Which statement about dispersal is false

In fact, it has to in order for them to be able to reach where they're going. Um, you know, does not need to happen over millions of years for thousands of years. So C is false, and that is the answer. But we're gonna look a D just to be thorough. Absolutely true. If a species wants toe expand to new territory to new ecosystems, new habitats has to be able to disperse. That's what dispersal is. So see is the false answer, and we're going to circle it.

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View Full Video Already have an account? Sam J. Problem 6 Easy Difficulty Which statement about dispersal is false? Answer C View Answer. Discussion You must be signed in to discuss. Top Biology Educators Dr. Bridgette D. University of North Carolina at Wilmington. Torilis anthriscus , a burr; 6. Geum urbanum , a burr; 7. Pisonia aculeata , a viscid fruit; 8. Xanthium spinosum , a burr; 9. Cynoglossum pictum , a burr. See Sorensen for a review of seed dispersal by adhesion.

Many disseminules are adapted for movement by specific dispersal agents available in the environment, like wind, water, or another animal capable of active dispersal, or species may have a motile larval stage. Sessile adult animals that utilize passive dispersal include marine invertebrates like sponges and corals. Their disseminules are typically specialized buds or cells used in reproduction. For example, most corals sexually reproduce by releasing gametes directly into the water.

The male gametes are generally motile, and eggs are moved passively via ocean currents. Other sessile animals exemplify natal dispersal in that they have a free-living, aquatic juvenile stage, wherein larvae drift near the surface and are passively carried by water currents to other locations.

In plants, disseminules include seeds, spores, and fruits, all of which have modifications for movement away from the parent plant via available environmental kinetic energy. Distance traveled by a disseminule is a result of the velocity and direction of movement by the dispersal agent. Winds, flying animals, or water currents are some of the most successful agents of long-distance passive dispersal.

Seeds and fruits that have wings, hairs, or inflated processes are carried efficiently by wind. For example, modifications in Hypochaeris radicata Asteraceae seeds have allowed it to successfully disperse in a fragmented landscape in the Netherlands and counteract the negative effects of population isolation with substantial levels of gene flow Mix et al.

Furthermore, some plants have sticky or barbed seeds, or fruits, that adhere to the feathers or fur of mobile animals Figure 2. Some disseminules are explosively released over short distances whereas others fall to the ground at the base of the parent plant. On the ground, invertebrates, mammals, and birds compete for fallen seeds and fruits. Seeds and fruits are scattered during feeding and after ingestion are distributed in feces. These seeds are adapted to resist digestive juices and, consequently, can pass through the digestive tract while remaining viable.

The distance a disseminule travels by animal transportation, either via ingestion or attachment, is indefinite and depends on the dispersal behavior of their host.

For example, some animals may follow a nomadic or brief dispersal trajectory, resulting in variance in the distances traveled. Multiple processes influence juvenile and adult dispersal. Proximate causes vary but include local population conditions such as crowding and food availability. Environmental stochasticity e. Individuals that emigrate as a result of environmental conditions may experience more favorable conditions in the new location.

Additionally, climate change will impact dispersal. Since climate typically influences the distributions of species, the general warming trend that will occur as a result of global climate change will cause species' ranges to shift. As a result, many areas outside of current distributions may become climatically suitable. However, these areas may be beyond the dispersal capacity of many species. Ultimate causes of dispersal can be explained by avoidance of inbreeding and inbreeding depression.

Small, isolated populations can become inbred and result in decreased fitness, but dispersal can counteract these negative effects. Additionally, dispersal can reduce competition for resources and mates, thereby increasing individual fitness. In some situations, these ultimate causes will result in sex-biased dispersal.

For example, mammals typically exhibit male-biased dispersal, and birds typically exhibit female-biased dispersal. These dispersal strategies result mostly from males attempting to increase their access to females male-biased dispersal and in female-biased dispersal systems in birds from male resource defense female-biased dispersal in birds results Greenwood Despite the perceived benefits of dispersal, there can be costs.

First and foremost, there is a greater mortality risk during dispersal due to increased energy expenditure, unfamiliar habitat, or predation risk e. Second, dispersers may suffer reduced survival or reproductive success because of unfamiliarity with the new environment and the inability to acquire sufficient resources, resulting in decreased adaptive ability to the new habitat.

Dispersal affects organisms at individual, population, and species levels. Survival, growth, and reproduction at the level of individuals are intimately tied to both the distance and frequency of dispersal, factors which are typically mediated by aspects of local resource availability. At the population level, patterns of emigration and immigration within and among habitat patches associated with local population density, among other factors, drive temporal and spatial cycles of colonization and extinction.

The form of such movements, such as stepping-stone versus one-way migration, ultimately determines the genetic structure of populations, wherein genetic differentiation is directly proportional to the amount of gene flow among populations. For populations exhibiting frequent dispersal, ongoing gene flow within and among populations results in those populations becoming genetically similar to one another and ultimately evolving as a single unit.

Finally, over evolutionary time frames, a lack of dispersal among populations impacts organisms at the species level. If dispersal between populations ceases, these newly isolated populations accumulate novel genetic attributes via genetic drift or natural selection potentially leading to local adaptation.

Insurmountable landscape features, such as mountains and rivers, typically drive such processes, and in cases where genetic differentiation persists even after dispersal between formerly isolated populations could resume, such entities can then be designated as separate species Figure 3. Figure 3: Phylogenetic relationships of hypothetical populations that became isolated via dispersal Uppercase letters represent taxa, roman numerals represent geographic areas, black arrows represent dispersal events.

All rights reserved. Species exhibit geographic distributions that are constrained by a range of environmental variables — outside of which individuals may experience reduced survival and reproduction due to physical and physiological constraints. For example, species are often accustomed to particular temperature ranges, and dispersal to regions with temperatures outside those ranges reduces fitness. Additionally, resources necessary for population persistence may be insufficient at range edges and outside the range.

Physical barriers to dispersal consist of landscape features that prevent organisms from relocating. Mountains, rivers, and lakes are examples of physical barriers that can limit a species' distribution.

Anthropogenic barriers, like roads, farming, and river dams, also function as impediments to movement. It has been suggested that anthropogenic barriers are the most serious threats to dispersal. These barriers can effectively divide up a species' range into isolated fragments, and dispersal from one habitat patch to another can prove difficult.

Creating dispersal corridors has been suggested as a means to maintain connectivity between habitat patches. For example, Banff National Park in Alberta, Canada, contains 22 underpasses and 2 overpasses to facilitate wildlife dispersal within the park across a busy four-lane highway the Trans-Canada Highway.

Similarly, wildlife crossings, specifically designed for Florida panthers, were constructed along a forty-mile stretch of Interstate 75 in Florida. Corridors are not just for large mammals either: Salamanders have also benefited from miniature underpasses to facilitate dispersal. Additionally, recent research has focused on using modeling techniques to analyze available habitat to designate potential dispersal pathways for species whose ranges have been fragmented Figure 4.

Source populations in the West were as follows: A. Badlands, ND; B. Black Hills, SD; C. Kimble County, TX. Anabrus simplex with radio transmitters attached see Lorch et al.

Direct methods can be somewhat easier to use in larger animals simply because tracking the smallest organisms e. However, tracking devices are becoming increasingly more advanced and useful in small organisms Figure 5. Interpretation of results from direct measurement can sometimes prove difficult though. Low accuracy of spatial position, disproportionate mortality of marked individuals, labor intensity, and high costs are all deterrents to using direct measurement methods.

In contrast to direct methods, indirect methods infer the degree of dispersal without actually having to observe the dispersal movement.

Typically, indirect methods involve utilizing molecular markers to measure gene flow and deduce dispersal patterns based on within and among population genetic differences. Our expert Biology tutor, Kaitlyn took 5 minutes and 53 seconds to solve this problem. You can follow their steps in the video explanation above. If you forgot your password, you can reset it. Join thousands of students and gain free access to 23 hours of Biology videos that follow the topics your textbook covers.

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