,
all cited by Yunger et al, 2002). Increased foraging results in a lower GUD most likely because
of decreased predation risk, and vice versa (Wolf and Batzli, 2004; Yunger et al, 2002). These
seed trays mimic real-life situations for the mammals because they must dig through the sand
expend energy for obtaining seeds (it is not just “free food”), just like in their natural habitats
(Hughes et al, 1994). Another method for understanding the habitat choices of small mammals
is through direct observation. Bos and Carthew (2003) propose a method that involves live
capturing of mammals. The use of traps to capture individuals allows investigators to compare
and contrast the distribution and abundance of different species across various microhabitats
(Bos and Carthew, 2003).
Studies using foraging stations in covered and uncovered areas demonstrate that small
mammals prefer to forage in habitats closer to or containing more plant cover. This not only
reduces the risk of predation, but also provides a more optimal microclimate (Taraborelli et al,
2003). Habitats that are on the edges of forest systems, called ecotones (Wilkin et al, 2007)
usually have high amounts of vegetative cover, which can reduce the risk of predation (Matlack,
1993; Murcia, 1995; Meiners and Pickett, 1999, all cited by Wolf and Batzli, 2002). Wolf and
Batzli (2004) claim that predation decreases moving from the outside of the ecotone towards the
forest.
In our study comparing seed depredation and small mammal abundance across three
habitats of the flood plain in Plymouth, New Hampshire, we predicted that seed depredation
would be highest in the ecotone and the forest and lowest in the field, where there is very little
cover from predators. The use of artificial foraging stations allowed us to quantify data on seed
depredation within these habitats, and live capturing allowed us to analyze the distribution and
abundance of resident species within these same habitats.
Methods
Our study took place at the Pemigewassett flood plain in Plymouth, New Hampshire and
spanned two time periods. The flood plain, located in the woods behind Plymouth State
University’s hockey arena, is adjacent to the Pemigewassett River, which runs from Franconia
through Franklin, New Hampshire. The study site comprised an open field that bordered a
woodland area adjacent a wetland marsh. The seed depredation experiment was set up on
September 23, 2010 and data were collected for 7 days from September 24 through September
30, 2010. The traps for the mammal collection were set up on October 2, 2010 and data was
collected from October 3 through October 7, 2010.
In our seed depredation experiment, 30 seed foraging stations of buckets filled half with
sand and 50 sunflower seeds each were strategically placed in the field, ecotone, and forest
habitats of the flood plain. Ten buckets were placed in a transect in each location (one transect
per habitat) and were spaced 5m apart, each transect being 10m apart. The seeds were mixed
throughout the sand so they were not aggregated in one area within the bucket, which mimics a
natural scenario for the granivores. The seed depredation was measured each morning for seven
days, where we recorded the number of seeds that had been removed by local mammals by
taking the number of seeds observed and subtracting that from 50. The seeds that remained in
the bucket were measured by sifting the sand through a sieve and counting those that were still
intact (some empty shells remained in the buckets). We replaced all of the seeds that were
depredated so there were always 50 seeds in the buckets at the start of each new 24 hour period.
The traps for the mammal collection were set up using the same method for the buckets
in the seed depredation study; three Sherman traps (two big, one small) were placed in the same
locations where the buckets had been in each row, totaling 90 traps for the entire area. Each trap
was set up with some polyester bedding and a handful of sunflower seeds. The traps were
checked twice a day for five days, once in the early morning (dawn) and once in the evening
(dusk). Those mammals that were caught and observed in the morning were considered
nocturnal and those caught in the evening were considered diurnal. After the mammals were
recorded, the traps were reset with fresh seeds and fresh bedding (only if it was too soiled or
wet). On the final day, the traps were checked in the morning and mid-afternoon when the traps
were collected and brought back to the lab.
A two-way Analysis of Variance (ANOVA) with equal sample sizes was performed to
determine the significance of the day and habitat of seed depredation. This allowed us to
understand the role of time and location on the intensity of seed foraging. A paired t-test
assuming equal variances was performed to determine the overall significance of diurnal and
nocturnal species within the flood plain. And lastly, a single factor ANOVA was performed to
determine if there were any significant differences in the field, ecotone, or forest abundances of
small mammals.
Results
In the flood plain, the most seed depredation occurred in the ecotone and forest habitats
and least in the field (Figure 1). The depredation in the ecotone and forest remained relatively
consistent across the 7-day period, with a slight increase from day 1 to day 2. There was an
increased amount of foraging in the field from days 1 through 4, then a gradual decrease through
the end of the study. There was a significantly higher rate of foraging in the forest and ecotone
than in the field (df = 2, F = 195.56, p < 0.0001). Also, there was a significantly greater amount
of seed depredation in the field midway through the week, after which foraging began to
decrease toward the end of the week (df = 6, F = 5.60, p < 0.0001). The interaction between
habitat and day of the week was not statistically significant (df = 12, F = 0.580, p = 0.86).
In the analysis of small mammal distribution and abundance in the flood plain, we
observed a total of nine species. These include the eastern chipmunk (Tamias striatus), grey
squirrel (Sciurus carolinensis), woodland jumping mouse (Napaeozapus insignis), short-tailed
shrew (Blarina brevicauda), meadow vole (Microtus pennsylvanicus), red-backed vole (Myodes
species), Peromyscus species, short-tailed weasel (Mustela ermine), and red squirrel (Sciurus
vulgaris). The majority of the mammals we captured were nocturnal (Figure 2). Peromyscus
species were the most abundant nocturnal mammals, while the most abundant diurnal species
was the eastern chipmunk, although it was observed moderately as a nocturnal species as well.
We observed that the nocturnal small mammal population was significantly larger in the flood
plain than the diurnal population (df = 8, t = 7.19, p < 0.0001).
The majority of mammals we observed were in the ecotone, most of these being eastern
chipmunks and Peromyscus species (Figure 3). The next most populous habitat was the forest
(inhabited mostly by Peromyscus), while the field was the least populated. The ecotone
population was significantly larger than the field and forest habitats (df = 14, F = 42.02, p <
0.0001).
Discussion
The purpose of our study was to understand the relationship between small mammal
distribution and foraging preferences in the habitats of the flood plain in Plymouth, New
Hampshire. The use of artificial foraging stations allowed us to measure the seed depredation of
sunflower seeds in field, ecotone, and forest within the flood plain. Live capturing of small
mammals within these same habitats helped us to understand population dynamics and habitat
selection in the flood plain. We predicted that seed depredation would be greatest in the ecotone
and forest and the least in the field. We also predicted that the greatest distribution and
abundance of small mammal residents would be in these same habitats, with Peromyscus being
the most abundant species because it is very common in northeast deciduous forests (Wolf and
Batzli, 2004).
Price and Waser (1985) state that microhabitat structures differ in physical structure of
vegetation, seed abundances (food availability), soil quality, and predation risk. Therefore, they
can differ in net rate of energy harvest. Our seed depredation data were consistent with the
literature in that most foraging took place in the ecotone and forest, the habitats with the most
vegetative cover, where the least occurred in the field. These data were statistically significant,
suggesting that habitat selection plays an important role in granivory of small mammals because
of differences in energy gain. Foraging and storing seeds requires certain behaviors to generate
the best overall energy gain, which involves avoiding predators as well as coexisting with
competing species (microhabitat partitioning). Foraging closer to shelter helps to avoid
predation by providing cover (Parmenter and MacMahaon, 1983; Kotler et al, 1991, 1994a;
Hughes and Ward, 1993, all cited by Taraborelli et al, 2003). Carrying and storing food at
sheltered sites not only provides protection while eating, but also shortens time exposed in more
open habitats (Vander Wall, 1990; Huges and Ward, 1993; Vasquez, 1994, all cited by
Taraborelli et al, 2003). As noted earlier, mammals will make tradeoffs in energy gain against
predation risk when foraging in hazardous areas (Taraborelli et al, 2003).
The date of depredation of the seeds was also significant. The inclining trend in the early
part of the week-long experiment could indicate that the residents learned about the prolonged
presence of food. Throughout the week of observation there was a lot of rainfall, so this also
could have prompted the residents to venture out into the riskier areas to forage because of the
potential for fewer predators in the area. However, the rate of depredation began to decrease
after the fourth day. It is possible that the small mammal residents were becoming more cautious
to the threats of spending increased time in the risky habitat, so they started spending less time in
the field. They could have also been more aware of the seeds present in the ecotone and forest
and began to forage more at these locations. The rain could have been more of a factor in this
trend because it may have not been energetically feasible to forage at that time. This shows that
mammals are capable of adapting and responding to different cues in their environment.
However, we found that the interaction between the location of foraging and time in the
week was not significant. There is an increase in foraging in the field as well as the forest and
ecotone between the first and second days of observation, but foraging in the sheltered
environments was relatively consistent throughout the duration of the study while in the field it
was a steady increase. Because there was not a consistent pattern in the way time may have
influenced the seed depredation in the ecotone and forest versus the field, there was no
significant interaction. This suggests that even with the greater amount of food in the field, small
mammal residents in the flood plain still prefer the sheltered habitats of the forest and ecotone.
Our seed depredation data parallel our mammal population data – the majority of our
small mammals were caught in the ecotone while few were caught in the forest and even fewer
in the field. The two most abundant species were Peromyscus species and the eastern chipmunk,
with the former being far more abundant. A similar study by Wolf and Batzli (2002) found that
densities of Peromyscus species were more often higher within 15m of woodland margins than
35-40m inside the woodland areas. The observed Peromyscus species were mainly nocturnal,
which is also consistent with literature (Wolf and Batzli, 2004). Another species, the eastern
chipmunk, a primarily diurnal species according to our data, presided mainly in the ecotone.
These data suggest that the ecotone’s vegetative cover could be the preferable microhabitat
because of decreased predation risk and/or adequate resource availability. Another diurnal
species, the brush-tailed rat (Octodon degus), prefers to forage under shrubs rather than in open
habitats, where the risk of predation is low (Kelt et al, 2004).
The factors that influence microhabitat vary across species; what is the driving force of
partitioning for one species may differ for another (Yunger et al, 2002). Species will rank
habitats based on net energy gain. It is possible that the risk of predation is one of the main
reasons for staying in the covered habitats. Yunger et al (2002) suggests that predation is a key
selective force in driving microhabitat partitioning with small mammals, particularly in deserts
(Rosenzweig, 1973; Thompson, 1982a, b; Price, 1984; Kotler and Brown, 1988; Kotler et al,
1988; Hugest et al, 1994, Vasquez, 1994). We can also predict that resource availability
intraspecific and interspecific competition among and between species could be a reason these
areas are foraged in the most. It is important to remember that in our study we increased the
food availability in the ecotone and forest as well as in the field, so it’s possible the stronger
individuals could outcompete others for the resources at the sheltered foraging stations, driving
subordinate individuals to forage in the riskier habitats. Seasonal changes could also be another
potential factor in habitat partitioning. Seasonal changes bring about different types of weather,
so different physiological responses (Yunger et al, 2002) may be necessary to overcome
thermoregulatory constraints of different species (Kelt et al, 2004). Differing seasons may also
bring about seasonal changes in predators (Kelt et al, 2004).
Much of the literature presents research on habitat and foraging selection within desert
habitats and all show consistent results. One such study was put forth by Taraborelli et al (2003)
in the Monte Desert in Mendoza, Argentina. Using artificial foraging sites to measure the rates
of depredation of millet and sunflower seeds, the researchers found that seed consumption and
hoarding were higher in sheltered habitats. Similar results were presented for deserts in South
Africa (Hughes et al, 1994), Chile (Kelt et al, 2004), Israel (Abramsky et al, 2002), and North
America (Kelt et al, 2004). The results from desert foraging studies parallel those performed in
deciduous forests. Studies by Wolf and Batzli (2004) in the deciduous forests of Illinois in the
United States aimed to discern the more preferable habitat by Peromyscus species. Their studies
uncovered that field mice prefer living in the dense forest habitats over living out in the open.
So, we can suggest that despite habitat type (desert vs. woodland), sheltered locations are the
preferred microhabitat of small mammals.
We can conclude that a great deal of complex behaviors are exhibited by small mammals
in selecting optimal habitats. Bos and Carthew (2003) state that different habitats are valued for
specific purposes, and therefore, species rank habitats according to the greatest net energy gain.
To get a better understanding of the foraging behavior of small mammals in a deciduous habitat,
it would be prudent to understand the seed foraging by nocturnal and diurnal mammals. In our
study, we analyzed the seed depredation once a day in the early morning, so it was unclear if
most of the foraging took place during the day or at night. A study by Kelt et al (2004) using
artificial foraging stations in semi-arid Chile found that the majority of depredation was diurnal.
It would also be useful to extend the time period for observing foraging habits and population
distributions; by only sampling for two weeks, we only obtained a fraction of the population
dynamics at that given time. Kelt et al (2004) states that this method creates a snapshot of a
particular ecosystem and does not cover all of the population dynamics of that system. This
study has been performed for three years and similar (although not identical) results have been
obtained each year. These cumulative results further strengthen the optimality of sheltered
habitats. However, extending the study to longer than a week’s time could allow us to observe
(if any) habitat-choice changes across seasons. Also, because some mammals show preference to
particular types of food (based on differences in net energy gain), it would be interesting to find
what the food preferences of the flood plain residents would be, which would provide a deeper
understanding of behavior in response to biotic and abiotic factors.
Acknowledgements
This study was performed by the students in Dr. Leonard Reitsma’s Ecology class at
Plymouth State University in Plymouth, New Hampshire. Many thanks to Dr. Reitsma and my
classmates who worked hard in collecting and compiling the data from the flood plain.
Literature Cited
Abrahams, M. V. and L. M. Dill. 1989. A determination of the energetic equivalence of the risk
of predation. Ecology. 70: 999-1007.
Abramsky, Z., M.L. Rosenzweig, and A. Subach. 1997. Gerbils under threat of owl predation:
isoclines and isobars. Oikos. 78: 81-90.
Abramsky, Z., M. L. Rosenzweig, and A. Subach. 1998. Do gerbils care about competition or
about predation? Oikos. 83: 75-84.
Abramsky, Z., E. Strauss, A. Subach, and B. P. Kotler. 1996. The effect of barn owls (Tyto
alba) on the activity and microhabitat selection of Gerbillus allenbyi and G. pyramidum.
Oecologia. 105: 313-319.
Abramsky, Zvika, Michael L. Rosenzweig, and Aziz Subach. 2002. The costs of apprehensive
foraging. Ecology. 83(5): 1330-1340.
Bos, Darren G. and Susan M. Carthew. 2003. The influence of behavior and season on habitat
selection by a small mammal. Ecography. 26:810-820.
Brown, J. S. 1988. Patch use as an indicator of habitat preference, predation risk, and
competition. Behavioral Ecology and Sociobiology. 22: 37-47.
Brown, J. S., A. Morgan, and B. D. Dow. 1992. Patch use under predation risk: II. A test with
fox squirrels, Sciurus niger. Annales Zoologici Fennici (Helsinki). 28: 331-318.
Brown, J. S., B. P. Kotler, and T. J. Valone. 1994. Foraging under predation: a comparison of
energetic and predation costs in rodent communities of the Negev and Sonoran deserts.
Australian Journal of Zoology. 42: 435-438.
Caswell, H. H. 1978. Predator-mediated coexistence: a non-equilibrium model. American
Naturalist. 112: 127-154.
Hanski, I. 1983. Predator-mediated coesixtence. Annales Entomologica Fennici. 42: 33-35.
Hughes, J. J. and D. Ward. 1003. Predation risk and distance to cover affect foraging behavior
in Namib Desert gerbils. Anim. Behav. 46: 1243-1245.
Hughes, Jessica J., David Ward, and Michael R. Perrin. 1994. Predation risk and competition
affect habitat selection and activity of Namib Desert gerbils. Ecology. 75(5): 1397-1405.
Kelt, Douglas A., Peter L. Meserve, Matthew L. Forister, L. Karina Nabors, and Julio R.
Gutierrez. 2004. Seed predation by birds and small mammals in semiarid Chile. Oikos.
104: 133-141.
Kelt, Douglas A., Peter L. Meserve, and Julio R. Gutierrez. 2004. Seed removal by small
mammals, birds, and ants in semi-arid Chile, and comparison with other systems. J.
Biogeogr. 31: 931-942.
Kelt, Douglas A. Peter L. Meserve, karina Nabors, Matthew L. Forister, and Julio R. Gutierrez.
2004. Foraging ecology of small mammals in semiarid Chile: the interplay of biotic and
abiotic effects. Ecology. 85(2): 383-397.
Kotler, B. P. 1984a. Risk of predation and the structure of desert rodent communities. Ecology.
65: 689-701.
Kotler, B. P. 1984b. Harvesting rates and predatory risk in desert rodents: a comparison of two
communities on different continents. Journal of Mammalogy. 65: 91-96.
Kotler, B. P. and J. S. Brown. 1988. Environmental heterogeneity and the coexistence of desert
rodents. Annual Review of Ecology Systematics. 19: 281-307.
Kotler, B. P., J. s. Brown, R. J. Smith, and W. O. Wirtz II. 1988. The effects of morphology and
body size on rates of owl predation on desert rodents. Oikos. 53: 145-152.
Kotler, B. P., J. S. Brown, and O. Hasson. 1991. Factors affecting gerbil foraging behavior and
rates of owl predation. Ecology. 72: 2249-2260.
Kotler, B. P., Y. Ayal, and A. Subach. 1994a. Effect of predatory risk and resource renewal on
the timing of foraging activity in a gerbil. Oecologia. 100: 391-396.
Kotler, B. P., and L. Blaustein. 1995. Titrating food and safety in heterogeneous environments:
when the risky patch of value. Oikos. 74: 251-258.
Kotler, B. P., J. S. Brown, and W. A. Mitchell. 1994b. The role of predation in shaping the
behavior, morphology and community organization of desert rodents. Australian Journal
of Zoology. 42: 1-20.
Kotler, B. P., J. S. Brown, and A. Subach. 1993. Mechanisms of species coexistence of optimal
foragers: temporal partitioning by two species of sand dune gerbils. Oikos. 67: 548-556.
Lima, s. L. and L. M. Dill. 1990. Behavioral decisions made under the risk of predation: a
review and prospectus. Can. J. Zool. 68: 619-640.
Lima, S. L. 1998. Stress and decision-making under risk of predation: recent developments from
behavioral, reproductive, and ecological perspectives. Advances in the Study of
Behavior. 27: 215-290.
Lockard, R. B., and D. H. Owing. 1974. Seasonal variation in moonlight avoidance by
bannertail kangaroo rats. Journal of Mammalogy. 55: 189-193.
Longland, W. S. and M. V. Price. 1991. Direct observations of owls and hetermyid rodents: can
predation risk explain microhabitat use? Ecology. 72: 2261-2273.
Matlack, G. R. 1993. Microenvironment variation within and among forest edge sites in the
eastern United States. Biol. Conserve. 66:185-194.
Meiners, S. J. and S. T. A. Pickett. 1999. Changes in community and population responses
across a forest-field gradient. Ecography. 22: 261-267.
Meyer, M. D., and T. J. Valone. 1999. Foraging under multiple costs: the importance of
predation, energetic, and assessment error costs to a desert forager. Oikos. 87: 571-579.
Mitchell, W. A., and J. S. Brown. 1990. Density-dependent harvest rates by optimal foragers.
Oikos. 57: 180-190.
Murcia, C. 1995. Edge effects in fragmented forests: implications of conservation. Trends
Ecol. Evol. 10: 58-62.
Parmenter, R. R. and J. A. MacMahon. 1983. Factors determining the abundance and
distribution of rodents in a shrub-steppe ecosystems: the role of shrubs. Oecologia. 59:
145-156.
Price, M. V. 1984. Microhabitat use in rodent communities: predator avoidance or foraging
economics? Netherlands Journal of Zoology. 34: 63-80.
Price, Mary V, and Nickolas M. Waser. 1985. Microhabitat use by heteromyid rodents: effects
of artificial seed patches. Ecology. 66(1): 211-219.
Rosenzweig, M. L. 1973. Habitat selection experiments with a pair of coexisting heteromyid
species. Ecology. 54: 111-117.
Sih, A. 1980. Optimal behavior: can foragers balance two conflicting demands? Science. 210:
1041-1043.
Stephens, D. W., and J. R. Krebs. 1986. Foraging theory. Princeton University Press,
Princeton, New Jersey, USA.
Taraborelli, Paula A., Mariana Dacar, and Stella M. Giannoni. 2003. Effect of plant cover on
seed removal by rodents in the Monte Desert (Mendoza, Argentina). Austral Ecology.
28: 651-657.
Thompson, S. D. 1982a. Microhabitat utilization and foraging behavior of bipedal and
quadrupedal heteromyid rodents. Ecology. 63: 1303-1312.
Vander Wall, S. B. 1995. Salivatory water loss during seed husking in deer mice and great
basin pocket mice. Physiol. Zool. 68: 878-886.
Vasquez, R. A. 1994. Assessment of predation risk via illumination level: facultative central
place foraging in the cricetid rodent Phyllotis darwini. Behavioral Ecology and
Sociobiology. 34: 375-381.
Werner, E. E., J. F. Gilliam, D. J. Hall, and G. G. Mittelbach. 1983. An experimental test of the
effect of predation risk on habitat use in fish. Ecology. 61: 233-242.
Wilkin, Teddy A., Dany Garant, Andrew G. Gosler, and Ben C. Sheldon. 2007. Edge effects in
the Great Tit: analyses of long-term data with GIS techniques. Conservation Biology.
21(5): 1207-1217.
Wolf, Mosheh and George O. Batzli. 2002. Effects of forest edge on populations of whitefooted mice Peromyscus leucopus. Ecography. 25: 193-199.
Wolf, Mosheh and George Batzli. 2004. Forest Edge – High or low habitat for white food mice
(Peromyscus leucopus)? Ecology. 85(3): 756-769.
Yunger, John A., Peter L. Meserve, and Julio R. Gutierrez. 2002. Small-mammal foraging
behavior: Mechanisms for coexistence and implication for population dynamics.
Ecological Monographs. 72(4): 561-577.
Tables and Figures
Seed Depredation in Habitats of the
Flood Plain, Plymouth, NH
Average Number of Seeds Depredated
60
50
40
Field
30
Ecotone
20
Forest
10
0
1
2
3
4
5
6
7
Dates in September, 2010
Figure 1. Average number of seeds depredated in the field, ecotone, and forest habitats of the
flood plain in Plymouth, New Hampshire. The ecotone and forest displayed the most seed
depredation, while the field displayed the least. The gradual increase in depredation in the field
could be a result of the mammals’ realization of the presence of the seeds, so their rate of
foraging increased.
Frequency of Individuals
Nocturnal vs. Diurnal Small Mammal
Frequencies at Flood Plain, Plymouth, NH
30
25
20
15
10
5
Nocturnal
0
Diurnal
Species Identified
Figure 2. The frequencies of small nocturnal and diurnal mammals in the flood plain in
Plymouth, New Hampshire. Nocturnal mammals were observed more frequently than diurnal
mammals. Peromyscus species were the most abundant nocturnal species, while the eastern
chipmunk was the most frequent diurnal species. p < 0.0001
Frequency of Individuals
Small Mammal Abundance and Distribution
in Flood Plain Habitats in Plymouth, NH
30
25
20
15
10
Field
5
Ecotone
0
Forest
Species Identified
Figure 3. The distribution and abundance of small mammals in the field, ecotone, and forest
habitats of the flood plain, Plymouth, New Hampshire. The ecotone was the most populous
habitat, inhabited predominantly by the eastern chipmunk and Peromyscus species. The forest
was the next populous habitat and the field was the least populated. p < 0.0001