Copyright (c) 2013 University of Iowa All rights reserved. http://ir.uiowa.edu/biology_pubs Recent documents in Department of Biology Publications en-us Tue, 21 May 2013 14:06:43 PDT 3600 http://ir.uiowa.edu/biology_pubs/31 http://ir.uiowa.edu/biology_pubs/31 Tue, 13 Sep 2011 14:43:52 PDT The forest annual, Amphicarpaea bracteata L. can reproduce via aerial chasmogamous, aerial cleistogamous, and subterranean cleistogamous flowers. Both plant size and light intensity influenced the utilization of the three modes of reproduction. Chasmogamous and aerial cleistogamous flower number and the ratio of chasmogamous flowers to the total number of aerial flowers increased with plant size. The latter demonstrated a shift to xenogamy and outbreeding in larger plants. Light intensity indirectly influenced reproductive modes through its influence on plant size. Seed set by both types of aerial flowers was low and unrelated to plant size. Subterranean seed number and the total dry weight of subterranean seeds per plant increased with size. The subterranean seeds of Amphicarpaea bracteata are thirty-four times larger than the aerial seeds (fresh weight). Under field conditions, subterranean seeds had greater germination after one year than aerial seeds. The plants arising from subterranean seeds were significantly larger and more fecund than those from aerial seeds. Seeds produced by aerial cleistogamous, hand self-pollinated chasmogamous, and naturally pollinated chasmogamous flowers had equivalent germination rates and produced plants of equal size and fecundity. This suggests that the outbred progeny from chasmogamous flowers have no advantage over the inbred progeny from aerial cleistogamous flowers.

]]> E. Joseph Trapp et al. http://ir.uiowa.edu/biology_pubs/30 http://ir.uiowa.edu/biology_pubs/30 Tue, 13 Sep 2011 14:43:51 PDT Abstract.? 1. Dispersal plays an integral role in determining spatial population structure and, consequently, the long-term survival of many species. Theoretical studies indicate that dispersal increases with population density and decreasing habitat stability. In the case of monophagous insect herbivores, the stability of host-plant populations may influence their spatial population structure. 2. The tallgrass prairie in Iowa, U.S.A. is highly fragmented and most prairie insects face a landscape with fewer habitat patches and smaller host-plant populations than 150 years ago, potentially making dispersal between patches difficult. Some herbivores, however, use native plant species with weedy characteristics that have increased in abundance because of disturbances. 3. Mark?recapture data and presence?absence surveys were used to examine dispersal and spatial population structure of two monophagous beetles with host plants that exhibit different population stability and have responded differently to fragmentation of tallgrass prairie. 4. Chrysochus auratus Fabricius exhibits a patchy population structure and has relatively large dispersal distances and frequencies. Its host plant is variable locally in time and space, but is more abundant than 150 years ago. The other species, Anomoea laticlavia Forster, exhibits a metapopulation or non-equilibrium population structure and has relatively small dispersal distances and frequencies. Its host-plant populations are stable in time and space. 5. The results indicate that dispersal ability of monophagous beetles reflects the life-history dynamics of their host plants, but the spatial population structure exhibited today is strongly influenced by how the host plants have responded to the fragmentation process over both time and space.

]]> Matthew J. St Pierre et al. http://ir.uiowa.edu/biology_pubs/29 http://ir.uiowa.edu/biology_pubs/29 Tue, 13 Sep 2011 14:43:49 PDT Abstract.? 1.?Dispersal capabilities of organisms are critical in determining the landscape population structure of species as well as their likelihood of survival in fragmented landscapes. Using mark?recapture techniques on the monophagous weevil Rhyssomatus lineaticollis Say (Curculionidae), within- and between-patch dispersal capabilities, landscape level population structure, and the role of beetle density and host patch characteristics in setting distances, amounts, and timing of dispersal were studied. 2.?The data indicate that R. lineaticollis is sedentary, with 50% of recaptured beetles moving

]]> Matthew J. St Pierre et al. http://ir.uiowa.edu/biology_pubs/28 http://ir.uiowa.edu/biology_pubs/28 Tue, 13 Sep 2011 14:43:47 PDT Loss of insect pollinators due to habitat fragmentation often results in negative effects on plant reproduction, but few studies have simultaneously examined variation in the bee community, site characteristics and plant community characteristics to evaluate their relative effects on plant reproduction in a fragmented habitat. We examined the reproduction of a common tallgrass prairie forb, Amorpha canescens (Fabaceae), in large (>40 ha) and small (<2 ha) prairie remnants in Iowa and Minnesota in relation to the diversity and abundance of its bee visitors, plant population size, and species density of the forb flowering community. We found significant positive effects of the diversity of bees visiting A. canescens on percent fruit set at a site in both years of the study and in 2002 an additional significant positive effect of plant species density. Abundance of bees visiting A. canescens had a significant positive effect on percent fruit set in 2002, but was only marginally significant in 2003. In 2003 but not 2002, the plant species density at the sites had a significant negative effect on the diversity and abundance of bees visiting A. canescens, indicating community-level characteristics can influence the bee community visiting any one species. Site size, a common predictor of plant reproduction in fragmented habitats did not contribute to any models of fruit set and was only marginally related to bee diversity one year. Andrena quintilis, one of the three oligolectic bee species associated with A. canescens, was abundant at all sites, suggesting it has not been significantly affected by fragmentation. Our results show that the diversity of bees visiting A. canescens is important for maintaining fruit set and that bee visitation is still sufficient for at least some fruit set in all populations, suggesting these small remnants act as floral resource oases for bees in landscapes often dominated by agriculture.

]]> Malinda W. Slagle et al. http://ir.uiowa.edu/biology_pubs/27 http://ir.uiowa.edu/biology_pubs/27 Tue, 13 Sep 2011 14:43:45 PDT Experiments assessing rates of avian nest predation often find that nests near forest edges are at high risk of predation, suggesting the importance of forest fragmentation in recent population declines of ground-nesting passerines. However, the use of quail (Coturnix spp.) eggs in nest predation experiments may confound conclusions about edge effects because only large-mouthed predators are able to consume these relatively large eggs, but both large and small-mouthed predators consume smaller passerine eggs. We directly compared predation rates on artificial nests baited with quail eggs or with zebra finch (Poephila guttata) eggs; the latter are similar in size to the eggs of many neotropical passerines. In 1998 and 1999 we placed 392 artificial ground nests at edge and interior locations in two east-central Iowa forest fragments. Predation on these nests varied with egg type (quail or finch) and location (edge or interior) and there was a significant interaction between egg type and location: predation on quail eggs was greater at edges than in the interior, whereas finch egg predation was high in both edge and interior locations. Based on tooth imprints in clay eggs, we determined that large-mouthed predators were six times more active at edges, whereas activity of small-mouthed nest predators was evenly distributed between edge and interior locations. We suggest that the use of only quail eggs can exaggerate edge effects and that finch eggs or clay eggs used in conjunction with quail eggs in artificial nests can be used to estimate relative predation rates by large- and small-mouthed predators.

]]> Amanda C. Niehaus et al. http://ir.uiowa.edu/biology_pubs/26 http://ir.uiowa.edu/biology_pubs/26 Tue, 13 Sep 2011 14:43:43 PDT Kyle Skyle S. Kwaiser et al. http://ir.uiowa.edu/biology_pubs/25 http://ir.uiowa.edu/biology_pubs/25 Tue, 13 Sep 2011 14:43:41 PDT Heather M. Hines et al. http://ir.uiowa.edu/biology_pubs/24 http://ir.uiowa.edu/biology_pubs/24 Tue, 13 Sep 2011 14:43:40 PDT We investigated changes in the reproduction of Pastinaca sativa which result in compensatory reproduction when herbivore feeding destroys the first infloresence produced. Late developing infloresences of damaged plants produce more flowers and a greater proportion of hermaphroditic flowers than late developing infloresences of control plants. In damaged plants the proportion of hermaphroditic flowers producing seeds in late developing infloresences also increases. These effects are due to the mechanical damage resulting from larval feeding. The herbivore acts as a mediator in a number of important plant processes affecting fecundity, including expression of sex.

]]> Stephen D. Hendrix et al. http://ir.uiowa.edu/biology_pubs/23 http://ir.uiowa.edu/biology_pubs/23 Tue, 13 Sep 2011 14:43:38 PDT Stephen D. Hendrix et al. http://ir.uiowa.edu/biology_pubs/22 http://ir.uiowa.edu/biology_pubs/22 Tue, 13 Sep 2011 14:43:36 PDT The effect of seed mass on emergence, survival, and recruitment to flowering in Pastinaca sativa, a species that produces progressively smaller seeds on the primary, secondary, and tertiary umbels, was analyzed in two field experiments begun in 1982 and 1983. In both experiments, overall emergence was positively related to seed mass, but the effects of seed mass on emergence in fall cohorts was relatively unimportant. Initial seed mass was positively related to overwintering survival in one experiment but not the other, possibly due to differences in winter conditions. Survival to flowering was positively related to seed mass in the 1982 experiment but negatively related to seed mass in the 1983 experiment. This difference is due to greater survival of seedlings from small seeds during short-term droughts, a previously unrecognized advantage of small seeds. Because of differences in survival in the two experiments, recruitment (number of flowering plants/number of seeds sown) was positively related to seed mass in the 1982 experiment but not in the 1983 experiment. The effects of timing of emergence on survival generally disappeared within 12 months. Our results suggest that the relationship between initial seed mass and recruitment in Pastinaca represents a distribution of outcomes, variable from year to year. However, because short-term droughts in Iowa are common, we hypothesize that in most years, seed mass has little impact on recruitment. Furthermore, small scale heterogeneity may often overwhelm any potential effects of seed mass and timing of emergence on recruitment.

]]> Stephen D. Hendrix et al. http://ir.uiowa.edu/biology_pubs/21 http://ir.uiowa.edu/biology_pubs/21 Tue, 13 Sep 2011 14:43:34 PDT Patterns and causes of inter- and intraspecific variation in individual seed mass were investigated in three prairie and four woodland species of perennial umbellifer. Except for Cryptotaenia canadensis, seeds from woodland species were significantly heavier than those from prairie species. Within species, the magnitude of variation in individual seed mass ranged from three- to 16-fold. All the distributions of individual seed masses for the seven species were significantly leptokurtotic and except for Osmorhiza longistylis, all were significantly skewed. Variation between plants was significant in one prairie species (Oxypolis rigidior) and all woodland species. Mean seed mass in a plant was significantly correlated with plant size in three species. Within plant variation in seed mass accounted for 52-98% of total variation. No one factor consistently affected intraspecific variation in seed mass, although seed number per umbel, timing of umbel production and location of umbel were all important for at least one species. It is postulated that intraspecific variation in seed mass is the rule rather than the exception because of the influence of developmental factors such as seed number, timing of inflorescence production and location of different inflorescences. However, these factors may act in conflicting directions, making it difficult to assign causality to within plant variation in seed mass.

]]> Stephen D. Hendrix et al. http://ir.uiowa.edu/biology_pubs/20 http://ir.uiowa.edu/biology_pubs/20 Tue, 13 Sep 2011 14:43:32 PDT Previous field studies of recruitment in Pastinaca sativa L. indicate that more seedlings from small seeds than from large seeds survive short-term droughts. To explore this phenomenon, the effects of variation in seed biomass in Pastinaca sativa on embryo size and seedling characteristics 10, 20, 30 and 40 days after emergence were investigated. On the basis of most characteristics, seedlings from large seeds should be superior to seedlings from small seeds. Embryo length and cotyledon area were positively related to seed biomass, as were above ground biomass, total leaf area, and root biomass in all harvests. Total seedling biomass was positively related to seed biomass in the 10, 20, and 30 day harvests, but not the 40 day harvest. However, the ratio of maximum root length/total leaf area was negatively related to seed biomass in the 10 and 20 day harvests, suggesting that, under drought conditions, seedlings from small seeds may transpire less water than those from large seeds relative to their ability to reach water supplies. Although seedlings from larger seeds had greater root biomass, this may be of little advantage under drought conditions since approximately 90% of the root biomass is in the upper 10 cm of soil which dries out quickly. The advantage that seedlings from small seeds have under drought conditions is short-lived, lasting about 20 days in the glasshouse and an estimated 60-90 days in the field. This advantage is short-term because the relationship between seed biomass and resource allocation patterns changes during early seedling development.

]]> Stephen D. Hendrix et al. http://ir.uiowa.edu/biology_pubs/19 http://ir.uiowa.edu/biology_pubs/19 Tue, 13 Sep 2011 14:43:29 PDT Herbivore damage to fronds of Polybotrya cervina. Thelypteris turrialbae. and Adiantum obliquum from Finca La Selva, Costa Rica, was measured, and types of damage were distinguished. Herbivores removed 9.9, 5.5, and 7 3 percent of the leaf tissue, respectively The amount removed did not differ significantly among the species, although the proportion of fronds with different types of damage was different. In this study the levels of damage to ferns are similar to those reported for tropical angiosperms, suggesting that the vegetative parts of tropical ferns and angiosperms are utilized equally by herbivores. The variety of damage types suggests that tropical ferns host a varied insect fauna. These results support the hypothesis that underutilization of ferns by herbivores is largely an artifact of inadequate sampling.

]]> Stephen D. Hendrix et al. http://ir.uiowa.edu/biology_pubs/18 http://ir.uiowa.edu/biology_pubs/18 Tue, 13 Sep 2011 14:43:27 PDT We analyzed the relationships between population size and reproductive characteristics in the perennial prairie forb Phlox pilosa, an obligate outcrossing butterfly-pollinated species. We examined 27 populations ranging in size from 9 to over 75,000 flowering ramets in two regions of the state of Iowa (eastcentral and northwest) in 1993 and 1994. We collected flowers from each population and scored them for pollen arrival to stigmas and number of pollen tubes. We collected fruiting ramets from each population at the end of the Phlox growing season and scored them for height, biomass, and reproductive variables, including the number of flowers initiated and opened and the number of capsules initiated and matured. In both years, population size was significantly correlated with the number of capsules matured per ramet. Differences between populations in capsule production were set primarily at the pollination stage. In 1993, pollen arrival to stigmas was significantly lower than in 1994 and was correlated with population size in eastcentral Iowa populations, indicating that lower reproduction in small populations that year was at least partially due to inadequate amounts of pollen being moved. In 1993, weather conditions likely depressed pollinator activity, but absolute capsule formation was high because of high flower production per ramet and high population densities. In 1994, when pollen arrival to stigmas was relatively high and unrelated to population size, outcross pollen movement was greater in larger populations. Increased efficacy of outcross pollen movement in 1994 may have resulted from lower flower production and less dense populations forcing greater pollinator movement between ramets or from variation between years in fine-scale spatial genetic substructuring of populations. Our results indicate that the viability of Phlox pilosa can be best ensured by protecting and creating populations of at least 1000-2000 flowering ramets.

]]> Stephen D. Hendrix et al. http://ir.uiowa.edu/biology_pubs/17 http://ir.uiowa.edu/biology_pubs/17 Tue, 13 Sep 2011 14:43:25 PDT Stephen D. Hendrix et al. http://ir.uiowa.edu/biology_pubs/16 http://ir.uiowa.edu/biology_pubs/16 Tue, 13 Sep 2011 14:43:23 PDT The effects of insect herbivores on plant community characteristics of early secondary succession were compared in an Old World site (southern Britain) and a New World site (Iowa, U.S.A.). Plant species richness, species diversity, cover abundance, foliage height diversity, and a height index, used as a measure of vegetational structure, were significantly greater at the New World site than at the Old World site. At the Old World site during the first year of succession on bare ground, exclusion of foliar herbivores by the use of non-persistent insecticides significantly increased plant species richness, diversity and the cover abundance of the vegetation. These differences were due to an increase in the annual species in insecticide-treated plots. In the second year the removal of herbivores significantly increased cover abundance due to the enhanced growth of perennial grasses. These results indicate that at the Old World site insect herbivores begin to slow the rate of succession as early as the second year because of their impact on perennial grasses. At the New World site, none of the community characteristics measured were altered by herbivore exclusion. This is due to the relatively small contribution of annuals to species richness and cover abundance during the first year and of perennial grasses to cover abundance during the second year. We suggest that insect herbivores will only affect secondary succession in old fields at the New World site when perennial grasses become abundant, normally three to four years after succession begins.

]]> Stephen D. HENDRIX et al. http://ir.uiowa.edu/biology_pubs/15 http://ir.uiowa.edu/biology_pubs/15 Tue, 13 Sep 2011 14:43:21 PDT The ability of the biennial herb, Pastinaca sativa L. (wild parsnip), to respond to and compensate for destruction of primary umbel seeds by the larvae of Depressaria pastinacella (Lepidoptera: Oecophoridae) was analyzed by comparing umbel and seed production of damaged and undamaged plants collected from five populations. Plants with a basal stem diameter smaller than 8 mm suffer a reduction in seed set of about 50% when the primary umbel is destroyed but larger plants are able to compensate for loss of primary umbel seeds by increased seed set of tertiary umbels. Depending on plant size, this is due to either an increase in the number of tertiary umbels that reach maturity or an increase in the number of seeds per tertiary umbel. Although seeds of tertiary umbels are significantly smaller than those of primary or secondary umbels, their viability is equivalent to that of secondary seeds and may be greater than that of primary seeds. Characteristics of P. sativa's reproduction, such as the long flowering period and the initiation of more umbels than the plant is normally able to bring to maturity, are important to P. sativa's ability to compensate for the effects of herbivore damage.

]]> Stephen D. Hendrix http://ir.uiowa.edu/biology_pubs/14 http://ir.uiowa.edu/biology_pubs/14 Tue, 13 Sep 2011 14:43:20 PDT Heracelum lanatum, an andromonoecious perennial plant, reacted to herbivorous destruction of its primary (first) umbel by Depressaria pastinacella by an increase in the proportion of hermaphroditic flowers in late-developing umbels and a subsequent increase in seed set on these umbels. However, these reactions were not sufficient to offset completely the damage sustained; control plants produced 40% more seeds than damaged plants and seed biomass was 53% greater. Plant size (measured by basal stem diameter of the flowering stalk) was significantly correlated with total flower production, seed number, and seed biomass in both control and damaged plants. Plant size was also significantly correlated with the number of hermaphroditic flowers in the primary umbel of control plants and secondary umbels of damaged plants. Hermaphroditic flower production by the secondary umbels of control plants was negatively correlated with flower number in these umbels. Pastinaca sativa, another andromonoecious host plant of D. pastinacella, shows the same type of reactions as H. lanatum, but in P. sativa, compensation, at least in terms of seed number, is complete. The difference between the two species in replacement of lost offspring is interpreted in terms of frequency of reproduction. The interoparous h. lanatum may maximize reproduction in later seasons by increasing vegetative growth rather than by replacing all lost offspring. In contrast, the semelparous P. sativa maximizes replacement of destroyed offspring during its single reproductive bout.

]]> Stephen D. Hendrix http://ir.uiowa.edu/biology_pubs/13 http://ir.uiowa.edu/biology_pubs/13 Tue, 13 Sep 2011 14:43:18 PDT Stephen D. Hendrix http://ir.uiowa.edu/biology_pubs/12 http://ir.uiowa.edu/biology_pubs/12 Tue, 13 Sep 2011 14:43:15 PDT Considerable attention has recently been focused on using levels of developmental instability among members of a population to detect environmental or genetic stresses on animals or plants. It is not yet clear, however, that high developmental instability in a sample of individuals always indicates environmental stress or poor genetic quality. We studied 13 fragmented populations of prairie phlox (Phlox pilosa L.) to test the hypothesis that developmental instability should decrease with increasing population size-as expected if small populations suffer genetic problems associated with inbreeding or are exposed to more environmental stress than larger populations. We used two different measures of developmental instability, each calculated for two different traits: radial asymmetry of flowers (for petal width and petal length) and modular fluctuating asymmetry of leaves (for leaf widths at two points along the leaf). There were weak but significant correlations among individuals for four of six pairwise combinations of these measures. Surprisingly, three of our four measures of developmental instability showed strong population size effects that were opposite to those expected: developmental instability increased with population size. We conclude that measures of developmental instability cannot be applied uncritically for biomonitoring without considerable knowledge of developmental mechanisms, natural history, and population biology of the species in question.

]]> Stephen B. Heard et al.