The Relationship Between Age, Size, and Reproduction in Trillium Grandiflorum (Liliaceae)

Hanzawa, Frances M.; Kalisz, Susan

doi:10.1002/j.1537-2197.1993.tb13819.x

Cited by 78 publications

(82 citation statements)

References 29 publications

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“…Small three leaf plants (<5cm leaf length) can regress to the 1-leaf stage but cannot advance to the reproductive stage, while the opposite is true for large (>5 cm leaf length) 3-leaf plants. Both 3-leaf and reproductive plants can enter a dormant stage, in which they remain below ground for one or more growing seasons (Hanzawa and Kalisz 1993). However, dormancy was rare in this study.…”

Section: Demographic Analysismentioning

confidence: 59%

Population growth rate of a common understory herb decreases non-linearly across a gradient of deer herbivory

Knight

Caswell

Kalisz

2009

Forest Ecology and Management

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(247 words).Overabundant white-tailed deer (Odocoileus virginianus) are a significant management problem in North America that exert unprecedented herbivory pressure on native understory forest communities. Conserving understory plant populations requires quantifying a sustainable level of deer herbivory. To date, most population projection models consider only deer presence and absence. To estimate population growth rate along a gradient of herbivory, we focused on Trillium grandiflorum because it is a common understory species and a bellwether of deer effects and forest decline. We used matrix population models, and employed both prospective and retrospective analyses using a regression life table response experiment (LTRE).Deer affect size, stage and population dynamics of T. grandiflorum. Because deer target flowering and large non-flowering stages of T. grandiflorum, these individuals do not produce seed in the year they are browsed and are more likely to regress in stage and size in the following growing season relative to non-browsed plants. Importantly, sustained high browse levels result in populations dominated by small, non-flowering individuals. Our LTRE revealed a significant negative and decelerating relationship between herbivory and λ. This non-linearity occurs at the highest herbivory levels because highly browsed populations become dominated by stages that deer do not consume and are thus buffered from rapid decline. However, population extinction is expected when herbivory is greater than the pivotal value of ~15%. Our study demonstrates that levels of deer herbivory commonly experienced by forest understory perennials are sufficient to cause the loss of T. grandiflorum and likely other co-occurring palatable species.

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Section: Demographic Analysismentioning

confidence: 59%

Population growth rate of a common understory herb decreases non-linearly across a gradient of deer herbivory

Knight

Caswell

Kalisz

2009

Forest Ecology and Management

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“…Reproductive individuals bear both a whorl of three leaves and a single flower and fruit. A minimum size threshold must also be met for nonreproductive three-leaf plants to transition to the reproductive stage (Hanzawa and Kalisz 1993). We classified all plants in our study area into the three stages and estimated their ages using the relationship of size and age determined for this population (Hanzawa and Kalisz, 1993).…”

Section: Study Species and Site Descriptionmentioning

confidence: 99%

“…A minimum size threshold must also be met for nonreproductive three-leaf plants to transition to the reproductive stage (Hanzawa and Kalisz 1993). We classified all plants in our study area into the three stages and estimated their ages using the relationship of size and age determined for this population (Hanzawa and Kalisz, 1993). During this study, the population contained 128 juveniles (age range 1-8 years), 866 nonreproductives that did not flower at any time during the 1990-1993 field seasons (age range 9-26 years), and 328 reproductives that flowered at least once during 1990-1993 (age range 17-42 years).…”

Section: Study Species and Site Descriptionmentioning

confidence: 99%

Spatial Population Genetic Structure in Trillium Grandiflorum: The Roles of Dispersal, Mating, History, and Selection

Kalisz

Nason²,

Hanzawa³

et al. 2001

Evolution

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173

122

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Abstract. The roles of the various potential ecological and evolutionary causes of spatial population genetic structure (SPGS) cannot in general be inferred from the extant structure alone. However, a stage-specific analysis can provide clues as to the causes of SPGS. We conducted a stage-specific SPGS analysis of a mapped population of about 2000 Trillium grandiflorum (Liliaceae), a long-lived perennial herb. We compared SPGS for juvenile (J), nonreproductive (NR), and reproductive (R) stages. Fisher's exact test showed that genotypes had Hardy-Weinberg frequencies at all loci and stage classes. Allele frequencies did not differ between stages. Bootstrapped 99% confidence intervals (99%CI) indicate that F-statistic values are indistinguishable from zero, (except for a slightly negative F IT for the R stage). Spatial autocorrelation was used to calculate f, the average kinship coefficient between individuals within distance intervals. Null hypothesis 99%CIs for f were constructed by repeatedly randomizing genotypic locations. Significant positive fine-scale genetic structure was detected in the R and NR stages, but not in the J stage. This structure was most pronounced in the R stage, and declined by about half in each remaining stage: near-neighbor f ϭ 0.122, 0.065, 0.027, for R, NR, and J, respectively. For R and NR, the near-neighbor f lies outside the null hypothesis 99%CI, indicating kinship at approximately the level of half-sibs and first cousins, respectively. We also simulated the expected SPGS of juveniles post dispersal, based on measured R-stage SPGS, the mating system, and measured pollen and seed dispersal properties. This provides a null hypothesis expectation (as a 99%CI) for the J-stage correlogram, against which to test the likelihood that post-dispersal events have influenced J-stage SPGS. The actual J correlogram lies within the null hypothesis 99%CI for the shortest distance interval and nearly all other distance intervals indicating that the observed low recruitment, random mating and seed dispersal patterns are sufficient to account for the disappearance of SPSG between the R and the J stages. The observed increase in SPGS between J and R stages has two potential explanations: history and local selection. The observed low total allelic diversity is consistent with a past bottleneck: a possible historical explanation. Only a longitudinal stage-specific study of SPGS structure can distinguish between historical events and local selection as causes of increased structure with increasing life history stage. Two major factors are thought to contribute to the extent of spatial population genetic structure (SPGS) either within or among plant populations: the patterns and distances of pollen and seed dispersal (Ennos 1994) and the extent of local selection (Hedrick 1986). The predicted effects of various patterns of pollen and seed dispersal are well understood (Slatkin 1985;Ennos 1994), as are the theoretical consequences of local selection (Felsenstein 1976;Slatkin 1985). However, the relative i...

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“…For many organisms, however, fecundity and the risk of mortality depend as much on size as age per se, although the two may often covary (Werner and Caswell 1977;Hughes and Connell 1987;Ebenman and Persson 1988;Hanzawa and Kalisz 1993). Since size at any given age is the sum of growth increments during earlier life-history stages, growth rate (the onto-genetic change in size per unit time) defines the relationship between size and age and itself plays an important role in life-history evolution.…”

Section: Introductionmentioning

confidence: 99%

Faster Is Not Always Better: Selection on Growth Rate Fluctuates across Life History and Environments

Monro

Marshall²

2014

The American Naturalist

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. abstract: Growth rate is increasingly recognized as a key life-history trait that may affect fitness directly rather than evolve as a byproduct of selection on size or age. An ongoing challenge is to explain the abundant levels of phenotypic and genetic variation in growth rates often seen in natural populations, despite what is expected to be consistently strong selection on this trait. Such a paradox suggests limits to how contemporary growth rates evolve. We explored limits arising from variation in selection, based on selection differentials for age-specific growth rates expressed under different ecological conditions. We present results from a field experiment that measured growth rates and reproductive output in wild individuals of a colonial marine invertebrate (Hippopodina iririkiensis), replicated within and across the natural range of succession in its local community. Colony growth rates varied phenotypically throughout this range, but not all such variation was available for selection, nor was it always targeted by selection as expected. While the maintenance of both phenotypic and genetic variation in growth rate is often attributed to costs of growing rapidly, our study highlights the potential for fluctuating selection pressures throughout the life history and across environments to play an important role in this process.

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The Relationship Between Age, Size, and Reproduction in Trillium Grandiflorum (Liliaceae)

Cited by 78 publications

References 29 publications

Population growth rate of a common understory herb decreases non-linearly across a gradient of deer herbivory

Population growth rate of a common understory herb decreases non-linearly across a gradient of deer herbivory

Spatial Population Genetic Structure in Trillium Grandiflorum: The Roles of Dispersal, Mating, History, and Selection

Faster Is Not Always Better: Selection on Growth Rate Fluctuates across Life History and Environments

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