Reproductive Asynchrony in Spatial Population Models: How Mating Behavior Can Modulate Allee Effects Arising from Isolation in Both Space and Time

Summary1. In small fragmented plant populations, reproductive failure due to pollen limitation is often attributed to spatial isolation of individuals. While flowering time has been shown to affect seed set, its role in pollen limited fragmented populations is less understood. 2. In this study, we quantified near-neighbour distances, flowering phenology, and how they interact to affect seed set in individual plants. We followed the daily flowering phenology of over 2400 heads on over 500 Echinacea angustifolia individuals and quantified the resulting seed set during three consecutive flowering seasons. The study was conducted in an experimental plot where we randomized planting locations to eliminate spatial patterns of mate availability which are common in fragmented populations of Echinacea, a self-incompatible plant. 3. We found that individual flowering time had a larger and more consistent effect on seed set than did spatial location. Seed set in the earliest flowering plants exceeded seed set in the latest by 46-70% in all three years. The role of spatial isolation, characterized both by individual distance to conspecific plants and by location in the plot, was less consistent and showed a weaker relationship with seed set than did flowering phenology. The most isolated plants set 20-27% less seed than the least isolated plants in [2005][2006] with no difference in 2007. 4. In one year, we quantified seed set by floret position within a flowering head. We found significant positional effects; however, effects due to flowering time were much greater. These results were more consistent with the pollen limitation hypothesis than the resources limitation hypothesis. 5. Synthesis. Our results illustrate that flowering time and distance to neighbouring conspecifics can cause reproductive failure in fragmented populations, even in the absence of mate limitation caused by mating incompatibility. These findings suggest that flowering time may be an underappreciated contributor to reproductive failure in small fragmented populations. Key-words: Allee effect, edge effect, flowering phenology, habitat fragmentation, pollen limitation, reproductive ecology, seed set, spatial isolation, tallgrass prairie IntroductionThe proportion of ovules that develop into seeds (i.e. seed set) is a measure of an individual plant's annual reproductive fitness. Many of the factors that affect reproduction, such as resource limitation, pollen limitation and seed predation, often vary with the density of flowering conspecific plants (e.g. Campbell & Halama 1993;Krupnick & Weis 1999;Knight et al. 2005). In addition, these factors often vary with the flowering time of the individual (e.g. English-Loeb & Karban 1992;Gross & Werner 1983). Quantifying the relative and absolute contributions of these effects on reproduction is necessary to understand the demography and ongoing evolution in plant populations, especially in small and fragmented populations where reproduction is often limited by receipt of pollen (reviewed in Knight et al. 2005)....

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“…; Fagen et al . ). Small insect populations greatly exacerbated temporal Allee effects which could lead to potential demographic Allee effects.…”

Section: Discussionmentioning

confidence: 97%

Both flowering time and distance to conspecific plants affect reproduction in Echinacea angustifolia, a common prairie perennial

Ison

Wagenius²

2014

Journal of Ecology

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“…Yet, if we consider dispersal kernels that include long distances too, we find conditions where also females run into risk of remaining mate‐less: active mate searching by males will not help females if no such males exist nearby. Newer studies have indeed pointed out that spatiotemporal variation associated with dispersal can easily create conditions in which females too run the risk of remaining mateless (Calabrese et al 2008, Fagan et al 2010).…”

Section: Discussionmentioning

confidence: 99%

Mate limitation causes sexes to coevolve towards more similar dispersal kernels

Meier

Starrfelt

2011

Oikos

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Sex‐specific dispersal behavior has been documented in a wide range of different species. Avoidance of inbreeding and kin competition as well as different benefits of philopatry have been invoked as explanations for these patterns. All of these factors have, however, focused on explaining why dispersal behavior differs between the sexes. In this paper, we make the case that dispersal causes an increase in spatial variability in the sex ratio which can reduce the local availability of mates, and thus feed back to influence the evolution of sex‐specific dispersal and lead to more, rather than less, similar dispersal behavior in the sexes. We investigate this mechanism in two different models, first in a conceptually simple case showing why the coevolutionary effect arises, second in an individual‐based model where we model a population in explicit space with dispersal implemented as dispersal kernels. While our mechanism is not expected to completely remove sex‐bias in dispersal, it can act alongside other selection pressures to reduce such biases. Our model thus shows that dispersal of one sex can have an effect on the selective pressures on the opposite sex, without implementing inbreeding avoidance or differential benefits or costs of dispersal.

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“…Ample research has examined the role of spatial barriers in generating population structure and speciation (Mayr 1942;Coyne and Orr 2004). Not so extensively studied, however, are the roles of temporal barriers (i.e., allochronic differentiation) in diversification processes (Yamamoto and Sota 2009;Fagan et al 2010; reviewed in Coyne and Orr 2004).…”

Section: Introductionmentioning

confidence: 99%

Asynchrony of Seasons: Genetic Differentiation Associated with Geographic Variation in Climatic Seasonality and Reproductive Phenology

Quintero

González‐Caro

Zalamea

et al. 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: Many organisms exhibit distinct breeding seasons tracking food availability. If conspecific populations inhabit areas that experience different temporal cycles in food availability spurred by variation in precipitation regimes, then they should display asynchronous breeding seasons. Thus, such populations might exhibit a temporal barrier to gene flow, which may potentially promote genetic differentiation. We test a central prediction of this hypothesis, namely, that individuals living in areas with more asynchronous precipitation regimes should be more genetically differentiated than individuals living in areas with more similar precipitation regimes. Using mitochondrial DNA sequences, climatic data, and geographical/ecological distances between individuals of 57 New World bird species mostly from the tropics, we examined the effect of asynchronous precipitation (a proxy for asynchronous resource availability) on genetic differentiation. We found evidence for a positive and significant cross-species effect of precipitation asynchrony on genetic distance after accounting for geographical/ecological distances, suggesting that current climatic conditions may play a role in population differentiation. Spatial asynchrony in climate may thus drive evolutionary divergence in the absence of overt geographic barriers to gene flow; this mechanism contrasts with those invoked by most models of biotic diversification emphasizing physical or ecological changes to the landscape as drivers of divergence.

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Reproductive Asynchrony in Spatial Population Models: How Mating Behavior Can Modulate Allee Effects Arising from Isolation in Both Space and Time

Cited by 27 publications

References 48 publications

Both flowering time and distance to conspecific plants affect reproduction in Echinacea angustifolia, a common prairie perennial

Both flowering time and distance to conspecific plants affect reproduction in Echinacea angustifolia, a common prairie perennial

Mate limitation causes sexes to coevolve towards more similar dispersal kernels

Asynchrony of Seasons: Genetic Differentiation Associated with Geographic Variation in Climatic Seasonality and Reproductive Phenology

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