Reproductive Success of the Federally Endangered Leafy Prairie Clover, Dalea foliosa (A. Gray) Barneby (Fabaceae) in Illinois: a Third Year of Data

Castanea, Mar 2004 by Molano-Flores, Brenda

ABSTRACT

The federally-endangered species Dalea foliosa (leafy prairie clover) is a short-lived herbaceous perennial found in dolomite prairie. In Illinois, only five populations are known including one at the Midewin National Tallgrass Prairie (MNTP). In this paper, I present the results of a third year of reproductive success data and determine variation between years in reproductive success for this small isolated population. As in 1998 and 1999, 2000 reproductive success was high, although variation between years was found. Although the studied population of D. foliosa is small, isolated, and found in a fragmented habitat, these conditions do not appear to affect reproductive success.

INTRODUCTION

Dalea foliosa (A. Gray) Barneby or leafy prairie clover is a federally-endangered species (United States Fish and Wildlife Service 1991). This species is a short-lived herbaceous perennial endemic to cedar glades of central Tennessee and northern Alabama and has five disjunct populations in Will County, Illinois (Figure 1) (United States Fish and Wildlife Service 1996, Zambrana Engineering Inc. 1998). In Illinois, the species is found growing in prairie remnants along the Des Plains River in thin soils overlying dolomite (Kurz and Bowles 1981). One of the five Illinois populations was discovered in 1997 at the Midewin National Tallgrass Prairie (MNTP, Figure 1). Because this population was small (less than 180 individuals; Molano-Flores 2001) and isolated from any other D. foliosa population, particular interest was placed on determining the reproductive success of individuals. Several studies (e.g., Hendrix 1994, Agren 1996, Molano-Flores and Hendrix 1999, Charpentier et al. 2000, Cunningham 2000, Luijten et al. 2000) have found that the combination of habitat fragmentation, isolation, and small population, can decrease fruit set.

Although Dalea foliosa has been the subject of several studies [seed germination (Baskin and Baskin 1989, 1998), demographics (Glass et al. 1996, Molano-Flores 2001), and population genetics (Wiltshire 1994)], limited information is available regarding the reproductive success of the species (i.e., fruit or seed set). In a previous publication (Molano-Flores 2001), preliminary results of a two-year reproductive success study on the population of D. foliosa found at MNTP were presented. In this paper, I will present the results of a third year of data and describe year to year variation in reproductive success.

MATERIALS AND METHODS

Species and Study Site

Dalea foliosa (=Petalostemum foliosa, Fabaceae, leafy prairie clover) is a short-lived (

This study was conducted at the MNTP-Drummond Prairie, Will County, Illinois, during 1998-2000 (Figure 1). This area contains a mix of wet, mesic, and dry prairie. Dolomite, a calcium magnesium carbonate rock, can be found beneath the soil surface. At the study site, D. foliosa is found in the dry and dry-mesic dolomite prairies. all individuals were caged (either one or many per cage) from 1998-2001 because severe herbivory by deer or rabbits was associated with this site in 1997. The cages were built using chicken wire to exclude these large mammals, but not to exclude other types of herbivores such as seed predators (i.e., beetles). Many legumes have problems with seed predators (Haddock and Chaplin 1982, AuId 1983, Boe et al. 1988). Finally, the cages did not prevent pollinator access to the inflorescences.

Reproductive Success

To determine reproductive success of Dalea foliosa between 1998-2000, 20 inflorescences (one from each of 20 individuals) were randomly selected and tagged at the beginning of flowering head development. At the end of the fruiting season (late August-September), infructescences were collected. Infructescence length (cm) and biomass (g) were measured. Reproductive success was determined by following Hendrix (1994), where 50 fruits from each infructescence were classified as filled (plump, well rounded seeds), unfilled (dented, small seeds), unfertilized (no ovular development = flower), or attacked by seed predators. In addition, the number of branches and inflorescences were counted for each individual. To determine differences between years for reproductive success, infructescence length and biomass, number of branches, and number of inflorescences, a One-Way ANOVA was used followed by a Tukey test. If the normality or equal variance tests failed, a Kruskal-Wallis One-Way ANOVA on Eanks (K-W) was performed followed by a Dunn's test. Spearman's rank correlations were used to determine the relationship between infructescence length, infructescence biomass, number of inflorescences, number of stems, and reproductive success. P-values for all statistical analyses were significant at

RESULTS

Significant differences were found between years for fruits filled (K-W, H = 9.21, P = 0.01). In both 1998 and 2000 the percentage of fruits filled was more than 79% compared to 70% in 1999 (Table 1). However, significant differences were found only between 1998 and 1999 (Dunn's test 1999 > 2000 (Table 1).

As in 1998 and 1999 (Molano-Flores 2001) a significant and positive correlation was found between infructescence length and biomass (r = 0.626, P = 0.004) and between number of inflorescences and number of stems (r = 0.851, P = 0.000) in 2000. Finally, in contrast to 1998 and 1999, a significant negative correlation was found between unfertilized fruits and infructescence biomass (r = -0.481, P = 0.037) in 2000.