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14: Environmental Responses - Biology

14: Environmental Responses - Biology


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Animals can respond to environmental factors by moving to a new location. Plants have sophisticated systems to detect and respond to light, gravity, temperature, and physical touch (Figure (PageIndex{1})). Plants may grow towards or away from environmental stimuli, and these growth responses are called tropisms. Environmental factors, particularly temperature and the hours of light and dark each day, also control flowering in many species. Plants detect the latter through photoperiodism. In the absence of light, plants respond physiologically to increase the chance of accessing light. Finally, plants rely on environmental cues to break dormancy in seeds and buds on winter twigs.

Figure (PageIndex{1}): The first flower to bloom in space. The International Space Station provides a unique opportunity to study the growth of plants under microgravity. Image by NASA (CC-BY-NC).

Attributions

Curated and authored by Melissa Ha using 30.6: Plant Sensory Systems and Responses from General Biology by OpenStax (licensed CC-BY). Access for free at openstax.org.

Thumbnail image: Sensitive plant (Mimosa pudica) exhibits a thigmonastic movement. The leaflets and leaves retract when it is touched. Image by piqsels (public domain)


Ecological responses to altered flow regimes: a literature review to inform the science and management of environmental flows

Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, U.S.A.

The Nature Conservancy, Bethesda, MD, U.S.A.

Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO, U.S.A.

The Nature Conservancy, Bethesda, MD, U.S.A.

Summary

1. In an effort to develop quantitative relationships between various kinds of flow alteration and ecological responses, we reviewed 165 papers published over the last four decades, with a focus on more recent papers. Our aim was to determine if general relationships could be drawn from disparate case studies in the literature that might inform environmental flows science and management.

2. For all 165 papers we characterised flow alteration in terms of magnitude, frequency, duration, timing and rate of change as reported by the individual studies. Ecological responses were characterised according to taxonomic identity (macroinvertebrates, fish, riparian vegetation) and type of response (abundance, diversity, demographic parameters). A ‘qualitative’ or narrative summary of the reported results strongly corroborated previous, less comprehensive, reviews by documenting strong and variable ecological responses to all types of flow alteration. Of the 165 papers, 152 (92%) reported decreased values for recorded ecological metrics in response to a variety of types of flow alteration, whereas 21 papers (13%) reported increased values.

3. Fifty-five papers had information suitable for quantitative analysis of ecological response to flow alteration. Seventy per cent of these papers reported on alteration in flow magnitude, yielding a total of 65 data points suitable for analysis. The quantitative analysis provided some insight into the relative sensitivities of different ecological groups to alteration in flow magnitudes, but robust statistical relationships were not supported. Macroinvertebrates showed mixed responses to changes in flow magnitude, with abundance and diversity both increasing and decreasing in response to elevated flows and to reduced flows. Fish abundance, diversity and demographic rates consistently declined in response to both elevated and reduced flow magnitude. Riparian vegetation metrics both increased and decreased in response to reduced peak flows, with increases reflecting mostly enhanced non-woody vegetative cover or encroachment into the stream channel.

4. Our analyses do not support the use of the existing global literature to develop general, transferable quantitative relationships between flow alteration and ecological response however, they do support the inference that flow alteration is associated with ecological change and that the risk of ecological change increases with increasing magnitude of flow alteration.

5. New sampling programs and analyses that target sites across well-defined gradients of flow alteration are needed to quantify ecological response and develop robust and general flow alteration–ecological response relationships. Similarly, the collection of pre- and post-alteration data for new water development programs would significantly add to our basic understanding of ecological responses to flow alteration.

Appendix S1. Studies used in literature review of relationships between hydrologic alteration and ecological response. All papers were included in qualitative analyses papers included in quantitative analyses are noted.

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5 - Responses to Environmental Change: Adaptation or Extinction

All populations are confronted with a plethora of environmental changes and must adapt, shift their range, or face extinction. Adaptation may take two forms:

The first option involves physiological acclimatization through phenotypic plasticity at the level of individuals.

Second, the genetic composition of populations may change through natural selection, a change that favors some genotypes at the expense of others.

Whereas plastic adaptation can only cope with environmental change of a limited extent, genetic adaptation allows populations to persist outside their previous tolerance ranges. Therefore, genetic adaptation is of primary concern in conservation biology, in terms of what is required to cope with major or sustained environmental changes. Feasibility and speed of genetic adaptations in response to environmental change depend on a variety of factors, such as a population's genetic diversity, the population size, generation time, and reproduction excess.

This chapter is organized as follows. In Section 5.2 we review the different types of abiotic environmental change that occur in nature, with an emphasis on their characteristic spatial and temporal scales. Section 5.3 explains how changes in local climate affect the physiological and phenological aspects of life histories and shows that evolutionary adaptations to altered climate conditions can be rapid. Sections 5.4 and 5.5 extend this conclusion to responses to thermal stress and pollution, and Section 5.6 highlights the special evolutionary challenges experienced by endangered species.


Plant Responses

Like animals, plants must also need to respond to external stimuli. This is important to:

  • Avoid predation.
  • Avoid abiotic (non-living) stress.
  • Maximise photosynthesis.
  • Obtain more light, water and minerals.
  • Ensure germination in suitable conditions/pollination.
  • Seed set/seeddispersal.
  • define the term tropism

Tropism – a directional growth response in which the direction of the response is determined by the direction of the external stimulus. Tropisms may be positive (a growth response towards the stimulus) or negative (a growth response away from the stimulus).

  • Phototropism (light) – shoots grow towards light – they are positively phototrophic.
  • Geotropism (gravity) – roots grow towards the pull of gravity.
  • Chemotropism (chemicals) – on a flower, pollen tubes grow down the style, attracted by chemicals, towards the ovary where fertilisation can take place.
  • Thigmotropism (touch) – shoots of climbing plants, such as ivy, wind around other plants or solidstructures and gain support.
  • explain how plant responses to environmental changes are co-ordinated by hormones, with reference to responding to changes in light direction

Hormones, also referred to as plant growth regulators, coordinate plant responses to environmental stimuli. Like animal hormones, plant hormones are chemical messengers that can be transported away from their site of manufacture, by active transport, diffusion and mass flow in the phloem sap or in xylem vessels, to act at target cells or tissues of the plant. They bind to receptors on the plasma membrane. Specific hormones have specific shapes, which can only bind to specific receptors with complementary shapes on the membranes of particular cells. This specific binding makes sure that the complementary shapes on the membranes of particular cells.

The cell wall around a plant cell limits the cell’s ability to divide and expand. Therefore, growth in plants happens where there are groups of immature cells that are still capable of dividing – these places are called meristems.

  • evaluate the experimental evidence for the role of auxins in the control of apical dominance and gibberellin in the control of stem elongation

Apical dominance – when a growing apical bud at the tip of the shoot inhibits growth of lateral buds further down the shoot. So if you break the shoot tip (the source of auxin) off a plant, the plant starts to grow side branches from lateral buds that were previously dormant.

Auxin is constantly made by cells at the tip of the shoot. It is then transported downwards, from cell-to-cell. This auxin accumulates in the nodes between the lateral buds. Somehow, its presence here inhibits their activity. Two simple experiments provide evidence for this mechanism:

  1. If we cut the tip off two shoots and apply IAA (synthetic auxin) to one of them, the one with IAA will continue toshow apical dominance and the side shoots will not grow. The one without IAA will branch out sideways.

If a growing shoot is tipped upside down, apical dominance is prevented and the lateral buds start to grow out sideways. This can be explained by the fact that auxin is not transported upwards against gravity, but only downwards. So in the upside-down shoot, the auxin produced in the apical meristem does not reach the lateral buds and therefore cannot affect them

Gibberellin and Stem Elongation:

Gibberellin – a group of plant hormones that stimulate cell elongation, germination and flowering.

In Japan, a plant disease called Bakanae is caused by a fungus and makes rice grow very tall. Attempts to isolate the fungal compounds involved identified a family of compounds called gibberellins. One of these was gibberellic acid (GA3). Scientists began applying GA3 to dwarf varieties of plants (e.g. maize, peas), which made these plants grow taller. These results seem to suggest that gibberellic acid is responsible for plant stem growth, but such a conclusion is too hasty.

Scientists compared GA1 concentrations of tall pea plants (homozygous for the dominant Le allele), and dwarf pea plants (homozygous for the recessive le allele), which were otherwise genetically identical. They found that plants with higher GA1 concentrations were taller. However, to show that GA1 directly causes stem growth, the researches needed to know how GA1 is formed. They worked out that the Le allele was responsible for producing the enzyme that converted GA20 to GA1.

They also chose a pea plant with a mutation that blocks gibberellin production between ent-Kaurene and GA12-aldehyde. Those plants produce no gibberellin and only grow to about 1cm in height. However, if you graft a shoot onto a homozygous le plant (which cannot convert GA20 to GA1), it grows tall. The shoot has no GA20 of its own, but it has the enzyme to convert GA20 to GA1 – this confirmed that GA1 caused stem elongation. Dwarf varieties of plants lack the dominant allele for an enzyme needed for synthesis of gibberellins.

Further studies have shown that gibberellins cause growth in the internodes by stimulating cell elongation (by loosening cell walls) and (by stimulating production of a protein that controls the cell cycle). Internodes of dwarf peas have fewer cells and shorter cells than those of tall plants, and mitosis in the intercalary meristems of deep-water rice plants increases with gibberellin treatment.

    describe how plant hormones are used commercially


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Acknowledgements

R.I.W. received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 791812. B.M.K. received support from the Belmont Forum, BiodivERsA and the German Research Foundation through the LimnoScenES project (AD 91/22-1). S.S. thanks John Magnuson, Gesa Weyhenmeyer, Johanna Korhonen, Yasuyuki Aono, Lars Rudstam, Nikolay Granin and Kevin Blagrave for their assistance updating the lake ice phenology records. J.D.L. thanks Martin Dokulil, Katrin Teubner, Pius Niederhauser and David Livingstone for their assistance updating the LSWT records. J.D.L. was supported, in part, by the Wisconsin Department of Natural Resources grant no. I02E01485 (New Innovations in Lake Monitoring). This work benefited from participation in GLEON (Global Lake Ecological Observatory Network). The Cumbrian Lakes monitoring scheme, which provided lake temperature data from Windermere, is currently supported by the Natural Environment Research Council award number NE/R016429/1 as part of the UK-SCaPE programme delivering National Capability.


Plant Responses to Gravity

Whether or not they germinate in the light or in total darkness, shoots usually sprout up from the ground, and roots grow downward into the ground. A plant laid on its side in the dark will send shoots upward when given enough time. Gravitropism ensures that roots grow into the soil and that shoots grow toward sunlight. Growth of the shoot apical tip upward is called negative gravitropism, whereas growth of the roots downward is called positive gravitropism.

Amyloplasts (also known as statoliths) are specialized plastids that contain starch granules and settle downward in response to gravity. Amyloplasts are found in shoots and in specialized cells of the root cap. When a plant is tilted, the statoliths drop to the new bottom cell wall. A few hours later, the shoot or root will show growth in the new vertical direction.

The mechanism that mediates gravitropism is reasonably well understood. When amyloplasts settle to the bottom of the gravity-sensing cells in the root or shoot, they physically contact the endoplasmic reticulum (ER), causing the release of calcium ions from inside the ER. This calcium signaling in the cells causes polar transport of the plant hormone IAA to the bottom of the cell. In roots, a high concentration of IAA inhibits cell elongation. The effect slows growth on the lower side of the root, while cells develop normally on the upper side. IAA has the opposite effect in shoots, where a higher concentration at the lower side of the shoot stimulates cell expansion, causing the shoot to grow up. After the shoot or root begin to grow vertically, the amyloplasts return to their normal position. Other hypotheses—involving the entire cell in the gravitropism effect—have been proposed to explain why some mutants that lack amyloplasts may still exhibit a weak gravitropic response.


14: Environmental Responses - Biology

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Spores and soil from six sides: interdisciplinarity and the environmental biology of anthrax (Bacillus anthracis)

Environmentally transmitted diseases are comparatively poorly understood and managed, and their ecology is particularly understudied. Here we identify challenges of studying environmental transmission and persistence with a six-sided interdisciplinary review of the biology of anthrax (Bacillus anthracis). Anthrax is a zoonotic disease capable of maintaining infectious spore banks in soil for decades (or even potentially centuries), and the mechanisms of its environmental persistence have been the topic of significant research and controversy. Where anthrax is endemic, it plays an important ecological role, shaping the dynamics of entire herbivore communities. The complex eco-epidemiology of anthrax, and the mysterious biology of Bacillus anthracis during its environmental stage, have necessitated an interdisciplinary approach to pathogen research. Here, we illustrate different disciplinary perspectives through key advances made by researchers working in Etosha National Park, a long-term ecological research site in Namibia that has exemplified the complexities of the enzootic process of anthrax over decades of surveillance. In Etosha, the role of scavengers and alternative routes (waterborne transmission and flies) has proved unimportant relative to the long-term persistence of anthrax spores in soil and their infection of herbivore hosts. Carcass deposition facilitates green-ups of vegetation to attract herbivores, potentially facilitated by the role of anthrax spores in the rhizosphere. The underlying seasonal pattern of vegetation, and herbivores' immune and behavioural responses to anthrax risk, interact to produce regular 'anthrax seasons' that appear to be a stable feature of the Etosha ecosystem. Through the lens of microbiologists, geneticists, immunologists, ecologists, epidemiologists, and clinicians, we discuss how anthrax dynamics are shaped at the smallest scale by population genetics and interactions within the bacterial communities up to the broadest scales of ecosystem structure. We illustrate the benefits and challenges of this interdisciplinary approach to disease ecology, and suggest ways anthrax might offer insights into the biology of other important pathogens. Bacillus anthracis, and the more recently emerged Bacillus cereus biovar anthracis, share key features with other environmentally transmitted pathogens, including several zoonoses and panzootics of special interest for global health and conservation efforts. Understanding the dynamics of anthrax, and developing interdisciplinary research programs that explore environmental persistence, is a critical step forward for understanding these emerging threats.

Keywords: Bacillus anthracis Bacillus cereus Etosha National Park anthrax disease ecology eco-epidemiology environmental transmission interdisciplinarity.


14: Environmental Responses - Biology

All articles published by MDPI are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by MDPI, including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited.

Feature Papers represent the most advanced research with significant potential for high impact in the field. Feature Papers are submitted upon individual invitation or recommendation by the scientific editors and undergo peer review prior to publication.

The Feature Paper can be either an original research article, a substantial novel research study that often involves several techniques or approaches, or a comprehensive review paper with concise and precise updates on the latest progress in the field that systematically reviews the most exciting advances in scientific literature. This type of paper provides an outlook on future directions of research or possible applications.

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to authors, or important in this field. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.


Watch the video: Responses to Environmental Stresses, Biology Lecture. (May 2022).