noc19-bt09 Lecture 03-Ecology and Evolution

Name: noc19-bt09 Lecture 03-Ecology and Evolution
Uploaded: 2019-01-21T07:01:04.000Z
Duration: 1 h 36 min 31 s

Understanding the Relationship Between Ecology and Evolution

Introduction to Evolution and Ecology

Namaste. Life on Earth began approximately four billion years ago, leading to diverse life forms, including humans.

The lecture will explore the relationship between ecology (the study of interactions among organisms and their environments) and evolution (genetic adaptation of organisms).

Key Concepts: Adaptation

Adaptation Defined: Any alteration in an organism's structure or function that enhances its ability to survive and reproduce in its environment.

Examples of adaptations include structural changes (e.g., developing wings instead of hands) or functional changes (e.g., using hands for different purposes).

Not all changes are adaptations; they must specifically improve survival and reproduction capabilities.

Case Study: Camel Adaptations

Camels exhibit several adaptations for desert survival:

Hump: Stores energy as fat and water, crucial for survival in arid conditions. Camels can drink large amounts of water at once to store it efficiently.

Blood Characteristics: Their blood can still circulate effectively even when dehydrated, ensuring nutrient delivery to cells.

Padded Legs: Larger surface area reduces pressure on sand, allowing camels to walk without sinking into it. This adaptation is critical for mobility in sandy environments.

Large Eyelashes: Protect eyes from sand exposure during windy conditions, enhancing their ability to navigate the desert landscape.

Genetics and Heritability

Genetics refers to heredity; adaptations must be heritable traits passed down through generations for them to be considered genetic adaptations. If a trait cannot be inherited, it does not contribute to evolution.

Understanding Fitness in Evolution

The Concept of Fitness

Organism A produced 10 offspring, while Organism B produced 100. Despite B's higher number, A has better fitness due to a higher survival rate of its offspring (9 out of 10 survived).

If only 7 out of B's 100 offspring survive due to lack of parental care, A demonstrates greater fitness by ensuring more offspring reach maturity.

Importance of Fitness in Evolution

Evolution maximizes fitness through natural selection, favoring organisms that leave more viable offspring. Characteristics leading to higher survival rates are inherited by future generations.

Over time, characteristics associated with higher fitness will dominate the population as less fit traits diminish.

Environment and Species Specificity

Fitness is environment-specific; what works in one context may not apply in another. For example, high predation environments favor parental care for offspring survival.

In resource-rich environments without predation, producing many offspring can enhance fitness since fewer resources are needed for their survival.

Measuring Fitness

High reproductive rates do not equate to high fitness; rather, it’s the survival rate of those progeny that matters most.

Long-term measurement across several generations is necessary to assess true fitness levels; short-term observations can be misleading.

Natural Selection Process

Natural selection operates at the organism level rather than focusing on individual traits like speed or size alone; all characteristics must be considered holistically.

The process involves five stages: variation among individuals is essential for selection to occur effectively.

Stages of Natural Selection

Variation: Individuals within a population exhibit different traits (e.g., height or color), which allows for selection based on adaptability.

Population Dynamics and Natural Selection

Static Population Growth

Organisms mating produce a static population, with each generation yielding only two offspring, resulting in no growth over time.

Ample resources can lead to overpopulation; for instance, two organisms may produce ten offspring in the next generation.

Exponential Growth and Resource Limitation

Overpopulation can result in exponential growth; a multiplication factor of five could lead from 2 to 10, then to 50, and so on.

Limited resources create a struggle for existence; not all offspring can be sustained, leading to natural selection where some individuals are eliminated.

Observations from Nature: Cheetah Hunting

In Kruger National Park (2018), cheetahs were observed hunting impalas. The stealthy approach highlights the struggle for survival.

Despite their efforts, four cheetahs failed to catch any impala, illustrating that food is not guaranteed even after significant energy expenditure.

Survival of the Fittest

Only the best-adapted individuals survive; if one cheetah cannot tolerate hunger or succumbs to disease due to lack of food, it will be eliminated.

"Survival of the fittest" emphasizes that those who efficiently obtain and utilize resources will reproduce successfully.

Changes in Gene Pool: The Peppered Moth Example

Changes in gene pool occur as inherited traits increase within populations. For example, peppered moth color variations illustrate this concept.

Before industrialization in England, lighter-colored moths blended into lichen-covered trees. Post-industrial pollution led to darker barks and increased visibility of lighter moths.

Natural Selection Illustrated by Camouflage

As lichens died off due to pollution, lighter moth variants became more visible and thus more susceptible to predation compared to darker variants.

Natural Selection and the Peppered Moth

Overview of Environmental Impact on Peppered Moths

The visibility of peppered moths in polluted environments varies; dark-colored moths are camouflaged, leading to preferential predation.

Before the Industrial Revolution, light-colored moths were more prevalent due to higher predation rates on dark-colored variants.

During and after the Industrial Revolution, increased pollution led to a rise in dark-colored moth populations as they became less visible to predators.

Following the Clean Air Act, air quality improved, resulting in a resurgence of light-colored moths as their camouflage returned with cleaner trees.

Mechanisms of Natural Selection

Variation among organisms is crucial for survival; different colors in peppered moth populations illustrate this diversity.

Overpopulation leads to competition for resources, creating a struggle for existence where not all individuals can survive.

"Survival of the fittest" occurs when certain traits (like coloration) provide advantages in specific environments.

Gene Pool Dynamics

Changes in gene pools do not lead to complete dominance by one variety; some variation must persist for adaptability.

If only one color variant existed during environmental changes, it could lead to extinction if that variant becomes disadvantageous.

Types of Natural Selection

Three types of selection are identified: directional selection, stabilizing selection, and disruptive selection.

Directional selection shifts population traits towards one extreme; an example includes changing preferences for darker or lighter shades based on environmental conditions.

Understanding Directional Selection

In directional selection, population frequency curves shift left or right depending on which traits become more favorable over time.

Natural Selection and Its Types

Disruptive Selection

In a scenario of disruptive selection, organisms at both extremes are favored while those in the middle are not. This can be illustrated with trees of varying colors where light and dark individuals blend into their environments, but middle-colored ones do not.

For example, in a forest setting, light-colored individuals on light bark and dark-colored individuals on dark bark avoid predation. However, middle-colored individuals lack camouflage and become prey.

Stabilizing Selection

Stabilizing selection occurs when extreme traits are eliminated over generations, leading to a narrower distribution of traits. An example is the reduction of shades 1 and 5 in subsequent generations.

The result is a shift towards more central traits; for instance, if only weights around 8 pounds survive better among newborns, this indicates stabilizing selection.

Directional Selection

Directional selection is exemplified by the Galapagos finches' beak size changes due to environmental pressures like drought. Initially preferred beak depth was 8.8 mm but shifted to 9.8 mm post-drought as harder seeds became prevalent.

The need for larger beaks to access tougher seeds illustrates how environmental changes can drive directional shifts in trait preferences.

Further Examples of Selection Types

Another example from the Galapagos Islands shows birds with preferred beak sizes at extremes (small or large), while medium-sized beaks are less advantageous due to competition for food resources.

Disruptive selection arises when two types of nuts exist—hard and soft—with no intermediate options available for birds that cannot effectively crack either type.

Coevolution

Coevolution involves two species evolving together through close interactions. A prime example includes bee hummingbirds feeding on specific flower shapes designed to attract them while ensuring pollination efficiency.

The relationship between hummingbirds and flowers highlights how adaptations occur; flowers produce nectar specifically tailored to attract certain bird species without cross-pollination issues between different flower species.

Co-evolution of Species

Flower and Bird Interaction

The relationship between flower structure and bird beak length is crucial for feeding efficiency. A longer, slender beak is necessary to access nectar from elongated flowers.

In a competitive scenario, birds with shorter beaks may struggle to feed on certain flowers, while those with longer beaks can access more resources. This competition influences evolutionary traits in both species involved.

Specificity and Fitness

Increased specificity in flower structure (e.g., longer funnels) correlates with higher reproductive success due to better pollen transfer among the same species. Thus, natural selection favors these traits over time.

As flowers evolve to have longer structures, birds must also adapt by developing longer beaks to maintain their feeding efficiency, illustrating a reciprocal evolutionary process known as co-evolution.

Examples of Co-evolution

Horn Evolution in Herbivores

The evolution of horns in herbivores like cape buffalo serves as a defense mechanism against predators such as lions; larger horns deter attacks by making it riskier for predators to approach adult animals.

Predators may adapt their strategies (e.g., approaching from behind) in response to the defensive adaptations of prey species, showcasing another layer of co-evolutionary dynamics.

Zebra Stripes and Predator Confusion

Zebras evolved stripes primarily as a survival tactic; when chased by predators like lions, the confusion created within groups helps individual zebras evade capture by blending into the herd.

This adaptation highlights how prey species develop features that counteract predation pressures exerted by their natural enemies, further exemplifying co-evolutionary relationships.

Speed Adaptations Between Impalas and Cheetahs

Impalas run fast as an evolutionary response to avoid being predated upon by cheetahs; this speed is essential for survival against faster predators. Conversely, cheetahs have evolved speed specifically to catch agile impalas, creating a continuous cycle of adaptation between predator and prey.

Interconnectedness of Evolutionary Processes

The interactions between closely related species lead to mutual dependencies in their evolutionary paths; changes in one species can significantly impact others within the ecosystem context. This interconnectedness emphasizes the importance of ecological relationships in shaping evolution over time.

Role of Ecology in Evolution

Understanding Community Ecology and Evolution

The Importance of Interactions in Ecology

Interactions within a population and between species are crucial for understanding community ecology, exemplified by the relationship between cheetahs and impalas.

Studying ecology is essential for grasping evolution, as ecological interactions inform how and why evolutionary processes occur.

Key concepts discussed include adaptations, genetic variations, natural selection, overpopulation, resource struggles, and the survival of the fittest—all fundamental to understanding evolution.

Co-evolution and Environmental Interaction

The lecture highlights co-evolution where different species influence each other's evolutionary paths through their interactions.