Relative Importance Of Intrinsic Factors Research Articles

Competition-driven growth of Atka mackerel in the Aleutian Islands ecosystem revealed by an otolith biochronology

Fish otolith increment biochronologies can reveal factors contributing to growth. These annually resolved, multi-decadal biochronologies have been used to identify temporal and spatial patterns in growth variability. Here, we used a linear mixed modeling approach to determine the relative importance of intrinsic factors (e.g., sex, age) and extrinsic factors (e.g., temperature, abundance of con-specifics and competitors) to growth of Atka mackerel (Pleurogrammus monopterygius), a commercially important groundfish dominant in the Aleutian Islands ecosystem. A yearly alternating pattern of wide and narrow increments was observed, and was negatively correlated with abundance of pink salmon (Oncorhynchus gorbuscha), suggesting possible competition over shared food resources such as large copepods (which were positively correlated with the otolith biochronology). There was no detectable effect of temperature on otolith growth, which could be a result of relative stability in water temperatures at the study site. We also contrast the otolith biochronology with a body condition index to examine the relationship between otolith and somatic growth. This represents the first otolith biochronology developed in the Aleutian Islands and provides insight into potential species interactions and their impacts on growth within this highly dynamic and productive ecosystem.

Colony size and depth affect wound repair in a branching coral

Coral colonies regularly suffer tissue damage from natural and anthropogenic sources. The resultant wounds can decrease colony fitness and act as sources of infection or algal overgrowth. By systematically breaking branches on 54 Pocillopora meandrina colonies and following in situ tissue regeneration (April–August 2017), variation in the wound recovery process was investigated within colonies, among colonies, and across four sites on O‘ahu, Hawai‘i. Ninety-five percent of all wounds healed, with an average healing time of 42 days. Average healing time was not different between initial and subsequent wounds. The relative importance of intrinsic factors, extrinsic factors, and disturbance history for the wound repair process was examined. Previous colony stressors, i.e., percent live coral tissue and bleaching history, were not correlated with wound healing time. These results indicate that wound repair is a priority for P. meandrina. Colony size and depth were significantly correlated with wound healing time: larger colonies healed 14 days faster than smaller colonies, and deeper colonies healed 25 days slower than shallower colonies. These findings support the hypothesis that larger colonies have more energy available for tissue regeneration. The observation of longer healing times for deeper colonies is likely driven by extrinsic factors that vary with depth, including temperature, wave energy, and irradiance. Overall, we show that wound healing in P. meandrina is physiologically resilient to previous stressors, but is affected by both colony size and depth. Understanding drivers of variation in regenerative processes for corals is critical for predicting coral population recovery after disturbances.

The need for new categorizations of dietary specialism incorporating spatio‐temporal variability of individual diet specialization

AbstractIn the last decade, an increasing body of research has addressed the extent to which different individuals within a species or population specialize in their exploitation of different food resources, which is referred to as individual diet specialization (IDS). Traditionally, researchers use the terms ‘specialist’ and ‘generalist’, despite the inability of these labels to capture all of the complexity of IDS. In this paper, we compare the dietary specialism of great tit Parus major and blue tit Cyanistes caeruleus at different temporal and spatial scales. We use these two species to illustrate the differences within and between species in individual levels of IDS. Both of these species show greater IDS in Mediterranean habitats, where resources are less plentiful and more variable than in Northern Europe. Additionally, we also emphasize that IDS within populations may change temporally. At the same time, there are differences between species, with great tits showing a higher capacity than blue tits to specialize at both the individual and the population level. Great tits can be considered generalists at the species level and specialists at the individual level, while blue tits can be considered generalists at both the species and the individual level. Our study demonstrates that there is a need for researchers to determine the relative importance of intrinsic factors (e.g. differences between species or individuals in their behavioral flexibility or cognitive capacity) and extrinsic factors (e.g. resource base) in shaping patterns of dietary specialization. We conclude that, within and among species, different individuals respond differently to similar environmental pressures, utilize different niches and develop different functions in the ecosystem depending on their type of IDS. Therefore, we propose that label ‘generalists’ should distinguish between facultative generalists, which can develop new specializations, and obligate generalists, which have a limited capacity to develop novel specializations.

Assessing the relative importance of intrinsic and extrinsic influence on sheep population dynamics on Hirta Island, UK

Identifying the relative importance of intrinsic factors and extrinsic environmental variations on population or ecosystem dynamics is important for ecological conservation research. Here, we use a systematic method proposed by De Menezes and Barabási [2004. Separating internal and external dynamics of complex systems. Physical Review Letters, 93, 068701] to reanalyse the long-term monitoring data of Soay sheep population fluctuations and climate variations on Hirta Island, UK. Our results indicate that the climate conditions have a higher impact than internal factors on the fluctuations of sheep population. The sheep population dynamics are internally self-regulating. The scaling relationships between sheep population and external and internal standard deviations are similar. The threshold of the sheep population on this island as determined by our study is around 1197, which is consistent with previous studies by other methods. Our study indicates that this systematic method may help to understand some of the complicated aspects of population dynamics about which detailed knowledge is limited.

Noise and determinism in synchronized sheep dynamics

A major debate in ecology concerns the relative importance of intrinsic factors and extrinsic environmental variations in determining population size fluctuations1,2,3,4,5,6. Spatial correlation of fluctuations in different populations caused by synchronous environmental shocks2,7,8 is a powerful tool for quantifying the impact of environmental variations on population dynamics8,9. However, interpretation of synchrony is often complicated by migration between populations8,10. Here we address this issue by using time series from sheep populations on two islands in the St Kilda archipelago11,12,13. Fluctuations in the sizes of the two populations are remarkably synchronized over a 40-year period. A nonlinear time-series model shows that a high and frequent degree of environmental correlation is required to achieve this level of synchrony. The model indicates that if there were less environmental correlation, population dynamics would be much less synchronous than is observed. This is because of a threshold effect that is dependent on population size; the threshold magnifies random differences between populations. A refined model showsthat part of the required environmental synchronicity can be accounted for by large-scale weather variations. These results underline the importance of understanding the interaction between intrinsic and extrinsic influences on population dynamics14.