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1. Biogeographic Patterns in Density, Recruitment, Body Size and Zonation of Rocky Intertidal Predators Suggest Increased Population Vulnerability Near Southern Range Limits

   https://doi.org/10.1111/jbi.15029  

   Gravem, Sarah A; Bachhuber, Silke; Bignami, Sean; Chiachi, Amanda E; Field, Laurel C; Gaddam, Rani N; Raimondi, Peter T; Menge, Bruce A (February 2025, Journal of Biogeography)

   ABSTRACT AimSurveying the demography of populations near species range edges may indicate their vulnerability to range contractions or local extinction as the climate changes. In the rocky intertidal, not only are latitudinal ranges constricted by thermal stress, but tides also create zonation or a ‘vertical range’ driven by sharp environmental gradients. By investigating demographics along the latitudinal and vertical ranges simultaneously, we can investigate whether populations may be vulnerable to a changing climate. LocationRocky intertidal habitats along west coast of the United States. TaxaOchre sea starPisaster ochraceus, six‐armed sea starLeptasteriasspp., emarginate whelks(Nucella ostrina and N. emarginata) and channeled whelkN. canaliculata. MethodsIn 2018, we surveyed the demographics of the taxa above at 33 sites spanning > 11° latitude from central Oregon to southern California, near the southern range limits of each taxon. We counted and sized individuals from the high to low intertidal zone. To understand how environmental stress changed with latitude, we evaluated intertidal temperaturesin situ, as well as tidal extremes, tidal amplitude and wave exposure using offshore buoys. ResultsFor all taxa, population density, the relative proportion of smaller individuals (except for emarginate whelks) and the upper vertical limits on the shore declined from north to south as temperatures increased and high tide height, tidal amplitude and wave heights decreased. In addition, smaller individualLeptasteriasspp. generally inhabited lower shore levels while smaller individual emarginate whelks inhabited higher shore levels coastwide. ForN. canaliculata, smaller animals were higher on shore northward, but lower on shore southward. Main ConclusionsWhile this study is a snapshot in time and cannot assess impacts of climate change, our surveys suggest environmentally‐related demographic limitation toward southern range limits and demographically vulnerable southern populations. Therefore, a warming climate may cause local extinctions or range contractions near southern limits. 

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2. Effects of maternal source and progeny microhabitat on natural selection and population dynamics in Alliaria petiolata

   https://doi.org/10.1002/ajb2.1299  

   Stinson, Kristina; Carley, Lauren; Hancock, Laura; Donohue, Kathleen (June 2019, American Journal of Botany)

   PremiseThe success or failure of propagules in contrasting microhabitats may play a role in biological invasion. We tested for variation in demographic performance and phenotypic trait expression during invasion byAlliaria petiolatain different microhabitats. MethodsWe performed a reciprocal transplant experiment withAlliaria petiolatafrom edge, intermediate, and forest understory microhabitats to determine the roles of the environment and maternal source on traits, fecundity, population growth rates (λ), and selection. ResultsObservations ofin situpopulations show that edge populations had the highest density and reproductive output, and forest populations had the lowest. In experimental populations, population growth rates and reproductive output were highest in the edge, and the intermediate habitat had the lowest germination and juvenile survival. Traits exhibited phenotypic plasticity in response to microhabitat, but that plasticity was not adaptive. There were few effects of maternal source location on fitness components or traits. ConclusionsAlliaria petiolataappears to be viable, or nearly so, in all three microhabitat types, with edge populations likely providing seed to the other microhabitats. The intermediate microhabitat may filter propagules at the seed stage, but discrepancies betweenin situobservations and experimental transplants preclude clear conclusions about the role of each microhabitat in niche expansion. However, edge microhabitats show the highest seed output in both analyses, suggesting that managing edge habitats might reduce spread to the forest understory. 

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3. Shift from income breeding to capital breeding with latitude in the invasive Asian shore crab Hemigrapsus sanguineus

   https://doi.org/10.1038/s41598-024-57434-y  

   Reese, Tanner C; Blakeslee, April_M H; Crane, Laura C; Fletcher, Laura S; Repetto, Michele F; Smith, Nanette; Stancil, Carter; Tepolt, Carolyn K; Toscano, Benjamin J; Griffen, Blaine D (December 2024, Scientific Reports)

   Abstract Organisms vary in the timing of energy acquisition and use for reproduction. Thus, breeding strategies exist on a continuum, from capital breeding to income breeding. Capital breeders acquire and store energy for breeding before the start of the reproductive season, while income breeders finance reproduction using energy acquired during the reproductive season. Latitude and its associated environmental drivers are expected to heavily influence breeding strategy, potentially leading to latitudinal variation in breeding strategies within a single species. We examined the breeding strategy of the Asian shore crabHemigrapsus sanguineusat five sites spanning nearly 10° of latitude across its invaded United States range. We hypothesized that the primary breeding strategy of this species would shift from income breeding to capital breeding as latitude increases. We found that though this species’ breeding strategy is dominated by capital breeding throughout much of the range, income breeding increases in importance at lower latitudes. This latitudinal pattern is likely heavily influenced by the duration of the foraging and breeding seasons, which also vary with latitude. We also found that reproductive characteristics at the northern and southern edges of the invaded range were consistent with continued range expansion. We suggest that the reproductive flexibility of the Asian shore crab is a key facilitator of its continued invasion success. Our results highlight the influence of latitude on the breeding strategy of a species and emphasize the need for further research regarding the ecological importance and implications of flexibility in breeding strategies within species. 

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4. Small scale, elevation- and environmental-related differences in life history strategies in a temperate resident songbird

   https://doi.org/10.1098/rsos.241777  

   Sonnenberg, Benjamin R; Branch, Carrie L; Pitera, Angela M; Heinen, Virginia K; Whitenack, Lauren E; Welklin, Joseph F; Pravosudov, Vladimir V (April 2025, Royal Society Open Science)

   Environmental drivers of within-population reproductive patterns are often hypothesized to lead to reproductive strategies tuned to local conditions. Organisms adjust energy allocation between survival and reproduction based on experience, age, lifespan and resource availability. Variation in these energetic investments can be described as different demographic tactics which are expected to optimize the fitness of local populations. These ideas are largely supported by both empirical and model-based studies but research identifying specific strategies and their corresponding environmental drivers within wild populations remains rare. Using 12 years of data, we investigated reproductive investment strategies in a relatively short-lived resident songbird, the mountain chickadee (Poecile gambeli), at two elevations that differ in environmental harshness in the North American Sierra Nevada mountains. Challenging winter environments at high elevations impose strong selection pressure on survival-related traits (e.g. specialized spatial cognition associated with food caching) and significantly shorten the length of the reproductive window. Here, we show that chickadees at a higher elevation lay smaller clutches (ca0.41 fewer eggs) and produce fewer (ca0.25 fewer nestlings) but larger offspring (ca0.4 g heavier) compared to lower elevation residents. Due to the harsher and less predictable environmental conditions at higher elevations, this investment strategy in this resident species likely leads to the production of offspring with greater chances of survival. Overall, our results show that within-species differences in life history strategies may evolve over a small spatial scale along strong environmental gradients. 

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5. Unraveling demographic patterns in tropical birds across an elevational gradient

   https://doi.org/10.1093/ornithapp/duae063  

   Neate-Clegg, Montague_H C; Saracco, James F; Rodríguez-Vásquez, Fabiola; Jones, Samuel_E I (November 2024, Ornithological Applications)

   ABSTRACT An increasing body of evidence has displayed upslope shifts in the high-diversity avian communities of tropical mountains. Such shifts have largely been attributed to warming climates, although their actual mechanisms remain poorly understood. One likely possibility is that changes in species-specific demographic rates underlie elevational range shifts. Fine-scale population monitoring and capture–mark–recapture (CMR) analysis could shed light on these mechanisms, but, until recently, analytical constraints have limited our ability to model multiple demographic rates across bird communities while accounting for transient individuals. Here, we used Bayesian hierarchical multi-species CMR models to estimate the apparent survival, recruitment, and realized population growth rates of 17 bird species along an elevational gradient in the cloud forests of Honduras. For 6 species, we also modeled demographic rates across elevation and time. Although demographic rates varied among species, population growth rates tended to be higher in lower elevation species. Moreover, some species showed higher population growth rates at higher elevations, and elevational differences in growth rates were positively associated with previous estimates of upslope shifts at the study site. We also found that demographic rates showed contrasting trends across the duration of the study, with recruitment decreasing and apparent survival increasing, and stronger effects at lower elevations. Collectively, we provide the methodological tools to encourage more multi-species demographic analyses in other systems, while highlighting the potential for the demographic impacts of global change. We provide a Spanish translation in the Supplementary Materials. 

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