Question

Consider this claim: Changes in environmental conditions always result in new ecosystems and loss of biodiversity characterized by an increase in the number of some species, the evolution of new species, and the extinction of some species.

Use what you have learned from the lesson, as well as reliable and reputable resources, to evaluate this claim. Use at least three examples from the lesson and other sources to support the valid ideas in the claim and refute the invalid ones. Add a list of your resources at the end of your response. Then, draw a conclusion about the stability of ecosystems, how and what can affect the stability of ecosystems, and how changes in the environment may affect the types and number of living things in an ecosystem.

Answer 1

Short answer: The claim is partly correct but too strong. Environmental changes often alter species abundances and community structure, and they can cause extinctions and (over long times) speciation. However, they do not always produce "new ecosystems" or always cause net biodiversity loss; increases in some species and recovery of communities are common, and the evolution of entirely new species is generally a long-term outcome, not an inevitable short-term consequence. Whether an ecosystem changes, recovers, or shifts to an alternative state depends on the type, scale, speed, and frequency of the change plus the system’s resilience and connectivity.

Below I evaluate the pieces of the claim, citing examples.

1) “Changes in environmental conditions always result in new ecosystems…”
- Not always. Many ecosystems are resistant or resilient: they maintain function and species composition after small or moderate disturbances (e.g., short droughts or seasonal storms). When disturbances are severe and/or frequent, or cross a threshold, they can trigger succession or a shift to a different ecosystem (an alternative stable state). Example contrasts:
- Mount St. Helens (1980 eruption): massive disturbance destroyed vegetation locally and initiated primary succession. Over decades new plant and animal communities developed on lava/ash — an example where change produced a new developing ecosystem (primary succession) (USGS).
- Many forests that experience a single fire undergo secondary succession and often return to a forested ecosystem over years-to-decades rather than become a totally different ecosystem type.
- In some cases, ecosystems flip to a different stable state (e.g., coral reef → algal-dominated system after repeated bleaching and overfishing), so a “new” ecosystem results only if thresholds are passed.

2) “…and loss of biodiversity characterized by an increase in the number of some species…”
- Partly true but ambiguous. Environmental change commonly leads to winners and losers: some species decline or go extinct locally while others increase (native opportunists, invasive species, or disturbance-tolerant species). That pattern can coincide with a net loss of biodiversity, but not always.
- Example supporting increase of some species: On Guam the invasive brown tree snake caused collapse of native forest bird populations; at the same time, snakes greatly increased in abundance and the ecosystem’s animal community composition changed dramatically (USGS/USFWS).
- Example of opportunistic increase after disturbance: In many coastal or estuarine systems, jellyfish blooms and other opportunists increase after overfishing and nutrient pollution even while overall biodiversity and fish stocks decline.
- Counterexample where biodiversity can increase: During intermediate stages of secondary succession, species richness often increases as more niches are temporarily available (classical intermediate disturbance hypothesis).

3) “…the evolution of new species…”
- Not a guaranteed or short-term outcome. Environmental change sets the stage for natural selection and can promote adaptive evolution; in some cases it can accelerate divergence and eventual speciation. But speciation typically requires long timeframes, genetic isolation, consistent selection, and/or reproductive barriers — it is not an automatic consequence of environmental change.
- Example of rapid evolution: Darwin’s finches on the Galápagos have shown measurable, rapid morphological evolution in response to shifting food supplies and climate variability (Grant & Grant). This demonstrates that evolutionary responses can be rapid in some organisms, but speciation (formation of entirely new species) is not guaranteed on short timescales.
- In many disturbed systems, populations are reduced and fragmented, making them less likely to persist long enough to speciate.

4) “…and the extinction of some species.”
- This part is generally correct: environmental change (especially large/rapid or human-caused changes) is a major driver of species extinctions, local and global. Examples:
- Coral bleaching and mass mortality events on the Great Barrier Reef and other reefs (driven by ocean warming and acidification) have caused loss of coral species and reef-dependent biodiversity (Hughes et al. 2017).
- Island species extinctions after invasive predators (e.g., Guam birds with brown tree snake) and habitat loss are well-documented.

Summary of examples (three or more):
- Mount St. Helens (primary succession after volcanic eruption): new communities established over decades — supports idea that environmental change can produce new ecosystems via succession (USGS).
- Guam + brown tree snake: invasive-driven extinctions of native birds and large increases in snake numbers — supports winners/losers and biodiversity loss (USGS/USFWS).
- Coral bleaching on reefs (climate warming): repeated bleaching reduces coral diversity and can shift reefs to algal-dominated states; also shows rapid biodiversity loss from environmental change (Hughes et al., Nature 2017).
- Darwin’s finches / rapid evolution studies: show adaptive change can be fast, but formation of new species is not automatic and is typically a longer-term process (Grant & Grant).

Why the claim is too absolute
- “Always” is the problem. Outcomes depend on magnitude, rate, and duration of change, the life histories and dispersal of species, genetic diversity, habitat connectivity, and human influence. Some changes are reversible or lead to recovery; others cause irreversible losses or regime shifts. Evolutionary responses may occur but are not inevitable, and speciation usually takes long timeframes.

Conclusions about ecosystem stability and effects of environmental change
- Stability has multiple meanings: resistance (ability to withstand change) and resilience (ability to recover). High biodiversity, functional redundancy, connectivity, and intact keystone species generally increase stability.
- Factors that affect stability: disturbance intensity/frequency, rate of environmental change (rapid changes are harder to adapt to), habitat fragmentation, pollution, invasive species, human land use, and climate change.
- Effects on types and numbers of organisms: environmental change tends to change species abundances (some increase, some decrease), can cause local or global extinctions (especially for small or specialized populations), and may open ecological space for colonizers or invasives. Evolutionary change (adaptation) can occur, and over long periods new species may arise, but this is not guaranteed and often cannot keep pace with rapid anthropogenic change.

Bottom line: environmental change often reshuffles ecosystems — producing winners and losers, and sometimes new community types — and frequently causes biodiversity loss and extinctions when changes are large/rapid. But it is not an absolute rule that change will always yield a new ecosystem or immediate speciation; outcomes are context-dependent and vary in scale and timing.

Resources
- U.S. Geological Survey (USGS), Mt. St. Helens ecological recovery overview: https://www.usgs.gov/volcanoes/mount-st-helens/mt-st-helens-ecological-recovery
- Hughes, T.P., et al. 2017. Global warming and recurrent mass bleaching of corals. Nature 543, 373–377. https://doi.org/10.1038/nature21707
- U.S. Geological Survey / U.S. Fish & Wildlife Service on brown tree snake and impacts to Guam birds: https://www.usgs.gov/centers/norcs/science/brown-tree-snake (and https://www.fws.gov/invasives/what-we-do/brown-tree-snake.html)
- Grant, P. R., & Grant, B. R. (2002). Unpredictable evolution in a 30‑year study of Darwin’s finches. Science 296: 707–711. (on rapid evolutionary responses)
- Intergovernmental Panel on Climate Change (IPCC) AR6: on ecological impacts of climate change and disturbance: https://www.ipcc.ch/report/ar6/wg2/
- IUCN/Global Invasive Species Programme, on invasive species impacts: https://www.iucn.org/resources/issues-briefs/invasive-species

If you want, I can: (a) create a short infographic summarizing outcomes of different types of environmental change (disturbance intensity × frequency), or (b) analyze a particular ecosystem you care about and predict likely responses to specified changes.