Ecology Lab Notebook
*Lab is not needed to complete this assignment* You are simply making notes based on facts as in what will happen in the situations. Answer all questions and make notes for all statements.
Rat Beats Panda?!
A rat would have difficulty taking on a panda in a fight. In fact, occasionally pandas even hunt for small rodents similar to rats. However, evolutionarily speaking, rats as a species are scoring big points over the panda species.
Pandas are adapted to a very narrow range of conditions. For example, 99% of their diet is bamboo. Therefore, if anything happens to the bamboo forests they need for food, the pandas are in big trouble. The number of giant pandas in the wild has been estimated at less than 2,000. Because of disruptions humans have made in the panda’s habitat, they are currently an endangered species, making it important to monitor their population size.
On the other hand, nobody really wants to know how many rats there are in the wild and in our homes. As humans disrupt natural environments, rats simply find more places to thrive. The brown rat, in particular, lives essentially everywhere people do. They eat almost anything including scrambled eggs, macaroni and cheese, and cooked corn. This adaptability has led rats to be one of the most evolutionarily successful species.
Therefore, in the fight for survival, rats have pandas beat.
Estimating Population Size
Ecology is the study of how organisms relate to each other and to their surroundings. Estimating how many individuals are in a population is an essential tool in any ecologist’s toolkit, especially for endangered species such as the panda. When selecting samples to make population size estimates, it is crucial that the samples truly represent the population being studied. Randomness and sample size have a large impact on the accuracy of a population estimation study.
Randomness is a strategy used to address the uneven distribution of populations. Populations tend to cluster around areas where food is readily available or where they are safe from predators. When samples are collected randomly throughout an area, different levels of population density have a better chance of being represented in the survey. To ensure that sampling areas are truly chosen at random, computer programs are now used.
The other important variable is sample size. A large enough sample needs to be collected, so that less commonly occurring members of the population are represented. Many factors contribute to what types of samples are needed, such as the complexity of the environment or the complexity of the sampled population’s distribution.
Numerous techniques exist for estimating population size. One called the mark and recapture method works exactly the way it sounds: members from the population under study are captured, marked so that they can be tracked (e.g., leg banding or collar tagging), and then released back into the population. Once they have had enough time to mix evenly back into the population, but not too much time that births, deaths, and migration occur, the population is resampled to find out what percentage of the sample has the mark from the first capture.
The total population size is then estimated using a simple proportion:
MN=mn
where M is the number of marked individuals in the first sample; N is the total population size; m is the number of marked individuals in the second, or recaptured, sample; and n is the total number of individuals in the second, or recaptured, sample.
This equation can be rearranged for easy use when calculating the estimated total population size (N):
N=M(nm)
The result is the estimated population size at the time of marking, not at the time of recapture.
The mark and recapture estimate makes several assumptions. The accuracy of the assumptions depends on the specifics of the natural population under study. Therefore, it is very important to be aware of those assumptions and, making an educated guess, estimate how accurately the assumptions reflect the studied population. The assumptions are (Brewer and McCann, 1982):
Marks are not lost or overlooked.
The population is not changed by reproduction, immigration or emigration, nor death between the marking session and the recapture session.
Marked and unmarked animals have the same chance of being caught, in both the first and second sampling sessions.
All methods for population estimation are just that, estimates. Moreover, they are all based on some kind of assumptions.
Population Changes in Response to Environmental Factors
Populations are constantly shifting in response to changes in their environment. Estimating population size before and after those environmental changes allows scientists to understand how populations respond under specific conditions. Numerous factors can affect a population, such as:
Temperature
Salinity
Water availability and quality
Food availability and quality
Predator/prey relationships
Habitat availability and quality
Light availability
Pollution
For example, it is generally hypothesized that the prey population size will decrease, at least at first, after the introduction of a predator. To test this hypothesis, the prey population size can be estimated before and after the predator introduction. The conditions of both estimations should be as similar as possible. For example, sampling in the same season, in the same sample locations, and with the same or similar equipment will eliminate the effect of these parameters on the outcome. That way any changes seen in population size can be attributed as much as possible to the predator introduction.
About This Lab
In the first part of this lab, you will use the mark and recapture method for estimating the population density of bluegills in the sample pond during the spring. Areas to sample have already been randomly selected.
In the second part of this lab, you will test how the bluegill population changes in response to the introduction of a predator fish, the bass. Bass were introduced to the sample pond in the fall after the spring sampling session.
Experiments
Follow the instructions in the Procedure to complete each part of the lab. When instructed to record your observations, record data, or complete calculations, record them for your own records in order to use them later to complete the post-lab assignment.
Experiment 1: Estimating Population Size
Part 1: Mark
1.Imagine you and your lab partner, after donning life jackets and sun-protective gear, take a rowboat out into the lake to be sampled. You have brought your fishing net and a cooler.
Stop and consider: Why is it important to work with a partner during this lab?
2.You head to the first of five sampling locations in the lake that were selected randomly. The five locations are shown in the overview map of the lake below. Your boat and the dock you launch from are in the middle of the bottom shore line.
3.You begin fishing by dipping the net into the water.
4.Because you are only interested in studying the bluegill population, you keep specimens of that species and return other types of fish to the lake.
5.Once you have collected 20 fish at that location, you put them in the cooler filled with lake water.
Stop and consider: Why do you fill the cooler with lake water instead of water from the lab sink?
6.You repeat steps 2 – 5 for the other four sampling locations.
7.With 100 fish in your cooler, you row back to the dock. You start processing the fish at your picnic table workstation.
Your workstation is equipped with the following:
Balance
Measuring tray
Fish tagger
8.To begin the measuring and tagging process, you place the measuring tray on the balance. The balance shows that the tray has a mass of 27.400 g.
9.You press the Zero button on the balance to reset the mass to zero. This way, the scale will only measure the mass of the fish you put on it, instead of measuring the mass of both the fish and the measuring tray.
10.You retrieve a fish from the cooler and place it in the measuring tray.
The tray gives a readout of the fish’s length in centimeters (cm). The balance gives a readout of the fish’s mass in grams (g).
11.You record the fish length and mass in your field notebook.
12.You use the fish tagger to apply a blue tag to the dorsal fin of the fish.
This type of tagging has been shown to minimally impact the ability of the fish to live normally once placed back in the lake. This is important, because one of the assumptions of the method is that tagged and untagged fish should be considered the same.
13.You put the fish into a second cooler filled with lake water.
14.You re-zero the balance after you remove the fish.
Stop and consider: Why is it important to re-zero the balance after you remove each fish from the tray?
15.You repeat this weighing and tagging process for the remaining 99 fish.
16.Once you finish processing all 100 fish, you row back out to the center of the lake and release the fish, which are all tagged now.
Below is the data you recorded in your field notebook for the day. Each of the four columns of the table holds length and mass data for 25 of the 100 fish you collected. Make sure to keep a copy to analyze the data later.
| Length (cm) | Mass (g) | Length (cm) | Mass (g) | Length (cm) | Mass (g) | Length (cm) | Mass (g) |
| 23.0 | 555.927 | 18.2 | 468.069 | 24.3 | 559.721 | 15.5 | 382.642 |
| 16.3 | 401.070 | 14.2 | 362.657 | 20.6 | 533.482 | 16.8 | 411.422 |
| 14.2 | 357.725 | 24.5 | 573.004 | 21.2 | 543.126 | 17.4 | 439.637 |
| 19.9 | 511.963 | 19.3 | 484.174 | 16.4 | 401.788 | 14.0 | 347.812 |
| 22.0 | 549.492 | 23.5 | 556.148 | 17.9 | 462.988 | 22.3 | 550.553 |
| 16.6 | 408.780 | 19.8 | 502.722 | 22.7 | 555.645 | 15.9 | 392.966 |
| 17.6 | 453.282 | 21.2 | 543.487 | 17.1 | 436.526 | 13.8 | 343.038 |
| 16.8 | 409.961 | 22.8 | 555.916 | 13.8 | 344.039 | 13.4 | 327.224 |
| 19.4 | 488.916 | 19.2 | 476.753 | 22.3 | 551.274 | 22.6 | 555.157 |
| 15.8 | 392.855 | 17.8 | 460.567 | 17.4 | 444.928 | 19.5 | 494.027 |
| 14.2 | 362.106 | 20.6 | 535.263 | 16.8 | 428.363 | 19.4 | 484.925 |
| 24.6 | 582.657 | 13.2 | 314.853 | 16.5 | 408.749 | 24.4 | 572.143 |
| 13.6 | 333.265 | 20.8 | 535.364 | 18.4 | 469.080 | 14.5 | 376.479 |
| 21.4 | 544.278 | 24.3 | 564.742 | 17.5 | 449.720 | 20.1 | 515.636 |
| 13.1 | 310.591 | 17.1 | 432.950 | 24.9 | 589.609 | 19.2 | 472.752 |
| 17.4 | 449.119 | 22.4 | 552.466 | 17.6 | 451.621 | 15.7 | 391.894 |
| 20.2 | 523.578 | 20.3 | 526.090 | 14.5 | 363.818 | 19.7 | 499.119 |
| 21.6 | 544.749 | 20.1 | 523.317 | 13.7 | 336.247 | 22.4 | 551.945 |
| 16.1 | 398.337 | 19.8 | 500.451 | 13.2 | 313.692 | 24.0 | 559.330 |
| 17.7 | 454.006 | 15.5 | 391.313 | 19.7 | 499.340 | 14.8 | 379.821 |
| 24.8 | 583.008 | 13.7 | 335.886 | 23.8 | 557.259 | 24.9 | 589.810 |
| 24.6 | 580.716 | 17.0 | 431.344 | 20.0 | 515.565 | 14.1 | 351.513 |
| 20.9 | 542.175 | 24.6 | 579.515 | 19.5 | 494.928 | 20.4 | 530.251 |
| 20.0 | 515.094 | 14.1 | 357.544 | 21.8 | 547.071 | 14.0 | 347.140 |
| 20.2 | 525.699 | 19.0 | 470.491 | 21.7 | 546.620 | 14.5 | 379.290 |
Note: You need to wait a sufficient amount of time before you sample them a second time, so you and your lab partner go home and come back the next day.
Stop and consider: Why do you need to wait before sampling the fish a second time?
Part 2: Recapture
1.After allowing the fish to redistribute themselves, you prepare for recapture by creating a separate section in your field notebook for the recaptured fish data. You will need a section to:
Record the mass and length as before
Keep a tally of how many fish are tagged and how many are untagged, so you can calculate the total number of tagged fish and the total number of untagged fish
2.You repeat the sampling procedure from Part 1 with the following two exceptions:
In step 11, you record whether the recaptured fish has a blue tag in its dorsal fin or not, in addition to the fish’s length and mass.
Step 12 is not performed, as retagging is unnecessary.
Below is the data you recorded in your field notebook for the day. Each of the four columns of the table holds length and mass data for 25 of the 100 fish you collected. The data sets marked with asterisks and highlighted in blue indicate fish you recaptured that were tagged the day before. Make sure to keep a copy to analyze the data later.
| Length (cm) | Mass (g) | Length (cm) | Mass (g) | Length (cm) | Mass (g) | Length (cm) | Mass (g) |
| 15.9 | 393.335 | 24.7 | 585.433 | 13.2 | 316.151 | 20.2 | 457.582 |
| 17.2* | 410.923* | 22.5 | 493.811 | 23.6 | 517.788 | 20.8 | 479.699 |
| 14.3 | 348.690 | 24.3 | 574.217 | 14.5 | 357.574 | 14.4* | 353.082* |
| 13.3 | 316.342 | 23.5 | 517.146 | 18.0 | 414.027 | 21.4 | 485.512 |
| 15.5 | 387.560 | 15.8 | 389.372 | 22.2 | 491.570 | 14.1 | 340.588 |
| 17.1 | 407.742 | 13.4* | 327.754* | 24.8 | 587.940 | 23.3 | 510.614 |
| 23.7 | 521.729 | 15.5 | 383.828 | 15.5 | 383.056 | 19.4 | 442.467 |
| 24.6* | 579.161* | 18.9 | 419.702 | 23.5 | 517.477 | 20.6 | 463.834 |
| 17.9 | 413.716 | 14.4 | 349.281 | 13.1 | 313.850 | 21.1 | 482.170 |
| 18.9 | 418.020 | 14.6 | 364.405 | 23.0 | 507.863 | 15.5 | 383.687 |
| 20.8 | 478.898 | 20.6 | 475.556 | 22.2 | 492.448 | 22.9 | 504.672 |
| 17.0* | 403.611* | 19.3 | 430.595 | 19.3 | 429.914 | 22.1 | 490.750 |
| 21.8 | 488.874 | 24.2 | 571.795 | 19.3 | 438.366 | 17.9 | 413.145 |
| 24.5 | 576.159 | 13.6 | 335.256 | 23.8 | 534.820 | 24.5 | 578.760 |
| 16.7 | 400.409 | 17.5 | 411.974 | 20.1 | 452.121 | 13.6* | 330.085* |
| 16.8 | 402.770 | 14.7 | 364.816 | 24.2 | 565.814 | 15.3 | 382.080 |
| 21.5 | 486.923 | 15.1* | 371.848* | 23.8* | 551.421* | 24.9 | 589.185 |
| 15.5 | 385.719 | 22.5 | 492.820 | 19.5 | 443.399 | 18.9 | 418.941 |
| 13.7 | 339.337 | 20.0 | 445.850 | 22.4 | 492.799 | 14.4 | 355.173 |
| 20.6 | 464.255 | 20.7 | 476.957 | 21.1 | 484.981 | 14.1* | 345.219* |
| 22.2* | 490.966* | 15.7 | 388.031 | 18.4 | 417.979 | 24.4 | 575.218 |
| 15.4 | 382.915 | 16.6 | 398.377 | 24.1 | 564.363 | 16.6 | 398.978 |
| 18.2 | 415.388 | 23.4 | 516.495 | 19.0 | 426.703 | 14.9 | 367.767 |
| 15.8 | 392.395 | 20.5 | 458.913 | 23.9 | 558.820 | 24.7 | 584.082 |
| 19.5 | 443.048 | 16.0 | 394.706 | 13.3 | 321.653 | 24.3 | 572.246 |
Note: Once you have measured all your fish and recorded the number of tagged fish, you have completed the initial Mark and Recapture section of this lab.
Experiment 2: Effect of Predator Introduction on Population Size
You have returned to the lake a year later to make another population estimate after the fish species bass, a predator of bluegill, has been introduced.
You repeat the sampling procedure from Experiment 1, except you use red tags instead of blue tags.
Stop and consider: Why is it important to use different tags when sampling the second time?
Below is the data you recorded in your field notebook for the first day. Each of the four columns of the table holds length and mass data for 25 of the 100 fish you collected. Make sure to keep a copy to analyze the data later.
| Length (cm) | Mass (g) | Length (cm) | Mass (g) | Length (cm) | Mass (g) | Length (cm) | Mass (g) |
| 20.2 | 583.108 | 15.2 | 462.069 | 11.5 | 392.492 | 10.1 | 358.172 |
| 15.9 | 477.618 | 10.6 | 359.084 | 12.1 | 406.058 | 19.2 | 551.640 |
| 11.1 | 377.570 | 16.1 | 482.880 | 15.0 | 458.257 | 11.8 | 397.075 |
| 15.2 | 461.578 | 17.2 | 514.924 | 17.9 | 535.891 | 11.6 | 393.143 |
| 16.1 | 485.951 | 12.2 | 413.610 | 13.7 | 453.032 | 13.2 | 444.190 |
| 16.7 | 505.508 | 13.1 | 441.569 | 18.6 | 544.377 | 10.1 | 354.931 |
| 19.6 | 567.145 | 20.2 | 576.927 | 12.4 | 417.902 | 14.9 | 455.360 |
| 11.1 | 374.919 | 19.9 | 568.366 | 14.4 | 454.735 | 16.1 | 481.479 |
| 17.5 | 525.037 | 12.9 | 439.678 | 22.0 | 618.560 | 12.8 | 438.197 |
| 12.6 | 426.024 | 21.7 | 599.896 | 15.4 | 467.991 | 21.2 | 595.724 |
| 12.8 | 427.865 | 15.6 | 472.715 | 20.9 | 593.232 | 12.8 | 430.226 |
| 16.3 | 490.663 | 18.5 | 543.926 | 16.4 | 499.774 | 17.3 | 521.536 |
| 12.5 | 423.561 | 10.0 | 346.340 | 10.9 | 365.786 | 16.7 | 502.616 |
| 17.6 | 526.778 | 17.1 | 511.073 | 15.5 | 469.203 | 16.2 | 488.352 |
| 16.8 | 509.361 | 20.8 | 589.731 | 21.8 | 600.337 | 10.9 | 367.747 |
| 14.0 | 453.373 | 15.5 | 471.604 | 13.4 | 448.851 | 16.7 | 505.619 |
| 20.4 | 583.999 | 19.3 | 562.272 | 18.2 | 541.554 | 10.2 | 358.843 |
| 16.7 | 505.357 | 19.5 | 562.913 | 17.8 | 530.890 | 15.3 | 466.820 |
| 18.2 | 541.785 | 11.7 | 395.134 | 18.8 | 548.499 | 18.6 | 545.768 |
| 10.7 | 359.745 | 16.7 | 506.380 | 12.2 | 413.239 | 18.1 | 539.313 |
| 15.5 | 469.132 | 17.2 | 515.895 | 21.5 | 598.225 | 15.7 | 473.716 |
| 20.7 | 588.460 | 11.8 | 402.386 | 12.0 | 402.757 | 17.8 | 527.339 |
| 12.3 | 413.931 | 17.9 | 536.812 | 21.9 | 603.028 | 12.6 | 425.203 |
| 19.2 | 560.211 | 16.5 | 501.155 | 11.4 | 380.591 | 14.1 | 454.114 |
| 10.9 | 374.158 | 21.1 | 593.733 | 15.8 | 476.970 | 17.1 | 509.862 |
Below is the data you recorded in your field notebook for the second day. Each column of the table holds length and mass data for 25 of the 100 fish you collected. The data sets marked with asterisks and highlighted in red indicate fish you recaptured that were tagged the day before. Make sure to keep a copy to analyze the data later.
| Length (cm) | Mass (g) | Length (cm) | Mass (g) | Length (cm) | Mass (g) | Length (cm) | Mass (g) |
| 19.3 | 553.237 | 20.7 | 592.981 | 20.9 | 594.032 | 19.4 | 556.078 |
| 18.3* | 526.278* | 17.7 | 511.392 | 18.7 | 542.930 | 10.5 | 348.443 |
| 20.6 | 589.940 | 15.0 | 428.196 | 19.4 | 565.990 | 20.0* | 575.445* |
| 12.0 | 373.276 | 12.4 | 379.800 | 16.0 | 476.218 | 14.0 | 410.013 |
| 12.2* | 374.447* | 15.1 | 438.497 | 17.9 | 519.717 | 19.9 | 572.084 |
| 10.9 | 356.899 | 20.1 | 577.247 | 17.8 | 515.143 | 21.9 | 618.198 |
| 18.7 | 543.854 | 11.9 | 370.264 | 21.7 | 611.576 | 16.2 | 478.649 |
| 10.6 | 353.267 | 15.6* | 454.611* | 13.7 | 403.439 | 19.6 | 566.871 |
| 18.4 | 527.280 | 10.5 | 348.092 | 10.2 | 343.070 | 16.4 | 489.484 |
| 19.9 | 569.313 | 21.8 | 614.467 | 20.2 | 581.148 | 12.3 | 377.889 |
| 18.2 | 521.035 | 17.6 | 511.191 | 15.6 | 448.180 | 12.7 | 391.684 |
| 12.2* | 376.418* | 19.2 | 548.125 | 21.3 | 602.765 | 16.2* | 485.232* |
| 10.6 | 352.696 | 10.5 | 348.524 | 12.9 | 395.196 | 10.7 | 356.798 |
| 17.5 | 503.129 | 20.1* | 575.536* | 16.0 | 476.177 | 17.6 | 505.510 |
| 12.7 | 386.793 | 21.2 | 602.194 | 18.6 | 540.232 | 18.5 | 538.281 |
| 18.3 | 526.279 | 10.6* | 350.550* | 14.1 | 410.257 | 15.9 | 468.786 |
| 15.5* | 445.579* | 11.0 | 358.411 | 10.5 | 343.941 | 14.6 | 418.743 |
| 19.7 | 567.352 | 11.4 | 362.822 | 20.5* | 587.959* | 16.2 | 485.201 |
| 18.2 | 524.736 | 10.9 | 358.010 | 13.0 | 396.617 | 17.3 | 492.356 |
| 15.8 | 466.565 | 14.7 | 424.094 | 14.2 | 416.562 | 17.3 | 493.517 |
| 15.1* | 440.138* | 19.4 | 559.179 | 14.6 | 421.802 | 13.1* | 402.048* |
| 12.8 | 392.095 | 11.5 | 367.933 | 15.6 | 459.532 | 16.0 | 468.827 |
| 17.4 | 494.738 | 21.0 | 595.463 | 22.0 | 618.859 | 12.6 | 385.341 |
| 11.9* | 372.635* | 12.7 | 385.462 | 17.1 | 492.055 | 19.3 | 549.356 |
| 15.8 | 460.694 | 15.7 | 460.183 | 14.9 | 427.725 | 16.3 | 487.873 |
